JP2000050529A - Method for limiting current of power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a cross current by forming a voltage command of a voltage control system according to a commercial power source voltage in the case of switching a commercial power source into an inverter output voltage, thereby controlling an amplitude of the output voltage to mach the commercial AC power source. SOLUTION: An input voltage(commercial AC power source 2) of an uninterruptible power source 1 is detected by a voltage detector 6, and its phase is detected by a phase detector 9. A reference sine wave voltage generator 10 contains a reference voltage setter, has a predetermined peak, forms voltage commands Vuv0, Vwv0 synchronized with the power source 2, and inputs it to a voltage command forming unit 4. A voltage control system 31 inputs command values Vuvr, Vwvr of an inverter line output voltage to be outputted from the unit 4, and voltage controls so that both coincide with the output voltage of an LC filter 14 as a feedback amount. The calculated voltage command is pulse-modulated by a PWM control system 32, and a gate signal for ON/OFF controlling a switching element of a voltage PWM inverter 13 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an uninterruptible power supply, in which an AC voltage having a desired magnitude and frequency is converted to a voltage type PWM.
The present invention relates to a current limiting method for a power conversion device that outputs power using an inverter.

[0002]

2. Description of the Related Art In an uninterruptible power supply, when an abnormality occurs in a power supply, a commercial power supply and an inverter output voltage are switched to supply power to a load without an instantaneous interruption. After the abnormality recovery of the uninterruptible power supply, the operation of switching from the commercial power supply to the inverter output voltage is performed again. In such a switching operation, if there is a difference voltage between the commercial power supply voltage and the inverter output voltage, the difference voltage causes a cross current flowing between the commercial power supply and the inverter. Since this cross current is limited only by the impedance of the commercial power supply system and the filter reactor on the inverter side, even a small difference voltage causes an excessive cross current. The operation of detecting the current, judging again as abnormal, and switching to the commercial power supply is repeated.
As described above, there is a problem that a satisfactory switching operation cannot be performed unless the overcurrent generated during the switching operation can be suppressed.

[0003]

As described above, during the switching operation between the commercial power supply and the inverter output voltage, a cross current flows between the commercial power supply and the inverter due to the difference voltage between the two.

In order to suppress this cross current, there is a method of precisely controlling the voltage and phase of the AC power supply by using a phase control device. However, when the commercial AC power supply fluctuates, an excessive cross current flows. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power converter capable of reliably limiting an excessive cross current flowing between a commercial AC power supply and an inverter output voltage in a switching operation for supplying power to a load without an instantaneous interruption. An object of the present invention is to provide a current limiting method for a device.

[0006]

In order to achieve the above object, a first means of the present invention is provided with means for detecting a commercial power supply voltage, takes in a commercial power supply voltage, and switches between a commercial power supply and an inverter output voltage. At this time, the voltage command value of the voltage control system that controls the inverter output voltage is a voltage command value created using the detected commercial power supply voltage. By changing the voltage command value by such means, the magnitude of the inverter output voltage can be controlled to match the commercial AC power supply, thereby suppressing the cross current.

The second means is to detect an inverter current flowing through the filter reactor on the inverter side and, if the detected inverter current exceeds a predetermined value, adjust an output voltage to reduce a voltage error. Using the output of the current limiting circuit set to a predetermined value, the voltage command value of the voltage control system is corrected, the magnitude of the inverter output voltage is controlled, and the cross current is reliably suppressed.

[0008]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. The uninterruptible power supply 1 includes a converter 11 for converting the output of a commercial AC power supply 2 into a DC voltage.
And a smoothing capacitor 12 for smoothing the DC voltage.
Voltage-type PWM for converting DC voltage to three-phase AC voltage
Inverter 13, LC filter 1 for removing a PWM component from the output voltage of voltage type PWM inverter 13
4. Here, the voltage type PWM inverter 13 has a configuration in which the common phase is the V phase and the line voltage between UV and WV is PWM-controlled. The LC filter 14 includes an AC reactor 141 provided for the U phase and the W phase.
142 and a capacitor 142 provided between lines between UV and VW
It consists of.

Next, a control device according to an embodiment of the present invention will be described.

The input voltage (commercial AC power supply 2) of the uninterruptible power supply 1 is detected by a voltage detection circuit 6, and the phase thereof is detected by a phase detection circuit 9. Reference sine wave voltage generation circuit 10
Has a built-in reference voltage setting device, has a predetermined peak value set by the setting device, generates voltage command values Vuv0 and Vwv0 synchronized with the commercial AC power supply 2 in accordance with the phase of the input voltage, and It is input to the command creation unit 4.

Voltage control device 3 for voltage source PWM inverter
Input the command values Vuvr and Vwvr of the inverter line-to-line output voltage output from the voltage command creating unit 4 and
4 is a voltage control system 31 that performs voltage control so that the two output voltages are equal to each other as a feedback amount. The voltage command value calculated by the voltage control system is applied to the PWM control system 32.
, And a gate signal for ON / OFF control of the switching element of the voltage-type PWM inverter 13 is obtained from the result. Here, the PWM control system 32
In this method, a voltage command value to the voltage-type PWM inverter is compared with a carrier signal 33 to perform pulse width modulation. Note that a voltage detector 143 for detecting the capacitor voltage of the LC filter 14 is used to detect the output voltage of the voltage source PWM inverter. The commercial power supply 2 is connected to a load via the bidirectional switch 5,
When the uninterruptible power supply 1 is abnormal, turn on the bidirectional switch 5
To supply power to the load.

The commercial AC power supply 2 is
, And the line voltages Vuvb and Vwvb are input to the voltage command creating section 4. The voltage command generation unit 4 includes a switch 41 for switching a voltage command to be input to the voltage control system 31. The voltage command generated by the reference sine wave voltage generation circuit 10 according to a voltage follow-up command from the host. Values Vuv0, Vwv0 and Line Voltage Vuv of AC Power Supply 2
b and Vwvb are changed and output to the voltage control system 31.

The voltage control system 31 detects a capacitor voltage for each line and performs a voltage control operation. here,
The voltage control calculation of the line voltage between UV will be described. The adder 311 calculates the deviation between the voltage command value Vuvr and the detection value Vuv of the line voltage detected by the voltage detector 143. Control calculation (Gv) 31 so that the deviation decreases.
Execute Step 2. Next, a voltage command value for PWM control is calculated by adding the voltage command value and the output of the control calculation by the adder 313. The power supply system of the uninterruptible power supply for supplying power to the load is a constant inverter power supply system.

Here, when the uninterruptible power supply enters an abnormal state such as overcurrent, the bidirectional switch 5 is turned on and the voltage source PW
The M inverter 13 is stopped, the output voltage is switched from the inverter output voltage to the commercial power supply voltage, and power is supplied to the load without any instantaneous interruption. After recovering from the abnormal state of the UPS, the voltage source PW
The M-inverter 13 is started, the commercial power supply is switched to the inverter output voltage, and power is supplied to the load without any instantaneous interruption. In such a case, the present embodiment will be described with an example in which the latter is switched from the commercial power supply to the inverter output voltage to supply power to the load.

In such a switching operation, if there is a difference voltage between the commercial power supply voltage and the inverter output voltage, the difference voltage causes a cross current flowing between the commercial power supply and the inverter. Since this cross current is limited only by the impedance of the commercial power system and the filter reactor on the inverter side, even a small difference voltage causes excessive cross current.For example, even when switching from commercial power to the inverter output voltage, the inverter side of the uninterruptible power supply unit , An operation of detecting an overcurrent and switching to the commercial power supply again is repeated. Therefore, at the time of such a switching operation, a voltage follow-up command is input to the voltage command generation unit 4 from a higher-level control command unit (not shown) that controls a sequence operation such as operation and stop as shown in FIG. This higher-level control command section is responsible for sequence operations such as operation and stop of the uninterruptible power supply, and for example, a control command for receiving an overcurrent detection signal and performing an operation of switching from an inverter output voltage to a commercial AC power supply. Is output to the control system of the uninterruptible power supply.

The switch 41 of the voltage command generation unit 4 is on the side a when the power is supplied to the load by the voltage-type PWM inverter 13, and the voltage command Vuvr from the reference sine wave voltage generation circuit 10 is set to Vuv0 to perform voltage control. The voltage is input to the system 31 and is controlled by the voltage control system 31 so that the inverter output voltage Vuv matches the voltage command Vuv0. However, the inverter output voltage at this time is synchronized with the commercial AC power supply 2 by the operation of the phase detection circuit 9, but does not always match the power supply voltage of the commercial power supply 2. Therefore, if the switching operation is performed in this state, an excessive cross current will flow due to a slight difference voltage between the commercial power supply voltage and the inverter output voltage as described above. Therefore, when switching from the commercial power supply voltage to the inverter output voltage, a voltage follow-up command is sent from the higher-order control command unit to the voltage command creation unit 4 according to the time chart shown in FIG. input. While the voltage follow-up command is being input to the voltage command creation unit 4, the switch 41 is connected to the b side, and the power supply voltage Vuvb of the commercial power supply 2 detected by the voltage detection circuit 6 is used as the voltage command Vuvr to the voltage control system 31. Output. Therefore, the voltage control system 31 controls the inverter output voltage Vuv so as to match the voltage command Vuvb. That is, as shown in the conceptual diagram of FIG. 3, Vuvr = Vuv0 before time t0 when the switching operation is performed, and Vuvr = Vuvb during the period from time t0 to t3 to control the inverter output voltage. The inverter output voltage Vwv is similarly controlled. At time t0 when the voltage follow-up command is input, the switch 41 is operated to change the voltage command, thereby controlling the output voltage of the voltage-type PWM inverter 13 and performing control so that the output voltage coincides with the commercial power supply voltage at the time of switching. .

By the operation described above, the bidirectional switch 5
In the ON state, the voltage of both the commercial power supply and the inverter output voltage coincides during the period in which the commercial power supply and the inverter output voltage overlap, so that excessive cross current can be suppressed.

The case of the single-phase output control shown in FIG. 4 will be described. In FIG. 4, the configuration of the voltage control system is the same, except that the voltage-type PWM inverter 13 has a single-phase output. In the case of this single-phase output, if there is no voltage follow-up command from the higher-level control command unit, the switch 4 of the voltage command creation unit 4
1 is connected to the a side, and the inverter output voltage V is controlled by the voltage control system 31 so that the inverter output voltage V matches the voltage command V0 with the inverter voltage command Vr as V0. When a voltage follow-up command is input from the higher-level control command unit to the voltage command creation unit 4 at the time of switching, the switch 41 is connected to the b side, and the power supply voltage Vb of the commercial power supply 2 detected by the voltage detection circuit 6 is changed to the voltage command. The voltage control system 31 controls the inverter output voltage V as Vr so as to match the voltage command Vb. That is, referring to the conceptual diagram of FIG. 3, Vr = V0 before time t0 when the voltage command value is changed, and Vr = Vb during the period from time t0 to t3 to control the inverter output voltage.
According to the operation described above, even when the commercial power supply and the inverter output voltage overlap while the bidirectional switch 5 is in the ON state, the voltages of the two become the same, so that excessive cross current can be suppressed.

A second embodiment of the present invention will be described with reference to FIGS. In FIG. 5, the difference from FIG. 1 is the current limiting circuit 8, and the rest is the same as the control system shown in FIG. In the present embodiment, the current limiting circuit 8 includes a current limiter 81, adders 82 and 83, a gain 84, and a switch 8
5.

In the switching operation for supplying power to the load by switching from the inverter output voltage to the commercial power supply or from the commercial power supply to the inverter output voltage, if there is a difference voltage between the commercial power supply voltage and the inverter output voltage, the difference voltage causes A cross current flows between the power supply and the inverter.
Since this cross current is limited only by the reactor of the commercial power supply system and the filter reactor on the inverter side, even a small difference voltage results in an excessive cross current.For example, even when switching from the commercial power supply to the inverter output voltage, the inverter side of the uninterruptible power supply unit , An operation of detecting an overcurrent and switching to the commercial power supply again is repeated. Therefore, at the time of such switching, a voltage follow-up command is input to the voltage command generation unit 4 from a higher-level control command unit (not shown) that controls a sequence operation such as operation and stop as shown in FIG. Is input to the current limiting circuit 8.

In response to these higher-level control commands, the voltage command generator 4 connects the switch 41 normally connected to the a side to the b side, and detects the power of the commercial power source 2 detected by the voltage detection circuit 6. The voltage Vuvb is output to the voltage control system 31 as a voltage command Vuvr, and the voltage control system 31 controls the inverter output voltage Vuv so as to match the voltage command Vuvb.
Further, the commercial power supply voltage detected by the voltage detection circuit 6 has a detection error and a phase difference due to a filter, an amplifier and the like constituting the voltage detection circuit 6, and a cross current due to a difference voltage generated by these detection errors is performed by the following operation. Suppress. That is, a higher-order control commander inputs a voltage follow-up command to the voltage command creator 4 and also inputs a limiter command to the current limiting circuit 8 separately from the voltage follow-up command.
Is turned on to correct the voltage command at the time of voltage follow-up and control the output voltage, whereby the cross current is more reliably and reliably suppressed. That is, in the embodiment shown in FIG. 5, the voltage command value is changed at the time of switching, and the magnitude of the line voltage Vuv and the line voltage Vwv is controlled by correcting the changed voltage command value, thereby reliably suppressing the cross current. Is what you do.

Here, the operation of the current limiting circuit 8 will be described.

As shown in the figure, in the current limiting circuit 8, the U-phase inverter current IinvU and the W-phase inverter current IinvW are detected and taken in by the current detector 144, and the V-phase inverter current IinvV is added by the adder 82 to IinvV =-(IinvU
+ IinvW), and the current limiter 81 detects the magnitude and direction of each inverter current. After passing through a current limiter 81 in which a predetermined dead zone for detecting the magnitude and direction of the inverter current is set, a voltage correction amount corresponding to the voltage command Vuv and a voltage correction corresponding to the voltage command Vwv are shown in FIG. The amount is calculated, multiplied by the gain 84, and output to the voltage control system 31. In the voltage control system 31, the voltage command Vuv from the voltage command creating unit 4 is output by the adder 314.
Correct r = Vuvb and Vwvr = Vwvb. That is, FIG.
As shown in the conceptual diagram of FIG. 5, Vuvr = Vuv0 before time t0, Vuvr = Vuvb in the period from time t0 to t3, and a voltage command of the voltage control system 31 according to the correction amount output from the current limiting circuit 8. to correct.

The voltage command correction method using the configuration of the current limiting circuit 8 shown in FIG. 5 is based on the assumption that the inverter current is positive (the current flowing out of the inverter is positive).
When the inverter current is larger than the dead band set in the current limiting circuit 8, a negative voltage correction amount is output when the inverter current is negative and the voltage command is corrected. That is, the voltage command value is reduced by the voltage correction amount, and the output voltage is controlled. By correcting the voltage command in this manner, the output voltage of the inverter can be controlled because the output voltage of the inverter can be controlled, and the difference voltage between the commercial power supply voltage and the output voltage of the inverter can be reduced. The inverter current flowing from the side can be suppressed to a predetermined value or less.

By the operation described above, the bidirectional switch 5
In the ON state, the excessive cross current during the period in which the commercial power supply and the inverter output voltage overlap can be more favorably suppressed.

FIG. 8 shows a modification of the second embodiment of the present invention shown in FIG.

In a modification of the second embodiment shown in FIG. 8, the gain 84 is varied according to a limiter command.
That is, when there is no limiter command from a higher-level control command unit, the gain Gc is set to 0 and no voltage correction amount is output. On the other hand, when there is a limiter command, a voltage correction amount is output as a predetermined value for setting the gain 84, and the voltage command of the voltage control system 31 is corrected. With such an operation, as in FIG. 5, an excessive cross current during a period in which the commercial power supply and the inverter output voltage overlap can be more favorably suppressed.

FIGS. 9 and 10 show an example in which the second embodiment of the present invention is applied to single-phase output control. 5 and 8, the configuration of the voltage control system is the same, except that the voltage-type PWM inverter 13 has a single-phase output. That is, as shown in the figure, in the current limiting circuit 8, the inverter current is detected and taken in by the current detector 144, the voltage correction amount is calculated via the current limiter 81 in which a dead zone is set, and the voltage correction system is multiplied by the gain 84. 31. Voltage control system 3
In the case of 1, the adder 314 corrects the voltage command Vr = Vb from the voltage command creating section 4 with the voltage correction amount from the current limiting circuit 8. Such an operation can suppress an excessive cross current during a period when the commercial power supply and the inverter output voltage overlap.

Although the embodiment of the present invention has been described by taking as an example the case where the commercial power supply is switched to the inverter output voltage, the same applies to the case where the inverter output voltage is switched to the commercial power supply in the same embodiment. By performing the operation, the excessive cross current during the period in which the commercial power supply and the inverter output voltage overlap can be more reliably and reliably suppressed.

FIG. 11 shows an example of the third embodiment of the present invention.
Shown in FIG. 11 shows a configuration in which the voltage command creating section 4 is omitted as shown in FIG. 5, and the configuration of the voltage control system is the same. That is, as shown in the figure, in the current limiting circuit 8, the inverter current is detected and taken in by the current detector 144, a voltage correction amount is calculated via the current limiter 81 or the like in which a dead zone is set, and the voltage is controlled by multiplying the gain 84. System 31
Output to The voltage control system 31 operates so that the adder 314 corrects the voltage command from the reference sine wave voltage generation circuit 10. Such an operation can suppress an excessive cross current during a period when the commercial power supply and the inverter output voltage overlap. It should be noted that, in a modification of the embodiment of the present invention, there is a case where a single-phase output is set or a case where the gain Gc is set to 0. In any case, when switching from the commercial power supply to the inverter output voltage, the inverter output voltage is changed. When the commercial power supply is switched to the commercial power supply, excessive cross current during the period in which the commercial power supply and the inverter output voltage overlap can be more reliably and reliably suppressed.

[0031]

According to the present invention, when switching from the commercial power supply to the inverter output voltage or from the inverter output voltage to the commercial power supply in the uninterruptible power supply, it is possible to reliably and reliably suppress the cross current generated during the overlap period between the two. . As a result, stable power can be supplied to the load without an instantaneous interruption, and reliability is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a first embodiment of the present invention.

FIG. 3 is a diagram illustrating a first embodiment of the present invention.

FIG. 4 is a configuration diagram of the first embodiment in the case of single-phase output.

FIG. 5 is a configuration diagram of a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a second embodiment of the present invention.

FIG. 7 is a diagram illustrating a second embodiment of the present invention.

FIG. 8 is a configuration diagram of a modified example of the second embodiment of the present invention.

FIG. 9 is a configuration diagram of a second embodiment in the case of single-phase output.

FIG. 10 is a configuration diagram of a modification of the second embodiment in the case of single-phase output.

FIG. 11 is a configuration diagram of a third embodiment of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 uninterruptible power supply device 2 AC power supply 3 voltage control device 4 voltage command generator 5 bidirectional switch 6 voltage detection circuit 7 load 8 current limiting circuit 9 phase Detection circuit, 10: Reference sine wave voltage generation circuit, 11: Converter, 12: Smoothing capacitor, 13: Voltage source PWM inverter, 14: LC filter, 31: Voltage control system, 32
... PWM control system, 33 ... Carrier signal, 41,85 ... Switch, 81 ... Current limiter, 82,83,311,31
3, 314: adder, 84: gain, 141: AC reactor, 142: capacitor, 143: voltage detector, 1
44 ... Current detector, 312 ... Control calculation.

Continued on the front page (72) Inventor Reiko Kanoda 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Keizo Shimada 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd., Hitachi Plant (72) Inventor Hideyasu Umezu 3-1-1, Yukicho, Hitachi, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Plant (72) Inventor Hideaki Kunisada, Yukicho, Hitachi, Ibaraki 3-1-1 1-1 F term in Hitachi, Ltd. Hitachi Plant (reference) 5G015 FA13 GA06 HA13 JA11 JA24 JA34 5H007 AA06 AA07 BB05 CA01 CB02 CB05 CC09 DA05 DA06 DB02 DB03 DC05 EA13 FA03 FA14 HA02

Claims (5)

[Claims] 1. A means for converting a DC voltage into an AC voltage having a desired magnitude and frequency by a voltage-type PWM inverter, and smoothing an output voltage of the voltage-type PWM inverter by an LC filter comprising an AC reactor and a capacitor. Means for detecting the output voltage of the LC filter and controlling the voltage so that the output voltage matches the voltage command value; and means for supplying power to a load using the voltage-type PWM inverter as an AC power supply. A power converter provided with a means for supplying the AC power to the load, when the load power is switched from one AC power to the other AC power, a voltage command value of an output voltage control system of the voltage type PWM inverter Means for generating the voltage command value of the voltage-type PWM inverter by providing means for creating the voltage from the commercial AC power supply voltage. Current limiting method for force converter. 2. A means for converting a DC voltage into an AC voltage having a desired magnitude and frequency by a voltage-type PWM inverter, and smoothing an output voltage of the voltage-type PWM inverter by an LC filter comprising an AC reactor and a capacitor. Means for detecting the output voltage of the LC filter and controlling the voltage so that the output voltage matches the voltage command value; and means for supplying power to a load using the voltage-type PWM inverter as an AC power supply. A power converter provided with means for supplying the AC power to the load, when switching the load power supply from one AC power to the other AC power, the voltage command value of the output voltage control system is changed to the commercial power supply voltage. A voltage command value is changed by detecting the inverter-side current of the voltage-type PWM inverter,
A voltage command correction amount is calculated from the detected current, the voltage command value of the output voltage control system created from the commercial power supply voltage is corrected, and the magnitude of the inverter output voltage is controlled. Current limiting method. 3. A means for converting a DC voltage into an AC voltage having a desired magnitude and frequency by a voltage-type PWM inverter, and smoothing an output voltage of the voltage-type PWM inverter by an LC filter comprising an AC reactor and a capacitor. Means for detecting the output voltage of the LC filter and controlling the voltage so that the output voltage matches the voltage command value; and means for supplying power to a load using the voltage-type PWM inverter as an AC power supply. A power converter provided with a means for supplying the AC power to the load, when the load power is switched from one AC power to the other AC power, the inverter-side current of the voltage-type PWM inverter is detected and detected. Calculates the voltage command correction amount from the obtained current, corrects the voltage command value of the output voltage control system, and controls the magnitude of the inverter output voltage. A current limiting method for a power converter. 4. The method according to claim 2, wherein the method of detecting an inverter side current of the voltage type PWM inverter and calculating a voltage command correction amount from the detected current is performed by a current limiter provided with a predetermined dead zone. A method for detecting and calculating the magnitude and direction of the obtained inverter current, and controlling the output of the voltage command correction amount by a switch. 5. The method according to claim 2, wherein the inverter-side current of the voltage-type PWM inverter is detected, and the voltage command correction amount is calculated from the detected current by a current limiter provided with a predetermined dead zone. Detecting and calculating the magnitude and direction of the obtained inverter current, and controlling the magnitude of the gain for adjusting the magnitude of the voltage command correction amount, thereby controlling the output of the voltage command correction amount. Current limiting method for a power converter.