JPH08317665A - Photovoltaic power generation apparatus - Google Patents

Abstract

PURPOSE: To provide a photovoltaic power generation apparatus by which the discharge output of a storage battery is converted with high efficiency so as to be supplied to a load and which can be self-operated continuously for a long period. CONSTITUTION: A mode setting means 13 by which a parallel operation mode to operate an inverter circuit 4 in conjunction with a commercial power system 5 and a self-operation mode operated so as to be paralleled off from the commercial power system 5 are changed over and set and a pulse generation means which generates a high-frequency switching pulse signal when the parallel operation mode is set and which generates a low-frequency switching pulse signal when the self-operation mode is set are installed in a photovoltaic power generation apparatus 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solar power generation device, and more particularly to a solar power generation device in which a power generation output of a solar cell or a discharge output of a storage battery is converted into an AC output by an inverter circuit and supplied to a load.

[0002]

2. Description of the Related Art In recent years, a photovoltaic power generation system for supplying a load to a commercial power system by connecting a distributed power supply system of a relatively small capacity of several kW using a direct current power source composed of solar cells to an commercial power system via an inverter circuit. Various devices have been proposed.

FIG. 4 is a schematic configuration diagram of a conventional solar power generation device. In the figure, 111 is a solar cell that directly converts the energy of sunlight into a DC voltage, 112 is a backflow prevention diode connected to the output of the solar cell 111, and 113 is connected to the solar cell 111 via the backflow prevention diode 112. Storage battery, 114 is an inverter circuit for converting the power generation output of the solar cell 111 or the discharge output of the storage battery 113 into alternating current, and 115 is an inverter control circuit for PWM-controlling the inverter circuit 114. The device is connected to the commercial power system 116 to supply power to the load 117, and at the time of system power failure, power is supplied to the load 117 independently.

The inverter control circuit 115 includes a differential amplifier 121, a multiplier 122 and an operational amplifier (error amplifier) 12
3. A feedback control system is composed of the PWM pulse generation circuit 124 and the bandpass filter 125 for extracting the reference frequency component of the output voltage, and the PW of a predetermined frequency
The M pulse is output to each switching element of the inverter circuit 114 as a gate control signal.

Specifically, in the inverter control circuit 115, an input error signal Sa indicating the difference between the output voltage Vi from the solar cell 111 and a predetermined voltage command value Vref, for example, is generated by the differential amplifier 121. The input error signal Sa is multiplied by the signal Sb corresponding to the fundamental frequency component of the commercial AC voltage of the commercial power system 116 in the multiplier 122 to generate Si indicating the control target value.

Then, the operational amplifier 123 generates a signal Sd indicating the difference between the current command signal Si and the output current value Sc of the inverter circuit 114, and the signal Sd is supplied to the PWM pulse generation circuit 124. , A PWM pulse having a pulse width corresponding to the magnitude of the signal Sd is generated, and the PWM pulse is generated.
The conduction control of the switching element of the inverter circuit 114 is performed by the pulse.

[0007]

In the conventional photovoltaic power generator, an inverter current and a voltage close to a sine wave are supplied from the inverter circuit so that the commercial power system and the load are not adversely affected. Therefore, in the conventional device, a PWM pulse is generated using a carrier wave having a frequency (for example, 15.36 kHz) that is sufficiently higher than the system frequency regardless of whether the current operating state is parallel operation or self-sustaining operation, and the inverter circuit The conduction of the switching element is controlled.

Further, in the event of a situation in which a commercial power system fails due to a natural disaster such as an earthquake or a fire and cannot be restored for a long period of time, the conventional device is operated in a self-sustaining manner to generate power from a solar cell or discharge output from a storage battery. It was possible to use lighting, air conditioning equipment, etc.

However, in the self-sustaining operation, the output of the storage battery is lower than that in the parallel operation due to the capacity of the device, and the power generation output of the solar cell cannot be obtained especially in bad weather or at night. It has to be done only by itself, resulting in a considerably low output state. In the low output state, the high frequency P with respect to the output
The ratio of the loss (switching loss) due to the switching of the inverter circuit due to the WM pulse becomes large,
As a result, the discharge output of the storage battery cannot be effectively used, and there is a fear that the self-sustaining operation cannot be continued for a long period of time.

The present invention has been made in view of the above point, and it is a solar power generation system capable of converting discharge output of a storage battery with high efficiency and supplying it to a load, and continuously operating for a long time in a self-sustaining manner. Provide a device.

[0011]

According to the present invention, in a photovoltaic power generator, a parallel operation mode in which an inverter circuit is operated in connection with a commercial power system and an independent operation mode in which the inverter circuit is operated by disconnecting from the commercial power system. And a pulse generation means for generating a high-frequency switching pulse signal when the parallel operation mode is set and a low-frequency switching pulse signal when the independent operation mode is set. It is characterized by

As a concrete configuration, the pulse generating means generates a switching pulse signal having a first frequency sufficiently higher than the system frequency when the parallel operation mode is set, and a second frequency which matches the system frequency when the independent operation mode is set. Of the switching pulse signal.

[0013]

According to the present invention, since the switching element of the inverter circuit is driven by the low-frequency switching pulse in the low output state during the self-sustaining operation, the switching loss can be reduced.

Further, when the self-sustained operation mode is set, by supplying the switching pulse signal of the system frequency,
Switching loss can be significantly reduced, and self-sustained operation can be continuously performed for a long period of time.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A solar power generator of the present invention will be described in detail below with reference to the drawings showing an embodiment thereof. FIG. 1 is a schematic configuration diagram of a photovoltaic power generation device using a solar cell to which the present invention is applied.

In the figure, a photovoltaic power generator 1 includes a solar cell 2 (in the present embodiment, a rated generated power of 3 kW) that converts the energy of sunlight into DC power, and a storage battery 3 that is charged by the generated power of the solar cell 2. And an inverter circuit 4 for converting the generated power of the solar cell 2 or the discharge power of the storage battery 3 into AC power and supplying a predetermined AC voltage (100 V in this embodiment). Power is supplied to a load 6 such as various home appliances connected to a distribution line in an interconnected manner with 5.

The inverter circuit 4 is composed of a plurality of (four in this embodiment) switching elements connected in a bridge, and a switching control signal is supplied to the inverter circuit 4 from an inverter control section 7 which performs various processes described later. The conduction of the switching element is controlled based on the applied control signal. The inverter control unit 7 is composed of a microcomputer.

Between the inverter circuit 4 and the commercial power system 5, an automatic restoration type interconnection relay 8 and a manual restoration type breaker 9 for system protection sandwiching the load 6 when viewed from the output side of the inverter circuit 4. The relay 8 and the breaker 9 are opened and closed based on the control signal from the protective relay control circuit 10 to connect or disconnect the solar power generation device 1 to the commercial power system 5. ing.

When the protective relay control circuit 10 detects an abnormal state in the photovoltaic power generator 1 or the commercial power system 5, the relay relay control circuit 10 sends a disconnection command signal to the relay 8 and the breaker 9 for photovoltaic power generation. The device 1 is disconnected from the commercial power system 5, and a stop signal is sent to the inverter control unit 7 to stop the supply of the switching control signal from the inverter control unit 7 to the inverter circuit 3.

Specifically, the protective relay control circuit 10 is composed of a microcomputer, and the detected value by the first voltage detecting means 11 composed of an isolation amplifier for detecting the output voltage of the solar cell 2 and the inverter circuit. The detection value by the second voltage detection means 12 composed of a transformer (PT) for detecting the output voltage of 4 is input, and the start signal and the stop signal are sent to the inverter control unit 7 based on the detection value,
The disconnection command signal is sent to the relay 8 and the breaker 9, and the interconnection command signal is sent to the relay 8.

In addition, in the protective relay control circuit 10, the relay 8
Also, the contact state of the breaker 9 is constantly monitored, and the contact state signal is input to the inverter control unit 7. Further, in the protective relay control circuit 10, the mode setting means 13 provided in the inverter control unit 7 sets the self-sustained operation mode in which the solar power generation device 1 is operated independently by disconnecting from the commercial power system 5. In response to the input of the self-sustained operation start signal from the inverter control unit 7, the interconnection command signal is transmitted to the relay 8 and the disconnection command signal is transmitted to the breaker 9 so that the solar power generation device 1 supplies power to the load 6 independently. Is enabled.

The mode setting means 13 switches and sets the parallel operation mode in which the inverter circuit 4 is connected to the commercial power system 5 to operate, and the independent operation mode in which the inverter circuit 4 is disconnected from the commercial power system 5 to operate. The analog switches SW1 to SW3 are switched from the a-contact side to the b-contact side in FIG. 1 according to the self-sustained operation mode setting by the mode setting means 13. The SW1 to SW3 are switched to the a contact side when the parallel operation mode is set by the mode setting means 13 and to the b contact side when the independent operation mode is set, in connection with the mode setting means 13.

As a result, when the parallel operation mode is set, the storage battery 3 is charged by the power generated by the solar cell 2 through the backflow diode 20, and when the self-sustaining operation mode is set, the power generation output of the solar cell 2 or the discharge output of the storage battery 3 is applied to the load 6. Will be supplied to the side.

Next, the operation of the inverter control section 7 will be described for each of the above setting modes by the mode setting means 13. First, in the parallel operation mode, SW1 to SW3 are a in FIG.
The output voltage of the solar cell 2 connected to the contact side and detected by the first voltage detecting means 11 becomes the voltage value Vref at the optimum operating point at which the maximum electric power is drawn from the solar cell 2, and is connected to the commercial power system 5. The inverter circuit 4 is provided with a pulse-width modulated switching control signal so that a current synchronized with the fundamental frequency component of the system point voltage is output from the inverter circuit 4. Therefore, when the inverter circuit 4 and the commercial power system 5 are interconnected, the operating power factor is 1 at the commercial frequency.
And the output current of the inverter circuit 4 is controlled so that the maximum electric power is drawn from the solar cell 2.

Specifically, the difference between the output voltage of the solar cell 2 detected by the first voltage detecting means 11 and the preset optimum operating point voltage Vref1 is amplified as an error signal by the first error amplifier 14. The error signal is used as one input signal of the multiplier 15. Then, the second voltage detection means 12
The fundamental frequency component of the interconnection point voltage detected by is extracted by the bandpass filter 16, and the extracted fundamental frequency component of the interconnection point voltage is input as the other input signal of the multiplier 15. In the multiplier 15, the first error amplifier 14
Is multiplied by the fundamental frequency component signal from the bandpass filter 16 to generate a current command value of the inverter current. Therefore, this current command value is synchronized with the system voltage waveform during the interconnection operation with the commercial power system 5,
It has a value for controlling the output voltage of the solar cell 2 to the optimum operating point voltage Vref. Then, the difference between the current command value from the multiplier 15 and the inverter current of the inverter circuit 4 detected by the inverter current detection means 18 including a current transformer (CT) is amplified by the second error amplifier 17, It is input to the inverter control unit 7 as a current error signal. In the inverter control unit 7, the current error signal from the second error amplifier 17 is compared with the reference triangular wave signal of 15.36 kHz, and the current error signal from the second error amplifier 17 is adjusted to zero. A switching signal is supplied to the switching element to perform PWM (pulse width modulation) control of the output current of the inverter circuit 4, and the inverter operation of the inverter circuit 4 is controlled in accordance with the start signal or the stop signal input from the protective relay control circuit 10. It has been started or stopped.

On the other hand, in the self-sustaining operation mode, SW1 to SW3 are connected to the b-contact side in FIG. 1, and the inverter output voltage detected by the second voltage detecting means 12 is a predetermined value Vref2 (effective value 100V in this embodiment). The switching current of the commercial frequency (60 Hz in this embodiment) whose amplitude is controlled is supplied to each switching element of the inverter circuit 4 so as to increase or decrease the output current of the inverter circuit 4.

Specifically, the inverter output voltage detected by the second voltage detecting means 12 and the preset Vref2
The difference between and is amplified by the second error amplifier 17 as an error signal and input to the inverter control unit 7 as a voltage error signal. In the inverter control unit 7, the second error amplifier
Based on the voltage error signal from 17, multiplication with a square wave signal of 60 Hz is performed, and an amplitude-modulated switching control signal is given to the inverter circuit 4. Therefore, at the time of self-sustaining operation, a square wave signal of 60 Hz is supplied as a switching signal to each switching element of the inverter circuit 4 to control the output current of the inverter circuit 4, and the protective relay control circuit 8
The inverter operation of the inverter circuit 4 is stopped according to the input of the stop signal from.

FIG. 2 shows a specific configuration of the inverter control section 7 of the present invention. As shown in the figure, according to the setting mode by the mode setting means 13, the PWM pulse from the comparator 31 is given to the inverter circuit 4 as a switching control signal during the parallel operation, while the amplitude modulation from the multiplier 32 is performed during the self-sustaining operation. The analog switch 33 is switched so that the 180-degree conduction pulse is given to the inverter circuit 4 as a switching control signal.

In the comparator 31, the triangular wave conversion circuit 35 is based on the high frequency signal from the 15.36 kHz oscillator 34.
2nd error amplifier 17 and the reference triangular wave signal generated in
The current error signal from P is input, the two are compared, and the current error signal from the second error amplifier 17 is set to zero.
A WM pulse is being generated.

Further, the multiplier 32 has a frequency of 60 at a predetermined amplitude.
From the energization pulse generator circuit 36 that generates a square wave signal of Hz
The 180-degree conduction pulse is multiplied by the voltage error signal from the second error amplifier 17 to generate a signal obtained by amplitude-modulating the 180-degree conduction pulse. The above comparator 31, multiplier 32,
The analog switch 33, the oscillator 34, the triangular wave conversion circuit 35, and the energization pulse generation circuit 36 constitute pulse generation means 200 for generating a switching pulse signal to the inverter circuit 4.

As a result, the PWM pulse from the comparator 31 or the amplitude-modulated 180-degree conduction pulse from the multiplier 32 is supplied to the inverter circuit 4 as a switching control signal according to the setting mode to control the conduction of each switching element. .

FIG. 3 shows a PWM pulse or a 180-degree conduction pulse (a) (b) to be supplied to the four switching elements constituting the above-mentioned inverter circuit 4 and a waveform of the inverter output current (ha) ) (D) is a comparison between the parallel operation mode and the independent operation mode.

In the parallel operation mode, high-frequency switching is performed as shown in FIG. 7B, and a 60 Hz sine wave output current is obtained as shown in FIG. On the other hand, in the self-sustained operation mode, switching is performed at the commercial frequency (= 60 Hz) as shown in (b) of the figure, and the output current is a square wave as shown in (d) of the figure. Therefore, in the independent operation mode,
The switching loss of the inverter circuit 4 can be reduced, the discharge output of the storage battery 3 during the self-sustained operation can be effectively used, and the self-sustained operation can be continued for a long time.

In the above embodiment, the case where the switching pulse signal matching the system frequency is supplied to the inverter circuit 4 in the self-sustained operation mode has been described. If it is a switching signal, it is possible to reduce switching loss. However, in this case, the switching loss increases in proportion to the increase of the switching frequency as compared with the case of supplying the switching pulse signal of the system frequency.

[0035]

As described above, according to the present invention, since the switching element of the inverter circuit is driven by the low-frequency switching pulse in the low output state during the self-sustaining operation, the switching loss can be reduced. The discharge output of the storage battery is converted with high efficiency and supplied to the load, enabling continuous operation for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a solar power generation device to which the present invention is applied.

FIG. 2 is a block diagram showing a configuration of an inverter control unit 7 of the present invention.

FIG. 3 is a waveform diagram for each setting mode by the mode setting means 13.

FIG. 4 is a schematic configuration diagram of a conventional solar power generation device.

[Explanation of symbols]

 1 Photovoltaic power generator 2 Solar cell 3 Storage battery 4 Inverter circuit 5 Commercial power system 6 Load 7 Inverter control unit 8 Automatic restoration type interconnection relay 9 Manual restoration type breaker 10 Protection relay control circuit 11 First voltage detection means (iso 12) Second voltage detection means 13 Mode setting means 14 First error amplifier 15 Multiplier 16 Bandpass filter 17 Second error amplifier 18 Inverter current detection means 20 Reverse current prevention diode 200 Pulse generation means

Claims (2)

[Claims] 1. A solar cell, a storage battery connected to the solar cell via a backflow prevention element, an inverter circuit for converting DC power from the solar cell or the storage battery into AC power of a predetermined voltage, and the inverter circuit. In the solar power generation device, which includes an inverter control unit for controlling conduction of the switching element of, and supplies power to the load by being connected to the commercial power system, the inverter control unit includes the inverter circuit connected to the commercial power system. Mode setting means for switching and setting a parallel operation mode for operating in a system and an independent operation mode for operating by disconnecting from a commercial power system; and a high-frequency switching pulse signal is generated when the parallel operation mode is set, A pulse generating means for generating a low-frequency switching pulse signal when the self-sustained operation mode is set is provided. Solar power generation device that. 2. The pulse generation means generates a switching pulse signal having a first frequency sufficiently higher than a system frequency when the parallel operation mode is set, and a second frequency of a second frequency which matches the system frequency when the independent operation mode is set. The solar power generation device according to claim 1, wherein a switching pulse signal is generated.