JP2008289211A - System-cooperative inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system-cooperative inverter suppressing variations in switching and DC components of AC output current. <P>SOLUTION: The system-cooperative inverter has a voltage detecting means 8 for detecting a voltage between a midpoint of two capacitors C1, C2 and positive and negative busbars 201, 202 and a voltage between the positive and negative busbars; and an inverter output current control means 12 for controlling the DC components of an output current command of an inverter so that the voltage between the midpoint of the two capacitors and the positive and negative busbars may be 1/2 of the voltage between the positive and negative busbars. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a grid-connected inverter device, and more particularly to a transformer-less grid-connected inverter device that connects a power supply source such as a DC power source and a generator to a commercial AC power system that is linked without using a transformer. Is.

  In a grid-connected single-phase three-wire inverter, there is a circuit system in which a neutral wire is taken out from the middle point of two capacitors connected in series between a positive bus and a negative bus in order to create a neutral point. There is a problem that a direct current component is generated in the output current due to the switching fluctuation of the PWM inverter and the output current detection offset error. Specifically, the initial voltage at the middle point of the two capacitors is Vn0, the total capacity of the two capacitors is C, the U-phase current DC component is Idu, the V-phase current DC component is Idv, and the AC voltage component is ignored. Then, when obtaining the neutral line capacitor voltage Vn,

It becomes. As a result, the DC component current flows through the two capacitors connected in series by the DC component, and the middle point potential of the capacitor is biased to the voltage between the positive bus and the negative bus, exceeding the breakdown voltage of the capacitor. There is also a problem.

As a countermeasure against the above problem, there is a method in which resistors are connected in parallel to the two capacitors connected in series to balance the voltages of the capacitors (see Patent Document 1).
JP 2007-97355 A

  However, the method of balancing with the resistance has a problem that there is a lot of loss because a high voltage is applied to the resistance, and there is a problem that the DC component of the AC output current cannot be controlled by the variation in switching and the AC output current detection offset.

  The present invention has been made in view of the above problems, and provides a grid-connected inverter device that suppresses switching variations and a DC component of an AC output current.

  In order to solve the above problems, a grid-connected inverter device according to the present invention includes a DC power source, a positive bus connected to the DC power source, and a negative bus. The first and second buses are connected between the positive bus and the negative bus. The switch element and the third and fourth switch elements are connected in series, and each intermediate point is connected to the U-phase voltage output terminal of the single-phase three-wire power system and the V-phase of the single-phase three-wire power system via a reactor. Connected to the voltage output terminal and connected to the neutral line of the single-phase three-wire power system from the middle point of the two capacitors connected in series between the positive bus and the negative bus to convert to AC power In the system inverter, voltage detecting means for detecting a voltage between a midpoint of the two capacitors and the bus and a voltage between the positive bus and the negative bus, and between the midpoint of the two capacitors and the bus Is the positive bus and negative bus And having an inverter output current control means for controlling the DC component of the output current command of the inverter so that the half of the voltage between.

  Further, the grid-connected inverter device according to the present invention has a DC power source, a positive bus connected to the DC power source and a negative bus, and between the positive bus and the phase voltage output of the single-phase two-wire power system, and the negative bus The first and second switch elements are connected in series via a reactor between the phase voltage output terminals of the single-phase two-wire power system, and two connected in series between the positive bus and the negative bus In a grid-connected inverter that is connected to the phase voltage output terminal of the single-phase two-wire power system from the midpoint of the capacitor and converts it to AC power, the voltage between the midpoint of the two capacitors and the bus A voltage detecting means for detecting a voltage between the positive bus and the negative bus; and an inverter so that a voltage between a midpoint of the two capacitors and the bus is ½ of a voltage between the positive bus and the negative bus Controls the DC component of the output current command System interconnection inverter apparatus characterized by having an inverter output current control means that.

  An AC current value is detected between the reactor and the U-phase voltage output terminal, between the reactor and the negative bus and the single-phase three-wire power system V-phase voltage output terminal, or between the reactor and the phase voltage output terminal. An AC current detecting means is provided.

  Further, the voltage between the midpoint of the two capacitors detected by the voltage detecting means and the bus and the voltage between the positive bus and the negative bus are compared, and this comparison value is 1 / DC input voltage. Subtract from the value of 2 and control to consider this value as a DC component of the AC output.

  Further, only the AC output non-direct current component and a sine wave current waveform generated in advance are added, and the direct current component detected by the alternating current detection means is subtracted from the added value obtained by the addition. It is characterized by removing.

  According to the present invention, by controlling the DC component of the output current command of the inverter so that the voltage between the midpoint of the two capacitors and the positive / negative bus is ½ of the voltage between the positive bus and the negative bus. The DC component of the output current caused by the switching variation and the output current detection offset error can be suppressed. Further, since it is not necessary to connect a voltage balance circuit to the two capacitors, the circuit can be simplified and the cost can be reduced.

  A circuit diagram of the best mode for carrying out the invention is shown in FIG. First, the main circuit of the grid interconnection inverter shown in FIG. 1 will be described. First, the grid interconnection inverter according to the present embodiment is a single-phase three-wire grid interconnection inverter, and includes a DC power source 1, a positive bus 201 and a negative bus 202 connected thereto. Two capacitors C1 and C2 are connected in series between the positive bus 201 and the negative bus 202. Further, the first switch element Q1 and the second switch element Q2 are connected in series between the positive bus 201 and the negative bus 202 to constitute the first arm 3, and in parallel with these, A second arm 4 is configured by connecting a third switch element Q3 and a fourth switch element Q4 in series.

  The U-phase voltage output terminal 101 of the single-phase three-wire power system is connected from the middle point of the first arm 3, and the V-phase voltage output terminal 102 of the single-phase three-wire power system is connected from the middle point of the second arm 4. It is. A neutral line 103 of a single-phase three-wire power system is connected from the midpoint of the series circuit 2 of two capacitors C1 and C2.

  A reactor L1 is connected between the midpoint of the first arm 3 and the U-phase voltage output terminal 101 of the single-phase three-wire power system, and the midpoint of the second arm 4 and the single-phase three-wire type A reactor L2 is connected between the V-phase voltage output terminal 102 of the power system.

  Then, the control circuit of the grid connection inverter which concerns on a present Example is demonstrated. First, in the present embodiment, voltage detection means for detecting the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202 and the voltage between the positive bus 201 and the negative bus 202, Is provided with a DC output voltage detector 8. The voltage detector 8 compares the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202 with the voltage between the positive bus 201 and the negative bus 202.

  A subtractor 11 is provided for subtracting the comparison value output from the voltage detector 8 from a voltage that is ½ of the DC input voltage Ed of the DC power supply 1. The DC voltage signal output from the subtractor 11 is supplied to the gain 14. Entered. In the gain 14, the DC voltage signal output from the subtractor 11 is regarded as a DC component of the AC current in the grid-connected inverter device according to the present embodiment.

  The control circuit for the grid-connected inverter according to this embodiment includes adders 15 and 16. One adder 15 is configured to add not only the AC output output from the gain 14 but also the sine wave power waveform 21 to be output in the U phase. The other adder 16 is configured to add not only the AC output output from the gain 14 but also the sine wave power waveform 22 to be output in the V phase.

  On the other hand, a U-phase current detector 27 for detecting a U-phase AC current is provided between one reactor L1 and the U-phase voltage output terminal 101 on the AC power side. Further, a V-phase current detector 28 for detecting a V-phase AC current is provided between the other reactor L2 and the V-phase voltage output terminal 102.

  The control circuit for the grid-connected inverter according to the present embodiment includes subtractors 17 and 18. One subtracter 17 subtracts the U-phase current detected by the U-phase current detector 27 from the U-phase current command sine wave including only the AC output and the DC correction component. The other subtracter 18 subtracts the V-phase current detected by the V-phase current detector 28 from the V-phase current command sine wave including only the AC output and the DC correction component.

  The control circuit for the grid-connected inverter according to this embodiment includes current controllers 12 and 13. The current error signals output from the subtractors 17 and 18 are calculated by the current controllers 12 and 13 and output as error control signals. Specifically, in this embodiment, the error control signal is output by PI control that combines proportional control (P control) and integral control (I control).

  The control circuit for the grid-connected inverter according to the present embodiment includes U-phase and V-phase PWM modulators 9 and 10, respectively. The U-phase PWM modulator 9 converts the error control signal output from the U-phase current controller 12 into a PWM modulation signal, and outputs the PWM control signal to the switch elements Q 1 and Q 2 of the first arm 3. On the other hand, the V-phase PWM modulator 10 converts the error control signal output from the V-phase current controller 13 into a PWM modulation signal and outputs the PWM modulation signal to the switch elements Q3 and Q4 of the second arm 4.

  The grid-connected inverter device configured as described above operates as follows. First, the DC output voltage detector 8 detects the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202, and the voltage between the positive bus 201 and the negative bus 202. The voltage between the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202 is compared with the voltage between the positive bus 201 and the negative bus 202.

  The subtractor 11 subtracts the comparison value output from the voltage detector 8 from a voltage that is 1/2 of the DC input voltage Ed of the DC power supply 1. The DC voltage signal output from the subtractor 11 is input to the gain 14. In the gain 14, the DC voltage signal output from the subtractor 11 is regarded as a DC component of the AC current in the grid-connected inverter device according to the present embodiment. The adder 15 adds the alternating current output non-direct current component output from the gain 14 and the sine wave power waveform 21 to be output in the U phase. The adder 16 adds the sine wave power waveform 22 to be output in phase.

  On the other hand, on the AC power side, a U-phase AC current is detected by a U-phase current detector 27 provided between one reactor L1 and the U-phase voltage output terminal 101. A V-phase AC input current is detected by a V-phase current detector 28 provided between the other reactor L2 and the V-phase voltage output terminal 102.

  One subtractor 17 subtracts the U-phase current detected by the U-phase current detector 27 from the U-phase sine wave power waveform including only the AC output and the DC component. The other subtracter 18 subtracts the V-phase current detected by the V-phase current detector 28 from the V-phase sine wave power waveform including only the AC output and the DC component. With this subtraction process, the DC component of the AC output can be removed. The signals from which the DC components of the AC output are removed by the subtractors 17 and 18 are subjected to PI control calculation by the current controllers 12 and 13 and are output as error control signals.

  The error control signal output from the U-phase current controller 12 is converted into a PWM modulation signal by the U-phase PWM modulator 9 and output to the switch elements Q1 and Q2 of the first arm 3. On the other hand, the error control signal output from the V-phase current controller 13 is converted into a PWM modulation signal by the V-phase PWM modulator 10 and output to the switching elements Q3 and Q4 of the second arm 4.

  From the above, by controlling the DC component of the output current command of the inverter so that the voltage between the midpoint of the two capacitors and the positive / negative bus is half of the voltage between the positive bus and the negative bus, The direct current component of the output current caused by the variation and the output current detection offset error can be suppressed. Further, since it is not necessary to connect a voltage balance circuit to the two capacitors, the circuit can be simplified and the cost can be reduced.

  Subsequently, a second embodiment will be described. The grid interconnection inverter according to the second embodiment is a single-phase two-wire grid interconnection inverter, and includes a DC power source 1, a positive bus 201 and a negative bus 202 connected thereto. Two capacitors C1 and C2 are connected in series between the positive bus 201 and the negative bus 202. Further, the arm 3 is configured by connecting the first switch element Q1 and the second switch element Q2 in series between the positive bus 201 and the negative bus 202.

  The AC voltage output terminal 101 of the single-phase two-wire power system is connected from the middle point of the arm 3. A neutral line 103 of a single-phase two-wire power system is connected from the middle point of the series circuit 2 of two capacitors C1 and C2. A reactor L1 is connected between the midpoint of the arm 3 and the AC voltage output terminal 101, and a reactor L2 is connected between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the AC power supply 7. It is.

  Then, the control circuit of the grid connection inverter which concerns on a present Example is demonstrated. First, in the present embodiment, voltage detection means for detecting the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202 and the voltage between the positive bus 201 and the negative bus 202, Is provided with a DC output voltage detector 8. The voltage detector 8 compares the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202 with the voltage between the positive bus 201 and the negative bus 202.

  A subtractor 11 is provided for subtracting the comparison value output from the voltage detector 8 from a voltage that is ½ of the DC input voltage Ed of the DC power supply 1. The DC voltage signal output from the subtractor 11 is supplied to the gain 14. Entered. In the gain 14, the DC voltage signal output from the subtractor 11 is regarded as a DC component of the AC current in the grid-connected inverter device according to the present embodiment.

  The control circuit according to this embodiment includes an adder 15. The adder 15 is configured to add not only the AC output output from the gain 14 but also the sine wave power waveform 21 to be output in the AC portion. On the other hand, on the AC power side, a current detector 27 that detects an AC current is provided between one reactor L1 and the AC voltage output terminal 101.

  The control circuit according to this embodiment includes a subtracter 17. The subtracter 17 subtracts the AC current detected by the AC current detector 27 from a sine wave power waveform including only an AC output and a DC component. With this subtraction process, the DC component of the AC output can be removed.

  The control circuit according to this embodiment includes a current controller 12. The signal from which the DC component of the AC output is removed by the subtractor 17 is subjected to PI control calculation by the current controller 12 and output as an error control signal. The control circuit according to this embodiment includes a PWM modulator 9. The PWM modulator 9 converts the error control signal output from the current controller 12 into a PWM modulation signal and outputs the PWM modulation signal to the switch elements Q1 and Q2 of the arm 3.

  The grid-connected inverter device configured as described above operates as follows. First, the DC output voltage detector 8 detects the voltage between the midpoint of the series circuit 2 of the two capacitors C1 and C2 and the buses 201 and 202, and the voltage between the positive bus 201 and the negative bus 202. The voltage at the midpoint of the series circuit 2 of the two capacitors C1 and C2 is compared with the voltage between the positive bus 201 and the negative bus 202.

  The subtractor 11 subtracts the comparison value output from the voltage detector 8 from a voltage that is 1/2 of the DC input voltage Ed of the DC power supply 1. The DC voltage signal output from the subtractor 11 is input to the gain 14. In the gain 14, the DC voltage signal output from the subtractor 11 is regarded as a DC component of the AC current in the grid-connected inverter device according to the present embodiment. The adder 15 adds only the AC component output from the gain 14 and the sine wave power waveform 21 to be output in the AC part. On the other hand, on the AC power side, an AC current is detected by an AC current detector 27 provided between one reactor L1 and the AC voltage output terminal 101.

  The subtracter 17 subtracts the AC current detected by the current detector 27 from the sine wave power waveform including only the AC output and the DC component. With this subtraction process, the DC component of the AC output can be removed. The signal from which the DC component of the AC output is removed by the subtractor 17 is subjected to PI control calculation by each current controller 12 and output as an error control signal. The error control signal output from the current controller 12 is converted into a PWM modulation signal by the PWM modulator 9 and output to the switch elements Q1 and Q2 of the first arm 3.

  From the above, by controlling the DC component of the output current command of the inverter so that the voltage between the midpoint of the two capacitors and the positive / negative bus is half of the voltage between the positive bus and the negative bus, The direct current component of the output current caused by the variation and the output current detection offset error can be suppressed. Further, since it is not necessary to connect a voltage balance circuit to the two capacitors, the circuit can be simplified and the cost can be reduced.

  According to the present invention, by controlling the DC component of the output current command of the inverter so that the voltage between the midpoint of the two capacitors and the positive / negative bus is ½ of the voltage between the positive bus and the negative bus. The DC component of the output current caused by the switching variation and the output current detection offset error can be suppressed. Further, since it is not necessary to connect a voltage balance circuit to the two capacitors, the circuit can be simplified and the cost can be reduced, and the invention can be used industrially.

1 is a circuit diagram of the best mode for carrying out the invention in a grid-connected inverter device according to the present invention. It is a circuit diagram of the Example in the grid connection inverter apparatus different from FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply C1, C2 Capacitor 2 Series circuit Q1, Q2, Q3, Q4 with capacitor C1, C2 Switch element 3, 4 Arm 7 AC power supply 8 DC output voltage detector 9, 10 PWM modulator 11 Subtractor 12, 13 Current controller 14 Gain 15, 16 Adder 17, 18 Subtractor 21, 22 Sine wave power waveform 27, 28 AC current detector 101, 102 AC voltage output terminal 103 Neutral wire 201 Positive bus 202 Negative bus L1 Reactor

Claims (5)

A DC power source and a positive bus and a negative bus connected thereto, and the first and second switch elements, and the third and fourth switch elements are connected in series between the positive bus and the negative bus, The intermediate point is connected to the U-phase voltage output terminal of the single-phase three-wire power system and the V-phase voltage output terminal of the single-phase three-wire power system via a reactor, and connected in series between the positive bus and the negative bus In the grid-connected inverter that is connected to the neutral line of the single-phase three-wire power system from the midpoint of the two capacitors that are converted into AC power,
Voltage detecting means for detecting a voltage between a midpoint of the two capacitors and the bus and a voltage between the positive bus and the negative bus; and a voltage between the midpoint of the two capacitors and the bus. An inverter output current control means for controlling a direct current component of an output current command of the inverter so that the voltage between the positive bus and the negative bus is ½. DC power source and positive and negative buses connected to it, phase voltage output terminals between the positive bus and the single-phase two-wire power system, and between the negative bus and the single-phase two-wire power system The first and second switch elements are respectively connected in series via a reactor in between, and the single-phase two-wire power system from the midpoint of two capacitors connected in series between the positive bus and the negative bus In the grid-connected inverter that is connected to the phase voltage output terminal and converts to AC power,
Voltage detecting means for detecting a voltage between a midpoint of the two capacitors and the bus and a voltage between the positive bus and the negative bus; and a voltage between the midpoint of the two capacitors and the bus. An inverter output current control means for controlling a direct current component of an output current command of the inverter so that the voltage between the positive bus and the negative bus is ½. An AC current value is detected between the reactor and the U-phase voltage output terminal, between the reactor and the negative bus and the single-phase three-wire power system V-phase voltage output terminal, or between the reactor and the phase voltage output terminal. 3. The grid-connected inverter device according to claim 1, further comprising AC current detecting means. The voltage between the midpoint of the two capacitors detected by the voltage detection means and the bus is compared with the voltage between the positive bus and the negative bus, and this comparison value is ½ of the DC input voltage. 4. The grid-connected inverter device according to claim 1, wherein control is performed so that the value is subtracted from the value and the value is regarded as a direct current component of the alternating current output. Adds only the AC output DC component and the sine wave current waveform generated in advance, and subtracts the AC current value detected by the AC current detection means from the added value to remove the DC component The system interconnection inverter apparatus according to claim 4, wherein

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