JPH0429527A - Synchronous control circuit and control method - Google Patents

Abstract

PURPOSE:To bring first and second AC power supplies into synchronous state where fluctuation of frequency is suppressed, without producing DC component, by providing means for detecting phase difference between the first and second AC power supplies and controlling a frequency command circuit so that the phase difference will be zero. CONSTITUTION:A phase limiter means 11 for limiting a differential phase signal detected through a phase difference detecting circuit 7 is provided in order to suppress fluctuation rate of inverter output frequency. Furthermore, a frequency command circuit 9 is provided with a frequency limiter means 12 in order to limit the inverter output frequency within a set value even if a bypass AC power supply fluctuates considerably. A sine wave generating circuit 13 generates a single cycle sine wave pattern comprising symmetrical positive and negative half waves for the frequency signal from the frequency command circuit 9 in order to eliminate DC component in the inverter output voltage. Consequently, AC power supply having fluctuating frequency can be followed up smoothly and stably.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a synchronous control method for an inverter device, and particularly to a control method that achieves stable and smooth follow-up performance for an AC power source whose frequency varies.

[Conventional technology]

An uninterruptible power supply is taken as an example of an AC power supply having a synchronous control function, and a conventional example will be explained with reference to FIG. An uninterruptible power supply normally obtains DC power from AC human power 1 or from a storage battery 3 in the event of a power outage, converts it into stable AC power with an inverter 4, and supplies power to the load. The switch 5 switches to a bypass AC power source 6 of another system to supply power to the load. At the time of this switching, if the AC output of the inverter is synchronized with the bypass AC power supply, stable AC power with less disturbance can be supplied.

Synchronous control of the bypass AC power supply 6 and the inverter 4 is configured as follows. That is, a phase difference detection circuit 7 detects a phase difference from each voltage, a calculation circuit 8 calculates a voltage signal such that the phase difference becomes zero from the input phase difference signal, and a frequency command circuit 9 detects a voltage signal. is converted into a frequency signal and the signal is provided to the inverter 4 via the PWM generation circuit 10. By controlling the output frequency of the inverter in this manner, the phase difference is brought to zero and a synchronized state is achieved.

[Problem to be solved by the invention]

In the above conventional technology, when the frequency of the bypass AC source 6 fluctuates or when the phase difference with the inverter output becomes large, the detected value of the phase difference detection circuit 7 increases, and the arithmetic circuit 8
Since the voltage signal of inverter 4 also increases, as a result, inverter 4
The fluctuation rate of the output frequency increases. Furthermore, if the bypass AC power source is a diesel generator or the like, there may be a large deviation from the commercial power source frequency, and the inverter frequency will change accordingly. In either case, the quality of the power source deteriorates, which is undesirable.

Further, when the bypass AC power supply 6 fluctuates from time to time, the phase difference detection circuit 7. Since the calculation circuit 89 and the frequency command circuit 9 also change continuously to control the frequency of the inverter 4,
A time difference occurs between the positive half-wave and the negative half-wave of the inverter output voltage, making them asymmetrical and generating a DC component. When a transformer is connected to the load side of the inverter, this DC component causes the transformer to become biased, causing an excessively biased current to flow through the primary winding of the transformer, potentially damaging the inverter 4.

An object of the present invention is to bring both types of power sources into a synchronized state with little frequency fluctuation and without generating a DC component when performing synchronous control or follow-up control of a controllable AC power source with an AC power source whose frequency fluctuates. be.

[Means to solve the problem]

In order to achieve the above purpose, a phase limiter means is provided for the phase difference signal detected by the phase difference detection circuit to suppress the fluctuation rate of the inverter output frequency, and a frequency limiter means is provided in the frequency command circuit to suppress the fluctuation rate of the inverter output frequency. Even if the AC power source fluctuates greatly, the inverter output frequency can be limited to within a certain set value. Further, if a sine wave pattern of one cycle is generated from the frequency signal of the frequency command circuit using a sine wave generation circuit so that the positive half wave and the negative half wave are targeted, the DC component of the inverter output voltage can be eliminated.

[Effect]

In the phase difference limiter means, if the phase difference signal of the phase difference detection circuit is smaller than the limiter value, the phase difference signal is followed, and if it is larger than the limiter value, the limiter value is output to the arithmetic circuit, so that the frequency fluctuation rate of the inverter can be suppressed. . The same applies to the frequency limiter means; if the frequency signal of the frequency command circuit is smaller than the limiter value, it follows the frequency signal, and if it is thicker than the limiter value, it outputs the limiter value, so the inverter frequency can be suppressed to the limiter value. .

〔Example〕

An embodiment of the invention is shown in FIG. In this embodiment, in addition to the conventional example shown in FIG. 2, one cycle of a sine wave is generated from the outputs of the phase difference limiter circuit 11, the frequency limiter circuit 12, and the frequency limiter circuit 12 so that the positive half wave and the negative half wave are targeted. and an internal frequency command circuit that issues a frequency command for the inverter when there is no bypass AC power supply.

A phase difference detection circuit 7 detects a phase difference from the voltages of the bypass AC power supply 6 and the inverter 4, and a phase difference limiter circuit 11 sets the detection signal below a limiter value. Arithmetic circuit 8
calculates a voltage that makes the input phase difference signal zero, and converts it into a frequency signal in the frequency command circuit 9. The frequency limiter circuit 12 limits the frequency signal so that it does not exceed a limiter value, and the sine wave generation circuit 13 generates a sine wave pattern that does not generate a DC component, and provides the signal to the inverter 4 via the PWM generation circuit 1o. .

Furthermore, if there is no bypass AC power supply 6, the output of the phase difference detection circuit 7 becomes unstable and the frequency of the inverter cannot be controlled.
By switching the frequency to the internal frequency command circuit 14, the inverter can be controlled to the frequency of the internal frequency command circuit.

FIG. 3 shows an example of synchronous control according to this embodiment. In the figure, the frequency of the bypass AC power supply is indicated by Fb, the frequency of the inverter is indicated by Fl, and the upper limit value of the frequency limiter is Fh, and the lower limit value is Fl.

The frequency of the internal frequency command circuit is Fc. At t<tl, there is no bypass AC power supply, and Fi=Fc. At t=t 1, the bypass AC power is turned on, and at t 1
<t<t During the 2 period, the inverter frequency Fi changes its frequency at a rate of change limited by the phase limiter, and becomes synchronized at t=t2. Even if Fb changes at t2<t<t3, F
i follows synchronously and at t3<t<t4 when Fb>Fh, Fi=Fh due to frequency limiter control. t=t
Even if Fb suddenly changes at t=t5, it gradually approaches Fb at a rate of change limited by the phase limiter and becomes synchronized at t=t5.

In this way, even when the bypass AC power source suddenly changes or the frequency fluctuates greatly, stable follow-up control with low fluctuation rate can be performed.

FIG. 4 shows an embodiment of a sine wave generating circuit. As shown in FIG. 1, the sine wave generation circuit generates a sine wave pattern from the frequency signal of the frequency limiter circuit.
so that half is the negative half-wave time, that is, T1=T2
A sine wave pattern is generated so that =T/2. In this way, since the positive and negative half waves are targeted, no direct current component is generated in the inverter output voltage.

〔Effect of the invention〕

According to the present invention, even if there is a steep frequency fluctuation, it is possible to achieve a synchronized state with a constant frequency change rate, and by placing a limit on the frequency tracking range, the frequency change range can be arbitrarily limited. Furthermore, no direct current component is generated in the inverter output voltage during the synchronous control process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a conventional example, FIG. 3 is a diagram showing an example of synchronous control according to this embodiment, and FIG. 4 is a diagram showing an example of a sine wave generation circuit. FIG. 1. AC input, 2. Rectifier, 3. Storage battery, 4.
・Inverter, 5. AC switch, 6. Bus path AC power supply, 7. Phase difference detection circuit, 8. Arithmetic unit, 9..
Frequency command circuit, 10-PWM generation circuit, 11... Phase limiter circuit, 12... Frequency limiter circuit, 13.
Sine wave generation circuit, 14・Internal frequency command circuit Figure 2 ζ

Claims (1)

[Claims] 1. A first AC power source whose frequency fluctuates, an inverter that converts the DC power source into an AC power source, a frequency command circuit for controlling the output frequency of the inverter, and a sine power source whose frequency varies according to the frequency command circuit. PWM required to drive the inverter with the sine wave generation circuit that generates the wave and the output of the sine wave generation circuit
In a second AC power source comprising a PWM generation circuit that converts into a signal, a means for detecting a phase difference between the first AC power source and the second AC power source is provided, and the frequency command circuit is configured to adjust the phase difference so that the phase difference becomes zero. A synchronous control method characterized by controlling. 2. A synchronous control method in the sine wave generating circuit according to claim 1, characterized in that the frequency of the sine wave is controlled so that the time of the positive half wave and the negative half wave of the sine wave are equal. 3. The synchronous control method according to claim 1, characterized in that the frequency command circuit has a function of outputting a preset command value when the first AC power supply is not available. 4. The synchronous control circuit according to claim 1, wherein the frequency command circuit is provided with a frequency limiter function to prevent the command frequency from exceeding a certain value. 5. In claim 1, when controlling the phase difference between the first AC power source and the second AC power source to a certain constant value, the frequency change rate of the second AC power source does not exceed a certain constant value. A synchronous control circuit characterized in that a frequency command circuit is provided with a phase limiter function.