JP3499942B2 - Solar power generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generator, and more particularly, to power supply to a load by parallel operation of a distributed power supply having an inverter circuit and a commercial power system. The present invention relates to a solar power generation device to be supplied. 2. Description of the Related Art In recent years, a relatively small-capacity distributed power supply facility of several kW using a DC power supply composed of a solar cell is connected to a commercial power system via an inverter circuit to supply power to a load. Various solar power generation devices have been proposed. FIG. 3 is a schematic configuration diagram of a conventional solar power generation device. In the figure, 31 is a solar cell that directly converts sunlight energy into a DC voltage, 32 is an inverter circuit for converting DC power output from the solar cell 31 into AC, and a DC output from the solar cell 31 Is converted into AC by an inverter circuit 32 and supplied to a load 34 and a commercial power system 35 via an insulating transformer 33. [0004] A system interconnection switch 36 is interposed between the insulating transformer 33 and the commercial power system 35. When the operation condition of the inverter circuit 32 is adjusted, the switch 36 is closed. The interconnection operation will be started. The switch 36 is controlled by a protection relay control circuit 37. The protection relay control circuit 37 monitors the output voltage of the solar cell 31, the system voltage of the commercial power system 35, and the like.
Alternatively, it is determined that the commercial power system 35 is in an abnormal state, and the switch 36 is opened. Thereafter, when the cause of the abnormality is eliminated, the switch 36 automatically closes, and after a lapse of a predetermined time, the inverter circuit is closed.
32 starts. [0006] In the conventional photovoltaic power generation system, the inverter circuit 32 is designed to prevent the inverter circuit 32 from repeatedly starting and stopping during low sunlight such as morning and evening. Instead of restarting as soon as the operating conditions are satisfied, the inverter circuit 32 is restarted after a certain time (for example, 20 minutes) has elapsed after the inverter circuit 32 was stopped. For this reason, when the inverter circuit 32 is stopped due to an abnormality in the commercial power system 35 during high sunlight such as during the day, even if the cause of the abnormality is eliminated, the inverter circuit 32 is not restarted immediately, and Restarting after a lapse of time. Therefore, when the amount of solar radiation is large and the solar cell 31 is capable of high output, the inverter circuit 32 is not liable to repeatedly start and stop.
Has been stopped for a certain period of time, there has been a problem that the power generated by the solar cell 31 cannot be used effectively. The present invention has been made in view of the above points, and provides a solar power generation device capable of effectively utilizing the power generated by a solar cell. [0010] The present invention provides a solar cell,
An inverter circuit for converting a direct current generated from the solar cell into an alternating current of a predetermined voltage, a voltage detecting means for detecting an output voltage of the solar cell, and a control means for controlling activation of the inverter circuit; Is a photovoltaic power generator characterized in that a start-up time of the inverter circuit is changed based on an open circuit voltage of the solar cell when the inverter circuit is stopped. According to the present invention, the start-up time of the inverter circuit is changed on the basis of the open-circuit voltage of the solar cell when the inverter circuit is stopped. The time can be set appropriately. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a photovoltaic power generator according to the present invention will be described in detail with reference to the drawings showing one embodiment. FIG. 1 is a schematic configuration diagram of a solar power generation device using a solar cell to which the present invention is applied. In FIG. 1, a solar power generation device includes a solar cell 1 (in this embodiment, a rated power of 3 kW) for converting sunlight energy into DC power, and a DC power of the solar cell 1 converted to AC power. And an inverter circuit 2 for supplying a predetermined AC voltage (in this embodiment, 100 V). The inverter circuit 2 is connected to a commercial power system 3 and connected to a load 4 such as various home appliances connected to a distribution line. Power is being supplied to it. The inverter circuit 2 is composed of a plurality of switching elements connected in a bridge. The inverter circuit 2 has an inverter control unit 5 for performing various processes described later.
Provides a pulse width modulated switching control signal. The inverter control unit 5 is constituted by a microcomputer. A winding ratio of 1: 1 between the inverter circuit 2 and the commercial power system 3 when viewed from the output side of the inverter circuit 2
Are provided with an isolation transformer 6 and a system interconnection switch (hereinafter abbreviated as switch) 7 for system protection, and the switch 7 responds to a control signal from a protection relay control circuit 8. ,
The contacts are opened and closed to connect to or disconnect from the commercial power system 3. Here, the contact of the switch 7 is closed by the input of the interconnection command signal from the protection relay control circuit 8, and the contact is opened by the input of the disconnection command signal from the protection relay control circuit 8. Has become. Next, the protection relay control circuit 8 and the inverter control unit 5 will be described. The protection relay control circuit 8 includes a microcomputer, and includes a first amplifier including an isolation amplifier that detects an output voltage of the solar cell 1.
A value detected by the voltage detecting means 9 and a value detected by the second voltage detecting means 10 comprising a transformer (PT) for detecting a voltage at a connection point with the commercial power system 3 are inputted. In this way, a start signal or a stop signal is sent to the inverter control unit 5 and a connection command signal or a disconnection command signal is sent to the switch 7. Then, the protection relay control circuit 8 detects the output voltage of the solar cell 1 by the first voltage detecting means 9, and the open voltage of the solar cell 1 is reduced while the inverter operation of the inverter circuit 2 is stopped. The output voltage of the commercial power system 3 detected by the second voltage detecting means 10 is equal to or higher than a predetermined value (set to 170 V in the present embodiment) that enables interconnection to the appropriate range (81 to 114 V) in the operation regulation. If it is within the range, as described later, after waiting for a predetermined time, a start signal is sent to the inverter control unit 5 and an interconnection command signal is sent to the switch 7. On the other hand, when the output voltage of the solar cell 1 falls below a predetermined value (set to 160 V in this embodiment) at which the interconnection operation with the commercial power system 3 cannot be performed during the inverter operation of the inverter circuit 2, It determines that the inverter circuit 2 is in a standby state due to a decrease in the output of the solar cell 1, sends a stop signal to the inverter control unit 5, and sends a disconnection command signal to the switch 7. Further, the voltage at the interconnection point with the commercial power system 3 is detected by the second voltage detecting means 10, and if the interconnection point voltage is out of the above-mentioned proper range in the operation regulation, an overvoltage abnormality of the commercial power system 3 or It determines that the inverter circuit 2 is in a standby state due to the occurrence of an undervoltage abnormality, sends a stop signal to the inverter control unit 5, and sends a disconnection command signal to the switch 7. As described above, the protection relay control circuit 8 detects whether or not the operating conditions of the inverter circuit 2 are satisfied. In addition to sending a stop signal, it sends a disconnection command signal to the switch 7. On the other hand, if it is determined that the interconnection of the inverter circuit 2 is possible, a start signal is sent to the inverter control unit 5, and An interconnection command signal is sent to the switch 7. The protection relay control circuit 8 prevents the inverter circuit 2 from repeatedly starting and stopping when the amount of solar radiation is small and the amount of power generated by the solar cell 1 is small, such as in the morning or evening. The start signal is sent to the inverter control unit 5 when the operating conditions of the inverter circuit 2 are satisfied, after a lapse of a predetermined time after the inverter circuit 2 is stopped. Specifically, the output voltage (open-circuit voltage) of the solar cell 1 when the inverter circuit 2 is stopped is detected by the first voltage detecting means 9, and the open-circuit voltage of the solar cell 1 is set to a predetermined power generation amount (this embodiment). In the example, an open-circuit voltage value (190 V in the present embodiment) in a state capable of outputting 300 W which is 10% of the rated output).
If it is smaller, 20 times after the inverter circuit 2 is stopped.
After waiting for one minute, as soon as the operating conditions of the inverter circuit 2 are satisfied, a start signal is sent to the inverter control unit 5 and an interconnection command signal is sent to the switch 7. When the open-circuit voltage of the solar cell 1 at the time of the stop of the inverter circuit 2 is 190 V or more, after the inverter circuit 2 is stopped, it waits for one minute, and as soon as the operation conditions of the inverter circuit 2 are set, the inverter is turned off. An activation signal is sent to the control unit 5 and an interconnection command signal is sent to the switch 7. This is, as shown in FIG.
Of the maximum power generation P of the solar cell 1 tends to increase as the amount of solar radiation increases, and the open-circuit voltage Vs of the solar cell 1 when the maximum power generation P can be output is also increased. ing. FIG. 2 shows the voltage-power characteristics of the photovoltaic power generator according to the present embodiment.
Indicates a characteristic at the time of rated output, a curve (2) indicates a characteristic when the above-described output of 300 W is possible, and a curve (3) indicates a characteristic at the time of output capable of interconnection. With this, the inverter operation of the inverter circuit 2 is stopped due to the occurrence of an abnormality in the commercial power system 3, and when the solar cell 1 can output 300 W or more at that time, that is, the inverter circuit 2 is frequently started and stopped. If it is possible to generate power without fear, the inverter circuit
Without waiting, the activation of the inverter circuit 2 is started immediately as soon as the operating conditions of the inverter circuit 2 are set, and the power generated by the solar cell 1 can be effectively used, and the power generation efficiency can be improved. . On the other hand, the inverter control unit 5 determines that the output voltage of the solar cell 1 detected by the first voltage detecting means 9 becomes the voltage value Vref of the optimum operating point at which the maximum power is extracted from the solar cell 1, and that the commercial power A pulse width modulated switching control signal is provided to the inverter circuit 2 so that a current synchronized with the fundamental frequency component of the voltage at the interconnection point with the system 3 is output from the inverter circuit 2. Therefore, during the interconnection operation between the inverter circuit 2 and the commercial power system 3, the output power of the inverter circuit 2 is controlled so that the operating power factor becomes 1 at the commercial frequency and the maximum power is drawn from the solar cell 1. Specifically, the difference between the output voltage of the solar cell 1 detected by the first voltage detecting means 9 and the preset optimum operating point voltage Vref is amplified by the differential amplifier 12 as an error signal, The error signal is used as one input signal of the multiplier 13. The fundamental frequency component of the interconnection point voltage detected by the second voltage detection means 10 is
The fundamental frequency component of the extracted interconnection point voltage is input as the other input signal of the multiplier 13. The multiplier 13 multiplies the error signal from the differential amplifier 12 by the fundamental frequency component signal from the band-pass filter 14 to generate a current command value of the inverter current. Therefore, this current command value is a value that synchronizes with the system voltage waveform and controls the output voltage of the solar cell 1 to the optimum operating point voltage Vref during the interconnection operation with the commercial power system 3. The difference between the current command value from the multiplier 14 and the inverter current of the inverter circuit 2 detected by the inverter current detection means 11 comprising a current transformer (CT) is amplified by the error amplifier 15. , As a current error signal. The inverter control unit 5 includes an error amplifier 15
And a reference triangular wave signal of about 20 kHz, and supplies a switching signal to the switching element of the inverter circuit 2 so that the current error signal from the error amplifier 15 becomes zero. In addition to PWM (pulse width modulation) control, the inverter operation of the inverter circuit 2 is started or stopped according to the input of a start signal or a stop signal from the protection relay control circuit 8. Although the above embodiment has been described with reference to the case where the optimum operating voltage Vref is set to a predetermined constant value, the optimum operating voltage Vref may be increased in the direction in which the output power of the solar cell 1 increases.
f may be changed at any time. Although the case where the inverter control section 5 and the protection relay control circuit 8 are separately configured has been described, they may be configured by one microcomputer. As described above, according to the present invention, the start-up time of the inverter circuit is changed based on the open-circuit voltage of the solar cell when the inverter circuit is stopped. Accordingly, the start time of the inverter circuit can be appropriately set. Therefore, when the amount of power that can be generated by the solar cell is equal to or more than the amount of power generation that does not cause the inverter circuit 2 to frequently start and stop, the inverter circuit can be operated for a long time without waiting for a long time. As soon as is established, the inverter circuit can be started quickly, and the power generated by the solar cell 1 can be effectively used, and the power generation efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a solar power generation device using a solar cell to which the present invention is applied. FIG. 2 is a voltage-power characteristic diagram of a solar cell when the amount of solar radiation is used as a parameter. FIG. 3 is a schematic configuration diagram of a conventional solar power generation device. [Description of Signs] 1 Solar cell (solar cell) 2 Inverter circuit 3 Commercial power system 4 Load 5 Inverter control unit 6 Insulation transformer 7 Grid connection switch 8 Protection relay control circuit 9 First voltage detection means (Isolation) Amplifier) 10 second voltage detecting means 11 inverter current detecting means 12 differential amplifier 13 multiplier 14 band-pass filter 15 error amplifier

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kimihiko Furukawa 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Masahiro Maekawa 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd. (56) References JP-A-6-165518 (JP, A) JP-A 64-1480 (JP, A) JP-A-62-293937 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G05F 1/67 H01L 31/042 H02H 3/24 H02J 3/38

Claims (1)

(57) [Claim 1] A solar cell, an inverter circuit for converting a direct current generated from the solar cell into an alternating current of a predetermined voltage, and voltage detecting means for detecting an output voltage of the solar cell. And control means for controlling activation of the inverter circuit, wherein the control means changes the activation start time of the inverter circuit based on an open voltage of the solar cell when the inverter circuit is stopped. Solar power generator.