JPH05224765A - Method for controlling power factor - Google Patents

Abstract

PURPOSE:To enable high-accuracy output power factor control in an inverter control system to be operated while being interlocked with another power source (such as a commercial power source, for example.). CONSTITUTION:An operational amplifier 25 is provided to convert a U-V phase voltage to a rectangular wave through a transformer 26, and an operational amplifier 24 is provided to convert a W phase current to a rectangular wave through a CT 28. These two rectangular waves are inputted through two EX-OR circuits 21 and 22 and a NOT circuit 23 to an adder circuit 16 and added. Further, a power factor angle target value and the detected value of the adder circuit 16 are inputted through adder circuits 15 and 13 and an amplifier 14 to a multiplication circuit 12 and multiplied a power signal from a power detection circuit 11 or an active/reactive current signal, and the detected value is defined as a signal for power factor angle for power factor control in respect to the target value of the voltage signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to co-gene (Co-Gene).
The present invention relates to a method for controlling a power factor of an inverter output in an inverter control system that performs AC conversion of power generated by a fuel cell, a solar cell, or the like in a ration system and supplies the AC power, and that operates in parallel with a commercial AC power supply.

[0002]

2. Description of the Related Art FIG. 3 is a block circuit diagram showing a conventional power factor control method for an inverter. In FIG.
The three-phase inverter 1 is connected in parallel with another power source via the interconnection reactor 4 and supplies electric power to the load 6. The control of the three-phase inverter 1 is performed by controlling the other power supply voltage (target value) and 3 detected by the transformer 2 connected to the other power supply circuit.
The inverter output voltage detected by the transformer 3 connected to the output circuit of the phase inverter 1 is added to the adder circuit 10,
This is performed by the voltage control signal added in the circuit configured by 9, 7 and the amplifier 8. In addition, the power factor detection signal of the three-phase inverter 1 includes the U-V phase line voltage detected by the transformer 120 and the W-phase current (resistor 121 is a dummy resistor) detected by CT5 in the transformer 122. Rectifier circuits 123 and 124, two resistors 1
25 and 126, and two capacitors 127 and 128
Is detected by the circuit configured by.

The voltage vector and the current vector are as shown in FIG. 4, and the DC voltage difference between them is detected as the power factor. This DC differential voltage is fed back to the adder circuit 129 which inputs the power factor reference value, and the detected value of the adder circuit 129 is input to the adder circuit 10 as a voltage compensation amount for the voltage target value via the amplifier 130.

[0004]

In an inverter that operates in cooperation with another power source such as a commercial power source, the output power factor of the inverter is determined by the output voltage of the inverter and is not influenced by the power factor of the load. That is, when the output voltage of the inverter is increased, the power factor deteriorates with the delayed power factor, and the power factor with which the output voltage of the inverter is decreased deteriorates with the advanced power factor. Therefore, controlling the output power factor of the inverter controls the output voltage of the inverter according to the target power factor.

In the conventional power factor detection method shown in FIG. 3, when the power factor is 1 (the power factor control angle is 0), the target value becomes 0, so that the control can be performed. That is, the power factor angle, which is the voltage difference from that in FIG. 4, becomes zero. However, when the target value is other than the power factor of 1 and when the load is light and when the load is heavy, the voltage changes depending on the magnitude of the current vector, and the difference voltage also changes, and the accuracy cannot be kept constant. The operation with a power factor of 1 is most efficient for the inverter, but the power factor of a general load is often a delayed power factor. Therefore, unless reactive power is supplied from the inverter together with active power, a large amount of reactive power must be absorbed from the commercial power supply. That is, it is necessary for the inverter to be able to supply reactive power according to the load power factor, and to be able to be interconnected with the commercial power source in this state. The present invention has been made in order to solve the drawbacks of the prior art, and provides a power factor control method capable of highly accurate power factor control even when the power factor is not 1.

[0006]

In order to solve the above-mentioned problems, one example of the power factor angle detecting method used in the present invention is a line voltage, a waveform (for example, U-V phase) and a phase current waveform (for example, a waveform). By taking the EX-OR of two square waves made from the (W phase) and smoothing the output signal, a power factor angle signal that is hardly influenced by the change in the amount of current is detected. Further, this power factor signal is multiplied by the output power signal (or the active / reactive current signal) of the inverter to generate a highly accurate power factor control signal corresponding to the change of the output voltage of the inverter. Although the method of detecting the power factor angle is described here, the control is also possible by detecting the power factor and setting the power factor of 1 to 0v.

[0007]

[Operation] 0 of the current signal detected from the inverter output circuit
The operational amplifiers 24 and 25 are based on the point v and the point 0v of the voltage signal.
In this case, a square wave is created in EX-OR with each other.
By comparing through the circuits 21 and 22, the power factor angle of the inverter output, which is hardly influenced by the magnitude of the current amount, is detected.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block circuit diagram showing an embodiment of the present invention. In FIG. 1, the transformer 2, the 3, the adder circuits 7, 9, 10 and the amplifier 8 are the same as those in the conventional power factor angle detection method, and therefore description thereof will be omitted.

The detection current of the CT 28 having two dummy resistors provided in the W phase is converted into a square wave in the operational amplifier 24, and the U-V phase line voltage is square wave in the operational amplifier 25 via the transformer 26. Is converted to. The square wave of the current signal output from the operational amplifier 24 is EX-OR.
The square wave of the voltage signal that is input to one of the input terminals of the circuit 21 and the EX-OR circuit 22 and that of the output of the operational amplifier 25 is input to the other input terminal of the EX-OR circuit 21 and also via the NOT circuit 23. It is input to the other input terminal of the EX-OR circuit 22. EX-OR circuits 21 and 22
Output signal of the resistor 17 and the capacitor 19 and the resistor 18
And is input to the addition circuit 16 via the capacitor 20.
Since the polarities of the output signals from the EX-OR circuit 22 are inverted and added, the output signal of the adding circuit 16 becomes the power factor angle detection signal of the inverter output. That is, 0v of the voltage signal
By detecting 0v of the current signal, forming a square wave with 0v as a reference, and comparing the square waves with each other, a power factor angle detection signal that is less affected by the magnitude of the current amount can be obtained. This detection signal is input to the addition circuit 15 together with the power factor angle target value, and the detection signal is added together with the power factor angle target value in the addition circuit 13 via the amplifier 14.

The power detection circuit 11 based on the two power meter method is U-
The V-phase voltage, the V-W-phase voltage, the U-phase current via CT30, and the W-phase power via CT29 are input, and a power signal (or active / reactive current signal) is sent to the multiplier 12. In the multiplication circuit 12, the power factor control signal output from the addition circuit 13 is multiplied by the power signal (or the active / reactive current signal) output from the inverter of the power detection circuit 11 to improve the responsiveness of the control system. .

FIG. 2 is a vector diagram in the case of delay-controlling the inverter output. The inverter output current I, its effective current component and reactive current component are Ia and Ir, respectively, and the power factor angle is θ. If the output voltage V of the inverter based on this current is v as the total output voltage of the three-phase inverter 1 with the voltage loss jωLIa in the interconnection reactor 4 due to the active current component and the voltage loss jωLIr in the interconnection reactor 4 due to the reactive current component The voltage vector diagram of the inverter output shown in FIG. 2 is obtained.

[0013]

As described above, the power factor control method according to the present invention detects the power factor angle of the inverter output from the line voltage and the phase current of the inverter output and detects the power signal or the current signal of the inverter output. Then, the power factor angle detection signal is multiplied to detect the power factor angle control signal corresponding to the change in the output voltage of the inverter. Therefore, it is possible to perform highly accurate output power factor control in an inverter that is interconnected with another power source such as a commercial power source.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing a power factor control method according to the present invention.

FIG. 2 is a vector diagram of current and voltage of an inverter output.

FIG. 3 is a block circuit diagram of a conventional power factor control method.

FIG. 4 is a relationship diagram of a voltage vector and a current vector in the power factor detection method.

[Explanation of symbols]

 1 3 phase inverter 2,3,26 transformer 4 interconnection reactor 7,9,10,13,15,16 adder circuit 12 multiplier circuit 8,14 amplifier 21 and 22 EX-OR circuit 23 NOT circuit 24,25 operational amplifier 28, 29,30 CT

Claims (1)

[Claims] 1. A method for controlling a power factor of an inverter output in an inverter control system that is interconnected with a three-phase alternating current power supply, wherein a line voltage (eg, U-V phase) and a phase current (eg, W phase) of the inverter output are used. The power factor of the inverter output is detected, the power factor detection signal is fed back to the power factor target value to correct the power factor target value, and the correction value and the power signal or valid / invalid detected from the inverter output. A power factor control method, comprising: multiplying with a current signal; and using a detection value obtained by the multiplication as a voltage compensation value (power factor angle signal) for power factor control with respect to a target value of a voltage signal.