JPH0766300B2 - Inverter control method for photovoltaic power generation - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inverter control method for photovoltaic power generation.

[Prior Art and Problems] A method is used in which direct current generated by a solar cell is converted into alternating current using an inverter and connected to a system power supply.

FIG. 2 shows an example of an apparatus that implements the inverter control method for photovoltaic power generation. In the figure, 1 is a solar cell and 2 is an inverter circuit. The inverter circuit 2 has a configuration in which a normal power transistor is used as a switching element and is assembled in a bridge shape to apply a pulse width modulation signal to the switching element to perform AC conversion. Reference numeral 3 is a control circuit for giving the pulse width modulation signal to the inverter circuit 2, to which a DC voltage is input. Although not shown, the output side of the inverter circuit 2 is connected to the system side via a transformer.

Reference numeral 4 denotes a temperature detector, which is arranged close to the solar cell 1, inputs an electric signal from the temperature detector 4 into the control circuit 3, temperature-compensates the reference voltage of the inverter, and operates the inverter with the voltage. The voltage is used.

However, when only the temperature compensation as described above is performed, the operating voltage of the inverter can be compensated when the incident light intensity amount is constant, but the voltage at the maximum output point due to the change of the incident light intensity is different. The maximum output point cannot be compensated.

Further, since the temperature detector has to be mounted on the solar cell or in the vicinity thereof, it is necessary to manufacture the solar cell by incorporating it into the same module, or to mount the temperature detector separately, which increases the cost. Then, it is necessary to wire a temperature detector line between the solar cell and the inverter.

[Means for Solving the Problem] The present invention directly adopts a method in which the temperature compensation by the output of the temperature detector is not performed for 100% of the reference voltage value, and the temperature is limited to some percentage of the temperature compensation.

FIG. 3 shows the temperature characteristics of the solar cell. When the incident light intensity is constant, the higher the temperature, the lower the output voltage. or,
As shown in FIG. 4, when the incident light intensity is high, the operating point of maximum output is slightly higher and slightly higher when the incident light intensity is higher at a constant ambient temperature.

For example, published by the Institute of Electrical Engineers of Japan, Solar Cell Survey Special Committee, published by The Institute of Electrical Engineers of Japan, released by Corona Inc., "Solar Cell Handbook", 1st edition, 1st edition, page 244. From the average temperature monthly chart,
It can be seen that the amount of solar radiation in summer is 1.5 times that in winter.

In this case, considering winter as a reference, the temperature is high in summer, so the voltage at the operating point of maximum output decreases. However, because the amount of solar radiation is large in summer, the voltage at the operating point of maximum output rises slightly compared to winter. Therefore, the actual operating point of the combination of both is that the temperature characteristics are canceled out considerably.

Now, if the temperature of the battery is not compensated 100% and the amount of increase in the optimum operating point voltage in summer is reduced, it is possible to compensate the optimum operating point.

The present invention will be described below with reference to the embodiment shown in FIG. Second
The same parts as those in the figure are denoted by the same reference numerals. The inverter circuit 2 is connected to the solar cell 1. The inverter circuit 2 is formed by connecting switching elements in a bridge shape as described above. The DC voltage from the solar cell 1 is input to the control circuit 3, and the temperature detector 4 is arranged in the vicinity of the solar cell 1. The temperature detector 4 is connected to the control circuit 3 via the temperature compensation effect setting device 5.

The maximum and minimum ratio of monthly insolation is about 1.5, as already mentioned. Also, from Fig. 4, relative incident light intensities of 15 and 25
The point (25/15 = 1.67) is compared. The maximum output voltage is 0.58V and 0.62V, respectively. This difference is 0.04 V = 40 mV, the difference between the average temperature in summer and winter is 20 ° C from the table of the above publication, and the temperature rise of the solar cell itself is optimally 30 ° C, about 1 / 1.5 when the amount of solar radiation is small. That is, it will be about 20 ° C.

Therefore, the temperature difference ΔT _E of the solar cell element in the month with the highest amount of sunshine compared to the lowest month is the temperature difference 20 ° C, the difference in battery temperature rise 30−20 = 10 (° C) Therefore ΔT _E = 30 ° C Becomes

The difference in the generated voltage ΔV _T due to this is −2 mV / ° C for most devices in terms of temperature characteristics, so ΔV _T = −2 (mV / ° C) × 30 = −60 mV The voltage ΔV _C to be corrected by adding the difference is ΔV _C = −60 mV + 40 mV = −20 mV (1) That is, only 1/3 of the temperature characteristic needs to be corrected.

The solar cells made of silicon semiconductors, which are widely used at present, have the temperature characteristics and incident light intensity characteristics as shown in FIGS.

The above formula (1) is only an example, but in the conventional case, the correction value at the current temperature of the solar cell is directly detected by the output of the temperature detector 4 of FIG. , Which is determined by the optimum [maximum output] operating point voltage of the solar cell at the reference temperature) to obtain the DC output at the maximum output operating point commensurate with the current temperature. However, it cannot actually operate at the optimum operating point. The present invention is directed to the difference in incident light intensity (summer, winter,
In consideration of (daytime, morning and evening), miscompensation is prevented as much as possible, and the solar cell can be operated near the optimum operating point.

The temperature compensation effect setting device 5 adjusts the temperature output signal from the temperature detector 4 to an appropriate ratio (for example, 30 to 90%) lower than that, so as to compensate the reference voltage value. To do.

The above-mentioned embodiment is an example in which the temperature detector is arranged close to the solar cell, but since the compensation amount of the temperature characteristics may be small, the temperature detector is not attached to the solar cell side and the inverter, or in the vicinity thereof. May be attached. Reference numeral 4'indicated by a dotted line in FIG. 1 indicates a temperature detector arranged on the inverter side.

The operation is different from the case where the input to the temperature detector 4'is placed close to the solar cell, but the temperature rise and fall show the same tendency at any of the above positions. Temperature detector 4 '
Are arranged to obtain the same effect as in the first embodiment.

In this case, the temperature detector 4 placed close to the solar cell
The circuit required for can be significantly shorted.

A silicon diode is suitable as the temperature detector used in the present invention. This is because the temperature characteristics of silicon solar cells generally have a characteristic of −2 mV / ° C, and the forward current of silicon diodes also generally have a temperature characteristic of −2 mV / ° C. If diodes having characteristics are used in the forward direction, both have the same characteristics and correspond to temperature. Therefore, if diodes are used for the temperature detector, compensation can be easily performed.

[Advantages of the Invention] According to the present invention, it is possible to operate the inverter circuit in the vicinity of the optimum operating point of the solar cell by compensating for the temperature characteristic and taking into account the change in the amount of solar radiation.

Further, even if the temperature detector is attached to the inverter circuit, the above-mentioned compensation effect can be obtained, and the circuit for the temperature detector can be shortened.

Furthermore, the use of a silicon diode having the same temperature characteristics as a silicon solar cell for the temperature detector has the effect of simplifying the compensation, and the present invention provides a control for controlling a relatively small photovoltaic inverter. It can be installed in the circuit at low cost.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 2 shows an example of an apparatus that implements the inverter control method for photovoltaic power generation. FIG. 3 is an illustration of the temperature characteristics of the solar cell when the incident light intensity is constant. FIG. 4 is an illustration of the characteristics of the solar cell when the ambient temperature is constant. 1 ... Solar cell, 2 ... Inverter circuit, 3 ... Control circuit, 4,4 '... Temperature detector, 5 ... Temperature compensation effect setting device, 6 ... Inverter.

Claims (3)

[Claims] 1. For controlling the maximum power of a photovoltaic power generation inverter using a solar cell as a power source, the generated voltage of the solar cell is used as a reference voltage, and the inverter voltage is controlled by temperature compensation of the reference voltage according to the temperature of the battery. When performing, the compensation value currently detected by the temperature detector installed near the battery,
The generated voltage fluctuation of the solar cell calculated from the difference between the maximum output point voltage of the solar cell caused by the difference in the relative incident intensity of sunlight and the ratio of the summer average insolation to the winter average insolation and the average temperature. In view of the fact that and are canceled out and become small, the value is adjusted to a value smaller than the compensation value to correct the reference voltage, and the inverter is controlled to control the inverter. 2. The maximum power control of an inverter for photovoltaic power generation using a solar cell as a power source, the generated voltage of the solar cell as a reference voltage, and the temperature of the battery compensates the reference voltage to control the inverter. When performing, the compensation value currently detected by the temperature detector installed in the vicinity of the inverter, the difference voltage of the maximum output point voltage of the solar cell caused by the difference in the relative incident intensity of sunlight and the summer average insolation In view of the fact that the generated voltage fluctuation of the solar cell calculated from the difference between the ratio to the average amount of solar radiation in winter and the average temperature cancels each other out and becomes smaller, the reference voltage is corrected by adjusting the value smaller than the compensation value. Then, the inverter control method for photovoltaic power generation is characterized by controlling the inverter. 3. The inverter control method for photovoltaic power generation according to claim 1 or 2, wherein a forward characteristic of a diode is used as the temperature detector.