JPH08103085A - System interconnection type inverter controller - Google Patents

Abstract

PURPOSE: To prevents backflow of a current or a transient current by setting an inverter output voltage equal to or several volts higher than the commercial system voltage when linking the commercial system power source to a systems interconnection type inverter controller. CONSTITUTION: A signal transfer section 18 selects an inverter output voltage detecting signal (d) as a feedback signal during starting. This feedback signal is compared to a reference sine wave signal (b) generated by a signal arithmetic processing unit 19 in an error amplifier 17. This result is output to the PWM controller 16, and the amplitude of the signal (d) is made equal to the amplitude of the signal (b). Amplitude of the signal (b) is determined in such a manner that the inverter output voltage becomes equal to or several volts higher than the setting voltage for the commercial system voltage. The signal arithmetic processing unit 19 outputs the signals for closing an interconnection relay 10 and also outputs signals for transferring the feedback signals from signal (d) to inverter output current detecting signal (c) to the signal transfer section 18.

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 device for converting DC power output from a DC power source such as a solar cell into AC power and linking it to a commercial grid power source, and particularly to a commercial power source. The present invention relates to a grid-connected inverter control device that stably links 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 interconnection type inverter control device is applied. In this system, the DC power of the solar cell 2 is pulse width modulated (PWM) by the grid interconnection type inverter control device 20.
It is controlled and converted into AC power, which is connected to the commercial power supply 3 through the commercial isolation transformer 4 and supplied to the load 5.

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 is composed of 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
On the basis of the commercial system voltage signal a detected by, the signal arithmetic processing unit 19 oscillates a reference sine wave signal b synchronized with it, and the reference sine wave signal b and an inverter output current detection signal c (inverter) which is a feedback signal. The signal obtained by amplifying the difference from the output current detector 13) by the error amplifier 17 is PWM-controlled by the PWM control circuit 16, and the gate drive circuit 15 outputs the gate drive signal to the switching elements Q1 to Q4.

During normal operation of the grid interconnection inverter controller 20, the grid interconnection relay 10 is turned on, the commercial grid power source 3 and the grid interconnection inverter controller 20 are interconnected, and the reference sine wave signal b is supplied. Control is performed so that the inverter output current becomes maximum, that is, by 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 the occurrence of an abnormality in the commercial system power source 3 or the system interconnection type inverter control device 20 is satisfied. , The interconnection relay 10 is cut off to disconnect the commercial system power source 3 from the system interconnection type inverter control device 20, and the operation of the FET bridge 7 is stopped.

Considering the start-up time, before that, the interconnection relay 10 is cut off, and the commercial system power source 3 and the system interconnection type inverter control device 20 are separated. At this time, the reference sine wave signal b is not controlled. Then, when the startup conditions such as the increase in the output voltage of the solar cell 2 and the recovery of the abnormality of the grid interconnection type inverter control device 20 are satisfied, the FET bridge 7 including the switching elements Q1 to Q4 is activated by the gate drive signal. To be done. After that, when the normal operation of the grid interconnection inverter controller 20 and the commercial grid power supply 3 is confirmed, the grid interconnection relay 10 is turned on to connect the commercial grid power supply 3 to the grid interconnection inverter control device 20, Power is supplied to the load 5. In this connection, the reference sine wave signal b has a predetermined minimum amplitude in order to prevent the reverse flow of current from the commercial system power source 3 to the system interconnection type inverter control device 20. At the time of turning 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 interconnection relay 10 is turned on.

[0007]

However, in the above-mentioned conventional example, the inverter output current detection signal c is used as a feedback signal before and during the interconnection of the commercial system power source 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 is impossible to accurately control the inverter output voltage. Therefore, when the commercial system power source 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 source 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
When the breakdown voltage of 1 to Q4 or the solar cell 2 is exceeded, the element is destroyed. To prevent backflow of current,
There is a method of inserting a backflow prevention diode between the solar cell 2 and the grid interconnection inverter 20, but in this case,
There is a problem that power loss occurs due to the resistance of the diode.

Further, when the inverter output voltage is abnormally high with respect to the commercial power supply 3, a transient current flows at the time of connection, so that the switching elements Q1 to Q4 are destroyed or the commercial power supply 3 is adversely affected. There is a risk of

In view of the above points, 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]

To achieve the above object, the present invention is an object to be controlled when the commercial system power source and the system interconnection type inverter control device are cut off. Instead of the inverter output current, an inverter output voltage is selected as a control target, and means for setting the inverter output voltage to a voltage equal to or higher than the commercial system voltage by several volts is provided.

[0012]

As described above, in the system interconnection type inverter control device of the present invention, the controlled object is switched depending on 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 cut 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 connected. At this time, the inverter output current detection signal is selected as the feedback signal. Further, when the commercial system power supply and the system interconnection type inverter control device are cut off, the inverter output voltage is set to the same voltage as the commercial system voltage or several volts higher. Therefore, the maximum power point tracking control can be performed when the commercial grid power source and the grid grid type inverter control device are linked, and the commercial grid power source and the grid grid type inverter control device are linked. In this case, the inverter output voltage is controlled to be equal to or higher than the commercial system voltage by several volts, so that it is possible to suppress the backflow of current from the commercial system power supply and the generation of transient current.

[0013]

1 is a circuit block diagram of a photovoltaic power generation system to which an embodiment of a grid interconnection type inverter control device of the present invention is applied. The grid interconnection type inverter control device 1 functions as an input capacitor 6, an FET bridge 7 composed of switching elements Q1 to Q4 for DC-AC conversion for suppressing fluctuations in the input power from the solar cell 2, an output filter, and PWM control. The output choke 8 and the smoothing capacitor 9 that convert the generated rectangular wave into a sine wave, and the connection for disconnecting the grid-connected inverter control device 1 from the commercial grid power supply 3 and the load 5 when the output of the solar cell 2 drops 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 calculation processing unit 19 composed of a digital circuit centering on a CPU. Composed of.

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

The system interconnection type inverter control device 1 is a PWM
By alternately turning on / off the pair of switching elements Q1 and Q2 and Q3 and Q4 in the FET bridge 7 based on the gate pulse signal output from the gate drive circuit 15 that is PWM-controlled by the control unit 16. By generating a rectangular wave and converting the rectangular wave into a sine wave by an output filter including the output choke 8 and the smoothing capacitor 9, the DC power of the solar cell 2 is converted into alternating current.

The operation of the control unit 11 is different between the normal operation and the startup of the grid interconnection type inverter control device 1. First,
During normal operation, that is, the interconnection relay 10 is turned on, the commercial system power source 3 and the system interconnection type inverter control device 1
The operation when is interconnected will be 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 a signal obtained by amplifying the error to the PWM control unit 16. The PWM control unit 16 generates a switching pattern signal as a PWM waveform by comparing the signal with a triangular wave serving as a switching carrier wave, 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 power of the solar cell 2 becomes maximum with respect to the sunshine conditions at that time, with the amplitude value when the interconnection relay 10 is closed being the minimum value (maximum). 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 is larger than the detected value before the amplitude is increased, and the amplitude is decreased if the amplitude is decreased. Further, when the amplitude of the reference sine wave signal b is changed in the decreasing direction, the amplitude is further decreased if the inverter output current is larger than the detected value before the amplitude is decreased, and the amplitude is increased if it is increased. 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 source 3 or the system interconnection type inverter control device 1 is used.
If there is an abnormality, the interconnection relay 10 is cut off and the operation of the grid interconnection type inverter setting device 1 is stopped.

The operation of the control unit 11 when the grid interconnection type inverter control device 1 is started up is as follows. At startup, grid-connected inverter controller 1 and commercial grid power supply 3
Are disconnected by the linkage 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 in the error amplifier 17 with the reference sine wave signal b generated by the signal calculation processing section 19. The result is output to the PWM control unit 16, the PWM pattern is changed, and the amplitude of the inverter output voltage detection signal d is induced so as 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 the same as the commercial system voltage or is several volts (0 to 5 volts in this example) higher setting voltage. However, the inverter output voltage does not reach the set voltage unless the release voltage of the solar cell 2 exceeds a certain value.

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

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

As described above, the system interconnection type inverter control device 1 of the present example can control the inverter output voltage to the same voltage as the commercial system voltage or a voltage higher by several volts when the commercial system power supply 3 is linked. Therefore, it is possible to suppress the backflow of the current from the commercial system power source 3 and the generation of the transient current that occur during the interconnection, and it is possible to prevent the destruction of the elements and the adverse effect on the commercial system power source 3. In addition, solar cell 2
Since it is not necessary to insert a diode between the inverter and the grid interconnection type inverter control device 1, 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 calculation processing section 19 will be shown below. First, the amplitude of a half cycle of a sine wave having a plurality of amplitudes is sampled at a certain time interval, and the data is stored in the signal calculation processing section 19. Then, a sine wave having an optimum amplitude is selected according to the control state, read out, and output. In this example, a sine wave with a frequency of 60 Hz and a half cycle of 1/120 second is used.
Sampling was performed at a time interval of 1/120 / n second obtained by dividing this into n equal parts. To generate the reference sine wave signal b, the built-in timer of the CPU is started by detecting the commercial system voltage zero cross, and at every sampling time interval (1/120 /
Data is sequentially read every n seconds), and the digital values thereof are D / A converted by a D / A converter. In addition, by detecting the positive and negative directions from the commercial system voltage signal a, aligning the positive and negative directions with the positive and negative directions of the sine wave that oscillates, and synchronizing with the 0 cross point detected from the commercial system voltage signal a, the commercial system voltage signal a Phase match with. In this 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 source and the system interconnection type inverter control device are interconnected,
Since the inverter output voltage can be controlled to the same voltage as the commercial system voltage or a voltage several volts higher, it is possible to suppress the occurrence of current backflow and transient current, and to establish a stable interconnection state that does not cause element destruction etc. can do.

[Brief description of drawings]

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

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

[Explanation of symbols]

 1 system interconnection type inverter control device 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 Arithmetic processing unit a Commercial system voltage signal b Reference sine wave signal c Inverter output current detection signal d Inverter output voltage detection signal

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiroshi Nakata 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Within the corporation

Claims (2)

[Claims] 1. A system interconnection type inverter control device for converting direct current power input from a direct current power source such as a solar cell into alternating current power and supplying it to a load by linking it to a commercial system power source, the commercial system power source and the commercial system power source A system interconnection type inverter control device comprising means for setting the inverter output voltage to a voltage equal to or higher than the commercial system voltage by several volts when the system interconnection type inverter control device is interconnected. 2. A grid interconnection inverter control device for converting direct current power input from a direct current power source such as a solar cell into alternating current power, and linking it to a commercial system power source to supply to a load, wherein the commercial system power source and the commercial system power source A means for connecting / disconnecting the grid interconnection type inverter control device, a means for detecting a commercial grid voltage, an inverter output current and an inverter output voltage, a commercial grid power source and the grid interconnection type inverter control device are connected. In the case where the commercial system voltage signal is generated, a variable amplitude reference sine wave signal that is synchronized with the commercial system voltage signal is generated. 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 source and the system interconnection type inverter. The inverter output voltage detection signal is selected when the data control device is cut 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 connected. A signal switching means, a means for error-amplifying the selected one of the inverter output voltage detection signal or the 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, and a grid interconnection inverter control device.