JP3245505B2 - Grid-connected inverter controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grid-connected inverter control apparatus for converting DC power output from a DC power supply such as a solar cell into AC power and connecting the AC power to a commercial power supply. The present invention relates to a grid-connected inverter control device that stably connects to a grid power supply.

[0002]

2. Description of the Related Art FIG. 2 shows a circuit block diagram of a photovoltaic power generation system to which a conventional grid-connected inverter control device is applied. In this system, the DC power of the solar cell 2 is pulse width modulated (PWM) by the grid-connected inverter control device 20.
The power is controlled to be converted into AC power, and is supplied to the load 5 via the commercial insulation transformer 4 in connection with the commercial power supply 3.

The system interconnection type inverter control device 20 includes an input capacitor 6, an FET bridge 7 composed of switching elements Q1 to Q4, an output choke coil 8 having an output filter function, a smoothing capacitor 9, an interconnection relay 10,
It comprises a control unit 11, a commercial system voltage detector 12, and an inverter output current detector 13.

The control unit 11 includes a commercial system voltage detector 12
The signal arithmetic processing unit 19 oscillates a reference sine wave signal b in synchronization with the commercial system voltage signal a detected by the above, and outputs the reference sine wave signal b and an inverter output current detection signal c (inverter) as a feedback signal. The signal amplified by the error amplifier 17 is subjected to PWM control by the PWM control circuit 16, and the gate drive signal is output to the switching elements Q 1 to Q 4 by the gate drive circuit 15.

During normal operation of the system interconnection type inverter control device 20, the interconnection relay 10 is turned on, and the commercial system power supply 3 and the system interconnection type inverter control device 20 are interconnected. Control is performed so that the inverter output current is maximized, that is, the solar cell maximum power point tracking. Then, when a stop condition such as a decrease in the output voltage of the solar cell 2 detected by a DC voltage detector (not shown) or occurrence of an abnormality in the commercial power supply 3 or the grid-connected inverter control device 20 is satisfied. Then, the interconnection relay 10 is cut off to disconnect the commercial system power supply 3 from the system interconnection type inverter control device 20, and the operation of the FET bridge 7 is stopped.

[0006] Considering the start-up time, before that, the interconnection relay 10 is shut off, and the commercial system power supply 3 and the system interconnection type inverter control device 20 are disconnected. At this time, the reference sine wave signal b is not controlled. Then, when a start condition such as an increase in the output voltage of the solar cell 2 or a recovery from an abnormality of the grid-connected inverter control device 20 or the like is satisfied, the FET bridge 7 including the switching elements Q1 to Q4 is started by the gate drive signal. Is done. After that, when the normal operation of the grid-connected inverter controller 20 and the commercial grid power supply 3 is confirmed, the grid relay 10 is turned on, and the commercial grid power supply 3 is connected to the grid-linked inverter controller 20; Power is supplied to the load 5. In this connection, in order to avoid the reverse flow of the current from the commercial system power supply 3 to the system interconnection type inverter control device 20, the minimum amplitude of the reference sine wave signal b is determined in advance. When the power supply is turned on, the reference sine wave signal b is fixed to the sine wave signal having the lowest amplitude, and the control of the inverter output current is started immediately after the connection relay 10 is turned on.

[0007]

However, in the above conventional example, the inverter output current detection signal c is used as a feedback signal before and during interconnection between the commercial system power supply 3 and the system interconnection type inverter control device 20. Therefore, even if the reference sine wave signal b is fixed to the sine wave having the predetermined minimum amplitude as described above, it has been impossible to accurately control the inverter output voltage. Therefore, when the commercial system power supply 3 and the system interconnection type inverter control device 20 are interconnected, the following problems occur.

When the inverter output voltage is lower than the commercial system voltage, a current flows backward from the commercial system power supply 3 to the system interconnection type inverter control device 20, so that the inverter input voltage becomes abnormally high. This voltage is the switching element Q
Exceeding 1 to Q4 or the withstand voltage of the solar cell 2 causes destruction of the element. To prevent the current from flowing backward,
There is a method of inserting a diode for preventing backflow between the solar cell 2 and the grid-connected inverter 20. In this case,
There is a problem that power loss occurs due to the resistance of the diode.

When the inverter output voltage is abnormally high with respect to the commercial system power supply 3, a transient current flows during connection, so that the switching elements Q1 to Q4 are destroyed or the commercial system power supply 3 is adversely affected. Might be.

In view of the above, the present invention provides a system interconnection type inverter control device which does not generate a reverse current or a transient current when the system interconnection type inverter control device 20 and the commercial system power supply 3 are interconnected. The purpose is to do.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is a control object when the commercial system power supply and the system interconnection type inverter control device are disconnected when they are disconnected. A means for selecting an inverter output voltage as a control target instead of the inverter output current and setting the inverter output voltage to the same voltage as the commercial system voltage or a voltage several volts higher than the commercial system voltage is provided. The present invention provides a system interconnection type inverter control device that converts DC power input from a DC power source such as a solar cell into AC power, and supplies the AC power to a commercial system power supply to a load. Means for connecting and disconnecting the interconnected inverter control device, means for detecting the commercial system voltage, the inverter output current and the inverter output voltage, and the commercial system power supply and the system interconnected inverter control device are interconnected. If it is, a variable amplitude reference sine wave signal synchronized with the commercial system voltage signal is generated, and when the commercial system power supply and the system interconnection type inverter control device are shut off, the inverter output voltage is Means for generating a reference sine wave signal set to be equal to or higher than the commercial system voltage by several volts, the commercial system power supply and the system interconnection type inverter A signal switch for selecting an inverter output voltage detection signal when the control device is shut off, and an inverter output current detection signal when the commercial system power supply and the system interconnection type inverter control device are interconnected. A means for amplifying an error between one of the selected inverter output voltage detection signal or the inverter output current detection signal and the reference sine wave signal; and a pulse based on a signal obtained by the error amplification. Means for performing width modulation control;
Provided is a system interconnection type inverter control device characterized by comprising:

[0012]

As described above, in the system interconnection type inverter control device of the present invention, the control target is switched according to the interconnection state with the commercial system power supply. That is, when the commercial system power supply and the system interconnection type inverter control device are shut off, the inverter output voltage detection signal is selected as a feedback signal, and the commercial system power supply and the system interconnection type inverter control device are interconnected. At this time, the inverter output current detection signal is selected as a feedback signal. In addition, when the commercial system power supply and the system interconnection type inverter control device are shut off, the inverter output voltage is set to the same or several volts higher than the commercial system voltage. Therefore, when the commercial system power supply and the system interconnection type inverter control device are interconnected, the maximum power point tracking control can be performed, and the commercial system power supply and the system interconnection type inverter control device are interconnected. At this time, the inverter output voltage is controlled to the same voltage or several volts higher than the commercial system voltage, so that it is possible to suppress the reverse current and the transient current from the commercial system power supply.

[0013]

FIG. 1 is a circuit block diagram of a photovoltaic power generation system to which an embodiment of a system interconnection type inverter control device according to the present invention is applied. The grid-connected inverter control device 1 functions as an input capacitor 6, an FET bridge 7 including switching elements Q1 to Q4 for DC-AC conversion, an output filter, and a PWM control, which suppresses fluctuation of input power from the solar cell 2. An output choke 8 and a smoothing capacitor 9 for converting the obtained rectangular wave into a sine wave, and a link for disconnecting the grid-connected inverter controller 1 from the commercial grid power supply 3 and the load 5 when the output of the solar cell 2 is reduced or an abnormality occurs. System relay 10, control unit 11, commercial system voltage detector 1
2, an inverter output current detector 13 and an inverter output voltage detector 14.

The control unit 11 includes a gate drive circuit 15 for driving and controlling the FET bridge 7, a PWM control unit 16, an error amplifier 17, a signal switching unit 18, and a signal operation processing unit 19 composed of a digital circuit mainly including a CPU. Consists of

Next, the operation of the solar cell power generation system of this embodiment will be described.

The system interconnection type inverter control device 1 is a PWM
A pair of switching elements Q1 and Q2 and a pair of switching elements Q3 and Q4 in the FET bridge 7 are alternately turned ON / OFF based on a gate pulse signal output from the gate drive circuit 15 subjected to PWM control by the control unit 16. By generating a rectangular wave and converting the rectangular wave into a sine wave with an output filter including an output choke 8 and a smoothing capacitor 9, the DC power of the solar cell 2 is converted into an AC.

The operation of the control unit 11 differs between the normal operation and the startup of the grid-connected inverter control device 1. First,
During normal operation, that is, when the interconnection relay 10 is turned on, the commercial system power supply 3 and the system interconnection type inverter controller 1
The operation when are connected is described. At this time, the signal switching unit 18 selects the inverter output current detection signal c as a feedback signal, and outputs it to the error amplifier 17. The error amplifier 17 compares the inverter output current detection signal c, which is a feedback signal, with the reference sine wave signal b, and outputs an amplified signal of the error to the PWM control unit 16. The PWM controller 16 generates a switching pattern signal as a PWM waveform by comparing the signal with a triangular wave serving as a switching carrier, and outputs the switching pattern signal to the gate drive circuit 15. Then, the gate drive circuit 15 outputs a gate pulse signal to the FET bridge 7 to control the inverter output current. At this time, the amplitude of the reference sine wave signal b is controlled so that the output value of the solar cell 2 is maximized under the sunshine conditions and the like, with the amplitude value when the interconnection relay 10 is turned on being the minimum value. Power point tracking control). That is, when the amplitude of the reference sine wave signal b is changed in the increasing direction, the amplitude is further increased if the inverter output current increases from the detection value before the amplitude is increased, and the amplitude is decreased if the inverter output current decreases. When the amplitude of the reference sine wave signal b is changed in the decreasing direction, the amplitude is further reduced if the inverter output current increases from the detected value before the amplitude is reduced, and the amplitude is increased if the inverter output current increases. As described above, the amplitude of the reference sine wave signal b is changed so that the inverter output current always increases.

Then, the output of the solar cell 2 is reduced, or the commercial system power supply 3 or the system interconnection type inverter controller 1
In the case where an abnormality occurs, the interconnection relay 10 is shut off, and the operation of the system interconnection type inverter setting device 1 is stopped.

The operation of the control unit 11 at the time of starting the system interconnection type inverter control device 1 is as follows. At startup, the grid-connected inverter control device 1 and the commercial grid power supply 3
Are separated by the link relay 10, and the signal switching unit 18 selects the inverter output voltage detection signal d as a feedback signal. The feedback signal is compared with the reference sine wave signal b generated by the signal operation processing unit 19 in the error amplifier 17. This result is output to the PWM control unit 16, and the PWM pattern changes to induce the amplitude of the inverter output voltage detection signal d to be equal to the amplitude of the reference sine wave signal b. The amplitude of the reference sine wave signal b is determined so that the inverter output voltage is equal to or higher than the commercial system voltage by several volts (0 to 5 volts in this example). However, the inverter output voltage does not reach the set voltage unless the release voltage of the solar cell 2 becomes higher than a certain value.

When the release voltage of the solar cell 2 becomes equal to or higher than a predetermined value due to an increase in the amount of sunlight and the like, and the inverter output voltage reaches the above-mentioned set voltage, that is, the inverter output voltage is equal to or several volts from the commercial system voltage (this example). Then 0 volts ~
(5 volts) When the voltage becomes high, the signal operation processing section 19 outputs a signal for turning on the interconnection relay 10, and switches a signal for switching the feedback signal from the inverter output voltage detection signal d to the inverter output current detection signal c. Output to the unit 18. The amplitude of the inverter output current detection signal c at the time of switching the feedback signal is gain-adjusted in advance so as to be substantially the same as the amplitude of the inverter output voltage detection signal d when the inverter output voltage matches the commercial system voltage. Accordingly, the switching of the feedback signal is performed smoothly.

The signal processing unit 19 does not change the amplitude of the reference sine wave signal b immediately after the interconnection relay 10 is turned on, that is, when the interconnection relay 10 is cut off, the inverter output voltage is the same as the commercial system voltage. Alternatively, the amplitude is fixed at a voltage set to a voltage several volts higher. Then, after the switching of the feedback signal is performed smoothly as described above, the amplitude of the reference sine wave signal b is gradually increased,
The maximum power point tracking control according to the sunshine intensity is performed.

As described above, the grid-connected inverter control apparatus 1 of the present embodiment can control the inverter output voltage to the same voltage as the commercial system voltage or a voltage several volts higher when linking with the commercial system power supply 3. Because of this, it is possible to suppress the reverse flow of the current from the commercial system power supply 3 and the occurrence of a transient current that occur at the time of interconnection, and to prevent the destruction of elements and the adverse effect on the commercial system power supply 3. In addition, solar cell 2
There is no need to insert a diode between the power supply and the grid-connected inverter control device 1, so that the power of the solar cell 2 can be efficiently supplied to the load without power loss due to the diode.

Next, an example of a method of generating the reference sine wave signal b in the signal processing unit 19 will be described below. First, the amplitude of a half cycle of a sine wave having a plurality of amplitudes is sampled at certain time intervals, and the data is stored in the signal operation processing unit 19. Then, a sine wave having an optimum amplitude is selected, read, and output according to the control state. In this example, a sine wave having a frequency of 60 Hz and a half cycle of 1/120 seconds is used,
Sampling was performed at a time interval of 1/120 / n seconds obtained by dividing this into n equal parts. The reference sine wave signal b is generated by starting a built-in timer of the CPU upon detection of the commercial system voltage 0 cross, and at every sampling time interval (1/120 / in this example).
(every n seconds), the data is sequentially read, and the digital values are D / A converted by a D / A converter. Further, by detecting the positive / negative direction from the commercial system voltage signal a, aligning the positive and negative directions with the positive and negative directions of the oscillating sine wave and synchronizing with the 0 cross point detected from the commercial system voltage signal a, the commercial system voltage signal a And phase matching. In the present embodiment, the above processing is realized by performing software control using a microcomputer.

[0024]

As described above, according to the present invention, when the commercial system power supply and the system interconnection type inverter control device are interconnected,
The inverter output voltage can be controlled to the same voltage or several volts higher than the commercial system voltage, so that the occurrence of reverse current and transient current can be suppressed, and a stable interconnection state that does not cause element destruction etc. is established. can do.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing one embodiment of the present invention.

FIG. 2 is a circuit block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grid connection type inverter control apparatus 10 Interconnection relay 11 Control part 12 Commercial system voltage detector 13 Inverter output current detector 14 Inverter output voltage detector 15 Gate drive circuit 16 PWM control part 17 Error amplifier 18 Signal switching part 19 Signal Processing unit a Commercial system voltage signal b Reference sine wave signal c Inverter output current detection signal d Inverter output voltage detection signal

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Nakata 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Satoshi Fujii 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (56) References JP-A-6-169577 (JP, A) JP-A-5-227757 (JP, A) JP-A-5-46265 (JP, A) JP-A-1-16220 (JP, A) JP-A-3-22829 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02M 7/48 G05F 1/67 H02J 3/38

Claims (1)

(57) [Claims] 1. A system interconnection type inverter control device that converts DC power input from a DC power source such as a solar cell into AC power, and supplies the AC power to a commercial system power supply to a load. Means for connecting and disconnecting the grid-connected inverter controller; means for detecting the commercial system voltage, the inverter output current and the inverter output voltage; and linking the commercial system power supply and the grid-connected inverter controller. In this case, a reference sine wave signal of variable amplitude synchronized with the commercial system voltage signal is generated, and when the commercial system power supply and the system interconnection type inverter control device are shut off, the inverter output voltage is Means for generating a reference sine wave signal which is set to be equal to or several volts higher than the commercial system voltage; and The inverter output voltage detection signal is selected when the power control device is shut off, and the inverter output current detection signal is selected when the commercial system power supply and the system interconnection type inverter control device are interconnected. Signal switching means; means for error-amplifying one of the selected inverter output voltage detection signal or inverter output current detection signal; and the reference sine wave signal; and a signal obtained by the error amplification. And a means for performing pulse width modulation control.