JPH0640708B2 - Solar power system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photovoltaic power generation system, and more particularly to a photovoltaic power generation system that suppresses voltage fluctuations in the grid when applied to a distribution grid.

[Background of the Invention]

As a measure against the recent increase in energy demand, the use of solar energy is expected to be promising, and its development is being promoted in various countries around the world. When the solar power generation system becomes popular, it is expected to be included in the distribution system. In this case, the solar energy is DC power and must be converted to AC power.

As a concrete method of this, a configuration of a photovoltaic power generation system as shown in FIG. 1 is generally considered. Referring to FIG. 1 in accordance with the figure numbers, 1 is a solar cell that converts sunlight energy into DC power, 2 is a commercial AC power, or an AC / DC converter that converts AC power into DC power,
Reference numeral 3 is a control device for controlling the AC-DC converter, 4 is a transformer, 5 is a harmonic voltage generated when converting DC power into AC power, an AC filter for absorbing current, and 6 is a distribution system ( Alternatively, reference numeral 7 denotes a load, and 8 denotes a rear power distribution system (including a load). The part indicated by the broken line in the figure is a PV system (PVS: Photo Vo).
ltaic System). Normally, the system operates at approximately a power factor of 1 when the solar cells are operating during the day.
However, when the system is stopped at night or in rainy weather, the AC filter 5 takes a forward current with respect to the fundamental wave, so that a forward operation with a power factor of 0 is performed. Since the capacity of this AC filter is as large as the capacity of the AC / DC converter, the terminal voltage of the photovoltaic power generation system increases due to the ferranch effect when the load of the distribution system is light.

FIG. 2 is for specifically explaining this phenomenon. In the figure, (A) shows the schematic view of FIG.
The same thing as the figure shows the same thing. Z is the impedance of the transmission line, V ₀ is the terminal voltage of the rear distribution system, and V _t
Represents the terminal voltage of the photovoltaic power generation system, and I represents the current flowing in the power transmission line. In the figure, (B) shows the voltage / current vector diagram of (A) in the daytime. Since the current flows with a delay by the power factor of the load, V _t is V ₀ due to the voltage drop of the transmission line.
Will be smaller than. In the figure, (C) shows the voltage / current vector diagram of (A) figure at night with a light load. The current leads the voltage due to the leading current of the AC filter of the photovoltaic power generation system, and V _t
Will be greater than V ₀ . This increase in voltage increases as the impedance of the power transmission line increases and as the AC filter capacity increases, threatening the insulation of surrounding equipment,
In the severest case, the equipment may be burned. The same applies to the case where another so-called delayed reactive power compensator such as a phase compensator such as a star converter is provided instead of the AC filter, and improvement has been desired.

[Object of the Invention]

The present invention solves the above-mentioned problems of the conventional technology, and provides a photovoltaic power generation system capable of suppressing an increase in the grid voltage even when the photovoltaic power generation system is stopped and the grid is lightly loaded. is there.

[Outline of Invention]

When the solar power generation system is stopped, the system becomes a light load,
In order to prevent the system voltage from rising due to the ferranch effect, in the present invention, a solar battery bypass circuit is provided on the DC side of the AC / DC converter so that the solar energy falls below a specified value and the solar power generation system stops. Sometimes the solar cell is switched to a bypass circuit, and the AC / DC converter is operated by reactive power control (lag power factor) to cancel the advance current of the delayed reactive power compensator such as AC filters and phase adjusting equipment. Is.

Example of Invention

An embodiment of the present invention is shown in FIG. Since the same numbers as those in FIG. 1 indicate the same items, different new items will be described. Reference numeral 9 indicates from the a side of the solar cell to the DC short-circuit bypass circuit b side by the system stop command COM when the solar energy decreases. A first switch for switching the connection point of the AC / DC converter 2, a reference numeral 10 is a current detector for detecting a current flowing through the converter, a reference numeral 11 is a reactive power detector for detecting reactive power of the photovoltaic power generation system, and a reference numeral 12 Is a control device for a photovoltaic power generation system including a reactive power control circuit.

Normally, as described above, sunlight energy is converted into AC power with a power factor of approximately 1 and sent to the distribution system. However, when the sunlight energy is below the specified value at night, in rainy weather, etc., the first switch 9 is switched from the a side to the b side by the system stop command COM. On the other hand, in the control device, the constant power control (or constant current control) operation is switched to the reactive power control operation, and the direct current of the AC / DC converter 9 is adjusted so that the reactive power required by the photovoltaic power generation system becomes equal to the command value Q _0. (In this case, the direct current voltage is controlled to control the direct current.).

The block diagram of the concrete circuit of the controller 12 is shown in FIG.
Shown in the figure. In the figure, reference numeral 121 is a set value Q of reactive power.
_A first adder for taking the difference between ₀ and the detected value Q of the reactive power, reference numeral 122 is a reactive power deviation amplifier, the output of which is a current command value I _q0 corresponding to the required delayed reactive power of the AC / DC converter 9.
Becomes Reference numeral 123 is a second switch that switches from the a side of the current command value (power command value divided by the DC voltage) a side of I _d0 to the b side of I _q0 when the solar energy decreases due to the stop command COM. Reference numeral 124 is a second adder that takes the difference between the current command value and the current detection value I _d, and 125 is a current deviation amplifier, the output of which serves as a control signal for the AC / DC converter 9. The operation of this circuit is such that in the current deviation amplifier 125, the AC / DC converter 9 is adjusted so that the current I _d flowing through the converter matches the current command value.
Is controlled, and the reactive power deviation amplifier 122 sets the reactive power Q of the photovoltaic power generation system to the reactive power set value Q _0.
It operates so that the current setting value is made to match.

FIG. 5 shows the operating state of the AC / DC converter 9. The horizontal axis of FIG. 5 represents the current flowing through the AC / DC converter, and the vertical axis represents the voltage on the DC side of the AC / DC converter. In the figure, l ₀ shows the voltage-current characteristics of the solar cell, and m ₀ , m ₁ , m ₂ show the operating characteristics of the AC / DC converter.
When the solar energy is equal to or higher than the specified value, the current setting value of the AC / DC converter is I _d0 , the AC / DC converter is in constant current control (or constant power control) operation, and the operating point is O ₀ . Further, when the current setting value is I _d1 , it is O ₁ , and when it is I _d2 , it is O ₂ . However, when the solar energy is below the specified value, the first switch 9 and the second switch 123 are switched from the a side to the b side, and the DC side of the AC / DC converter is short-circuited, so that the DC voltage becomes zero, When the current setting value I _q0 = I _d0 , q ₀ point, when I _q0 = I _d1 , q ₁ point, I _q0
When = I _d2 , the current setting value I _q0 is created according to the q ₂ point and the amount of reactive power required by the AC / DC converter 9, and reactive power control is performed.

As described above, when the solar energy decreases and the photovoltaic power generation system stops, the AC / DC converter controls the reactive power, so even if the AC filter is connected to the grid, Leading current does not flow, and even if the system is lightly loaded, the ferranch effect does not occur, so the voltage rise in the system does not occur.

Although only the AC filter is described as the delay reactive power compensating device for the AC / DC converter in the above-mentioned embodiment, as in the case where the AC / DC converter is composed of the separately excited type AC / DC converter, a phase adjustment such as a stacon other than the AC filter is performed. This is also the case when there is equipment, and the reactive power control of the AC / DC converter compensates for the advanced reactive power of the AC filter and the phasing equipment, so that the reactive power does not flow to the system.

In addition, as a stop command for the photovoltaic power generation system, as shown in FIG.
FIG. 4 shows the case where the stop command from the control device is used. As the stop command, active (reactive) power on the AC output side of the AC / DC converter of the photovoltaic power generation system is detected, and this is less than or equal to the specified value ( In the case of the above), a signal for stopping may be used. Also, when the solar power generation system is operating,
Since the system is operated so that the operating power factor becomes approximately 1, when the solar energy decreases and the solar power generation system stops, the operating power factor of the system decreases. Therefore, the driving power factor may be detected and a signal to stop the driving power factor when the driving power factor falls below a specified value may be used.

FIG. 6 shows another embodiment of the present invention. In the embodiment of FIG. 3, when the sunlight energy is below the specified value, the DC circuit is short-circuited and the AC / DC converter is operated at zero power factor. Batteries etc.) 13
Insert the solar cell to bypass it. Others are the same as in FIG. When the voltage of the battery 13 is V _d ,
The operating power factor cosφ of the AC / DC converter is approximately expressed by the following equation.

cosφ = V _d / (ke) (1) where e is the AC voltage of the AC / DC converter and k is a constant.

In this case, not only reactive power but also active power will be sent to the grid. The operation of the reactive power control is the same as that shown in FIG. 3. Therefore, in this case as well, the solar energy does not fall below the specified value and the ferranch effect does not occur even when the system is under light load, so there is no voltage increase in the system. .

〔The invention's effect〕

According to the present invention, the reactive power control operation of the AC / DC converter of the photovoltaic power generation system allows the reactive power to flow to the grid even when the solar energy is below the specified value and the grid is lightly loaded. Since it does not exist, it is possible to prevent a voltage increase in the grid due to this.

[Brief description of drawings]

Fig. 1 is a configuration diagram of the target photovoltaic power generation system, Fig. 2 is a voltage / current vector diagram during operation of the photovoltaic power generation system,
FIG. 3 is a block diagram of a photovoltaic power generation system according to an embodiment of the present invention, FIG. 4 is a block diagram of the control circuit of FIG. 3, and FIG. 5 is an operation operation explanatory diagram of the AC / DC converter of FIG. FIG. 6 is a configuration diagram of a photovoltaic power generation system according to another embodiment of the present invention. 1 ... Solar cell, 2 ... AC / DC converter, 3 ... Control device,
4 ... Transformer, 5 ... AC filter, 6 ... Transmission line, 7
...... Load, 8 ...... Back power system, 9 ...... Switch, 10
... current detector, 11 ... reactive power detector, 12 ... control device with reactive power control, 121,124 ... adder, 122,125 ... amplifier, 13 ... battery (secondary battery, etc.) ).

Claims (5)

[Claims] 1. A direct current power output from a solar cell is converted into an alternating current power by an AC / DC converter and output, and the output of the AC / DC converter is connected to a power system through an AC filter or a phasing facility. In the solar power generation system, a determination unit that determines whether to operate the solar power generation system to transmit the power from the solar cell to the power system and output a signal (COM) thereof, and bypass the solar cell. A bypass circuit, switching means for switching to the bypass circuit, reactive power detector for detecting reactive power on the AC output side of the AC-DC converter, and reactive power setting means for outputting a command value of reactive power, When the determination means determines that the result is no, the switching means is operated based on a signal from the determination means to switch to the bypass circuit, and the reactive power detector is used. Photovoltaic systems, wherein a detected value of al is so as to control the AC-DC converter such that the command value from the reactive power setting means. 2. The photovoltaic power generation system according to claim 1, wherein the bypass circuit is a DC short circuit. 3. The photovoltaic power generation system according to claim 1, wherein the bypass circuit comprises a secondary battery. 4. The claim 1 according to claim 1, wherein the determining means includes active power detecting means for detecting active power on the AC output side of the AC / DC converter, and based on a detection value from the detecting means. A solar power generation system characterized by being distinguished. 5. The determination unit according to claim 1, further comprising a power factor detection unit for detecting a power factor on the AC output side of the AC / DC converter, based on a detection value from the detection unit. A solar power generation system characterized by being distinguished.