JP3200283B2 - Inverter control method and inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts DC power generated by an independent DC power source such as a solar cell into AC power, and supplies power to a general AC load for home use, office use, or an existing commercial power system. The present invention relates to an inverter device for supplying the above.

[0002]

2. Description of the Related Art A conventional inverter device comprises an inverter bridge composed of several switching elements, a transformer for electrically insulating a DC power source from a commercial power system and a load, a low-pass filter, and A control circuit for controlling on / off of a plurality of switching elements constituting an inverter bridge is used. As the transformer, a commercial frequency transformer or a high frequency transformer for downsizing the device is used.

First, a conventional example of an inverter device using a commercial transformer will be described with reference to FIG. The DC power output from the solar cell 2 is input to the inverter 1, converted into AC power by the inverter bridge 32, and provided at the output end of the inverter 1 to insulate the solar cell 2 from the commercial power system 3. The power is supplied to the commercial power system 3 via the commercial transformer 33. Before the inverter bridge 32,
A DC capacitor 12 for suppressing a change in input power to the inverter 1 and a DC input current detector 13 are connected. Further, an AC filter 16 for removing harmonic components of the AC current and an inverter output current detector 14 are connected downstream of the inverter bridge 32, and a connection relay 15 is provided downstream of the AC filter 16 so that a commercial relay is provided. Interconnection with the power system 3 and disconnection are performed.

The control circuit 34 of the inverter 1 includes a gate drive circuit 35, a PWM modulation control unit 36, and an error amplifier 3
7, career signal generator 38, the signal processing unit 39, and a sine wave signal storage unit 40, A / D converter 41, D / A converter 42.

The PWM modulation control section 36 has a sine wave signal having the same frequency (50/60 Hz) as that of the voltage waveform of the commercial power system 3 and a high frequency (Equation 10) synchronized with the sine wave signal.
kHz or higher) and a second pulse train obtained by inverting the first pulse train signal obtained by comparison with the carrier signal.
, A third pulse train signal obtained by comparing the inverted sine wave signal with the inverted carrier signal obtained by inverting the carrier signal, and a fourth pulse train signal obtained by inverting the third pulse train signal. FIG. 9 shows these pulse train signal waveforms. In the drawing, a high frequency of several tens of kHz is schematically shown, so that the frequency is low.

The first to fourth pulse train signals are input to a gate drive circuit 35, and based on these signals, a gate drive signal having the same frequency as the carrier signal for the four switching elements Q1 to Q4 forming the inverter bridge 32 is generated. Q1 to Q4 are controlled to be on / off at the same frequency as the carrier signal. Thus, the output pulse train waveform Ei shown in FIG. 9 is output from the inverter bridge 32. Further, the output waveform Ei is subjected to removal and smoothing of harmonic components by the AC filter 16 at the next stage, and becomes a 50/60 Hz sine wave AC output. The sine wave AC output is connected to the commercial power system 3 after its input and output are insulated by the commercial transformer 33. In this case, the commercial transformer 33 is 50/60 Hz
Will be excited at the frequency of the sine wave AC output.

The A / D converter 41 converts a DC voltage signal VOUT, a DC current signal VIN, and a commercial power system voltage signal VOUT, which are analog signals from the solar cell 2, into a digital amount and converts the signal into a digital signal. Output the signal. In order to maximize the output power from the solar cell 2, the signal operation processing section 39 performs a maximum power point tracking operation for matching the solar cell operating point to the maximum point on the solar cell output characteristic curve, and the inverter 1 Is read from the sine wave signal storage unit 40 in which a plurality of sine wave signals (50/60 Hz) serving as current command values for controlling the sine wave signals having different amplitudes are stored in advance. The sine wave signal storage unit 40 quantizes the sine wave signal having a plurality of different amplitude values in proportion to the amplitude value of the rated output current waveform of the inverter 1 in half-cycle or one-cycle units and at certain time intervals. Stored as digital quantities. The D / A converter 42 converts the read sine wave signal into an analog signal and outputs the analog signal to the error amplifier 37. The error amplifier 37 includes the inverter output current detector 1
4 and the sine wave signal, and a reference wave signal obtained by amplifying a comparison error between the two is output to the PWM modulation control unit 36.
The carrier signal generator 38 similarly outputs a carrier signal (20 kHz) synchronized with the sine wave signal to the PWM modulation control unit 36. As a result, the output current of the inverter 1 changes following the sinusoidal signal serving as the current command value. Here, when the output current of the inverter 1 is controlled by the sine wave signal, the voltage is set to the same phase and the same frequency (50/60 Hz) as the voltage of the commercial power system 3 so that the existing commercial power system 3 AC power of rate 1 can be supplied.

Next, a case where a high-frequency transformer is used will be described. An apparatus using a commercial transformer is disadvantageous for reducing the size and weight of the inverter because the weight and capacity of the commercial transformer are large. On the other hand, such a problem can be solved by using a high-frequency transformer. In this case, it is necessary to excite the high-frequency transformer with a high-frequency voltage. An example using the instantaneous current value control method considered for this purpose will be described below with reference to FIG.

The inverter 1 is inserted between the solar cell 2 and the existing commercial power system 3, converts DC power generated by the solar cell 2 into AC power of 50/60 Hz, and connects the AC power to the commercial power system 3. And supply it to the load. In the inverter 1, the input DC power is converted into high-frequency AC by current instantaneous value control in a high-frequency inverter bridge 4 composed of switching elements Q <b> 1 to Q <b> 4 and supplied to the primary side of a high-frequency transformer 5. This high-frequency alternating current is rectified by the diode bridge 6 on the secondary side of the high-frequency transformer 5, and harmonics are removed and smoothed by a filter circuit composed of the DC reactor 7 and a capacitor connected in parallel. Further, the low-frequency inverter bridge 8 composed of the switching elements of S1 to S4 converts the power into commercial frequency AC power by loopback control.
Power is supplied to the commercial power system 3 via the interconnection relay 15 and the AC filter 16.

The signal operation processing unit 43 includes a voltage signal VIN of the solar cell 1 and a current signal II detected by the DC input current detector 3.
N, the current (inverter output current) signal IT of the primary side of the high-frequency transformer 5 detected by the inverter output current detector 14 and the voltage signal VOUT of the commercial power system 3 are input, and a current command signal and a polarity determination signal are input. Is output. The hysteresis comparator 44 inputs the primary current IT of the high-frequency transformer 5 detected by the inverter output current detector 14 and the current command signal, and the primary current of the high-frequency transformer 5 is an upper limit value centered on the current command signal. And the switching elements Q1, Q4, and Q constituting the high-frequency inverter bridge 4 so as to repeatedly reciprocate within a fixed width range having a lower limit value.
2 and Q3 are alternately turned on / off via a NOT circuit 45. That is, the current command signal (IRE
For F), an upper limit value I + and a lower limit value I− having a constant width ΔI are given to the hysteresis comparator 44 as set values. Then, the inverter output current detector 14 detects the current signal IT of the high-frequency transformer 5 and the primary side shown in FIG. 10 which is the actual value of the control amount, and inputs it to the hysteresis comparator 44 together with the current command signal. Then, the current signal IT which is the actual value of the control amount is equal to the upper limit set value I + (I +
= IREF + △ I), the switching elements Q1 and Q4 of the high-frequency inverter bridge 4 in FIG.
Then, through the NOT circuit 45, Q2 and Q3 are turned on so that the current gradient is in the decreasing direction, and the current signal IT in FIG. 11 is reduced, and the lower limit set value I− (I− = IREF−
When the value falls below ΔI), Q1 and Q4 are turned on, Q3 and Q4 are turned off, and control is performed so that the current signal IT increases. By performing such switching control, the actual value of the current signal IT changes so as to reciprocate between I + and I- every switching. Here, when a sine wave signal having the same frequency as the commercial power system 3 and having an arbitrary amplitude value is used as the current command signal (IREF), even if switching is performed at a very high speed, the current signal IT remains the same as the current command signal. ± △ around
A sinusoidal current waveform that changes so as to reciprocate and follow repeatedly in the width of I and is proportional to the amplitude value of the current command signal at the commercial frequency can be obtained. As described above, the current command signal (I
The magnitude of the current on the high-frequency transformer 5 and the primary side of the inverter 1, that is, the magnitude of the inverter output current, can be controlled by the amplitude value of REF).

The return control circuit 46 receives the polarity determination signal and receives a voltage signal VOUT of the commercial power system 3.
The switching elements S1, S4 and S2, S3 constituting the low-frequency inverter bridge 8 are alternately turned on / off in accordance with the polarity of. Under this control, the DC power rectified in a full-wave rectification manner by the diode bridge 6 becomes a sine-wave AC output at the subsequent stage of the low-frequency inverter bridge 8.

[0012]

In order to reduce the size and weight of the inverter device, it is preferable to use a high-frequency transformer. This is because the high-frequency transformer has a capacity ratio of about 1/30 and a weight ratio of about 1/20, compared to a commercial transformer.

However, although the current instantaneous value control method used as a method for exciting a high-frequency transformer with a high-frequency voltage is excellent, it is difficult to optimize the setting of the upper limit and the lower limit of the hysteresis width in the control method. ,
If the set value is too large, the distortion increases. If the set value is too small, the width of the pulse train signal obtained by comparing the current command value with the inverter output current becomes small.
The control system becomes unstable as compared with the PWM control in the case of the low frequency transformer. Further, there is a problem that the control circuit becomes complicated when a more stable control system is required.

In view of the above, the present invention does not require complicated control to reduce the size and weight of the inverter device.
An object of the present invention is to provide a control method of an inverter device capable of controlling a waveform distortion of an inverter output current to be sufficiently small, and an inverter device using the method.

[0015]

An inverter control device according to the present invention comprises: a power converter for converting DC power into AC power;
Transform the voltage of the AC power converted by the power conversion unit ,
An inverter control device comprising: a transformer for converting the transformed AC power to DC and then converting the converted AC power to AC and supplying the AC power to a load or a commercial power supply; and a control circuit for controlling the power conversion unit. The control circuit includes: a unit that generates a sine wave signal that is an output target value of the inverter control device; a unit that generates a carrier signal for performing PWM control using the sine wave signal; frequency are the same, and, exclusive means for generating a square wave signal whose phase is shifted by one cycle of 4 min, a signal and the square wave signal obtained by comparing the sine wave signal and the carrier signal Target
Means for generating a control signal obtained by performing an OR operation , wherein on / off control of a switching element included in the power conversion unit is performed by the control signal. Further, the inverter control method of the present invention converts DC power into AC power via a power converter, converts the AC power converted by the power converter into DC via a transformer, and then converts the AC power into AC.
A method of controlling a conversion to load or inverter device for supplying the commercial power, compared with the carrier signal for PWM control using a sine wave signal and the upper Symbol sinusoidal signal which is the output target value of the inverter device Signal obtained
When, the carrier signal and the frequency are identical, and, exclusive Washo of a rectangular wave signal whose phase is shifted by one cycle of 4 min
The on / off control of a switching element constituting the power conversion unit is performed by a control signal generated by processing.

As a method of inverting the positive and negative polarities of the PWM-modulated pulse train by PWM control every other time, the sine wave signal and the carrier signal are compared to obtain a first pulse train signal, and the first pulse train signal is obtained. Inverting the pulse train signal to obtain a second pulse train signal, generating an inverted carrier signal by inverting the carrier signal, comparing the inverted carrier signal with the sine wave signal to obtain a third pulse train signal, The third pulse train signal is inverted to obtain a fourth pulse train signal, and a rectangular wave signal having the same frequency as that of the carrier signal and having a phase shifted by 1/4 period is generated. Gate processing is performed on each of the first to fourth pulse train signals, and on / off control of four switching elements forming an inverter bridge is performed using four pulse train signals obtained by the gate processing. Cormorants method is good to use. In the gate processing, it is preferable to perform an exclusive OR processing, whereby four types of pulse train signals are generated.
4 types of pulse train signals constitute an inverter bridge
It is preferable to obtain the high-frequency AC signal having the same frequency as the carrier frequency by inputting to each switching element and performing on / off control of the switching element. In this case, a sine wave signal having a frequency of 50/60 to several hundreds Hz and a carrier signal having a frequency of several tens kHz or more are preferably used, and the inverter device is provided with an inverter bridge including four switching elements. .

Further, as a method for obtaining the four pulse train signals, a sine wave signal is compared with a carrier signal, and the first level is output if the sine wave signal is higher than the carrier signal, and the second level is output if the sine wave signal is lower than the carrier signal. Generates a first pulse train signal, inverts the first pulse train signal to generate a second pulse train signal, compares the inverted carrier signal obtained by inverting the carrier signal with the sine wave signal, and generates an inverted carrier signal. A third pulse train signal is generated by outputting a first level if exceeds a sine wave signal and a second level if below a sine wave signal, and a fourth pulse train signal is generated by inverting the third pulse train signal. Good to use. Note that the first level and the second level mean so-called High or Low levels.

In the method of the present invention described above, preferably, the high-frequency alternating current excited on the secondary side of the transformer is rectified by a rectifier (AC / DC converter), so that the PWM modulation is performed continuously with one polarity. It is preferable to convert the output to a pulse train output.

As an inverter device which enables the inverter control method of the present invention, a first power conversion unit for converting DC into AC and a second power converter for converting the AC voltage into a primary voltage to obtain a transformed secondary voltage. A transformer, a second power converter for converting an alternating current to a direct current to which two wires on the secondary side of the transformer are connected, and a reactor connected in series to each two wires of the output of the second power converter; A third power converter connected to the output of the reactor for converting a direct current into an alternating current; and a control circuit for controlling on / off of switching elements constituting the first power converter and the third power converter. The control circuit generates a sine wave signal as an output target value of the inverter; and a PWM using the sine wave signal.
3. A means for generating a carrier signal for performing control, means for generating a rectangular wave signal having the same frequency as the carrier signal and having a phase shifted by 1/4 period, and wherein the sinusoidal signal is generated by the method according to claim 2. From the wave signal and the carrier signal.
Means for gate processing the rectangular wave signal to these signals after generating the fourth pulse train signals from the first and second pulse train signals, and turning on / off the switching elements constituting the first power conversion unit with the pulse train signals after the gate processing. It is preferable to use an inverter device provided with means for performing off control. The first power converter converts a DC input into a high-frequency AC (ten-odd kHz).
It is preferable to use a high-frequency inverter bridge that converts the input and output sides of the high-frequency inverter bridge as the transformer. The second power conversion unit outputs the output of the high-frequency transformer. It is good to constitute with the diode bridge for rectifying high frequency alternating current at the end.

Further, the reactor is configured to smooth a rectified waveform and remove a high frequency component, and a third power conversion unit includes a low frequency inverter bridge that performs a return control at a low frequency (for example, 50/60 to several hundred Hz). It is good to consist of.

Further, in the inverter device of the present invention, an intermediate tap is further provided on the secondary side of the transformer, and a line from the intermediate tap is connected to a neutral line of a low-voltage single-phase three-wire distribution line; Connecting the reactor to two output lines of the second power converter, connecting capacitors vertically and symmetrically between each of the two lines and a line from the intermediate tap,
It is more preferable that the two output lines of the power conversion unit are connected to each line other than the neutral line of the low-voltage single-phase three-wire distribution line.

[0022]

According to the control method of the present invention, a required high-frequency AC signal can be obtained only by inverting every other PWM pulse train. And this inversion is, for example, 4
It is obtained by driving the gates of the switching elements forming the inverter bridge with the pulse train signals of various types.

Further, according to the inverter control method of the present invention, the high frequency alternating current obtained by inverting the polarity of every other PWM modulated pulse train becomes the same as the frequency of the carrier signal. In this case, an inverted signal of a sine wave signal may be used instead of the inverted signal of the carrier signal, and the same result is obtained.

Further, when the primary side of the transformer is controlled so that every other pulse train subjected to PWM modulation is excited by alternating positive and negative AC, the secondary side of the transformer transforms the primary side voltage. A high-frequency alternating current of which polarity is inverted is output every other similar PWM-modulated pulse train. Therefore, by rectifying this high-frequency AC, it is converted into a pulse train output that is PWM-modulated on one side.

On the other hand, according to the inverter device of the present invention,
As a result of adopting an inverter control method in which the primary side of the high-frequency transformer is PWM-modulated and pulse trains of every other pulse are inverted in positive and negative directions and the high-frequency AC having the same frequency as the carrier frequency is excited, the output waveform of the secondary side of the high-frequency transformer is also PWM. Since every other modulated pulse train has an inverted high-frequency AC waveform with positive and negative inversion, a diode bridge provided at the subsequent stage of the high-frequency transformer rectifies the PWM-modulated pulse train signal with positive and negative inverted every other. Thus, a continuous PWM pulse train waveform is obtained on the positive side. Then, the DC reactor provided at the subsequent stage of the diode bridge smoothes and removes high-frequency components, thereby obtaining a DC waveform similar to the full-wave rectified sine wave AC waveform having the same frequency as the sine wave signal. Further, in a commercial frequency inverter bridge at the subsequent stage, a sine wave AC waveform can be obtained by performing a folding control of inverting positive and negative every other DC waveform similar to the full-wave rectified sine wave AC waveform.

Further, by providing an intermediate tap on the secondary side of the high frequency transformer, three output lines can be obtained on the secondary side of the high frequency transformer by the intermediate tap and the other two output lines. Further, two line voltages having the same potential are generated between the intermediate tap and the other two output lines, and a line voltage twice as large as the line voltage is generated between the two lines other than the intermediate tap. I do. That is, a total of three line voltages can be obtained. The three line voltages are connected to the low-voltage single-phase three-wire distribution line of the commercial power system, but the three line voltages on the secondary side of the high-frequency transformer are sinusoidal waveforms of the commercial power system. , And every other PWM modulated pulse train has a positive and negative inverted high-frequency AC waveform in the same manner as described above. For this purpose, the three line voltages are once rectified by the diode bridge in the above configuration, smoothed by a low-pass filter composed of a DC reactor and a capacitor, and a high-frequency component-removed DC voltage waveform (sine wave of commercial frequency) Is a full-wave rectified waveform), and a sine-wave AC waveform of a commercial frequency is obtained by turning back the low-frequency inverter bridge.

With the above-described operation, the inverter device of the present invention can use a high-frequency transformer instead of a commercial transformer, and can realize a reduction in size and weight.
It is possible to obtain a stable sine wave AC waveform by a simple control method simply by adding a gate process typified by exclusive OR processing to the conventional PWM control, and further to obtain three line voltages (for example, 100 VAC and 100 VAC). , 200
VAC) can be connected to a low-voltage single-phase three-wire distribution line of a commercial power system with three output lines having VAC.

[0028]

【Example】

Embodiment 1 An embodiment of an inverter device according to the present invention will now be described.
This will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a grid-connected solar power generation system including an inverter according to the present invention.

Solar cell 2 (output 3.5 kW, open circuit voltage 2
The DC power output from the AC power supply is converted into AC power having the same phase and frequency of 50/60 Hz as that of the commercial power system 3 by the inverter 1 and supplied to the commercial power system 3.

The DC power input from the solar cell 2 to the inverter 1 is converted into high-frequency AC by the high-frequency inverter bridge 4 and supplied to the primary side of the high-frequency transformer 5. In the present embodiment, a high-frequency transformer of 16 to 19 KHz is used. The high-frequency transformer 5 has a role of insulating the solar cell 2 side (primary side) from the commercial power system 3 side (secondary side), and the insulated high-frequency AC is a diode bridge provided on the secondary side of the high-frequency transformer 5. 6 is rectified. Then, a high-frequency component contained in the rectified waveform is removed and smoothed by a filter circuit including the DC reactor 7 and a capacitor, and the rectified waveform is converted into a full-wave rectified waveform. In the low frequency inverter bridge 8,
Low frequency (50/60 Hz) direct current of the full-wave rectified wave shape
In this case, a low-frequency sine-wave alternating current can be obtained. The switching elements constituting the high-frequency inverter bridge 4 and the low-frequency inverter bridge 8 are subjected to on / off control by a control circuit 9 and gate drive circuits 10 and 11. A DC capacitor 12 and a DC input current detector 1 that suppress the fluctuation of the input power to the inverter 1
The inverter output current detector 14 is connected to the primary side or the secondary side of the high-frequency transformer 5, and is connected to and disconnected from the commercial power system 3 at a stage subsequent to the low-frequency inverter bridge 8. Interconnection relay 15 and A
A C filter 16 is provided. It is to be noted that although the connection is made on the primary side in the figure, it can also be made on the secondary side.

As shown in FIG. 2, the control circuit 9 includes an A / D converter 17, a signal operation processing section 18 for generating a sine wave signal (50/60 Hz) as an output target value of the inverter 1, and the sine wave signal Carrier signal (19 kHz) generator 19 for performing PWM control in conjunction with the above, a rectangular wave signal generator 20 having the same frequency as the carrier signal and having a phase shifted by 1/4 cycle, an inverting circuit 21, the sine wave A comparison circuit 22 for comparing the signal with the carrier signal, a NOT circuit 23,
An XOR (exclusive OR) circuit 24, and four switching elements Q1 of the high-frequency inverter bridge 4.
A pulse train signal for turning on / off .about.Q4 is output to the gate drive circuit 10 of FIG.

In the above configuration, the high-frequency inverter bridge 4 converts the DC power from the solar cell 2 into a high-frequency AC (19
kHz), and the input / output insulation is realized using the high-frequency transformer 5. On / off control in the high-frequency inverter bridge 4 is performed as follows based on FIG.
First, a first pulse train signal obtained by comparing a sine wave signal (50/60 Hz), which is an output target value of the inverter 1 generated by the signal operation processing unit 18, with a carrier signal (19 kHz), A third pulse train signal obtained by comparing a second pulse train signal obtained by inverting the pulse train signal, an inverted carrier signal obtained by inverting the carrier signal, and the sine wave signal, and a fourth pulse train obtained by inverting the third pulse train signal. Is obtained. Next, each of the first to fourth pulse train signals and the square wave signal having the same frequency as the carrier signal generated from the square wave signal generator 20 and shifted in phase by 1/4 period are XORed.
The circuit 24 performs exclusive OR processing to obtain first to fourth pulse train signals. Then, these first to fourth pulse train signals are output to the gate drive circuit 10 shown in FIG. 1 to perform on / off control of four switching elements constituting the high-frequency inverter bridge 4. Here, a series of the pulse train signals (first to fourth, first 'to fourth')
Is shown in FIG. The signal below the carrier signal with respect to the sine wave signal in FIG. 3 should be shown at a high frequency of several tens to several hundreds of kHz, but is schematically simplified here. As a result of the on / off control, the high frequency transformer 5 is excited at the same high frequency (19 kHz) Ei as the frequency of the carrier signal in which every other pulse train subjected to PWM modulation is inverted.

The output timing of the pulse train signal to the gate drive circuit 10 is synchronized with the voltage signal Vout of the commercial power system 3. As a result, the inverter output current is controlled to be in phase with the commercial power system voltage.

As described above, the output waveform of the high-frequency transformer 5 is a high-frequency alternating-current waveform in which every other PWM-modulated pulse train is inverted between positive and negative. 6
Rectifies the pulse train signal whose polarity is inverted every other pulse, and obtains a PWM pulse train waveform continuous on the positive side as shown by E0 in FIG. A filter circuit composed of a DC reactor 7 and a capacitor provided at the subsequent stage of the diode bridge 6 shown in FIG.
Smoothing is performed, and a DC waveform equivalent to a full-wave rectified sine wave AC waveform having the same frequency as the sine wave signal is obtained. Further, in the low-frequency inverter bridge 8 at the subsequent stage, a fold-back control is performed in which every other sine wave AC waveform of the full-wave rectification is inverted to positive and negative, and a sine wave AC waveform is obtained.

Embodiment 2 In the embodiment shown in FIG. 4, in the control circuit 9, the carrier signal generator 19, the rectangular wave signal generator 20, the inverting circuit 21, the comparing circuit 22, the NOT circuit 23, the XOR circuit shown in FIG. All of these means are processed in the signal operation processing unit 18 without using 24. That is, the control circuit 9 shown in FIG. 4 includes an A / D converter 17 and a signal operation processing unit 18.

Regarding the processing performed in the signal processing unit 18, the PWM processing is implemented by a digital circuit, so that it is not processed in a sequence, but
The processing is performed collectively by inputting the necessary signals to the signal operation processing unit 18, and as a result, the first ′ shown in FIG. 3 for turning on / off the four switching elements of the high-frequency inverter bridge 4 in FIG. The fourth to fourth 'pulse train signals are obtained. In the present embodiment, the signal operation processing unit 18 includes the CPU 25, the memories (the ROM 26 and the RAM 27) in FIG.
It comprises an I / O 28 and a timer 29. The operation in the signal processing unit 18 based on this configuration will be described with reference to FIG. It should be noted that the carrier signal in FIG. 3 should actually be shown at a high frequency, but is simplified here schematically.

In the signal processing section 18, the sine wave signal (5
0/60 to several hundred Hz) and a carrier signal (tens to hundreds of kHz)
z) (a dash-dot line), a first pulse train signal having a high level when the sine wave signal exceeds the carrier signal, and a low level when the sine wave signal falls below the carrier signal, and a second inverted pulse train of the first pulse train signal. A pulse train signal and an inverted carrier signal obtained by inverting the carrier signal (several tens to several hundreds of kHz)
z) When the inverted carrier signal exceeds the sine wave signal in the comparison between the (solid line) and the sine wave signal, the High level is set.
An operation is performed to generate a third pulse train signal that becomes a low level if it falls below, and a fourth pulse train signal that is the inverted third pulse train signal. In addition, in the above, if it exceeds, Lo
The w level may be used, and if it is lower than the w level, the high level may be used.

An operation method will be described with respect to a first pulse train signal generation method. First, the intersection of the sine wave signal and the carrier signal (dashed line) is determined. The time between each intersection corresponds to a pulse width which is an on-time or off-time of the pulse train signal. Next, this pulse width is calculated for one cycle of the sine wave signal (alternatively, it may be calculated for a half cycle). In the CPU 25 of FIG. 4, the pulse width is replaced by the timer count of the timer 29. And
A series of timer count strings corresponding to the pulse width calculated for one cycle of the sine wave signal is temporarily stored in the RAM 27. When a synchronization signal generated from the voltage signal Vout of the commercial power system 3 is input to the signal processing unit 18 via the I / O 28, the timer count sequence temporarily stored is stored in the RA.
It is read out sequentially from M27 and set in the timer 29. When a timer interrupt occurs, down counting is performed by the timer count set in the timer 29. At the same time, bit 1 corresponding to the high level of the pulse signal or bit 0 corresponding to the low level of the pulse signal is output to the I / O 28 times. By doing so, the High level or the Low level is maintained until the down count becomes 0, that is, the down count until the next timer interrupt occurs, and the gate drive circuit of FIG. By outputting the pulse signal to 10, a pulse signal having one pulse width is generated.

The above operation is executed by the CPU 25 by reading the instruction operation in the ROM 26. And these are R
When the timer count is temporarily stored in the AM 27, the first pulse train signal for one cycle of the sine wave signal is generated, and the gate drive circuit 10 shown in FIG.
Will be output to The second to fourth pulse train signals are similarly generated and output. In the gate drive circuit 10, on / off control of the four switching elements constituting the high-frequency inverter bridge 4 is performed, and as a result, the high-frequency transformer is PWM-controlled.
The same high frequency (several tens to hundreds of kHz) as the frequency of the carrier signal, in which the modulated pulse train is inverted every other sign
z) Excited at Ei. When the control circuit 9 is constituted by a digital circuit in this way, the simplification of the control circuit is realized.

Embodiment 3 An inverter device according to a third embodiment will be described with reference to FIG. The inverter 1 of the present invention is inserted between the solar cell 2 and the existing commercial power system 3, converts DC power generated by the solar cell 2 into AC power of 50/60 Hz, and connects the AC power to the commercial power system 3. In addition to supplying power to the load, reverse power flow to the commercial power system 3 is also performed. Here, the names of the respective lines of the single-phase three-wire distribution line of the commercial power system 3 are neutral lines o, u, and v, respectively, as shown in FIG.

The configuration of the inverter 1 according to the present invention will be described. The input capacitor 4 is provided to suppress a sudden change in the input voltage of the inverter 1 due to a change in solar cell output due to a change in solar radiation. The DC power input to the inverter 1 is guided to a high-frequency inverter bridge 4 composed of switching elements Q1 to Q4 and converted from DC to AC. Further, the output of the high-frequency inverter bridge 4 is supplied to the primary side of a high-frequency transformer 5 where it is electrically insulated. An intermediate tap is provided on the secondary side of the high-frequency transformer 5, and a line from this intermediate tap is connected to a neutral line o of a single-phase three-wire distribution line of a commercial power system via an interconnection relay 15. . The other two wires on the secondary side of the high-frequency transformer 5 are input to the AC input terminal of the diode bridge 6 and converted from AC to DC. The two wires from the DC output terminals of the diode bridge 6 are connected to the DC reactors 7a and 7b and the capacitors 30a and 30b inserted between the two wires and the neutral wire, respectively, in a vertically symmetric manner. After that, it is input to the low-frequency inverter bridge 8 composed of the switching elements S1 to S4, and is again converted from DC to AC. The two output lines of the low-frequency inverter bridge 8 are connected to the interconnection relay 15 and the neutral lines through filter circuits 31a and 31b arranged vertically symmetrically. It is configured to be connected to each of the two lines other than the neutral line o line, u line, and v line of the distribution line.

Next, the operation of the inverter according to the present invention will be described. First, in the high-frequency inverter bridge 4, the four IGBT elements (Q1 to Q4) that constitute it
Is generated by comparing a sine wave signal (50/60 Hz) with a high frequency carrier signal (19 kHz), so that the primary side of the high frequency transformer 5 has a sine wave PW
It is excited by an M-modulated pulse train signal. At this time, the primary side of the high-frequency transformer 5 is connected to a high-frequency AC (1
At the time of excitation at 9 kHz), in this embodiment, the pulse train signal subjected to the PWM modulation is excited by a pulse train as shown in FIG. Although shown schematically in the figure for simplicity, the frequency of this pulse train has the same frequency as the frequency of the high-frequency carrier signal. As described above, as a control method for exciting the high-frequency transformer 5 with the high-frequency AC, the gate drive signal of the IGBT element constituting the high-frequency inverter bridge 4 is set in the same manner as in the first embodiment or the second embodiment. Generate.

As described above, high-frequency AC (19 kHz)
z) is supplied to the primary side of the high-frequency transformer 5, and the high-frequency AC converted to a voltage corresponding to the turns ratio of the transformer is output to the secondary side of the high-frequency transformer 5. Here, the high-frequency transformer 5 has a function of electrically insulating the commercial power system 3 and the solar cell 2 and a function of transforming an output voltage with respect to an input voltage at a transformation ratio corresponding to a turns ratio. Further, the intermediate tap provided on the secondary side of the high-frequency transformer 5 causes the secondary side of the transformer to transmit the intermediate tap and the transformer output between the intermediate tap and the upper line of the transformer output, and the intermediate output from the secondary side of the transformer. Three line voltages are generated between the tap and the lower line of the transformer output, between the upper line of the transformer output, and between the lower line of the transformer output. These high-frequency transformers 5
The three line voltage waveforms on the secondary side are high-frequency alternating currents in which the PWM pulse train similar to the primary side shown in FIG.

The above three line voltages are rectified by the diode bridge 6 at the next stage, and are the DC voltages of the PWM-modulated pulse trains continuous on the positive side as shown in A, B and C in FIG. It becomes the line voltage, the second line voltage, and the third line voltage. Further, DC reactors 7a, 7b provided in series with the two output lines of the diode bridge 6, respectively.
And a capacitor 30 provided vertically symmetrically between the two output lines and the output line from the intermediate tap of the high-frequency transformer 5
a, 30b, the first line voltage, the second line voltage, and the third line voltage as shown in A ', B', and C 'of FIG. The high-frequency ripple component is removed and smoothed from the DC voltage waveforms of A, B, and C, and a DC voltage waveform similar to that obtained by full-wave rectification of a low-frequency sine wave is obtained.

Between the first line voltage and the second line voltage of the low-pass filter output indicated by A 'and B', and between the other two lines except for the line connected to the intermediate tap of the high-frequency transformer 5 Between the third line voltage which is the line voltage, C ′ in FIG.
As shown in (1), there is a relationship of first line voltage + second line voltage = third line voltage. Here, set the middle tap of the transformer to 2
At the midpoint of the secondary winding, the first line voltage and the second line voltage are equal, and the third line voltage has a voltage value twice the first line voltage or the second line voltage. Will be. In this embodiment, the current waveforms flowing through the two low-pass filter output lines other than the one line connected to the intermediate tap have the same phase as the voltage waveform as shown in FIG.

Further, two lines (other than one line connected to the intermediate tap) constituting the third line voltage are input to the low-frequency inverter bridge 8 at the next stage. Here, the four IGBT elements (S1
To S4) with the commercial terminal at the commercial frequency.
And S2 and S3 are alternately turned on and off. That is, in synchronization with the valley (0 V point) of the voltage value of each line voltage shown in FIG. 7, when S1 and S4 are on, S2 and S3 are turned on and off alternately such that S2 and S3 are off. As a result, the voltage and current waveforms shown in FIG. 7 are inverted symmetrically in the vertical direction with every other peak of each sine wave in a full-wave rectified form, and the voltage waveforms shown in FIG. Is converted to a commercial frequency sinusoidal AC waveform. Further, the signal is smoothed by AC filter circuits 31a and 31b vertically symmetrically arranged between the neutral line and the two output lines of the low-frequency inverter bridge 8 via the interconnection relay 15, and the harmonic components are removed. A waveform-shaped commercial frequency AC voltage waveform and current waveform can be obtained.

Here, the voltage between the output line from the AC filter circuit 31a and one line connected to the intermediate tap is connected to the first line voltage, the output line from the AC filter circuit 31b and the intermediate tap. Assuming that the voltage between the two lines is the second line voltage, and the voltage between the two lines output from the AC filter circuits 31a and 31b is the third line voltage, A ″, B ″,
C "respectively indicate a first line voltage waveform, a second line voltage waveform,
And a third line voltage waveform.

Here, similarly to the above, the third line voltage has a voltage value twice as large as the first line voltage or the second line voltage. 1
The line voltage, the second line voltage is 100 V, and the third line voltage is 2
The transformer ratio of the high-frequency transformer 5 is set to be 00 V (in this embodiment, the rated input voltage is 200 VDC, so the transformer turns ratio is 1: 2.2 to 2.7, and the transformer intermediate tap is the middle point of the secondary winding. In this inverter 1, the high-frequency transformer 5 is used to reduce the size and weight of the device, and the output of the inverter 1 is
It has three lines of u line, o line, and v line including neutral line, and each line voltage has a line voltage that can be connected to a single-phase three-wire distribution line of the commercial power system 3. Therefore, interconnection with the single-phase three-wire distribution line of the commercial power system 3 is also possible.

In the high-frequency transformer 5, besides the method of providing an intermediate tap on the secondary side, two secondary windings are prepared, and the beginning and end of each winding are connected. It is also possible.

A main circuit configuration of the inverter 1 in which an intermediate tap is provided in the high-frequency transformer 5 described above and the neutral line is connected to the commercial power system 3 and a pulse train subjected to PWM modulation in the high-frequency transformer 5 is alternately provided. By using the inverter control method of exciting with high-frequency alternating current of positive and negative inversion, as shown in this embodiment, connection with the same electric system as single-phase three-wire distribution line, which could not be realized conventionally, can be achieved. It is possible to realize an inverter device having a possible high-frequency transformer.

[0051]

As described above, according to the present invention, a high frequency transformer having a capacity ratio of about 1/30 and a weight ratio of about 1/20 can be used instead of a commercial transformer. Compared with the method used, the inverter can be made smaller and lighter.

Furthermore, a sine wave AC waveform having a sufficiently small distortion similar to the waveform output by the conventional PWM control can be obtained with a very simple configuration in which only the gate processing of, for example, exclusive OR processing is added to the conventional PWM control. Obtainable.

Further, it is possible to realize a high-frequency insulated inverter device which can be connected in the same electrical system as a single-phase three-wire distribution line of a commercial power system.

[Brief description of the drawings]

FIG. 1 is a block diagram of an inverter device according to a first embodiment.

FIG. 2 is a block diagram of a control circuit according to the first embodiment.

FIG. 3 is a diagram illustrating generation of a pulse train signal by exclusive OR processing of a pulse train signal and a rectangular wave signal according to the first embodiment.

FIG. 4 is a block diagram of a control circuit according to a second embodiment.

FIG. 5 is a block diagram of an inverter device according to a third embodiment.

FIG. 6 is a diagram for explaining waveforms of respective units according to the third embodiment.

FIG. 7 is a diagram for explaining waveforms at various parts according to the third embodiment.

FIG. 8 is a block diagram of a conventional inverter device.

FIG. 9 is a diagram illustrating generation of a conventional pulse train signal by comparing a sine wave signal and a carrier signal.

FIG. 10 is a block diagram of a conventional inverter device.

FIG. 11 is a diagram illustrating a waveform of a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Inverter 2 Solar cell 3 Commercial power system 4 High frequency inverter bridge 5 High frequency transformer 6 Diode bridge 7 DC reactor 8 Low frequency inverter bridge 9 Control circuit 10 Gate drive circuit 11 Gate drive circuit 12 DC capacitor 13 DC input current detector 14 Inverter output Current detector 15 Interconnection relay 16 AC filter 17 A / D converter 18 Signal operation processing unit 19 Carrier signal generator 20 Rectangular wave signal generator 21 Inverting circuit 22 Comparison circuit 23 NOT circuit 24 XOR circuit 25 CPU 26 ROM 27 RAM 28 I / O 29 Timer 30 Capacitor 31 Filter circuit 32 Inverter bridge 33 Commercial transformer 34 Control circuit 35 Gate drive circuit 36 PWM modulation generator 37 Error amplifier 38 Carry Signal generator 39 the signal processing unit 40 a sine wave signal storage unit 41 A / D converter 42 D / A converter 43 the signal processing unit 44 the hysteresis comparator 45 NOT circuit 46 folded control circuit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Satoshi Fujii 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-63-23565 (JP, A) JP-A-1- 234062 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 7/48

Claims (3)

(57) [Claims] A power converter for converting DC power into AC power; and a voltage converter for converting the voltage of the AC power converted by the power converter.
And transforms the transformed AC power into AC and then into AC
A transformer for supplying power to a load or a commercial power supply;
An inverter control device comprising: a control circuit that controls the power conversion unit; wherein the control circuit generates a sine wave signal that is an output target value of the inverter control device, and performs PWM control using the sine wave signal. Means for generating a carrier signal for performing the following, means for generating a rectangular wave signal having the same frequency as the carrier signal and having a phase shifted by a quarter cycle, and a means for generating the sine wave signal and the carrier signal. Compare with
The exclusive OR operation is performed on the obtained signal and the rectangular wave signal.
Means for generating a control signal obtained by performing the above-mentioned operation, wherein the control signal controls on / off of a switching element included in the power conversion unit. 2. A according to claim 1, characterized in that formed by connecting the neutral line of the single-phase three-wire distribution line of the intermediate tap provided on the secondary side of the transformer and the commercial electric power system Inverter control device. 3. DC power is converted into AC power through a power conversion unit, and AC power converted by the power conversion unit is converted into DC through a transformer, and then converted into AC and converted into a load or a commercial power supply. the control method for supplying the inverter device is obtained by comparing the carrier signal for PWM control using the above <br/> Symbol sinusoidal signal sine wave signal and a target output value of the inverter device signal And a control signal generated by performing an exclusive OR process with a rectangular wave signal having the same frequency as that of the carrier signal and having a phase shifted by a quarter period, and which constitutes the power conversion unit. And an on / off control of the inverter.