JPH0337388B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply system using solar cells, in which a solar cell and a storage battery as energy storage means are arranged side by side, and power is supplied from these to another power source or a single load.

Generally, this type of power supply system converts DC power into AC power using a power converter and supplies the AC power to another AC power source or an independent load.
In addition, the output of solar cells fluctuates widely depending on the amount of solar radiation and does not necessarily match the load demand, and storage batteries are often installed to reduce the capacity of power converters and to ensure stability during independent load operation. many.

FIG. 1 is a block diagram showing an example of a conventional power supply system of this type, particularly when connected to an AC power supply system. In the figure, 1 is a solar cell, 2 is a power converter with voltage control function, and 3 is a power converter with a voltage control function.
4 is a DC bus connecting the solar cell 1 and the power converter 2;
is a transformer provided on the AC side of the power converter 2 as necessary; 5 is an AC power supply system connected to this transformer 4; 6 is a storage battery connected to the DC bus 3; 7
8 is a current control circuit, 8 is a current command value to this current control circuit 7, and 9 is a current detection means provided on the DC bus 3.

Next, the operation will be explained. The power generated by the solar cell 1 and the output of the storage battery 6 are converted into alternating current by a power converter 2 and supplied to an alternating current power system 5 via a transformer 4. Here, since the voltage of the DC bus 3, that is, the input voltage of the power converter 2 is fixed to the voltage of the storage battery 6, the input current of the power converter 2 is detected by the current detection means 9, and the current control circuit 7 detects the input current of the power converter 2. The amount of power supplied is controlled by amplifying the deviation from the current command value 8 and adjusting the phase angle of the power converter 2.

The output characteristics of the solar cell 1 vary widely depending on the operating point voltage, as shown in the graph of FIG. Now, even if the rated voltage of the storage battery 6 is selected so that the solar cell 1 operates at the maximum output operating point S,
Since the storage battery voltage is always several percent higher than the rated voltage during charging and several percent lower when discharging, it actually operates at point C or D, and the output decreases accordingly. Further, the output P of the solar cell 1 varies depending on the temperature and the amount of solar radiation, as shown by the broken line, for example, and the operating point moves to C' and D' at that time. In this way, the solar cell 1 could not be operated at the optimum operating point, and a decrease in the output P could not be prevented.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and the first power converter controls the active power or output frequency to be supplied to another power source or load, and the second The object of the present invention is to provide a power supply system in which a power converter can prevent a decrease in the output of a solar cell by controlling the reactive power supplied by a first power converter or the power voltage supplied by a second power converter. .

FIG. 3 is a block diagram showing another example of a conventional power supply system. In the figure, 2 is exactly the same as the power converter shown in FIG. call. 10 is a second power converter, for example a DC-to-DC power converter, provided between the DC bus 3 and the storage battery 6; 11 is a voltage control circuit for controlling the second power converter 10; 12 is a voltage control circuit for controlling the second power converter 10; The voltage command value 13 is voltage detection means provided on the DC bus 3.

Next, the operation will be explained. The electric power generated by the solar cell 1 is converted into alternating current by the first power converter 2 and supplied to another alternating current power supply system 5. The current is detected by the current detecting means 9, and the current is commanded by the current control circuit 7. Controlling the first power converter 2 so that the value is equal to 8 is the same as in the conventional example shown in FIG. 1, but in the conventional example shown in FIG.
A second power converter 10 is provided between the DC bus voltage and the storage battery 6, a voltage detection means 13 detects the DC bus voltage, and a voltage control circuit 11 detects the deviation between the DC bus voltage and the voltage command value 12. The second power converter 10 is controlled so that the deviation becomes zero. As a result, the operating point voltage of the solar cell 1 can be maintained at an arbitrary value given by the voltage command value 12 regardless of the storage battery voltage, and therefore,
Maximum output operation is also possible by providing the optimum operating point with the voltage command value 12 according to the amount of solar radiation, temperature, etc.

Next, the second
As shown in FIG. 4, the power converter 10 is composed of a step-down chopper 100a and a step-up chopper 100b connected in antiparallel to the step-down chopper 100a. ，
102b, reactors 103a, 103b, etc. Terminal A or B is connected to DC bus 3, respectively.
and is connected to the storage battery 6. Voltage command value 12
The DC voltage detected by the voltage detecting means 13 is input to the voltage control circuit 11, the deviation is determined by the subtracter 111, and the DC voltage is amplified by the amplifier 112. This output is converted into a current command signal for each chopper 100a, 100b by function generators 113a, 113b. This signal and the current detector 104a, 1
The deviation from each chopper current detected in step 04b is obtained by subtracters 114a, 114b, amplified by amplifiers 115a, 115b, and phase shifters 116a, 115b.
116b and each chiyotsupa 100a, 100
b is converted into a conduction rate control signal and supplied to gate signal generation circuits 105a and 105b.

Here, function generators 113a and 11 that provide current command signals for the choppers 100a and 100b described above are provided.
As is clear from the figure, 3b is provided with an area where input signals are simultaneously output. As a result, the chopper 100a, 1 on the charging side and the discharging side
There is a mode in which 00b is activated at the same time and a circulating current flows. At this time, the charging and discharging current of the storage battery is 2
Since it is controlled by the difference between the two chopper currents, the transition between charging and discharging occurs continuously. Now, if the power generated by the solar cell 1 and the amount supplied to the AC power supply system 5 are almost balanced, and the power generated suddenly changes due to the amount of solar radiation, etc., and the power balance collapses, the storage battery 6 can be charged immediately. Discharge occurs and stable voltage control is possible.

FIG. 5 is a block diagram showing one embodiment of the present invention.

However, in the conventional example shown in FIG. 3, the first power converter 2 having a voltage control function is used, and the second power converter 10 controls the DC voltage to a desired value. In the embodiment of the present invention, the first power converter 2A uses a voltage control function (PAM or PWM), which is said to have a simple configuration and high efficiency.
Use a self-excited voltage type inverter that does not have That is, the first power converter 2 does not have a voltage control function.
A's output voltage and output current are detected, and the reactive power control circuit 14 controls the second power converter so that the reactive power supplied by the first power converter 2A is equal to the reactive power command value 15 instead of the above-mentioned DC voltage. In addition to controlling the first power converter 10, the first power converter 2A is controlled by an active power control circuit 16 and an active power command value 17 instead of the above-mentioned DC current.

In this case, since the DC voltage and the AC voltage are always fixed in a constant voltage ratio relationship, the output voltage of the first power converter 2A, that is, the DC voltage fluctuates somewhat,
Although the output of the solar cell 1 is somewhat reduced by the amount of deviation from the maximum output operating voltage of the solar cell 1, the proportion thereof is relatively small and sufficiently tolerable. Moreover, since the reactive power is controlled to be constant, it is possible to prevent the influence of reactive power fluctuations on the AC power supply system 5.

In the above embodiment, a case has been described in which the reactive power supplied to the AC power supply system 5 is controlled to be constant, but in particular, when supplying power only to the load as in an independent power supply system, instead of reactive power, The output voltage of the first power converter 2A is detected, and this value is
It is also possible to control the second power converter 10 using the voltage control circuit 11 in the conventional example so that the output voltage becomes equal to the command value. In this case, the first power converter 2A performs not active power control but constant output frequency control.

As described above, according to the present invention, the first power converter controls the active power (the output frequency when supplying power only to the load), and the second power converter controls the active power Since the reactive power (the output voltage of the second power converter when supplying power only to the load) is controlled, it is possible to prevent a drop in the output of the solar cells, and also to connect the second power converter in antiparallel. It is composed of connected charging and discharging choppers, and by passing a circulating current through both choppers, it is possible to stably control even sudden changes in the amount of solar radiation.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional power supply system using solar cells, Fig. 2 is a solar cell output characteristic curve diagram to explain the operation of the power supply system shown in Fig. 1, and Fig. 3 4 is a block diagram showing another example of the conventional power supply system, FIG. 4 is a configuration diagram showing an example of the second power converter and its voltage control circuit used in the power supply system shown in FIG. 3, and FIG.
The figure is a block diagram showing one embodiment of the power supply system of the present invention. In the figure, 1... solar cell, 2A... first power converter, 5... AC power supply system, 6... storage battery, 9... current detection means, 10... second power converter, 13... ... Voltage detection means, 14 ... Reactive power control circuit, 15 ... Reactive power command value, 16 ... Active power control circuit, 17 ... Active power command value, 10
0a...Buck power supply, 100b...Boost power supply. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A solar cell, a first power converter connected between the solar cell and another power source and having no voltage control function, and an output voltage and output of the first power converter. A detection means for detecting current, a second power converter connected between the solar cell and the storage battery, and active power and reactive power reaching predetermined values from the output voltage and output current detected by the detection means. A power feeding system comprising: a control means for controlling the first power converter and the second power converter so that the first power converter and the second power converter have the following characteristics. 2 The second power converter is configured by connecting in parallel a first chopper that boosts the voltage and supplies power in one direction, and a second chopper that steps down the voltage and supplies power in the opposite direction. Claim 1, characterized in that the device is operated so that a circulating current flows between the
Power supply system as described in section. 3. A solar cell, a first power converter connected between the solar cell and the load and having no voltage control function, and a detection means for detecting the output voltage and output current of the first power converter. , a second power converter connected between the solar cell and the storage battery; and a second power converter connected between the solar cell and the storage battery; A power supply system comprising: a power converter; and a control means for controlling the second power converter. 4 The second power converter is configured by connecting in parallel a first chopper that boosts the voltage and supplies power in one direction, and a second chopper that steps down the voltage and supplies power in the opposite direction. Claim 3, characterized in that the operation is performed so that a circulating current flows between them.
Power supply system as described in section.