JP2594052B2 - Grid-connected inverter device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field The present invention converts a DC power source generated by a solar cell or the like into an AC using an inverter, and uses it in a power supply system that 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 same figure, (1) is a solar cell that generates 2KVA output of a private house scale, (2) is a commercial power system including AC 100V, 1A commercial power and various home appliances driven by the commercial power, (3) a backflow prevention diode for protecting the solar cell (1) from back electromotive force flowing from the inverter (4) to the solar cell (1) due to commutation failure or the like; (5) a solar cell (1) and an inverter (4) is connected in parallel with the solar cell (1), and the solar cell (1)
Electrolytic capacitor that produces a voltage corresponding to the electromotive force of
(6) an AC switch for adjusting the phase and the like of the output current of the inverter (4) and supplying the output current to the commercial power system (2).

(7) a sequence control circuit, which inputs a voltage of the electrolytic capacitor (5) and a detection voltage of a voltage detection transformer (8) connected to an output side of the AC switch (6); An AC switch (6) is controlled by its output, and an inverter drive circuit (10) is controlled via a pulse width control circuit (9). The inverter (4) is controlled so that the solar cell (1) outputs an optimum output. ) Is controlled.

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 detection 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 specified current 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 (9). In other words, the error amplifier (14) compares the output current value of the inverter (4) detected by the current detection voltage unit (15) with the specified current 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.
Is controlled.

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 to the inverter (4), and the electrolytic capacitor (5) Absorbs the DC ripple flowing through the inverter (4). 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 converts the DC power into an AC switch (6).
Thus, it is connected in synchronization with the commercial power system (2).

When the power of the solar cell (1) and the commercial power system (2) are properly established, the sequence control circuit (7) turns on the AC switch (6) to turn on the inverter drive circuit (10).
Operate to turn 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 an error amplifier (14). The output of the error amplifier (14) becomes the current designated value of the inverter (4) as a result of the calculation based on the input of both signals, and is output via the pulse width control circuit (9) and the inverter drive circuit (10). The 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 It increases or decreases according to the generated power of 1). Here, the DC reference voltage source (12) is always supplied with the maximum power from the solar cell (1) to the commercial power system (2), and the efficiency of the system can be improved. Furthermore, in order to increase the efficiency of the power generation output utilization by the solar cell (1), the drive power supply of the inverter (4) is turned off in rainy weather when the solar cell (1) is not generating power or at night, and the system is fixed. Reducing losses is one way.

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, as described above, the output of the DC voltage constant control circuit (11) is changed. As a result, the inverter (4) stops supplying power to the commercial power system (2), and the voltage of the electrolytic capacitor (5) does not become lower than the voltage of the DC reference voltage source (12). Therefore, in order to detect a decrease in the generated power of the solar cell (1), it is necessary to further add a monitoring solar cell to the above circuit or to detect a 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 A problem to be solved by the present invention is to control the drive power supply of the inverter so that the solar battery is disconnected from the commercial power system when the generated power of the solar battery is reduced. .

(D) Means for solving the problems The present invention relates to a DC power supply, an inverter that converts a DC output of the DC power supply into an AC output, and connects the output to a commercial power system, and the DC power supply and an inverter. An electrolytic capacitor connected in parallel to the DC power supply, a sequence control circuit for detecting a drop in the output of the DC power supply based on the voltage value of the electrolytic capacitor, and a reference value for setting the voltage value of the electrolytic capacitor in advance. Only if greater than the voltage value,
A DC voltage constant control circuit that outputs a deviation signal; a zero voltage detection circuit that detects that the output of the deviation signal from the DC voltage constant control circuit is zero voltage; and a zero voltage detection circuit that detects the deviation signal from the DC voltage constant control circuit. An inverter drive circuit that controls the output of the inverter in accordance with the output, and controls the operation and stop of the inverter by the output of the sequence control circuit; and the inverter from the commercial power system by the output of the sequence control circuit. An AC switch to be arranged, wherein the sequence control circuit outputs an OFF signal to the inverter drive circuit and the AC switch according to an input of a detection output signal from the zero voltage detection circuit.

(E) Function The DC voltage constant control circuit compares the voltage with the DC reference voltage until the voltage of the electrolytic capacitor reaches a predetermined value, and the output of the DC voltage constant control circuit outputs a zero signal when the two voltages match. This is detected by the zero voltage detection circuit and transmitted to the sequence control circuit, and the output of the control circuit stops the oscillation of the inverter.

(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. This circuit differs from the conventional example of FIG. 2 in that a zero voltage detecting circuit (16) is connected to the output of the constant DC voltage control circuit (11). The sequence control circuit (7) receives the output signal of the zero voltage detection circuit (16), turns off the AC switch (6) and sends a signal to the inverter drive circuit (10), and the DC voltage constant control circuit ( It works to turn off the power supply (not shown) in 11).

By performing the control as described above, the output of the solar cell (1) decreases and the inverter current stops flowing, and at the same time, the inverter (4) is disconnected from the commercial power system (2), and further the inverter drive circuit (10) Is also turned on, thereby realizing a highly efficient system.

When the output of the solar cell (1) rises and the output voltage of the constant DC voltage control circuit (11) does not become zero, the power supply of the constant DC voltage control circuit (11) is turned off again by the sequence control circuit (15). When the power is turned on and the AC switch (6) is turned on, power is supplied again from the inverter (4).

Furthermore, a time delay element is added to the sequence control circuit (7) so that the power supply of the DC voltage constant control circuit (11) is not frequently turned on / off due to the output fluctuation of the solar cell (1), or the zero voltage detection circuit (16). ) May have hysteresis. In the latter case, the zero voltage detection circuit (16) inputs the voltage of the capacitor (5) via the resistor (R1) to the inverting input terminal and the resistor (R3) to the non-inverting input terminal as shown in FIG. A hysteresis comparator (17), which receives the voltage of the DC reference voltage (12) through the input terminal, is used. The output of the comparator (17) is fed back to the non-inverting input terminal via the resistor (R2). Then, as shown in the input / output characteristic diagram shown in FIG. 4, the values of the resistors (R1), (R2), and (R3) are appropriately selected, and a constant DC voltage control circuit (1) is obtained at point A (reference voltage) in the diagram.
1) Set to stop. Further, the DC voltage constant control circuit (11) is prevented from starting until the input reaches the point B, so that frequent start and stop of the circuit (11) can be prevented.

(G) Effects of the Invention As described above, according to the present invention, only by monitoring the voltage value of the electrolytic capacitor, a method of detecting the voltage on the cathode side of the backflow prevention diode as in the related art or through a monitor solar cell is used. The disadvantage of the insertion is eliminated, and it is possible to reliably detect a decrease in the DC power supply output, to stop the inverter, and to disconnect the inverter from the commercial power system.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a photovoltaic power generation system showing an embodiment of a system interconnection inverter device of the present invention, FIG. 2 is a circuit diagram of a conventional system corresponding to FIG. 1, and FIG. Circuit diagram of a hysteresis comparator showing the embodiment of
FIG. 4 is an input / output characteristic diagram of the comparator shown in FIG. (1) DC power supply (2) Commercial power system (4)
…… Inverter, (5) …… Electrolytic capacitor, (7)…
... sequence control circuit, (11) ... DC voltage constant control circuit, (16) ... zero voltage detection circuit.

Claims (1)

(57) [Claims] 1. A DC power supply, an inverter for converting a DC output of the DC power supply to an AC output, and connecting the output to a commercial power system, and a DC power supply in parallel with the DC power supply between the DC power supply and the inverter. A connected electrolytic capacitor, a sequence control circuit for detecting a decrease in the 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 constant-voltage control circuit that outputs a deviation signal; a zero-voltage detection circuit that detects that the output of the deviation signal from the direct-current voltage control circuit is zero voltage; and an output of the deviation signal from the direct-current voltage control circuit. An inverter drive circuit for controlling the output of the inverter in response to the output and controlling the operation and stop of the inverter by the output of the sequence control circuit. An AC switch for disconnecting the inverter from the commercial power system by an output of the sequence control circuit, wherein the sequence control circuit is configured to drive the inverter drive circuit according to an input of a detection output signal from the zero voltage detection circuit. And outputting an off signal to the AC switch.