JP3096378B2 - Power supply system start / stop control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for converting the DC power output from a solar cell into AC power by a current control type inverter and controlling the start and stop of a power supply system for supplying power to a load.

[0002]

2. Description of the Related Art In a photovoltaic power generation system, in Japan, a solar power system is installed on a roof of a private house or the like due to a complete commercial power system network and a problem of a land area using the solar cell. A grid-connected photovoltaic power generation system that connects a simple photovoltaic power generation system with a commercial power grid is promising.

FIG. 2 shows an example of a grid-connected photovoltaic power generation system which is an example of a power supply system. The DC power output from the solar cell 1 is converted into AC power by the inverter 2 and supplied to the commercial power system 3 and the load 4. An interconnection relay 5 is provided between the inverter 2 and the commercial power system 3 to interconnect with and disconnect from the commercial power system. Connected to the output terminal of the solar cell 1 are a backflow prevention diode 6, a DC capacitor 7 for suppressing fluctuations in input power to the inverter 2, and a DC input current detection CT8. The system control circuit 14 controls the operating point of the solar cell from the DC voltage and the DC current, and controls the start and stop of the system interconnection system. As a method of controlling the operating point of the solar cell, a method of controlling the operating point assuming that the voltage of the operating point at which the maximum power is taken out is constant, or a method of tracking the maximum power point to use the output power of the solar cell more effectively. A method or the like is used.

[0004] In the system interconnection system, when an abnormality occurs on the system interconnection system side or the commercial power system side or when the amount of solar radiation is zero at night or the like, the inverter 2 is stopped and the interconnection relay 5 is turned off.
To disconnect the grid-connected system from the commercial power system, and when the power returns from normal to normal, or when the amount of solar radiation at dawn rises from zero, the inverter 2 is started, and The relay 5 is turned on to connect the system interconnection system to the commercial power system.

Conventionally, the system interconnection system is started and stopped when the DC voltage of the DC capacitor 7 at the output terminal of the solar cell 1 exceeds a set value for start, and falls below a set value for stop. Had to be stopped if it had. However, in the morning, and during low solar radiation such as in the evening,
Since the DC voltage of the DC capacitor 7 may be lower than the set value for stop, and once the stop, the solar cell open-circuit voltage is equal to or higher than the set value for start.
There is a problem that the device is started immediately, and the stop operation and the start operation are frequently repeated, which adversely affects the reliability of the device.

To solve this problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 64-1480,
Rather than starting immediately when the DC voltage of the power supply exceeds the set value for startup, or immediately stopping when the DC voltage falls below the set value for stop, a start-up that responds to fluctuations in the amount of solar radiation by providing a delay time And a method of stopping, and a method of
In 56313, as shown in FIG. 3, the DC side relay 21 is provided in parallel with the output terminal of the solar cell 1, the DC side relay 21 is closed when the inverter 2 is stopped, and the output of the solar cell 1 is measured by the short-circuit current. When there is sufficient solar cell output, a method is adopted in which the DC relay 21 is opened to activate the inverter 2 and the interconnection relay 5 is turned on to operate the interconnection system.

[0007]

However, in the former method, the problem is not solved only by slightly reducing the number of times of starting and stopping, and in the latter method,
Since the solar cell output is directly measured, the problem of repeating the stop operation and the start operation is avoided, but the DC relay 21 itself involves a mechanical operation, and the DC relay 21 becomes large. However, there is a problem that the cost and size are greatly affected.

When the maximum power point tracking method is used to control the operating point of the solar cell, the vicinity of the maximum power point on the solar cell output curve becomes gentle when the solar radiation is low, and the detection accuracy of the maximum point decreases. Therefore, there is a problem that the set value for temporarily stopping the system may be temporarily reduced. However, such a problem cannot be avoided by the above-described means.

In order to solve these problems, the present invention suppresses the repetition of starting and stopping operations of a power supply system without using a mechanical operating device, and makes effective use of a solar cell output at low solar radiation. It is another object of the present invention to provide a control device that stably starts and stops the power supply system.

[0010]

SUMMARY OF THE INVENTION The present invention is an apparatus for controlling the start and stop of a power supply system for converting DC power output from a solar cell into AC power by an inverter and supplying power to a load. there are, a detector for detecting a DC voltage and the DC current of the solar cell, and the maximum power point tracking unit for determining the solar cell maximum power point from the DC voltage and the DC current detected by the detection unit, for controlling the inverter a sinusoidal pattern control unit for generating a sine wave pattern as a reference signal, a sine wave pattern adjustment unit for switching operation of the sinusoidal pattern control unit, a signal from the detecting unit, the system startup setting value A system start / stop control unit that starts the system when the value exceeds the value, and stops the system when the value falls below the set value for system stop.
The sinusoidal pattern adjustment unit DC voltage from the detector
If the detected signal is less than the set value for sine wave pattern adjustment set so that the set value for system stop <the set value for sine wave pattern adjustment <the set value for system start, the adjustment operation is performed. the signal input to the sinusoidal pattern control unit, if they exceed a sinusoidal pattern adjustment settings by entering the tracking operation signal to the sinusoidal pattern control unit, the sinusoidal pattern controller tracking operation signal When receiving the adjustment operation signal, a sine wave pattern that maximizes the output from the solar cell is output when receiving the adjustment operation signal. A power supply system stop / start controller that outputs a small sine wave pattern is provided.

As the signal of the detection section, the current and voltage values may be used as they are, or may be converted into signals that allow the current and voltage values to be known. As a method of generating a sine wave pattern in the sine wave pattern control unit, for example, a method of storing a plurality of sine wave patterns of different amplitudes in a memory in advance and reading out the sine wave pattern, or a method of generating a basic sine wave A method of generating a sine wave pattern by multiplying the pattern by an amplitude value is exemplified. The sine wave pattern having a predetermined amount of small amplitude output during the adjustment operation is defined as an amplitude value that is sufficient to exceed the set value for sine wave pattern adjustment again by moving the operating point of the solar cell to the open voltage side. Is a sine wave pattern in which is reduced. Stopping and starting the system means starting and stopping the inverter and connecting and disconnecting a relay to a load that supplies power. As a method of outputting a sine wave pattern such that the output from the solar cell becomes maximum, for example, a sine wave pattern prepared in advance is sequentially output, and a point at which the output of the solar cell at that time becomes maximum is obtained. There is a way to find out.

The above-mentioned load is a device using an alternating current,
It is a commercial power system, another existing power system, or the like, and may be connected to a single system or a plurality of systems.

[0013]

According to the present invention, the amount of insolation is reduced in the evening or the like by setting the DC voltage set value in the relation of "system stop set value <sine wave pattern adjustment set value <system start set value". As the voltage of the solar cell operating point that is tracking near the maximum point gradually decreases and falls below the set value for sine wave pattern adjustment, the sine wave pattern adjustment unit forcibly adjusts the amplitude of the sine wave pattern. A signal is generated to generate another sinusoidal pattern that is quantitatively reduced. With this signal, the sine wave pattern control unit
The generation of the sine wave pattern in which the output of the solar cell is maximized by the signal of the maximum power point tracking unit is stopped once, and the sine wave pattern in which the amplitude value is reduced by a predetermined amount is generated. As a result, the solar cell operating point temporarily moves from the vicinity of the maximum point to the open voltage side,
The solar cell operating point voltage exceeds the set value for sine wave pattern adjustment, the system is prevented from stopping, and the tracking operation of the maximum power point of the solar cell is started again.

However, if the amount of solar radiation is not sufficient, the value will be less than the set value for the sine wave pattern adjustment near the maximum point .
Again, the sine wave pattern controller generates a sine wave pattern with the amplitude value reduced by a predetermined amount. By repeating this operation, the system operates until the operating point voltage of the solar cell falls below the sine wave pattern set value when the sine wave pattern with the smallest amplitude value is input among the sine wave patterns generated by the sine wave pattern control unit. Avoid falling below the set value for stop.
Thereafter, when the amount of solar radiation further decreases and the solar cell operating point voltage falls below a set value for system stop smaller than the set value for sine wave pattern adjustment, the system start / stop control unit stops the inverter and shuts off the relay, and the power Shut down the supply system.

Also, when the system is started in the morning or the like, once the interconnected system is started, even if the amount of solar radiation is not sufficient, the amplitude of the sine wave pattern is forcibly set to a predetermined amount in the same manner as when the system is stopped. By using a different sine wave pattern with a smaller value, the operating point of the solar cell is temporarily moved from the vicinity of the maximum point to the open-circuit voltage side, thereby avoiding a value lower than the set value for system stop.

As described above, it is possible to prevent the system from falling below the set value for system stoppage when the amount of solar radiation immediately after start-up or immediately before stop is not sufficient, so that the system can be started and stopped stably.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the power supply system start / stop control device according to the present invention will be described below in detail with reference to FIG.

FIG. 1 is a diagram showing a system interconnection inverter system including a start / stop control device according to the present invention.

Solar cell 1 (output 3.5 kW, open circuit voltage 2
The output terminal is connected to a backflow prevention diode 6, a DC capacitor 7 for suppressing fluctuations in the input power to the inverter 2, and a DC input current detection CT8. The AC output current detection CT 9 is connected. As a control circuit of the grid interconnection system, an error amplification signal control circuit 10 that outputs an error signal from an output current signal from the inverter 2 and a sine wave pattern signal output from the sine wave pattern control unit, a triangular wave signal control circuit 11, From the output signal from the error amplification signal control circuit 10 and the output signal from the triangular wave signal generation circuit, P
PWM modulation control circuit 12 for generating a WM modulation signal, PWM
There are an inverter drive control circuit 13 that controls the inverter based on a signal output from the M modulation control circuit 12, and an interconnection system start / stop control device 14 of the present invention.

Further, the interconnection system start / stop controller 14
Are a DC voltage / current detector 15 for detecting the DC voltage and DC current of the solar cell, a maximum power point tracking unit 16 for determining the maximum power point based on the DC voltage and DC current output from the DC voltage / current detector 15 (sampling The time is set to 1/120 second), and the sine wave pattern adjusting unit 17 for adjusting the amplitude of the sine wave pattern (the sine wave pattern adjustment setting value is 160
V), a sine wave pattern control unit 18 (sine wave pattern control unit) that generates a sine wave pattern to be input to the error amplification signal control circuit 10 based on a signal output from the maximum power point tracking unit 16 or the sine wave pattern adjustment unit 17 The generation method is
A method in which 200 kinds of sine wave patterns obtained by equally dividing the amplitude of a sine wave having an amplitude of 10 V into 200 steps are stored in ascending order of amplitude, and a necessary sine wave pattern is read out. If the wave pattern value is lower than the set value, the sine wave pattern used at that time is 5
A system stop control means for simultaneously stopping the inverter 2 and shutting off the interconnection relay 5 by means of a DC voltage;
After starting the inverter 2, after a set time,
System start / stop control unit 19 also serving as a system start control unit for turning on the interconnection relay 5 (set to a system stop set value of 150 V and a system start set value of 170 V)
Consists of The DC power output from the solar cell 1 is converted into AC power by the inverter 2 and supplied to the commercial power system 3 and the load 4. An interconnection relay 5 is provided between the inverter 2 and the commercial power system 3 to connect to and disconnect from the commercial power system.

In this system interconnection system, P
The inverter 2 is switched by the WM-modulated pulse signal to control the output current of the inverter 2 so that a sine wave current flows, and to supply the output power from the solar cell 1 to the commercial power system 3 and the load 4. doing. At this time, the solar cell operating point is tracked near the maximum point on the solar cell output characteristic curve in order to maximize the output of the solar cell 1, but the solar cell operating point is controlled by a PWM pulse signal for switching the inverter 2. Is performed by changing the duty ratio. Since the duty ratio of the PWM pulse signal is determined by the amplitude of an arbitrary sine wave pattern read out by the sine wave pattern control unit 17, by controlling the amplitude of the sine wave pattern, the control of the solar cell operating point and the inverter 2 The magnitude of the output current is determined.

First, the control operation of the sine wave pattern will be described. First, the sine wave pattern having the minimum amplitude value is read from the sine wave patterns stored in the sine wave pattern control unit. At this time, the output of the inverter becomes minimum,
At this time, the input voltage and input current to the inverter of the solar cell are detected by the DC voltage / current detection unit 15, the output power of the solar cell is calculated from the product thereof, and the value is temporarily stored in the maximum power point tracking unit. It is stored in the storage unit. Next, a sine wave pattern having a one-step amplitude value larger than the amplitude value of the previous step is read out, the same operation is repeated, the output power from the solar cell is calculated by the maximum power tracking unit, and stored in the maximum power point tracking unit. .

Next, the previous output power value is compared with the current output power value. If the current output power value is larger, the larger current power value is stored in place of the previous power value and stored for one more step. A sine wave pattern with a large amplitude value is read. Then, the output power at this time is detected, and the same processing as the above-described processing is repeated. Conversely, if the current output power is smaller, a sine wave pattern with one step smaller amplitude value is read. Then, the output power value at that time is calculated, and the same processing as the above-described processing is repeated. In this way, at the time of starting the system, the maximum power point of the solar cell was tracked by selecting a sine wave pattern corresponding to the output of the solar cell.

Next, a stop operation when the amount of solar radiation decreases in the evening or the like, or an operation to avoid a malfunction due to a decrease in detection accuracy will be described.

As the amount of solar radiation decreases, the vicinity of the maximum point on the solar cell output characteristic curve becomes gentle, and the detection accuracy of the maximum point decreases. Therefore, the fluctuation range of the solar cell operating point tracking near the maximum point is widened, and the operating point voltage of the solar cell may temporarily fall below the sine wave pattern set value. Also, the voltage of the solar cell itself falls below the set value of the sine wave pattern. When the operating point voltage of the solar cell falls below the set value for sine wave pattern adjustment in this manner, the signal of the sine wave pattern adjustment unit 17 causes the sine wave pattern of the sine wave pattern determined by the signal of the maximum power point tracking unit 16 to be used. The reading is stopped, and the sine wave pattern in which the sine wave pattern is forcibly reduced in five steps in the direction of smaller amplitude is read.

As a result, the solar cell operating point temporarily moves from the vicinity of the maximum point to the open voltage side, and the solar cell operating point voltage becomes larger than the set value for sine wave pattern adjustment. afterwards,
The maximum operating point of the solar cell starts to be tracked again starting from the sine wave pattern having the reduced amplitude value in the five steps. However, due to the low solar radiation, the solar cell operating point voltage falls again below the set value for the sine wave pattern adjustment near the maximum point, but as a result of the processing by the sine wave pattern adjusting unit 17, the solar cell operating point voltage becomes The set value for system stop does not fall below the set value for system stop. Thereafter, while the amount of solar radiation decreases to a certain value, the above-described phenomenon is repeated, and the operation of the grid interconnection system is stopped without stopping the grid interconnection system, that is, stopping the inverter 2 and shutting off the interconnection relay 5. It was conducted.

When the amount of solar radiation further decreases and the amplitude of the sine wave pattern cannot be further reduced, the solar cell operating point voltage falls below the system stop set value which is smaller than the sine wave pattern adjustment set value. The system start / stop controller 19 controls the stop of the inverter 2 and the connection relay 5
Was shut down and the grid interconnection system was shut down.
On the other hand, when the amount of solar radiation rises from zero and gradually increases in the morning or the like, when the solar cell open-circuit voltage exceeds the system start set value, the system start / stop control unit 19 first starts the inverter 2. Do. And after a set time,
When the interconnection relay 5 is turned on and the connection with the commercial power system 3 is to be performed, a voltage drop occurs when the inverter 2 is started. Is below the set value for system startup and the interconnecting relay 5
Without turning on the inverter, the inverter 2 is restarted and the operation is started again. Thereafter, this state is repeated. During this time, the amount of solar radiation further increases, and when the increase in the solar cell open-circuit voltage exceeds the voltage drop when the inverter 2 is started, the start of the inverter 2 and the connection of the interconnection relay 5 And the interconnection between the system interconnection system and the commercial power system 3 is performed.

Then, the maximum power point tracking unit 16 starts tracking the solar cell operating point at the maximum point on the solar cell output characteristic curve. May be less than the set value for the sine wave pattern adjustment. Also in this case, by repeating the same operation as the stop operation in the evening or the like, the solar cell operating point voltage did not fall below the system stop set value. Therefore, it has been found that the power supply system start / stop control device of the present invention is also effective for stable start-up of the power supply system.

[0029]

As described above, by using the power supply system start / stop control device of the present invention, it is possible to prevent the start / stop phenomenon that is frequently repeated when the amount of solar radiation is low, and to improve the reliability of the device. Start and stop operations of the system interconnection system can be performed stably without adversely affecting the system.

[Brief description of the drawings]

FIG. 1 is a diagram of a grid-connected inverter system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a first example of a conventional system interconnection system start / stop control device.

FIG. 3 is a diagram showing a second example of a conventional system interconnection system start / stop control device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 solar cell 2 inverter 3 commercial power system 4 load 5 interconnection relay 6 backflow prevention diode 7 DC capacitor 8 CT for detecting DC input current 9 CT for detecting AC output current 10 Error amplification signal control circuit 11 Triangular wave signal control circuit 12 PWM modulation Control circuit 13 Inverter drive control circuit 14 System control circuit 15 DC voltage / current detection unit 16 Solar cell maximum power point tracking unit 17 Sine wave pattern adjustment unit 18 Sine wave pattern control unit 19 System start / stop control unit 20 DC side relay

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsukasa Takebayashi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-6-35555 (JP, A) JP-A-2-2 156313 (JP, A) JP-A 64-1480 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G05F 1/67

Claims (1)

(57) [Claims] 1. A in-current power output from the solar cell
Converter by converting into AC power, a device for controlling the start and stop of the power supply system supplying power to a load, a detector for detecting a DC voltage and the DC current of the solar cell, by the detection unit a maximum power point tracking unit for determining the solar cell maximum power point from the detected DC voltage and DC current, the sinusoidal wave pattern control unit for generating a sine wave pattern as a reference signal for controlling the inverter, the sinusoidal pattern a sinusoidal pattern adjustment unit for switching the operation of the control unit, the signal from the detection unit, when exceeded system startup settings to start the system, the system when below the system stop set value and the system start-stop control section for stopping, made, the sinusoidal pattern adjustment unit DC voltage from the detector
If the detected signal is less than the set value for sine wave pattern adjustment set so that the set value for system stop <the set value for sine wave pattern adjustment <the set value for system start, the adjustment operation is performed. the signal input to the sinusoidal pattern control unit, if they exceed a sinusoidal pattern adjustment settings by entering the tracking operation signal to the sinusoidal pattern control unit, the sinusoidal pattern controller tracking operation signal When receiving the adjustment operation signal, a sine wave pattern that maximizes the output from the solar cell is output when receiving the adjustment operation signal. A power supply system start / stop control device for outputting a small sine wave pattern.