WO2025013779A1 - Resonant inverter - Google Patents

Abstract

A resonant inverter (1) is a three-level converter and operates under zero voltage turn-on control at a time of discharge. An auxiliary resonance circuit (2) includes a negative-side resonance path (rn) that has a current polarity limited to a direction from a resonance inductor (Lr) to a neutral point (A), and that is opened and closed by a switch element (Tr6). The auxiliary resonance circuit (2) includes a positive-side regeneration path (D5 + Dsp) that has a current polarity limited to a direction from the resonance inductor (Lr) to a positive-side DC line (P). The auxiliary resonance circuit (2) includes a negative-side regeneration path (D6 + Dsn) that has a current polarity limited to a direction from a negative-side DC line (N) to the resonance inductor (Lr).

Description

Resonant Inverter

The present invention relates to a resonant inverter having an auxiliary resonant circuit.

A power storage system such as an uninterruptible power supply comprises a power storage device and a PCS (power conditioner unit) with a built-in inverter that converts AC and DC between the external power system and the power storage device. The power storage device is, for example, composed of multiple power storage modules, each having multiple storage elements. In recent years, power storage devices have become higher in voltage and larger in capacity.

As the voltage and capacity of power storage devices increases, the increase in switching loss and electromagnetic interference (EMI) noise in the inverter becomes a major problem. Resonant inverters are used as a method for reducing switching loss and EMI noise (see, for example, Patent Documents 1, 2, and 3).

Patent No. 5195161 Patent No. 5569204

In the resonant inverter of Patent Document 1, when all switches are off, a path for the energy stored in the resonant inductor is secured by a snubber circuit, but efficiency drops due to snubber loss.

In the resonant inverter of Patent Document 2, when all switches are off, the energy stored in the resonant inductor is regenerated to the DC link without loss by the auxiliary resonant circuit. The auxiliary resonant circuit serves as a path for the energy stored in the resonant inductor, and no snubber loss occurs. However, the auxiliary circuit requires the same high-voltage withstand elements as the main circuit. There are only a few types of high-voltage withstand elements, and their switching speed is slow, which raises concerns about a decrease in efficiency.

One aspect of the present invention provides a resonant inverter in which a lossless auxiliary resonant circuit, which serves as a path for the energy stored in the resonant inductor, can be constructed from elements with a lower voltage resistance than the main circuit.

One aspect of the present invention is a resonant inverter comprising a positive side capacitor and a negative side capacitor connected in series between a positive side DC line and a negative side DC line, and a neutral point clamp circuit in which the connection point between the positive side capacitor and the negative side capacitor serves as a neutral point. The resonant inverter comprises an upper arm switch and a lower arm switch connected in series between the positive side DC line and the negative side DC line, and a main leg in which the connection point between the upper arm switch and the lower arm switch serves as an input/output point for the inverter current. The resonant inverter comprises a first resonant capacitor and a second resonant capacitor connected in parallel to the upper arm switch and the lower arm switch. The resonant inverter comprises a first anti-parallel diode and a second anti-parallel diode connected in anti-parallel to the upper arm switch and the lower arm switch. The resonant inverter includes a neutral phase leg having a positive side neutral phase switch and a negative side neutral phase switch that respectively open and close a positive side polarity path in which the current polarity is limited to the direction from the neutral point to the input/output point and a negative side polarity path in which the current polarity is limited to the direction from the input/output point to the neutral point. The resonant inverter includes an auxiliary resonant circuit including a resonant inductor having one end connected to the input/output point. The auxiliary resonant circuit includes a positive side resonant path in which the current polarity is limited to the direction from the neutral point to the resonant inductor and is opened and closed by a positive side resonant switch. The auxiliary resonant circuit includes a negative side resonant path in which the current polarity is limited to the direction from the resonant inductor to the neutral point and is opened and closed by a negative side resonant switch. The auxiliary resonant circuit includes a positive side regenerative path in which the current polarity is limited to the direction from the resonant inductor to the positive side DC line. The auxiliary resonant circuit includes a negative side regenerative path in which the current polarity is limited to the direction from the negative side DC line to the resonant inductor.

According to one aspect of the present invention, the lossless auxiliary resonant circuit, which serves as a path for the energy stored in the resonant inductor, is clamped to the neutral voltage by the positive and negative resonant paths, so that the elements that make up the auxiliary resonant circuit can be constructed with elements that have a lower voltage resistance than the elements of the main leg, which is the main circuit.

FIG. 2 is a diagram showing a circuit configuration for one phase of an embodiment of a resonant inverter. 2 is a timing chart showing a discharging operation of the resonant inverter shown in FIG. 1 . 3A to 3C are diagrams illustrating the operation of each mode shown in FIG. 2. 11 is a timing chart showing a clamp snubber operation in a positive direction. FIG. 5 is a diagram showing the operation of mode 5A shown in FIG. 4 . 2 is a timing chart showing a discharging operation of the resonant inverter shown in FIG. 1 . 7A to 7C are diagrams illustrating the operation of each mode shown in FIG. 6. 11 is a timing chart showing a clamp snubber operation in the negative direction. FIG. 9 is a diagram showing the operation of mode 15A shown in FIG. 8 . 2 is a timing chart showing a charging operation of the resonant inverter shown in FIG. 1 . 11A to 11C are diagrams illustrating the operation of each mode shown in FIG. 10. 2 is a timing chart showing a discharging operation of the resonant inverter shown in FIG. 1 . 13A to 13C are diagrams illustrating the operation of each mode shown in FIG. 12. FIG. 2 is a diagram illustrating a first application example of the auxiliary resonant circuit shown in FIG. FIG. 2 is a diagram illustrating a second application example of the resonant inverter illustrated in FIG. 1 . FIG. 13 is a diagram illustrating a third application example of the resonant inverter illustrated in FIG. 17 is a diagram illustrating the operation of the resonant inverter shown in FIG. 16.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. In the following embodiments, components exhibiting similar functions will be given the same reference numerals and descriptions will be omitted as appropriate.

Referring to FIG. 1, the resonant inverter 1 of this embodiment is a three-level inverter having an auxiliary resonant circuit 2 of an NPC (neutral point clamped) type ARCP (auxiliary resonant commutated pole) topology.

The resonant inverter 1 includes a neutral point clamp circuit 3 in which a positive side capacitor Cp and a negative side capacitor Cn are connected in series. The neutral point clamp circuit 3 is connected between a positive side DC line P and a negative side DC line N. The capacitors Cp and Cn are configured to have the same capacitance. The connection point between the capacitors Cp and Cn is the neutral point A where a voltage Vdc/2, which is half the voltage of the input DC voltage Vdc input between the positive side DC line P and the negative side DC line N, is generated.

The resonant inverter 1 has a main leg 4, which is a series circuit consisting of a switch element Tm1, which is an upper arm switch arranged in the upper arm, and a switch element Tm2, which is a lower arm switch arranged in the lower arm. The switch elements Tm1 and Tm2 are, for example, configured with insulated gate bipolar transistors (IGBTs). The switch elements Tm1 and Tm2 may also be configured with MOSFETs. The main leg 4 is connected between a positive side DC line P and a negative side DC line N. The switch element Tm1 has a collector connected to the positive side DC line P and an emitter connected to the collector of the switch element Tm2. The switch element Tm2 has an emitter connected to the negative side DC line N. The connection point between the emitter of the switch element Tm1 and the collector of the switch element Tm2 becomes an input/output point B of the inverter current Iinv, and is connected to the AC input/output terminal via the inductor L1.

The switch element Tm1 has an anti-parallel diode D1 connected in anti-parallel, i.e., the cathode and anode of which are connected to the collector and emitter of the switch element Tm1, respectively. The anti-parallel diode D1 is formed, for example, by the body diode of the switch element Tm1. The switch element Tm1 has a resonant capacitor C1 connected in parallel. The resonant capacitor C1 is formed by the stray capacitance of the switch element Tm1 or an external capacitor.

The switch element Tm2 includes an anti-parallel diode D2 connected in anti-parallel, i.e., with its cathode and anode connected to the collector and emitter of the switch element Tm2, respectively. The anti-parallel diode D2 is formed, for example, by the body diode of the switch element Tm2. The switch element Tm2 includes a resonant capacitor C2 connected in parallel. The resonant capacitor C2 is formed by the stray capacitance of the switch element Tm2 or an external capacitor.

The resonant inverter 1 has a neutral phase leg 5. The neutral phase leg 5 has a positive polarity path np and a negative polarity path nn. The positive polarity path np and the negative polarity path nn are connected in parallel between the neutral point A of the neutral point clamp circuit 3 and the input/output point B of the main leg 4.

The positive polarity path np is a series circuit consisting of a diode Dnp and a switch element Tn3, which limits the current polarity to one direction (from neutral point A to input/output point B) and is opened and closed by the switch element Tn3. The switch element Tn3 is composed of an IGBT or MOSFET. The anode of the diode Dnp is connected to the neutral point A, and the cathode is connected to the collector of the switch element Tn3. The emitter of the switch element Tn3 is connected to the input/output point B.

The negative polarity path nn is a series circuit consisting of a diode Dnn and a switch element Tn4, which limits the current polarity to one direction (from input/output point B to neutral point A) and is opened and closed by the switch element Tn4. The switch element Tn4 is composed of an IGBT or MOSFET. The collector of the switch element Tn4 is connected to the input/output point B, and the emitter is connected to the anode of the diode Dnn. The cathode of the diode Dnn is connected to neutral point A.

The auxiliary resonant circuit 2 includes a resonant inductor Lr, a positive resonant path rp, and a negative resonant path rn connected in parallel between the resonant inductor Lr, the input/output point B of the main leg 4, and the neutral point A of the neutral point clamp circuit 3.

The positive-side resonant path rp is configured as a series circuit including, from the other end of the resonant inductor Lr, one end of which is connected to the input/output point B, a switch element Tr5, which is a positive-side resonant switch, and a diode Drp. The switch element Tr5 is configured, for example, as an insulated gate bipolar transistor (IGBT). The switch element Tr5 may also be configured as a MOSFET.

One end of the resonant inductor Lr is connected to the input/output point B, and the other end is connected to the emitter of the switch element Tr5. The collector of the switch element Tr5 is connected to the cathode of the diode Drp, and the anode of the diode Drp is connected to the neutral point A.

The diode Drp limits the current polarity of the positive resonant path rp to one direction (from neutral point A to input/output point B). The switch element Tr5 opens and closes the positive resonant path rp.

The switch element Tr5 is provided with an anti-parallel diode D5, the cathode and anode of which are connected in anti-parallel to the collector and emitter of the switch element Tr5, respectively. The anti-parallel diode D5 is formed, for example, by the body diode of the switch element Tr5.

The auxiliary resonant circuit 2 includes a lossless regenerative clamp snubber diode Dsp that connects the connection point between the collector of the switch element Tr5 and the cathode of the diode Drp to the positive DC line P. The lossless regenerative clamp snubber diode Dsp has an anode connected to the connection point between the collector of the switch element Tr5 and the cathode of the diode Drp, and a cathode connected to the positive DC line P.

The anti-parallel diode D5 of the switch element Tr5 and the lossless regenerative clamp snubber diode Dsp form a positive regenerative path in which the current polarity is limited to one direction (from the resonant inductor Lr to the positive DC line P).

The negative resonant path rn is configured as a series circuit including, from one end of the resonant inductor Lr, which is connected to the input/output point B, a switch element Tr6, which is a negative resonant switch, and a diode Drn. The resonant inductor Lr is also used as the positive resonant path rp. The switch element Tr6 is configured, for example, as an insulated gate bipolar transistor (IGBT). The switch element Tr6 may also be configured as a MOSFET.

One end of the resonant inductor Lr is connected to the input/output point B, and the other end is connected to the collector of the switch element Tr6. The emitter of the switch element Tr6 is connected to the anode of the diode Drn, and the cathode of the diode Drn is connected to the neutral point A.

The diode Drn limits the current polarity of the negative resonant path rn to one direction (from input/output point B to neutral point A). The switch element Tr6 opens and closes the negative resonant path rn.

The switch element Tr6 is provided with an anti-parallel diode D6, the cathode and anode of which are connected in anti-parallel to the collector and emitter of the switch element Tr6, respectively. The anti-parallel diode D6 is formed, for example, by the body diode of the switch element Tr6.

The auxiliary resonant circuit 2 includes a lossless regenerative clamp snubber diode Dsn that connects the connection point between the emitter of the switch element Tr6 and the anode of the diode Drn to the negative DC line N. The lossless regenerative clamp snubber diode Dsn has a cathode connected to the connection point between the emitter of the switch element Tr6 and the anode of the diode Drn, and an anode connected to the negative DC line N.

The anti-parallel diode D6 of the switch element Tr6 and the lossless regenerative clamp snubber diode Dsn form a negative regenerative path in which the current polarity is limited to one direction (from the negative DC line N to the resonant inductor Lr).

The resonant inverter 1 includes a control circuit 6 that controls the on/off of each of the switch elements Tm1, Tm2, Tn3, Tn4, Tr5, and Tr6. The control circuit 6 turns on the switch element Tm1 at zero voltage during PWM control of the switch element Tm1 of the main leg 4 and the switch element Tn4 of the neutral phase leg 5. The control circuit 6 turns on the switch element Tm2 at zero voltage during PWM control of the switch element Tm2 of the main leg 4 and the switch element Tn3 of the neutral phase leg 5.

The discharge operation of the resonant inverter 1 when the output voltage Vo and the inverter current Iinv are positive will be described with reference to Figures 2 and 3. Figure 2 is a timing chart showing the operation of the resonant inverter 1. Figure 3 shows the operation in each mode shown in Figure 2 using an equivalent circuit of the resonant inverter 1.

Since the output voltage Vo is positive, the switch elements Tm1 and Tn4 alternate in PWM operation. When the inverter current Iinv is positive, the target of zero-voltage (ZV) turn-on control by resonance is the on-timing of the switch element Tm1.

The control circuit 6 operates the resonant inverter 1 as a two-level inverter by turning off the switch element Tn3 before resonant operation, creating a mode in which the anti-parallel diode D2 of the switch element Tm2 is conductive. When the inverter current Iinv is positive, the control circuit 6 controls the switch element Tr5 of the positive-side resonant path rp before and after turning on the switch element Tm1 to perform resonant operation on the positive side.

Mode 0 shown in Figure 3(a) is a state in which the inverter current Iinv flows back through the positive polarity path np of the neutral phase leg 5.

In mode 0, the collector-emitter voltages Vce of the switching elements Tm1 and Tm2 are both Vdc/2. The terminal voltages (Vce, reverse voltage VR) of the elements of the auxiliary resonant circuit 2 are Vdc/4 for Tr5, Tr6, Dsp, Dsn, Drp, and Drn. The terminal voltages of the elements of the neutral phase leg 5 are all 0V.

In mode 1, at time t1, the switch elements Tn3 and Tn4 are simultaneously turned off, and the inverter current Iinv is commutated to the anti-parallel diode D2 of the lower-arm switch element Tm2. All other switch elements Tm1, Tm2, Tr5, and Tr6 are in the off state. In mode 1, as shown in FIG. 3(b), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tn3 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 1, Vce of switch element Tm1 changes from Vdc/2 to Vdc, and Vce of switch element Tm2 changes from Vdc/2 to 0V. The terminal voltages of each element of the auxiliary resonant circuit 2, Tr5, Dsp, and Drn, change from Vdc/4 to Vdc/2, and Tr6, Dsn, and Drp, change from Vdc/4 to 0V. The terminal voltages of each element of the neutral phase leg 5, Tn3, and Dnn, change from 0V to Vdc/2.

In mode 2, at time t2, Vce of switch element Tm1 changes to Vdc and Vce of switch element Tm2 changes to 0 V, and the inverter current Iinv circulates through the anti-parallel diode D2 of the lower arm switch element Tm2, as shown in Figure 3(c).

In mode 2, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Tr5, Drn, and Dsp, and 0V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are Vdc/2 for Tn3 and Dnn, and 0V for the other elements.

In mode 3, at time t3 during the dead time DT, the switch element Tr5 in the positive resonant path rp is turned on under zero current (ZC) control, and the inverter current Iinv is commutated to the resonant inductor Lr (positive resonant path rp) as shown in FIG. 3(d). Mode 3 continues until the anti-parallel diode D2 of the switch element Tm2 is turned off.

In mode 3, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Dsp, Vdc/4 for Tr6, Drn, and Dsn, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 2.

In mode 4, the commutation to the resonant inductor Lr is completed at time t4, and the Vce of the switch element Tm1 and the switch element Tm2 changes sinusoidally due to resonance with the resonant capacitors C1 and C2 shown by the dotted lines in FIG. 3(e). In mode 4, the Vce of the switch element Tm1 changes from Vdc to 0 V, and the Vce of the switch element Tm2 changes from 0 V to Vdc.

In mode 4, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as those in mode 3. The terminal voltages of each element of the neutral phase leg 5, Tn4 and Dnp, change from 0 V to Vdc/2.
Tn3 and Dnn change from Vdc/2 to 0V, respectively.

The period of mode 3+4 is the sum of the first commutation time Tcom1 [Lr÷Vdcn×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. Lr is the inductance of the resonance inductor Lr, and Cr is the capacitance of the resonance capacitors C1 and C2. Vdcn is the voltage across the capacitor Cn in the neutral point clamp circuit 3. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is 1/2 the period of resonance at which the resonance frequency is (1/2π√(Lr×2Cr)).

In other words, the switch element Tr5 of the positive-side resonant path rp is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm1 and Tn3.

In mode 5, at time t5 when Vce of switch element Tm1 becomes 0V, as shown in FIG. 3(f), switch elements Tm1 and Tn3 are subjected to zero-voltage turn-on control, and the resonant inductor current ILr is commutated to switch element Tm1.

In mode 5, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 3. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn3 and Dnn, and Vdc/2 for the other elements.

The period of mode 5 is the second commutation time Tcom2 [Lr ÷ Vdcp × Iinv]. Vdcp is the voltage across the capacitor Cp in the neutral point clamp circuit 3. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switch element Tm1 is completed.

In other words, the switch element Tr5 of the positive-side resonant path rp is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm1 and Tn3.

In mode 6, when the commutation of the resonant inductor current ILr to the switch element Tm1 is completed, the switch element Tr5 is turned off at time t6, and power is discharged from the DC bus (positive DC line P) to the load (AC system) as shown in FIG. 3(g).

In mode 6, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Drp, Tr6, and Dsn, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 5.

In mode 7, the inverter current Iinv is commutated to the positive polarity path np of the neutral phase leg 5 by turning off the upper arm switch element Tm1 at time t7, and this is the period until the dead time DT has elapsed after the turn-off control of the switch element Tm1. In mode 7, as shown in FIG. 3(h), the resonant capacitor C1 of the switch element Tm1 is charged and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tm1 is subjected to zero-voltage turn-off control by the lossless snubber.

At time t8 when the dead time DT following the turn-off control of switch element Tm1 has elapsed, switch element Tn4 is subjected to zero-voltage turn-on control and returns to mode 0.

In mode 7, Vce of switch element Tm1 changes from 0V to Vdc/2, and Vce of switch element Tm2 changes from Vdc to Vdc/2. The terminal voltages of each element of the auxiliary resonant circuit 2 change from Vdc/2 to Vdc/4 for Drp, Tr6, and Dsn, and from 0V to Vdc/4 for Drn, Tr5, and Dsp. The terminal voltages of each element of the neutral phase leg 5 change from Vdc/2 to 0V for Tn4 and Dnp.

The above modes 0 to 7 are repeated, and the switch elements Tm1 and Tn3 are controlled to be turned on at zero voltage. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The terminal voltage of each element of the auxiliary resonant circuit 2 and the neutral phase leg 5 never exceeds Vdc/2 in any mode.

　The operation of the resonant inverter 1 when the switch element Tr5 turns off during the above-mentioned mode 5 is shown as mode 5A in Figs. 4 and 5. Fig. 4 is a timing chart showing the operation of the resonant inverter 1. Fig. 5 shows the operation in mode 5A shown in Fig. 4 using an equivalent circuit of the resonant inverter 1.

In mode 5A, the switch element Tr5 turns off due to element variation, calculation variation, malfunction, etc. at time t5A while the resonant inductor current ILr is commutating to the switch element Tm1. The energy excited in the positive direction in the resonant inductor Lr is regenerated to the DC bus without loss as the lossless regenerative clamp snubber diode Dsn and the anti-parallel diode D6 of the switch element Tr6 conduct, as shown by the dotted line in Figure 5. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, so each element of the auxiliary resonant circuit 2, including the switch element Tr5 (diode Drn, lossless regenerative clamp snubber diode Dsp), is clamped at Vdc/2.

The discharge operation of the resonant inverter 1 when the output voltage Vo and the inverter current Iinv are negative will be described with reference to Figures 6 and 7. Figure 6 is a timing chart showing the operation of the resonant inverter 1. Figure 7 shows the operation in each mode shown in Figure 6 using an equivalent circuit of the resonant inverter 1.

Since the output voltage Vo is negative, the switch elements Tm2 and Tn3 alternate in PWM operation. When the inverter current Iinv is negative, the target of zero-voltage turn-on control by resonance is the on-timing of the switch element Tm2.

The control circuit 6 turns off the switch element Tn4 before resonant operation, thereby operating the resonant inverter 1 as a two-level inverter and creating a mode in which the anti-parallel diode D1 of the switch element Tm1 is conductive. When the inverter current Iinv is negative, the control circuit 6 controls the switch element Tr6 of the negative side resonant path rn before and after turning on the switch element Tm2 to perform resonant operation on the negative side.

Mode 10 shown in FIG. 7(a) is a state in which the inverter current Iinv flows back through the negative polarity path nn of the neutral phase leg 5.

In mode 10, the collector-emitter voltages Vce of the switching elements Tm1 and Tm2 are both Vdc/2. The terminal voltages (Vce, reverse voltage VR) of the elements of the auxiliary resonant circuit 2 are Vdc/4 for Tr5, Tr6, Dsp, Dsn, Drp, and Drn. The terminal voltages of the elements of the neutral phase leg 5 are all 0V.

In mode 11, at time t11, the switch elements Tn3 and Tn4 are simultaneously turned off, and the inverter current Iinv is commutated to the anti-parallel diode D1 of the switch element Tm1 in the upper arm. All other switch elements Tm1, Tm2, Tr5, and Tr6 are in the off state. In mode 11, as shown in FIG. 7(b), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tn4 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 11, Vce of switch element Tm2 changes from Vdc/2 to Vdc, and Vce of switch element Tm1 changes from Vdc/2 to 0V. The terminal voltages of each element of auxiliary resonant circuit 2 change from Vdc/4 to Vdc/2 for Tr6, Dsn, and Drp, and from Vdc/4 to 0V for Tr5, Dsp, and Drn. The terminal voltages of each element of neutral phase leg 5 change from 0V to Vdc/2 for Tn4 and Dnp.

In mode 12, at time t12, Vce of switch element Tm2 changes to Vdc and Vce of switch element Tm1 changes to 0 V, and the inverter current Iinv circulates through the anti-parallel diode D1 of the upper arm switch element Tm1, as shown in FIG. 7(c).

In mode 12, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Tr6, Drp, and Dsn, and 0V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are Vdc/2 for Tn4 and Dnp, and 0V for the other elements.

In mode 13, at time t13 during the dead time DT, the switch element Tr6 of the negative resonant path rn is turned on with zero current, and the inverter current Iinv is commutated to the resonant inductor Lr (negative resonant path rn) as shown in FIG. 7(d). Mode 13 continues until the anti-parallel diode D1 of the switch element Tm1 is turned off.

In mode 13, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Dsn, Vdc/4 for Tr5, Drp, and Dsp, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 12.

In mode 14, the commutation to resonant inductor Lr is completed at time t14, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2 shown by dotted lines in FIG. 7(e). In mode 14, Vce of switch element Tm2 changes from Vdc to 0V, and Vce of switch element Tm1 changes from 0V to Vdc.

In mode 14, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 13. The terminal voltages of each element of the neutral phase leg 5, Tn3 and Dnn, change from 0V to Vdc/2, and Tn4 and Dnp change from Vdc/2 to 0V.

The period of mode 13+14 is the sum of the first commutation time Tcom1 [Lr÷Vdcp×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is 1/2 the period of resonance at which the resonance frequency is (1/2π√(Lr×2Cr)).

In other words, the switch element Tr6 of the negative resonant path rn is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm2 and Tn4.

In mode 15, at time t15 when Vce of switch element Tm2 becomes 0V, as shown in FIG. 7(f), switch elements Tm2 and Tn4 are subjected to zero-voltage turn-on control, and the resonant inductor current ILr is commutated to switch element Tm2.

In mode 15, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 13. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn4 and Dnp, and Vdc/2 for the other elements.

The period of mode 15 is the second commutation time Tcom2 [Lr ÷ Vdcn × Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switch element Tm2 is completed.

In other words, the switch element Tr6 of the negative resonant path rn is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm2 and Tn4.

In mode 16, the switch element Tr6 is turned off at time t16 when the commutation of the resonant inductor current ILr to the switch element Tm2 is completed. In mode 16, as shown in FIG. 7(g), power is discharged from the DC bus (negative DC line N) to the load (AC system).

In mode 16, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Drn, Tr5, and Dsp, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 15.

In mode 17, the inverter current Iinv is commutated to the negative polarity path nn of the neutral phase leg 5 by turning off the lower arm switch element Tm2 at time t17, and this is the period until the dead time DT has elapsed after the turn-off control of the switch element Tm1. In mode 17, as shown in FIG. 7(h), the resonant capacitor C2 of the switch element Tm2 is charged and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tm2 is subjected to zero-voltage turn-off control by the lossless snubber.

At time t18 when the dead time DT following the turn-off control of switch element Tm2 has elapsed, switch element Tn3 is subjected to zero-voltage turn-on control, returning to mode 10.

In mode 17, Vce of switch element Tm2 changes from 0V to Vdc/2, and Vce of switch element Tm1 changes from Vdc to Vdc/2. The terminal voltages of each element of the auxiliary resonant circuit 2 change from Vdc/2 to Vdc/4 for Drn, Tr5, and Dsp, and from 0V to Vdc/4 for Drp, Tr4, and Dsn. The terminal voltages of each element of the neutral phase leg 5 change from Vdc/2 to 0V for Tn4 and Dnp.

The above modes 10 to 17 are repeated, and the switch elements Tm2 and Tn3 are controlled to be turned on at zero voltage. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The terminal voltage of each element of the auxiliary resonant circuit 2 and the neutral phase leg 5 never exceeds Vdc/2 in any mode.

The operation of the resonant inverter 1 in the case where the switch element Tr6 turns off during the above-mentioned mode 15 is shown as mode 15A in Figs. 8 and 9. Fig. 8 is a timing chart showing the operation of the resonant inverter 1. Fig. 9 shows the operation in mode 15A shown in Fig. 8 using an equivalent circuit of the resonant inverter 1.

In mode 15A, at time t15A while the resonant inductor current ILr is commutating to the switch element Tm2, the switch element Tr6 is turned off due to element variation, calculation variation, malfunction, etc. The energy excited in the negative direction in the resonant inductor Lr is regenerated to the DC bus without loss as the lossless regenerative clamp snubber diode Dsp and the anti-parallel diode D5 of the switch element Tr5 conduct, as shown by the dotted line in Figure 9. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, so each element of the auxiliary resonant circuit 2, including the switch element Tr6 (diode Drp, lossless regenerative clamp snubber diode Dsn), is clamped at Vdc/2.

The charging operation of the resonant inverter 1 when the output voltage Vo is positive and the inverter current Iinv is negative will be described with reference to Figures 10 and 11. Figure 10 is a timing chart showing the operation of the resonant inverter 1. Figure 11 shows the operation in each mode shown in Figure 10 using an equivalent circuit of the resonant inverter 1.

Since the output voltage Vo is positive, the switch elements Tm1 and Tn4 alternate in PWM operation. When the inverter current Iinv is negative, the target of zero-voltage turn-on control by resonance is the on-timing of the switch element Tn4.

Mode 20 shown in FIG. 11(a) is a state in which the inverter current Iinv circulates through the anti-parallel diode D1 of the switch element Tm1. As shown in FIG. 11(a), power is being charged from the load (AC system) to the DC bus (positive DC line P).

In mode 20, Vce of switch element Tm2 is Vdc. The terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Tr6, Drp, and Dsn, and 0V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn3 and Dnn, and Vdc/2 for the other elements.

In mode 21, as shown in FIG. 11(b), at time t21, switch elements Tm1 and Tn3 are simultaneously turned off. In mode 21, there is no change in state from mode 20.

In mode 22, at time t22 during the dead time DT, the switch element Tr6 of the negative resonant path rn is subjected to zero current turn-on control, and the inverter current Iinv is commutated to the resonant inductor Lr (negative resonant path rn) as shown in FIG. 11(c). Mode 22 continues until the anti-parallel diode D1 of the switch element Tm1 is turned off.

In mode 22, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Dsn, Vdc/4 for Tr5, Drp, and Dsp, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 21.

In mode 23, the commutation to resonant inductor Lr is completed at time t23, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2 shown by dotted lines in FIG. 11(d). In mode 23, Vce of switch element Tm2 changes from Vdc to 0 V, and Vce of switch element Tm1 changes from 0 V to Vdc.

In mode 23, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 22. The terminal voltages of each element of the neutral phase leg 5, Tn3 and Dnn, change from 0V to Vdc/2, and Tn4 and Dnp change from Vdc/2 to 0V.

The period of mode 22+23 is the sum of the first commutation time Tcom1 [Lr÷Vdcp×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is 1/2 the period of resonance at which the resonance frequency is (1/2π√(Lr×2Cr)).

In other words, the switch element Tr6 of the negative resonant path rn is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm2 and Tn4.

In mode 24, as shown in FIG. 11(e), at time t24 when Vce of switch element Tm2 becomes 0V, switch element Tm2 and switch element Tn4 are subjected to zero voltage turn-on control. In mode 24, the resonant inductor current ILr is commutated to switch element Tm2 without being commutated to neutral phase leg 5.

In mode 24, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 23. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn4 and Dnp, and Vdc/2 for the other elements.

The period of mode 24 is the second commutation time Tcom2 [Lr ÷ Vdcn × Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switch element Tm2 is completed.

In other words, the switch element Tr6 of the negative resonant path rn is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm2 and Tn4.

In mode 25, the switch element Tr6 is turned off at time t25 upon completion of the commutation of the resonant inductor current ILr to the switch element Tm2.

In mode 25, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Drn, Tr5, and Dsp, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 24.

In mode 26, the inverter current Iinv is commutated to the negative polarity path nn of the neutral phase leg 5 by controlling the turn-off of the lower arm switch element Tm2 at time t26. In mode 26, as shown in FIG. 11(g), the resonant capacitor C2 of the switch element Tm2 is charged, and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tm2 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 26, Vce of switch element Tm2 changes from 0V to Vdc/2, and Vce of switch element Tm1 changes from Vdc to Vdc/2. The terminal voltages of each element of the auxiliary resonant circuit 2 change from Vdc/2 to Vdc/4 for Drn, Tr5, and Dsp, and from 0V to Vdc/4 for Drp, Tr4, and Dsn. The terminal voltages of each element of the neutral phase leg 5 change from Vdc/2 to 0V for Tn3 and Dnn.

Mode 27 is a state in which commutation is completed and inverter current Iinv is circulating through the negative polarity path nn of neutral phase leg 5. In mode 27 after commutation to the negative polarity path nn of neutral phase leg 5 is completed, a series of zero voltage turn-ons is completed by controlling switch element Tn3 to be turned on at zero current.

In mode 27, the collector-emitter voltages Vce of the switching elements Tm1 and Tm2 are both Vdc/2. The terminal voltages (Vce, reverse voltage VR) of the elements of the auxiliary resonant circuit 2 are Vdc/4 for Tr5, Tr6, Dsp, Dsn, Drp, and Drn. The terminal voltages of the elements of the neutral phase leg 5 are all 0V.

In mode 28, at time t28, the switch element Tn4 is turned off and the inverter current Iinv is commutated to the switch element Tm1. In mode 28, as shown in FIG. 11(i), the resonant capacitor C2 of the switch element Tm2 is charged and the resonant capacitor C1 of the switch element Tm1 is discharged. Therefore, the switch element Tn4 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 28, Vce of switch element Tm2 changes from Vdc/2 to Vdc, and Vce of switch element Tm1 changes from Vdc/2 to 0V. The terminal voltages of each element of the auxiliary resonant circuit 2, Tr6, Dsn, and Drp, change from Vdc/4 to Vdc/2, and Tr5, Dsp, and Drn, change from Vdc/4 to 0V. The terminal voltages of each element of the neutral phase leg 5, Tn4, and Dnp, change from 0V to Vdc/2.

At time t29 when the dead time DT following the turn-off control of switch element Tn4 has elapsed, switch element Tm1 is subjected to zero-voltage turn-on control and returns to mode 20.

The above modes 20 to 28 are repeated, and the switch elements Tm1 and Tn4 are controlled to be turned on at zero voltage. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The terminal voltage of each element of the auxiliary resonant circuit 2 and the neutral phase leg 5 never exceeds Vdc/2 in any mode.

If the switch element Tr6 is turned off during the above mode 24, the energy negatively excited in the resonant inductor Lr is regenerated to the DC bus without loss, similar to mode 15A shown in FIG. 9. The lossless regenerative clamp snubber diode Dsp and the anti-parallel diode D5 of the switch element Tr5 are conductive. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, so each element of the auxiliary resonant circuit 2, including the switch element Tr6 (diode Drp, lossless regenerative clamp snubber diode Dsn), is clamped at Vdc/2.

The charging operation of the resonant inverter 1 when the output voltage Vo is negative and the inverter current Iinv is positive will be described with reference to Figures 12 and 13. Figure 12 is a timing chart showing the operation of the resonant inverter 1. Figure 13 shows the operation in each mode shown in Figure 12 using an equivalent circuit of the resonant inverter 1.

Since the output voltage Vo is negative, the switch elements Tm2 and Tn3 alternate in PWM operation. When the inverter current Iinv is positive, the target of zero-voltage turn-on control by resonance is the on-timing of the switch element Tn3.

Mode 30 shown in FIG. 13(a) is a state in which the inverter current Iinv circulates through the anti-parallel diode D2 of the switch element Tm2. As shown in FIG. 13(a), power is being charged from the load (AC system) to the DC bus (negative DC line N).

In mode 30, Vce of switch element Tm1 is Vdc. The terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Tr5, Drn, and Dsp, and 0V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn4 and Dnp, and Vdc/2 for the other elements.

In mode 31, as shown in FIG. 13(b), at time t31, switch elements Tm2 and Tn4 are simultaneously turned off. In mode 31, there is no change in state from mode 30.

In mode 32, at time t32 during the dead time DT, the switch element Tr5 in the positive resonant path rp is turned on with zero current, and the inverter current Iinv is commutated to the resonant inductor Lr (positive resonant path rp) as shown in FIG. 13(c). Mode 32 continues until the anti-parallel diode D2 of the switch element Tm2 is turned off.

In mode 32, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Dsp, Vdc/4 for Tr6, Drn, and Dsn, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 31.

In mode 33, the commutation to resonant inductor Lr is completed at time t33, and Vce of switch element Tm1 and switch element Tm2 changes sinusoidally due to resonance with resonant capacitors C1 and C2 shown by dotted lines in FIG. 13(d). In mode 33, Vce of switch element Tm1 changes from Vdc to 0V, and Vce of switch element Tm2 changes from 0V to Vdc.

In mode 33, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 32. The terminal voltages of each element of the neutral phase leg 5 change from 0V to Vdc/2 for Tn4 and Dnp, and from Vdc/2 to 0V for Tn3 and Dnn.

The period of mode 32+33 is the sum of the first commutation time Tcom1 [Lr÷Vdcn×Iinv] and the resonance time Tres [π×√(Lr×2Cr)]. The first commutation time Tcom1 is the time until the commutation of the inverter current Iinv to the resonance inductor Lr is completed. The resonance time Tres is 1/2 the period of resonance at which the resonance frequency is (1/2π√(Lr×2Cr)).

In other words, the switch element Tr5 of the positive-side resonant path rp is controlled to be turned on (first commutation time Tcom1+resonant time Tres) before the turn-on timing of the switch elements Tm1 and Tn3.

In mode 34, as shown in FIG. 13(e), at time t34 when Vce of switch element Tm1 becomes 0V, switch element Tm1 and switch element Tn3 are subjected to zero voltage turn-on control. In mode 34, the resonant inductor current ILr is commutated to switch element Tm1 without being commutated to neutral phase leg 5.

In mode 34, the terminal voltages of each element of the auxiliary resonant circuit 2 are the same as in mode 33. The terminal voltages of each element of the neutral phase leg 5 are 0V for Tn3 and Dnn, and Vdc/2 for the other elements.

The period of mode 34 is the second commutation time Tcom2 [Lr ÷ Vdcp × Iinv]. The second commutation time Tcom2 is the time until the commutation of the inverter current Iinv to the switch element Tm1 is completed.

In other words, the switch element Tr5 of the positive-side resonant path rp is controlled to be turned off after (the second commutation time Tcom2) the turn-on timing of the switch elements Tm1 and Tn3.

In mode 35, the switch element Tr5 is turned off at time t35 upon completion of the commutation of the resonant inductor current ILr to the switch element Tm1.

In mode 35, the terminal voltages of each element of the auxiliary resonant circuit 2 are Vdc/2 for Drp, Tr6, and Dsn, and 0 V for the other elements. The terminal voltages of each element of the neutral phase leg 5 are the same as in mode 34.

In mode 36, the upper arm switch element Tm1 is turned off at time t36, thereby commutating the inverter current Iinv to the positive polarity path np of the neutral phase leg 5. In mode 36, as shown in FIG. 13(g), the resonant capacitor C1 of the switch element Tm1 is charged, and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tm1 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 36, Vce of switch element Tm1 changes from 0V to Vdc/2, and Vce of switch element Tm2 changes from Vdc to Vdc/2. The terminal voltages of each element of the auxiliary resonant circuit 2 change from Vdc/2 to Vdc/4 for Drp, Tr6, and Dsn, and from 0V to Vdc/4 for Drn, Tr5, and Dsp. The terminal voltages of each element of the neutral phase leg 5 change from Vdc/2 to 0V for Tn4 and Dnp.

Mode 37 is a state in which commutation is completed and inverter current Iinv is flowing back through the positive polarity path np of neutral phase leg 5. In mode 37 after commutation to the positive polarity path np of neutral phase leg 5 is completed, a series of zero voltage turn-ons is completed by controlling switch element Tn4 to be turned on at zero current.

In mode 37, the collector-emitter voltages Vce of the switching elements Tm1 and Tm2 are both Vdc/2. The terminal voltages (Vce, reverse voltage VR) of the elements of the auxiliary resonant circuit 2 are Vdc/4 for Tr5, Tr6, Dsp, Dsn, Drp, and Drn. The terminal voltages of the elements of the neutral phase leg 5 are all 0V.

In mode 38, at time t38, the switch element Tn3 is turned off and the inverter current Iinv is commutated to the switch element Tm2. In mode 38, as shown in FIG. 13(i), the resonant capacitor C1 of the switch element Tm1 is charged and the resonant capacitor C2 of the switch element Tm2 is discharged. Therefore, the switch element Tn3 is subjected to zero-voltage turn-off control by the lossless snubber.

In mode 38, Vce of switch element Tm1 changes from Vdc/2 to Vdc, and Vce of switch element Tm2 changes from Vdc/2 to 0V. The terminal voltages of each element of the auxiliary resonant circuit 2, Tr5, Dsp, and Drn, change from Vdc/4 to Vdc/2, and Tr6, Dsn, and Drp, change from Vdc/4 to 0V. The terminal voltages of each element of the neutral phase leg 5, Tn3, and Dnn, change from 0V to Vdc/2.

At time t39 when the dead time DT following the turn-off control of switch element Tn3 has elapsed, switch element Tm2 is subjected to zero-voltage turn-on control and returns to mode 30.

The above modes 30 to 38 are repeated, and the switch elements Tm2 and Tn3 are controlled to be turned on at zero voltage. The auxiliary resonant circuit 2 serves as a path for the energy stored in the resonant inductor Lr. The terminal voltage of each element of the auxiliary resonant circuit 2 and the neutral phase leg 5 never exceeds Vdc/2 in any mode.

If the switch element Tr5 is turned off during the above mode 34, the energy excited in the positive direction in the resonant inductor Lr is regenerated to the DC bus without loss, similar to mode 5A shown in FIG. 5. The lossless regenerative clamp snubber diode Dsn and the anti-parallel diode D6 of the switch element Tr6 are conductive. During this regeneration, the auxiliary resonant circuit 2 is clamped to the neutral point A of the DC bus, so each element of the auxiliary resonant circuit 2, including the switch element Tr5 (diode Drn, lossless regenerative clamp snubber diode Dsp), is clamped at Vdc/2.

FIG. 14 shows a T-NPC type inverter circuit 10 to which an auxiliary resonant circuit 2 is applied. In the T-NPC type inverter circuit 10, the switch elements Tn3 and Tn4 are connected in series as a neutral phase leg 5a connected between the neutral point A and the input/output point B so that they can be controlled to have opposite withstand voltage directions. The collector of the switch element Tn3 is connected to the neutral point A and the emitter is connected to the emitter of the switch element Tn4, and the collector of the switch element Tn4 is connected to the input/output point B.

In the neutral phase leg 5a, the switch element Tn3 and the anti-parallel diode D4 of the switch element Tn4 function as a positive polarity path np that is opened and closed by the switch element Tn3. The switch element Tn4 and the anti-parallel diode D3 of the switch element Tn3 function as a negative polarity path nn that is opened and closed by the switch element Tn4.

FIG. 15 shows a full-bridge inverter circuit 11 to which the resonant inverter 1 is applied. The full-bridge inverter circuit 11 is a resonant inverter 1 configured in a full-bridge configuration. The full-bridge inverter circuit 11 includes a U-phase main leg 4u, a U-phase neutral leg 5au of the U-phase main leg 4u, and a U-phase auxiliary resonant circuit 2u. The full-bridge inverter circuit 11 includes a W-phase main leg 4w, a W-phase neutral leg 5aw of the W-phase main leg 4w, and a W-phase auxiliary resonant circuit 2w.

The U-phase control circuit 6u and the W-phase control circuit 6w control the U-phase auxiliary resonant circuit 2u and the W-phase auxiliary resonant circuit 2w separately at different timings. The control of the U-phase auxiliary resonant circuit 2u operates differently depending on the switching state of the W phase. The control of the W-phase auxiliary resonant circuit 2w operates differently depending on the switching state of the U phase.

FIG. 16 shows a three-phase inverter circuit 12 to which the resonant inverter 1 is applied. The three-phase inverter circuit 12 is a three-phase configuration of the resonant inverter 1. The three-phase inverter circuit 12 includes a U-phase main leg 4u, a U-phase neutral phase leg 5au of the U-phase main leg 4u, and a U-phase auxiliary resonant circuit 2u. The three-phase inverter circuit 12 includes a V-phase main leg 4v, a V-phase neutral phase leg 5av of the V-phase main leg 4v, and a V-phase auxiliary resonant circuit 2v. The three-phase inverter circuit 12 includes a W-phase main leg 4w, a W-phase neutral phase leg 5aw of the W-phase main leg 4w, and a W-phase auxiliary resonant circuit 2w.

The U-phase control circuit 6u, V-phase control circuit 6v, and W-phase control circuit 6w control the U-phase auxiliary resonant circuit 2u, V-phase auxiliary resonant circuit 2v, and W-phase auxiliary resonant circuit 2w at individual timings. The control of the U-phase auxiliary resonant circuit 2u operates differently depending on the switching states of the V and W phases. The control of the V-phase auxiliary resonant circuit 2v operates differently depending on the switching states of the U and W phases. The control of the W-phase auxiliary resonant circuit 2w operates differently depending on the switching states of the U and V phases.

The case where the switch element Tm1 of the U-phase main leg 4u is turned on at zero voltage while the switch element Tm1 of the V-phase main leg 4v and the W-phase main leg 4w are both on will be described with reference to FIG. 17. The U-phase current is positive, and the V-phase current and the W-phase current are all negative.

Mode 40 shown in FIG. 17(a) is a state in which the inverter current Iinv flows back through the anti-parallel diode D2 of the switch element Tm2 of the U-phase main leg 4u, and the anti-parallel diode D1 of the switch element Tm1 of the V-phase main leg 4v and the W-phase main leg 4w.

In mode 41, the switch element Tr5 in the U-phase auxiliary resonant circuit 2u of the U-phase main leg 4u is turned on, so that the inverter current Iinv is commutated to the positive resonant path rp (resonant inductor Lr) of the U-phase auxiliary resonant circuit 2u, as shown in FIG. 17(b).

In mode 42, commutation to resonant inductor Lr of U-phase auxiliary resonant circuit 2u is completed. In mode 42, Vce of switch element Tm1 and switch element Tm2 of U-phase main leg 4u changes sinusoidally due to resonance with resonant capacitors C1 and C2 of U-phase main leg 4u shown by dotted lines in FIG. 17(c). In mode 42, Vce of switch element Tm1 of U-phase main leg 4u changes from Vdc to 0V, and Vce of switch element Tm2 of U-phase main leg 4u changes from 0V to Vdc.

In mode 43, as shown in FIG. 17(d), when Vce of the switch element Tm1 of the U-phase main leg 4u becomes 0V, the switch element Tm1 of the U-phase main leg 4u is subjected to zero-voltage turn-on control. In mode 43, the resonant inductor current ILr is commutated to the switch element Tm1 of the U-phase main leg 4u.

In mode 44, when the resonant inductor current ILr is commutated to the switch element Tm1, the switch element Tr5 is turned off, and the current flows back between the inverter input and output points, as shown in FIG. 17(e).

The above is the operation of the U-phase by the U-phase control circuit 6u. The V-phase control circuit 6v and the W-phase control circuit 6w control the V-phase and W-phase at separate timings, just like the U-phase.

(summary)
The resonant inverter according to each embodiment of the present invention can also be described as follows.
(1) A resonant inverter 1 according to one embodiment of the present invention includes a neutral point clamp circuit 3 including a capacitor Cp (positive side capacitor) and a capacitor Cn (negative side capacitor) connected in series between a positive side DC line P and a negative side DC line N. In the neutral point clamp circuit 3, a connection point between the capacitor Cp and the capacitor Cn serves as a neutral point A. The resonant inverter 1 includes a main leg 4 connected in series between the positive side DC line P and the negative side DC line N. The main leg 4 includes a switch element Tm1 (upper arm switch) and a switch element Tm2 (lower arm switch), and a connection point between the switch element Tm1 and the switch element Tm2 serves as an input/output point B of the inverter current. The resonant inverter 1 includes a resonant capacitor C1 (first resonant capacitor) and a resonant capacitor C2 (second resonant capacitor) connected in parallel to the switch element Tm1 and the switch element Tm2. The resonant inverter 1 includes an anti-parallel diode D1 (first anti-parallel diode) and an anti-parallel diode D2 (second anti-parallel diode) connected in anti-parallel to the switch element Tm1 and the switch element Tm2. The resonant inverter 1 includes a neutral phase leg 5 provided with a positive polarity path np in which the current polarity is limited to the direction from the neutral point A to the input/output point B, and a negative polarity path nn in which the current polarity is limited to the direction from the input/output point B to the neutral point A. The neutral phase leg 5 includes a switch element Tn3 (positive side neutral phase switch) and a switch element Tn4 (negative side neutral phase switch) that open and close the positive polarity path np and the negative polarity path nn, respectively. The resonant inverter 1 includes an auxiliary resonant circuit 2 including a resonant inductor Lr having one end connected to the input/output point B. The auxiliary resonant circuit 2 includes a positive side resonant path rp in which the current polarity is limited to the direction from the neutral point A to the resonant inductor Lr, and which is opened and closed by a switch element Tr5 (positive side resonant switch). The auxiliary resonant circuit 2 includes a negative-side resonant path rn whose current polarity is limited to the direction from the resonant inductor Lr to the neutral point A and which is opened and closed by a switch element Tr6 (negative-side resonant switch). The auxiliary resonant circuit 2 includes a positive-side regenerative path (anti-parallel diode D3 of switch element Tr3 + lossless regenerative clamp snubber diode Dsp) whose current polarity is limited to the direction from the resonant inductor Lr to the positive-side DC line P. The auxiliary resonant circuit 2 includes a negative-side regenerative path (anti-parallel diode D4 of switch element Tr4 + lossless regenerative clamp snubber diode Dsn) whose current polarity is limited to the direction from the negative-side DC line N to the resonant inductor Lr.

According to the resonant inverter 1 described in (1) above, the auxiliary resonant circuit 2 becomes a lossless regenerative path of the energy stored in the resonant inductor Lr. The auxiliary resonant circuit 2 is clamped to the voltage of the neutral point A by the positive side resonant path rp and the negative side resonant path rn. The elements constituting the auxiliary resonant circuit 2 can be composed of elements with a lower withstand voltage than the elements of the main leg 4, which is the main circuit. The range of elements to be selected for the auxiliary resonant circuit 2 is wider, and the auxiliary resonant circuit 2 can be constructed at low cost. The lossless regenerative clamp snubber diodes Dsp and Dsn become a regenerative path of the energy of the resonant inductor Lr, enabling highly efficient overvoltage protection measures. By applying the auxiliary resonant circuit 2 to the resonant inverter 1, which is a three-level inverter, the efficiency of the resonant inverter 1 can be further improved. The resonant inverter 1 is optimal for charging and discharging applications because soft switching is possible even at power factors other than 1. The resonant inverter 1 has a heat dissipation effect due to the provision of the auxiliary resonant circuit 2, and therefore the heat dissipation mechanism is inexpensive.

(2) In the resonant inverter 1 described in (1) above, during a discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between, the switch element Tn3 may be controlled to be turned off simultaneously with the switch element Tn4 and may be controlled to be turned on simultaneously with the switch element Tm1.

According to the resonant inverter 1 described in (2) above, during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between, the resonant inverter 1 can be treated as a two-level converter, making it easy to control the resonant operation.

(3) In the resonant inverter 1 described in (2) above, the switch element Tr5 may be turned on during the dead time DT before the switch element Tm1 is turned on, and the switch element Tr5 may be turned off after the switch element Tm1 is turned on.

The resonant inverter 1 described in (3) above allows the inverter current Iinv to be commutated to the auxiliary resonant circuit 2 during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between, thereby causing a resonant operation.

(4) In the resonant inverter 1 described in (2) or (3) above, the switch element Tr5 may be turned on at a timing before the timing of the turn-on control of the switch element Tm1, which is the sum of the first commutation time Tcom1 (first positive side commutation time) and the resonant time Tres. The first commutation time Tcom1 (first positive side commutation time) is the time until the commutation of the inverter current Iinv to the resonant inductor Lr is completed by the turn-on control of the switch element Tr5. The resonant time Tres is 1/2 the period of the resonance of the resonant inductor Lr and the resonant capacitors C1 and C2.

The resonant inverter 1 described in (4) above can achieve zero-voltage turn-on control of the switch element Tm1 during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between.

(5) In the resonant inverter 1 described in any one of (2) to (3) above, the switch element Tr5 may be turned off at a timing after a second commutation time Tcom2 (second positive side commutation time) from the timing of the turn-on control of the switch element Tm1. The second commutation time Tcom2 (second positive side commutation time) is the time until the commutation of the resonant inductor current ILr from the resonant inductor Lr to the switch element Tm1 is completed by the turn-on control of the switch element Tm1.

The resonant inverter 1 described in (5) above can quickly terminate the resonant operation after the zero voltage turn-on control of the switch elements Tm1 and Tn3 during the discharge operation in which the switch elements Tm1 and Tn4 are alternately controlled with a dead time DT in between.

(6) In the resonant inverter 1 described in (1) above, during a discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with a dead time DT in between, the switch element Tn4 may be controlled to be turned off simultaneously with the switch element Tn3 and may be controlled to be turned on simultaneously with the switch element Tm2.

According to the resonant inverter 1 described in (6) above, during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with a dead time DT in between, the resonant inverter 1 can be treated as a two-level converter, making it easy to control the resonant operation.

(7) In the resonant inverter 1 described in (6) above, the switch element Tr6 may be turned on during the dead time DT before the switch element Tm2 is turned on, and the switch element Tr6 may be turned off after the switch element Tm2 is turned on.

According to the resonant inverter 1 described in (7) above, during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with a dead time DT in between, the inverter current Iinv can be commutated to the auxiliary resonant circuit 2 to cause a resonant operation.

(8) In the resonant inverter 1 described in (6) or (7) above, the switch element Tr6 may be turned on at a timing before the timing of the turn-on control of the switch element Tm2, which is the sum of the first commutation time Tcom1 (first negative commutation time) and the resonant time Tres. The first commutation time Tcom1 (first negative commutation time) is the time until the commutation of the inverter current Iinv to the resonant inductor Lr is completed by the turn-on control of the switch element Tr6.

The resonant inverter 1 described in (8) above can achieve zero-voltage turn-on control of the switch element Tm2 during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with a dead time DT in between.

(9) In the resonant inverter 1 described in any one of (6) to (7) above, the switch element Tr6 may be turned off at a timing after a second commutation time Tcom2 (second negative commutation time) from the timing of the turn-on control of the switch element Tm2. The second commutation time Tcom2 (second negative commutation time) is the time until the commutation of the resonant inductor current ILr from the resonant inductor Lr to the switch element Tm2 is completed by the turn-on control of the switch element Tm2.

The resonant inverter 1 described in (9) above can quickly terminate the resonant operation after the zero voltage turn-on control of the switch elements Tm2 and Tn4 during the discharge operation in which the switch elements Tm2 and Tn3 are alternately controlled with the dead time DT in between.

The present invention has been described above using specific embodiments, but the above embodiments are merely examples, and it goes without saying that the present invention can be modified and implemented without departing from the spirit of the invention.

1 Resonant inverter 2, 2u, 2v, 2w Auxiliary resonant circuit 3 Neutral point clamp circuit 4 Main leg 4u U-phase main leg 4v V-phase main leg 4w W-phase main leg 5 Neutral phase leg 5a Neutral phase leg 5au U-phase neutral phase leg 5av V-phase neutral phase leg 5aw W-phase neutral phase leg 5u U-phase neutral phase leg 5w W-phase neutral phase leg 6 Control circuit 6u U-phase control circuit 6v V-phase control circuit 6w W-phase control circuit 10 T-NPC type inverter circuit 11 Full bridge inverter circuit 12 Three-phase inverter circuit C1, C2 Resonant capacitor Cn, Cp Capacitor D1, D2, D3, D4, D5, D6 Anti-parallel diode Dnn, Dnp, Drn, Drp Diode Dsn, Dsp Lossless regenerative clamp snubber diode L1 Inductor Lr Resonant inductor N Negative side DC line P Positive side DC line Tm1, Tm2, Tn3, Tn4, Tr5, Tr6 Switch element nn Negative side polarity path np Positive side polarity path rn Negative side resonant path rp Positive side resonant path

Claims (9)

a neutral point clamp circuit including a positive side capacitor and a negative side capacitor connected in series between a positive side DC line and a negative side DC line, the connection point between the positive side capacitor and the negative side capacitor being a neutral point;
a main leg including an upper arm switch and a lower arm switch connected in series between the positive DC line and the negative DC line, the connection point between the upper arm switch and the lower arm switch being an input/output point of an inverter current;
a first resonant capacitor and a second resonant capacitor connected in parallel to the upper arm switch and the lower arm switch;
a first anti-parallel diode and a second anti-parallel diode connected in anti-parallel to the upper arm switch and the lower arm switch;
a neutral phase leg including a positive side neutral phase switch and a negative side neutral phase switch for opening and closing a positive polarity path, the polarity of which is limited to a direction from the neutral point to the input/output point, and a negative polarity path, the polarity of which is limited to a direction from the input/output point to the neutral point, respectively;
an auxiliary resonant circuit including a resonant inductor having one end connected to the input/output point;
The auxiliary resonant circuit includes:
a positive-side resonant path in which a current polarity is limited to a direction from the neutral point to the resonant inductor and which is opened and closed by a positive-side resonant switch;
a negative-side resonant path in which a current polarity is limited to a direction from the resonant inductor to the neutral point and which is opened and closed by a negative-side resonant switch;
a positive-side regenerative path in which a current polarity is limited to a direction from the resonant inductor to the positive-side DC line;
a negative-side regenerative path whose current polarity is limited to a direction from the negative-side DC line to the resonant inductor. The resonant inverter according to claim 1, in which the upper arm switch and the negative side neutral phase switch are alternately controlled with a dead time between them during a discharge operation, and the positive side neutral phase switch is controlled to be turned off simultaneously with the negative side neutral phase switch. The resonant inverter according to claim 2, wherein the positive side resonant switch is controlled to be turned on during the dead time before the upper arm switch is controlled to be turned on, and the positive side resonant switch is controlled to be turned off after the upper arm switch is controlled to be turned on. 3. The resonant inverter according to claim 2, wherein the positive side resonant switch is turned on at a timing before the timing of the turn-on control of the upper arm switch, the timing being a sum of a positive side first commutation time until the commutation of the inverter current to the resonant inductor is completed by the turn-on control of the positive side resonant switch, and a resonance time which is 1/2 the period of resonance by the resonant inductor, the first resonant capacitor, and the second resonant capacitor. The resonant inverter according to claim 2, wherein the positive-side resonant switch is turned off at a timing that is a second positive-side commutation time after the upper arm switch is turned on and until the commutation of the resonant inductor current from the resonant inductor to the upper arm switch is completed by the upper arm switch turn-on control. The resonant inverter according to claim 1, in which the lower arm switch and the positive side neutral phase switch are alternately controlled with a dead time between them during a discharge operation, and the negative side neutral phase switch is controlled to be turned off simultaneously with the positive side neutral phase switch. The resonant inverter according to claim 6, wherein the negative-side resonant switch is controlled to be turned on during the dead time before the lower-arm switch is controlled to be turned on, and the negative-side resonant switch is controlled to be turned off after the lower-arm switch is controlled to be turned on. 7. The resonant inverter according to claim 6, wherein the negative side resonant switch is turned on at a timing before the timing of the turn-on control of the lower arm switch, the timing being a sum of a negative side first commutation time until the commutation of the inverter current to the resonant inductor is completed by the turn-on control of the negative side resonant switch, and a resonance time which is 1/2 the period of resonance by the resonant inductor, the first resonant capacitor, and the second resonant capacitor. The resonant inverter according to claim 6, wherein the negative-side resonant switch is turned off at a timing that is a second negative-side commutation time after the timing of the turn-on control of the lower arm switch, the time until the commutation of the resonant inductor current from the resonant inductor to the lower arm switch is completed by the turn-on control of the lower arm switch.

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