JPH0359660B2 - - 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 are arranged side by side as energy storage means, and power is supplied from the solar cell to another power source or a single load.

Typically, this type of system converts the DC output of a solar cell into AC using a power converter and supplies it to another AC power source or an independent load.
In addition, the output of solar cells varies widely depending on the amount of solar radiation, and does not necessarily match the load demand.
A storage battery is often installed to reduce the capacity of the power converter and improve stability during independent load operation.

FIG. 1 is a block diagram showing an example of a conventional power supply system of this type. In the figure, 1 is a solar cell, 2 is a power converter, here an inverter, 3 is a DC bus connecting solar cell 1 and inverter 2, and 4
is a transformer provided as necessary for the inverter output, 5 is another power supply system or independent load, 6 is a storage battery connected to the DC bus 3, 7 is a current control circuit, 8 is the same command value, and 9 is a It is a current detection means.

Next, the operation will be explained. The power generated by the solar cell 1 and the storage battery 6 is converted into alternating current by the inverter 2 and supplied to another power supply system 5 via the transformer 4. Since the voltage of the DC bus 3, that is, the inverter input voltage, is fixed at the voltage of the storage battery 6, the input current is detected by the current detection means 9, and the deviation from the command value 8 is amplified by the current control circuit 7, and the inverter input current is detected by the current detection means 9. By adjusting the firing phase of 2, the power supplied by the inverter is controlled.

By the way, as for the output characteristics of a solar cell, the output P varies widely depending on the operating point voltage V, as shown in FIG. 2 as an example. Now, even if the rated voltage of the storage battery 6 is selected so that the solar cell operates at the maximum output operating point S,
When charging, the storage battery voltage is always a few percent higher than the rated voltage, and when discharging it is several percent lower, so it actually operates at point C or D, and the output decreases by that amount.Also, solar cells vary depending on the temperature and amount of solar radiation. , for example, changes as shown by the broken line, and at this time the operating point moves to C' and D'. In this way, the solar cell could not be operated at its optimum operating point, and a decrease in output could not be prevented.

Furthermore, although the output of the solar cell 1 changes every moment according to the amount of solar radiation, the output of the inverter 2 is controlled to be equal to the command value 8, so the power difference is entirely covered by charging and discharging the storage battery 6. As a result, unless the capacity of the storage battery is sufficiently increased, the storage battery has to undergo repeated rapid charging and discharging, resulting in a shortened lifespan.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. A chopper is provided between the solar cell output DC bus and the storage battery, and the voltages of both are separated and independent to reduce the output drop of the solar cell as much as possible. In addition, by controlling the charging and discharging current of the storage battery, it is possible to prevent the life of the storage battery from decreasing, and by controlling the power converter, the DC voltage of the DC bus is adjusted so that the power generated by the solar cell is maximized. The operating point voltage is as follows.

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 10 is a DC-DC power converter (chopper) provided between the DC bus 3 and the storage battery 6. The output of the current control circuit 7 is connected to control the conduction angle of the chopper 10, unlike in FIG. In addition, the current detection means 9 is connected to the chopper 1.
It is connected to detect zero current, that is, the charging/discharging current of the storage battery. On the other hand, 11 is a voltage control circuit, 12 is a voltage command, 13 is a voltage detection means, and the output of the voltage control circuit is used to control the inverter 2.

Next, the operation will be explained. The power generated by the solar cell 1 is converted into alternating current by the inverter 2,
The current is supplied to another power supply system 5, and a chopper 10 is provided between the DC bus 3 and the storage battery 6. The current of this chopper is detected by a current detection means 9, and is used as a starting point for operation planning, etc. Specified command value 8
If the current control circuit 7 amplifies the deviation from the current value and controls the conduction rate of the chopper 10 so that the deviation becomes zero, the charging/discharging current of the storage battery can always be maintained at a predetermined value. On the other hand, the voltage of the DC bus 3 can also operate regardless of the voltage of the storage battery 6. This is detected by the voltage detection means, and the deviation from the voltage command value 12 is amplified by the voltage control circuit 11, thereby controlling the phase advance angle of the inverter 2 with respect to the AC system voltage 5, thereby setting the DC bus voltage to a predetermined value. can be maintained at the value of As a result, maximum output operation is also possible if an operating point voltage that maximizes the output of solar power is given as the voltage command value.

Note that when a separately excited inverter is used as the power converter 2, the output voltage of the inverter is determined by the grid voltage, but automatic (voltage type) inverters that can also operate independent loads, especially the relationship between DC input voltage and output voltage A normal inverter with a fixed
When using a PWM inverter (not a PWM inverter), the above voltage control can also be used as output voltage control. In other words, in addition to constant pressure control that keeps the voltage command 12 constant, system voltage follow-up control that detects the voltage of the power supply system 5 and uses this as a command value, and reactive power that uses reactive power instead of voltage to control the reactive power supplied by the inverter. The phase advance angle of the inverter can be controlled so that the inverter becomes constant. In this case, although the solar cell output decreases somewhat, the influence of reactive power on the grid is reduced.

Note that when an inverter having a voltage adjustment means such as a PAM type or PWM type inverter is used as the power converter 2, in addition to the DC voltage control shown in the embodiment shown in FIG. can be done.

The above explanation is for the case where the inverter is connected to another AC power source, but it goes without saying that when the inverter is an independent load, the phase control of the inverter cannot be performed and the inverter operates at a constant frequency.

In addition, when supplying to a DC power source or a DC load, the power converter 2 uses DC-DC power conversion,
Using this, it is possible to control the DC bus to a desired value and prevent a decrease in solar cell output. Furthermore, the present invention can be applied even without the power converter 2, as long as it is limited to a field where power is supplied to a DC load.
In this case, the DC bus voltage cannot be controlled directly and arbitrarily, and is adjusted by changing the charging/discharging current setting value 8 of the storage battery to prevent a decrease in the output of the solar cell and to prevent a decrease in the life of the storage battery. Although it will be difficult to satisfactorily satisfy both of these requirements, at least the latter can be fully achieved.

Furthermore, as the current command value 8 of the chopper, it is naturally possible to change the setting within an allowable value in accordance with the amount of solar radiation and the output of the solar cell 1 or the inverter 2, in addition to the initially determined value.

As described above, according to the present invention, a chopper is provided between the DC bus and the storage battery to separate the operating point voltages of the storage battery and the solar cell. In addition to preventing a drop in output due to mismatch, it also controls the charging and discharging current of the storage battery by adjusting the current flow rate of the chopper, preventing rapid charging and discharging, which prevents shortening of the life of the storage battery, and also controls the power converter. As a result, the DC voltage of the DC bus is set to an operating point voltage at which the power generated by the solar cell is maximized, so there is an effect that the solar cell can always be operated at maximum output.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an example of a power supply system using conventional solar cells, Fig. 2 is a diagram showing an example of the voltage-output characteristics of a solar cell to explain the operation of Fig. 1, and Fig. 3 1 is a configuration diagram showing an embodiment of a power feeding system according to the present invention. In the figure, 1... Solar cell, 2... Power converter (inverter), 3... DC source, 4... Output transformer, 5... Power supply system or independent load, 6... Storage battery, 7... Current control circuit, 8...Current command, 9
. . . Current detection means, 10 . . . Chopper (direct-to-direct power converter), 11 . In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a power supply system that supplies power from a solar cell and a storage battery connected in parallel to the solar cell to another power source or load, a power supply system that is inserted between the DC bus to which the solar cell is connected and the storage battery. a current detecting means for detecting a charging or discharging current of the storage battery flowing through the chopper; and a current controlling the charging or discharging current of the storage battery to be equal to a command value by adjusting the conduction rate of the chopper. a control means; a power converter connected between the DC bus and the other power source or load; voltage detection means for detecting the DC voltage of the DC bus; A power supply system comprising voltage control means for controlling the DC voltage of the bus bar to an operating point voltage at which the power generated by the solar cell is maximized.