JP2527546B2 - System interconnection inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention is a system used for a power supply system that converts a direct current power source such as a solar cell generated by electricity into an alternating current by an inverter and operates in parallel with an existing commercial power system. The present invention relates to an interconnection inverter device.

(B) Conventional technology A conventional grid-connected inverter device will be described with reference to an example of a photovoltaic power generation system shown in FIG.

In the figure, (1) is a solar cell that produces an output of 2 KVA in a private house scale, (2) is a commercial power system including commercial power of 100 V AC, 1 A and various household electric appliances driven by the commercial power, (3) is a backflow prevention diode that protects the solar cell from the counter electromotive force that flows from the inverter (4) to the solar cell (1) due to commutation failure, and (5) is the solar cell (1) and the inverter (4). And an electrolytic capacitor connected in parallel to the solar cell (1) to generate a voltage corresponding to the electromotive force of the solar cell (1), and (6) the output current of the inverter (4) This is an AC switch for adjusting the phase and supplying it to the commercial power system (2).

(7) is a sequence control circuit, which receives the voltage of the electrolytic capacitor (5) and the detection voltage of the voltage detection transformer (8) connected to the output side of the AC switch (6) as input. The AC switch (6) is controlled by its output, and the inverter drive circuit (10) is controlled via a pulse width control circuit (9) so that the solar cell (1) outputs an optimum output. ) Is to control.

In order to keep the output voltage of the solar cell (1) constant, the voltage of the electrolytic capacitor (5) is compared with a DC reference voltage source (12) by a DC voltage constant control circuit (11). The output of (11) is calculated by the multiplier (13) together with the output of the voltage detecting transformer (8).

That is, the DC voltage constant control circuit (11) compares the voltage value of the electrolytic capacitor (5) with the reference voltage value of the DC reference voltage source (12), and determines that the voltage value of the electrolytic capacitor (5) is higher than the reference voltage value. If it is larger, a positive deviation signal corresponding to the comparison result is output. Then, the multiplier (13) multiplies the positive deviation signal by the system voltage of the commercial power system (2) to generate a current command value synchronized with the system voltage waveform. Therefore, when the voltage value of the electrolytic capacitor (5) is equal to or less than the reference voltage value and the deviation signal is zero, the current command value is also zero.

An error amplifier (14) receives the output of the inverter (4) via a current detection transformer (15) and receives the output of the multiplier (13) to compare the two.
The result is output to the pulse width control circuit.

That is, the error amplifier (14) compares the output current value of the inverter (4) detected by the current detection transformer (15) with the current command value from the multiplier (13) and amplifies the error. To the pulse width control circuit (9). Then, in the pulse width control circuit (9) and the inverter drive circuit (10), the inverter (4) is controlled so that the output current value of the inverter (4) becomes the current command value.

In the above conventional system, the power generated by the solar cell (1) is connected to the electrolytic capacitor (5) via the backflow prevention diode (3) and is also connected to the inverter (4). The ripple component of the direct current flowing through the inverter (4) is absorbed. Therefore, the electrolytic capacitor (5) needs to have a sufficiently large capacity so that the operating point of the solar cell (1) does not change.
The inverter (4) converts DC power stored in the electrolytic capacitor (5) into AC power, and an AC switch (6).
Is tuned and connected to the commercial power system (2).

The sequence control circuit (7) turns on the AC switch (6) and turns on the inverter drive circuit (10) if the power of the solar cell (1) and the commercial electrode system (2) are established in an appropriate state.
Works like turning on the power. The voltage of the commercial power system (2) is detected by a voltage detecting transformer (8) and applied to one input of a multiplier (13). Further, the voltage of the electrolytic capacitor (5) is applied to a DC voltage constant control circuit (11) together with a DC reference voltage source (12), and the DC voltage constant control circuit (11) makes the electrolytic capacitor (5) higher than the reference voltage value. Is operated to apply the positive deviation signal to the other input of the multiplier (13) only when the voltage is large.

The output of the multiplier (13) is applied to one input of the error amplifier (14). A signal obtained by detecting the output current of the inverter (10) by the current detecting transformer (15) is applied to the other input of the error amplifier (14). The output of the error amplifier (14) becomes a current command value of the inverter (4) as a result of calculation based on the inputs of both signals, and the inverter (4) is passed through the pulse width control circuit (9) and the inverter drive circuit (10). Control of 4) is performed.

The current supplied from the inverter (4) to the commercial power system (2) by the control operation of the circuit as described above has the same phase (power factor 1) as the voltage of the commercial power system (2), and its amplitude is the solar cell ( It increases or decreases depending on the power generated in 1). Here, if the DC reference voltage source (12) is selected as a voltage near the optimum operating point of the solar cell (1), the solar cell (1) always supplies the maximum power to the commercial power system (2), resulting in high system efficiency. Can be realized. Furthermore, in order to increase the efficiency of utilization of power generation output by the solar cell (1), the solar cell (1)
One method is to turn off the drive power of the inverter (4) to reduce the fixing loss of the system in the rain or when night when the power is not generated.

However, in the conventional system shown in FIG. 2, when the output of the solar cell (1) decreases and its voltage value falls below the DC reference voltage value, the output of the DC voltage constant control circuit (11) as described above. Becomes zero, the electric power is not supplied from the inverter (4) to the commercial power system (2), and the voltage of the electrolytic capacitor (5) does not fall below the voltage of the DC reference voltage source (12). Therefore, in order to detect the fixed price of the generated power of the solar cell (1), it is necessary to add a solar cell for monitoring to the above circuit or detect the DC voltage on the cathode side of the backflow prevention diode (3). .
However, in the former case, there is a problem that an extra monitor solar cell is required, and in the latter case, the overvoltage of the electrolytic capacitor (5) cannot be detected.
-86-68, 2KVA photovoltaic power generation system control method and insulation method, see July 1986).

(C) Object of the invention The problem to be solved by the present invention is to control the drive power source of the inverter so as to reliably disconnect the solar cell from the commercial power system when the generated power of the solar cell decreases. .

(D) Means for Solving Problems The present invention provides a DC power supply, an inverter, an electrolytic capacitor connected between the DC power supply and the inverter in parallel to the DC power supply, and a voltage value of the electrolytic capacitor. A sequence control circuit for detecting a decrease in output of the DC power supply, a DC voltage constant control circuit for outputting a deviation signal only when the voltage value of the electrolytic capacitor is larger than a preset reference voltage value, and the DC voltage A bias voltage applying circuit that applies a predetermined bias voltage to the deviation signal from the constant control circuit, and the output of the inverter is controlled according to the output of the deviation signal to which the bias voltage is applied by the bias voltage applying circuit. Together with an inverter drive circuit that controls the operation and stop of the inverter according to the output of the sequence control circuit, An AC switch for disconnecting the inverter from the commercial power system by the output of a sequence control circuit, the sequence control circuit confirms that the voltage value of the electrolytic capacitor has become equal to or lower than a preset undervoltage value. It detects and outputs the inverter drive circuit and the AC switch-off signal.

(E) Operation According to the present invention, the output control of the inverter is continued based on the bias voltage even when the voltage of the electrolytic capacitor reaches the reference voltage value and the deviation signal from the constant thickness control circuit is zero due to direct current. Therefore, a minute voltage is supplied from the inverter to the commercial power system. Then, in the sequence control circuit, the voltage of the electrolytic capacitor drops to an undervoltage value or less due to this minute power supply, and by detecting the output drop of the DC power supply, the inverter drive circuit and the AC switch-off signal are output.

(F) Embodiment FIG. 1 shows a system circuit diagram in which an embodiment of the grid-connected inverter device of the present invention is applied to a photovoltaic power generation device, and a detailed description thereof will be given below. The circuit is different from the conventional circuit shown in FIG. 2 in that a bias voltage applying circuit (16) is connected to the output of the direct voltage constant control circuit (11). As a result, the voltage applied to the multiplier (13) by the voltage application circuit (16) is applied to the multiplier (13) even when the generated power of the solar cell (1) decreases and the output of the DC voltage constant control circuit (11) becomes zero. This bias voltage is input and this multiplier (13)
A current command having an amplitude of the bias is output as the output of the inverter, and the inverter (4) tries to supply power to the commercial power system (2) based on this command. Therefore, the voltage value of the electrolytic capacitor (5) becomes lower than the voltage value of the DC reference voltage source (12).

Therefore, the sequence control circuit (7) can detect the decrease in the generated power of the solar cell (1) based on the DC voltage value of the electrolytic capacitor (5). Then, the sequence control circuit (7) turns off the AC switch (6) when the DC voltage value of the electrolytic capacitor (5) becomes less than or equal to the value set as the undervoltage value, and the commercial power system (2) and the inverter (4). And disconnect the inverter drive circuit (10)
Turn off the power. Therefore, the inverter (4) is in a standby state of low power consumption when the power generated by the solar cell (1) is reduced,
That is, the power is disconnected from the commercial power system (2), and the entire system becomes a highly efficient power generation system with little power loss.

The output value of the bias voltage application circuit (16) is preferably selected to be small enough not to affect the DC constant control circuit.

(G) Effect of the Invention As described above, according to the present invention, by only monitoring the voltage value of the electrolytic capacitor, the method of detecting the voltage on the cathode side of the backflow prevention diode as in the prior art or the monitor solar cell is used. The problem of insertion is eliminated, the decrease in the output of the DC power supply can be reliably detected, and the inverter can be stopped and disconnected from the commercial power system.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a photovoltaic power generation system showing an embodiment of a grid interconnection inverter device of the present invention, and FIG. 2 is a circuit diagram of a conventional system corresponding to FIG. (1) DC power supply (2) Commercial power system (4)
…… Inverter, (5) …… Electrolytic capacitor, (7)…
… Sequence control circuit, (16) …… Bias voltage application circuit.

Claims (1)

(57) [Claims] 1. A DC power supply, an inverter for converting a DC output of the DC power supply into an AC output, and connecting the output to a commercial power system, and between the DC power supply and the inverter in parallel with the DC power supply. A connected electrolytic capacitor, a sequence control circuit that detects a decrease in output of the DC power supply according to the voltage value of the electrolytic capacitor, and a deviation signal only when the voltage value of the electrolytic capacitor is larger than a preset reference voltage value. A DC voltage constant control circuit that outputs a bias voltage applying circuit that applies a predetermined bias voltage to the deviation signal from the DC voltage constant control circuit; and the deviation signal to which the bias voltage is applied by the bias voltage applying circuit. The output of the inverter is controlled according to the output of the inverter and the output of the sequence control circuit controls the operation of the inverter. An inverter drive circuit that controls the stop, and an AC switch that disconnects the inverter from the commercial power system by the output of the sequence control circuit, the sequence control circuit, the voltage value of the electrolytic capacitor is preset. A system interconnection inverter device, which outputs an off signal to the inverter drive circuit and the AC switch by detecting that the voltage becomes equal to or less than the undervoltage value.