JPH04183228A - Reverse power flow preventing method for bilateral power converter - Google Patents

Abstract

PURPOSE:To prevent occurrence of reverse power flow by detecting effective power of a commercial power supply, and driving solar cells at an optimal operating point when thus detected effective power has a positive value whereas feeding a current command value, obtained by subtracting a value proportional to the effective power corresponding to thus detected effective power from a current command value at the optimal operating point, if thus detected effective power has a negative value. CONSTITUTION:Since effective power of a commercial power supply 1 has a positive value, a function generator 94 outputs 0V in a range where the effective power has a positive value and solar cells 3 are controlled to operate at an optimal operating point by means of a CPU 91 through a control means 9. When the output of the solar cells 3 increases to cause power flow toward the commercial power supply 1 and the effective power decreases to have a negative value, an adder 97 subtracts a value proportional to the reduction of the effective power from a current command value fed from a multiplier 96. The difference is then fed to a bilateral power converting means 5 in order to control the effective power of the commercial power supply 1 to stay in positive state.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a method for preventing reverse power flow in a bidirectional power converter that supplies power to a DC load by using both power generated by a solar cell and commercial power.

(b) Conventional technology Conventionally, when using solar battery private power generation equipment, there have been methods to install a storage battery, charge the energy generated by the solar battery to the storage battery, and use the power effectively, and to connect the solar battery in parallel with the commercial power system. A device is used that operates the generator and returns the generated power to the grid for effective use.

However, when using storage batteries, there are problems in terms of cost and maintenance of the storage batteries themselves, and even when solar cells are operated in parallel with the grid, technical and legal issues remain, and it is still at the stage of practical use. has not yet been reached.

Therefore, solar cells are connected to a commercial power grid after converting direct current to alternating current through a power conversion device such as an inverter, and the solar cells are controlled so that the power supplied to the pond does not exceed the load power. , devices that prevent reverse power flow from flowing into the grid are being considered.

Conventionally, such devices use a monitoring solar cell to
The solar cells were controlled to track the optimal operating point by observing in advance the output characteristics under different solar radiation conditions and storing this data in a microcomputer, etc.

However, due to aging of solar cells and changes in the surrounding environment,
There was a discrepancy between the data obtained from the solar cells in the device and the monitoring solar cells, and it could not be said that optimal control was being performed.

In addition, a device disclosed in Japanese Patent Publication No. 56-19384 detects the active power and reactive power of the power system,
The amplitude of the inverter output voltage and the phase difference between the system voltage and the inverter output voltage are controlled so that these values are equal to the set values. However, if the amplitude and phase difference of the output voltage are changed, the active power and the reactive power change in conjunction with each other, making accurate control difficult.

(c) Problems to be Solved by the Invention The problems to be solved by the present invention are to accurately prevent the occurrence of reverse power flow for safe and stable grid-connected operation of power converters connected to the commercial power supply system. The goal is to prevent it.

(d) Means for Solving the Problems The present invention includes a commercial power source, a solar cell, an AC load connected to the commercial power source, and a system that converts the AC power of the commercial power source into direct current, and converts the AC power of the commercial power source into direct current. a bidirectional conversion means capable of converting DC power to AC; a DC load that inputs the DC power of the large FIAt pond and inputs AC power of the commercial power source via the bidirectional conversion means; A bidirectional power conversion device comprising: a control means for adjusting the input/output of the bidirectional conversion means so as to operate the solar cell at an optimum operating point; and an active power detection means for detecting the active power of the commercial power source. and while the detection value of the detection means is a positive value, the control means adjusts a current command value for the solar cell side input of the bidirectional power conversion means to drive the solar cell at an optimal operating point. , when the detected value becomes negative, a value proportional to the active power corresponding to the detected value is subtracted from the current command value at the optimum operating point, and a current command value is supplied to the bidirectional power conversion means. .

(E) When the active power of the active commercial power source is detected and the value becomes negative, a current command value obtained by subtracting a value proportional to the active power from the current command value is supplied to the bidirectional power conversion means. death,
The effective power is controlled to be positive.

(f) Example The present invention will be described in detail below with reference to an embodiment of the drawings.

FIG. 1 is a block circuit diagram showing a bidirectional power converter. In the figure, 1 is a commercial power supply, 2 is an AC load driven by the AC output of the commercial power supply 1, 3 is a solar battery, and 4 is a DC load with a built-in inverter circuit driven by the DC output of the solar battery 3. It's a load. Reference numeral 5 denotes a bidirectional power conversion means constituted by a rectifier that enables power flow, and the negative input/output side is connected to the commercial power supply 1 and the AC output is converted to DC to convert the AC output into DC load 4. The other input/output side is connected to the solar cell 3 to play the role of converting the surplus DC power into AC. 6 is a first current detector for detecting the output current of the bidirectional power converting means 5; 7 is a second droplet detector for detecting the output current of the solar cell 3; and 8 is the output current of the commercial power source 1. An active power detector 9 detects the active power by detectors 81 and 82 that detect the active power and the voltage, and 9 indicates the detection values of the active power detector 8, the two current detectors 6.7, and the commercial power source 1, which will be described later. This control means generates a current command value for adjusting the solar cell side input current value of the bidirectional power conversion means 5 based on the voltage and the voltage of the solar cell 3.

The control means 9 is a central processing unit that checks whether the solar cell 3 is operating at maximum power based on the detected values of the second droplet detector 7 and the voltage detector 10, calculates a necessary gain, and outputs it. 91, a D/A converter 92 that converts the digital output of the central processing unit 91 into an analog signal, a bandpass filter 93 that detects the fundamental wave component of the voltage of the commercial power supply l, and the active power detector 8. a function generator 94 that receives the detection output of and generates an output according to a function to be described later, a triangular wave generator 95 that generates a reference triangular wave, the D/A converter 92, and the bandpass filter 9.
a multiplier 96 that calculates the current command value of the bidirectional conversion means 5 by multiplying the voltage fundamental wave component of the commercial power supply 1 by the gain by the output of the D/A converter 92 and the function generator 94; , and an adder 97 for obtaining a signal obtained by subtracting a correction signal based on the output current of the bidirectional power conversion means obtained through the droplet detector 6 and the active power from the current command value by the output of the multiplier 96; The comparator 98 compares the output of the generator 97 with the output of the triangular wave generator 95 and outputs a switching pulse to the bidirectional power conversion means 5.

As shown in FIG. 2, the pre-M self-function generation 594 generates Ov, when the detected value of the active power is a positive value, according to the detected value of the active power.
When the value is negative, a positive voltage output proportional to the value is generated. In the figure, the horizontal axis represents the detected value (input) of the active power detector 8, and the vertical axis represents the output of the function generator 94, which has a characteristic that the output increases in proportion only when the input is negative.

In the bidirectional power conversion device having the above configuration, since the active power is normally a positive value due to the output of the commercial power source 1, the function generator 94 outputs O to O in the range where the active power is a positive value. ', during which time the central processing unit 91
Control is performed via the control means 9 so that the solar cell 3 maintains the optimum operating point.

On the other hand, when the output of the solar cell 3 increases and reaches a value that causes a power flow to the commercial power source 1 side, and the active power decreases and takes a negative value, a value proportional to the amount of decrease The current command value is subtracted from the current command value by the adder 97, and the subtracted current command value is input to the bidirectional power conversion means 5, which is controlled to maintain the active power of the commercial power source 1 in a positive state. . Therefore, from the solar cell 3 side to the commercial power supply 1
As a result, the reverse flow to the side is suppressed.

(G) Effects of the Invention As described above, the present invention is provided with an active power detection means for detecting the active power of a commercial power source, and while the detection value of the detection means is a positive value, the control means The current command value for the solar cell side input of the power conversion means is adjusted to drive the solar cell at the optimum operating point, and when the detected value becomes negative, the current command value at the optimum operating point is changed to the detected value. Since the current command value is supplied to the bidirectional power conversion means by subtracting a value proportional to the corresponding active power, the active power is detected and a limiter is applied to the supplied current from the bidirectional conversion means to the commercial power source. This makes it possible to accurately prevent the occurrence of reverse power flow, and to enable safe and stable grid-connected operation of the solar cells and bidirectional power conversion means linked to the commercial power source.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing the basic structure of a bidirectional power converter using the reverse power flow prevention method of the present invention, and FIG.
This figure shows the input/output characteristics of a function generator using the output of the active power detector shown in the figure as an input signal. 1 Commercial power source, 2 AC load, 3 Solar battery, 4 DC load, 5 Bidirectional power conversion means, 8 Active power detector, 9 Control means.

Claims (1)

[Claims] (1) A commercial power source, a solar cell, an AC load connected to the commercial power source, and both capable of converting the AC power of the commercial power source into DC and the DC power of the solar cell into AC. a direct current converting means, a direct current load inputting the direct current power of the solar cell and inputting the alternating current power of the commercial power source via the bidirectional converting means; A bidirectional power conversion device comprising a control means for adjusting input and output of the bidirectional conversion means, and an active power detection means for detecting the active power of the commercial power source, and a detection value of the detection means is a positive value. For a certain period of time, the control means adjusts the current command value for the solar cell side input of the bidirectional power conversion means to drive the solar cell at the optimum operating point, and when the detected value becomes negative, the optimum operation is performed. A method for preventing reverse power flow in a bidirectional power converter, characterized in that a current command value is supplied to the bidirectional power converting means by subtracting a value proportional to the active power corresponding to the detected value from the current command value at a point.