JPH0640706B2 - AC power supply - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC power supply device that operates a plurality of motor generators in parallel, and more specifically, when the motor generator is changed from an independent operation state to a parallel operation state. The present invention relates to an AC power supply device that suppresses transient fluctuations in output voltage that occur.

(Problems to be solved by the prior art and the invention) By operating a plurality of AC generators in parallel, the total power capacity is increased, or a spare AC generator is operated in parallel.
That is, a method is adopted in which redundant parallel operation is performed to enhance reliability as a power source.

When the AC generators are operated in parallel, it is necessary to suppress fluctuations in the output voltage and frequency in order to prevent the load to be fed from being adversely affected.

When a stopped AC generator is started and operated in parallel with the AC generator that is supplying power, unless special measures are taken, the output voltage fluctuates significantly and the load is adversely affected.
In addition, an excessive reactive circulating current may flow between the AC generators to overload the AC generators.

If there is a large phase difference between the output voltage of the AC generator being fed and the output voltage of the started AC generator, even if the frequency and the voltage effective value are the same, the instantaneous voltage level According to the difference, the reactive circulating current flows between the AC generators, and the voltage fluctuation increases.

In order to suppress the voltage fluctuation when the parallel operation is turned on, a method of inserting impedance has been conventionally used.

FIG. 5 is a block diagram of a conventional AC power supply device. In the figure, MG1 and MG2 are motor-generators in which an induction motor and a generator are integrated. Motor generator MG1,
The MG2 is driven by the electric power of the commercial power supply AC, synthesizes the generated electric power, and supplies AC power to the load L.

Now, when the switches K11, K12, K13 are turned on and only the motor generator MG1 is supplying power, when the motor generator MG2 is operated in parallel, first, the switch K21 is closed and the motor generator MG2 is started. After the output voltage reaches the specified frequency and voltage level, the switch K22 is closed and the parallel operation state is established via the impedance Z2. A current corresponding to the phase difference between the alternating-current generators of the both motor-generators MG1 and MG2 flows through this impedance Z2, so that the slip of the induction motors of both the motor-generators MG1 and MG2, and thus the frequency of the alternating-current generator changes. To do. This causes the phase difference to change periodically. The current is monitored and when the current becomes small, that is, when the phase difference is close to zero, the switch K23 is closed to complete the parallel operation input.

In this conventional example, it is necessary to provide an impedance Z2 using a reactor or a resistor and a switch K23,
In addition, there is a drawback in that it is necessary to secure a mounting space for these and perform heat treatment. Further, there is a problem that the above parallel operation requires a high degree of skill.

(Object of the invention) The present invention has been proposed in view of the above-mentioned problems, and does not provide an impedance, a switch, or the like that is used only when the parallel operation of the motor generator is turned on, and does not cause a large fluctuation in the output voltage. An object is to provide an AC power supply device that can be turned on.

(Means for Solving the Problems) In order to achieve the above object, the present invention is directed to an AC power supply device in which a plurality of motor generators that supply electric power to a load via an electromagnetic switch are operated in parallel. And the time when the phase difference between both output voltages of the following motor generator is minimized, and the operation delay time of the electromagnetic switch is added to this,
In a device provided with a control circuit for giving a command to turn on an electromagnetic switch of a later motor generator, the control circuit is provided with an output voltage of a preceding motor generator and an output voltage of a subsequent motor generator, respectively, and converts a sine wave into a square wave. A waveform shaping circuit to be converted, a timer counter provided with a signal from the waveform shaping circuit, extracting a signal with a varying pulse width of the square wave signal from the waveform shaping circuit, and obtaining a time point at which the pulse width becomes minimum; An arithmetic processing circuit (microprocessor) provided with a signal from a timer counter and a signal from a memory that stores the operation delay time of the electromagnetic switch, and detects the output frequency and the phase difference of the preceding and succeeding motor generators. Then, after the phase difference becomes zero, that is, in phase, the time at which the phase becomes the next is estimated, and the operation delay of the electromagnetic switch is based on this point. In which mode of the invention an AC power supply apparatus characterized by sending an operating signal of the electromagnetic switch only early during.

(Operation) According to the present invention, when the two motor generators are operated in parallel, the output voltages of the two motor generators are shaped into waveforms and are compared as square waves, so that there is no waveform distortion or voltage difference. However, the in-phase point can be accurately detected, and the electromagnetic switch can be controlled to be turned on at the moment when the phase difference becomes the smallest.

Conventionally, in order to detect the phase difference between the outputs of the two generators, the voltage waveforms of the outputs are butted to form a beat signal, and the time point when the beat signal becomes zero (minimum) is the same phase. This method has a drawback that the in-phase point cannot be accurately detected if the output voltage has a waveform distortion or a voltage difference.

In the present invention, since the output voltage is shaped into waveforms and then matched with each other as a square wave, the common-mode point can be accurately detected even if there is a waveform distortion or a voltage difference, and the electromagnetic switch is turned on at the moment when the phase difference becomes the smallest. It proposes a controllable device.

(Example) Next, the Example of this invention is described.

1 to 4 show an embodiment of the present invention.
FIG. 1A is a block diagram of the entire device, and FIG. 1B is a block diagram of a signal processing circuit. 2 is a waveform diagram, FIG. 3 is an implementation circuit,
FIG. 4 shows a flowchart.

In FIG. 1, AC is a commercial power source, K1 and K2 are switches, MG1 and MG2 are motor generators, T1 and T2 are waveform shaping circuits that make a sine wave a square wave, M is a memory, μC is a processing circuit, and EX- OR indicates an exclusive OR circuit.

Now, in the figure, the switch K1 is closed and the motor generator MG1 is operating, and the motor generator MG1 is to be operated in parallel with the motor generator MG2.

Figure 1 (a), (b) and FIG. 2, T1 and T2 are converted into a DC voltage signal Y1 and Y2 of the square wave as the input signal a ₂ and b sinusoidal waveform shaping circuit. The processing circuit μC receives the signal Y1 as input, obtains the half cycle 1/2 ₁ of the input voltage a ₂ from the pulse width, and stores the result in the memory M. Just as seeking half cycle 1/2 _second input voltage b from the signal Y2, and stores it in the memory M. Also, from 1/2 ₁ and 1/2 ₂ , the half cycle of beat 1 /
| ₁ - ₂ | computes and stores the result in the memory M. The exclusive OR circuit EX-OR takes the exclusive OR of the signals Y1 and Y2 and outputs a signal α having a varying pulse width of the signals Y1 and Y2. Therefore, when the phase difference between the input signals a ₂ and b is the minimum, the signal α pulse width is the minimum, and when the phase difference is the maximum, that is, when the phase difference is close to 180 °, the pulse width of the signal α is It will be the maximum. The processing circuit μC measures the pulse width of the signal α and determines that the time when the pulse having the minimum width is input is P ₀ , that is, the time when the input signals a ₂ and b are in phase. Next, the delay time ΔT of the electromagnetic switch MS2 stored in the memory M, the half cycle of the beat 1 / |
₁ - ₂ | from _{P 0} (1 / as a base point a _{| 1} - _{2 |} - △ T only in time sends a signal _{P 0} at the time has elapsed, the on signal of the electromagnetic switch which is turned on the electric generator MG2 to a load give.

Next, a circuit diagram of this embodiment is shown in FIG. 3 and a program flow chart is shown in FIG. In these figures, sinusoidal AC voltages (input signals) a ₂ and b are input. Resistors R1, R2, R3, R4 and photo coupler PC
1, PC2 converts into a square wave DC voltage signal. This signal is waveform shaped by a waveform shaping circuit including resistors R5 and R6, capacitors C1 and C2, and Schmitt IC1 and IC2. This output is flip-flop FF1, F
It is converted to a double cycle by F2 and input to the gate of the counter timer CTC.

On the other hand, the input signal a ₂ whose waveform has been shaped into the exclusive OR IC3
The DC voltage signals of b and b are input, the phase difference between the two signals is obtained, and the signal with a varying pulse width is extracted. This signal is input to the gate of the counter timer CTC. The counter timer CTC inputs the clock signal from the oscillator CL,
Only when the gate input is at the H level, the number of pulses of the clock signal is counted. Since the cycle of the clock signal is known in advance, the microprocessor CPU inputs the count number from the counter timer CTC, so that the gate input of the counter timer CTC is at the H level, that is, the sine wave AC voltages a ₂ and b. the period _1/1, 1 /
Ask for ₂ . Then, the contents are stored in the memory M (FIG. 4,).

Next, the pulse signal α, which is the phase difference between the input signals a ₂ and b, is detected, and when it is detected that they are in phase (fourth phase).
Then, the microprocessor CPU calculates the time until it becomes in phase next, based on the contents of the memory M. [1 / |
_{1 - 2 | = (T 1} × T 2) / | T 1 -T 2 | ] (FIG. 4 ,,), minus the operation delay time △ T of the electromagnetic switch which is stored to this time in the memory M time set in the timer _{(1 / | 1 - 2 |} - △ T ( fourth
Figure), the timer outputs the P ₀ the activation signal through the output circuit PIO upon completion (Figure 4).

Note that when it is detected that the input signals a ₂ and b are in phase, the difference between the cycles of the input signals a ₂ and b, that is, 1 /
₁ and comparing the difference of _1/2. When this value is below a certain value (when the beat frequency period is long and the operating time of the electromagnetic switch can be ignored), the closing signal can be sent to operate the electromagnetic switch (FIG. 4).

(Effect of the Invention) In order to detect the phase difference between the outputs of two conventional generators, a beat signal is created by matching the voltage waveforms of the outputs of the respective generators, and the time point at which this beat signal becomes zero (minimum) is detected. In phase. However, this method has a drawback that the in-phase point cannot be accurately detected when the output voltage has a waveform distortion or a voltage difference.

However, according to the present invention, since the output voltage is shaped into a waveform and then matched as a square wave, the common-mode point can be accurately detected even if there is a waveform distortion or a voltage difference, and the electromagnetic switch has the smallest phase difference. It has an effect that it can be controlled so that it is put into

Further, according to the present invention, it is possible to eliminate the impedance components required only for parallel operation, which have been conventionally required, and power components such as a switch for shortening the impedance components, and it is possible to improve the reliability and downsize the device. Also, the effect of contributing to cost reduction can be obtained.

[Brief description of drawings]

1 (a) is a block diagram of the entire apparatus, (b) is a block diagram of a signal processing circuit, FIG. 2 is a waveform diagram, FIG. 3 is an implementation circuit, FIG. 4 is a flowchart, and FIG. 5 is a conventional example. Indicates. K1, K2 ... Switch MG1, MG2 ... Motor generator MS1, MS2 ... Electromagnetic switch L ... Load T1, T2 ... Waveform shaping circuit M ... Memory μC ... Processing circuit EX-OR ... Exclusive OR circuit

Claims (1)

[Claims] 1. In an AC power supply device in which a plurality of motor generators for supplying electric power to a load via electromagnetic switches are operated in parallel, the phase difference between the output voltages of the preceding motor generator and the following motor generator is minimized. In a device including a control circuit that predicts a time point at which the operation delay time of the electromagnetic switch is added and gives a command to turn on the electromagnetic switch of the subsequent motor generator, the control circuit is the output voltage of the preceding motor generator. And the output voltage of the subsequent motor generator is respectively given, a waveform shaping circuit for converting a sine wave into a square wave, a signal from the waveform shaping circuit is given, and the pulse width of the square wave signal from the waveform shaping circuit A timer counter that takes out a changing signal and finds a time point when the pulse width becomes the minimum, a signal from the timer counter, and a memory that stores the operation delay time of the electromagnetic switch. And a phase difference between the output frequency and the phase difference of the preceding and subsequent motor generators, and when the phase difference becomes zero, that is, the same phase, the next phase becomes the same phase. The AC power supply device is characterized in that the operation signal of the electromagnetic switch is sent earlier by the operation delay time of the electromagnetic switch based on this point.