JPS5989537A - Control system for inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an inverter in a power supply device that performs uninterrupted switching between an inverter output and another AC power source using a changeover switch, and supplies uninterruptible power to a load. It is related to the control method.

[Technical background of the invention]

Conventionally, as an uninterruptible power supply, even in the event of a commercial N source power outage, the output of an inverter that supplies uninterruptible power using a storage battery power source as input and a direct commercial power source is connected by a changeover switch,
Normally, power is supplied to the 9 loads by the inverter via the changeover switch, and when the inverter fails or when the inverter is maintained or inspected, the changeover switch is switched to direct commercial power and power is supplied directly to the load, and after the failure is recovered or maintenance and inspection is completed. , a device is widely used in which the changeover switch is switched back to the inverter side to continue supplying power to the load continuously.

FIG. 1 is a block diagram showing an example of an uninterruptible power supply as described above. In the figure, 1 is a direct commercial power source, 2 is a commercial power source, 3 is a rectifier, 4 is a storage battery charged by the rectifier 3, and 5 is an inverter that receives DC power from the rectifier 3 or storage battery 4 and converts it into AC power. , 6 is an AC filter that improves the rectangular wave output of the inverter 5 to a sine wave, 7.9 is a static changeover switch, 8 is a load, and 11 is a detecting phase difference between the direct commercial power supply 1 and the output of the inverter 5. Phase difference detector (PHD), 12 is phase difference detector 11
13 is a voltage controlled oscillator (WO input, 1
Reference numeral 4 denotes an inverter 5 which controls the output type of the inverter 5 to a constant voltage using the output of the voltage controlled oscillator 13 as a frequency reference.
15 is a changeover switch control circuit that controls the changeover switch 7.9.

The phase difference detector 11, the low-pass filter 12, and the voltage-controlled oscillator 13 are PLL (Phase Locked L).
ocp) circuit is configured to control the frequency of the inverter 5 so that the output phase of the inverter 5 matches the phase of the direct commercial power supply l. Normally, the changeover switch 7 is ON, the changeover switch 9 is OFF, and the inverter 5 supplies power to the load 8. On the other hand, if the inverter 5 breaks down for some reason,
Immediately, the changeover switch 9 is turned on and the changeover switch 7 is turned on.
is turned off, power is directly supplied to the load 8 by the direct commercial power supply 1 without momentary interruption. Further, when performing maintenance and inspection on the inverter 5, by manually switching from the changeover switch 7 to the changeover switch 9, power is directly supplied from the direct commercial power supply 1 in the same manner as described above. Subsequently, when the inverter 5 recovers from the fault, or when maintenance and inspection are completed, the switch is switched from the changeover switch 9 to the changeover switch 7 again, and the T
@Forwarding business? ! Power is returned from the source 1 to the inverter 5 to supply power to the fence 8 without momentary interruption.

[Problems with background technology]

However, when the direct commercial power supply 1 is returned to the inverter 5, the load changes suddenly from no load to full load for the inverter 5, so the output voltage fluctuates greatly during the switching transition, which adversely affects the load 8. Furthermore, even if a sufficient wrap period is provided between the changeover switch 9 and the changeover switch 7 when switching from the changeover switch 9 to the changeover switch 7, the impedance of the AC filter 6 connected to the output of the inverter 5 is
The force is large compared to the impedance of the normal direct commercial power supply 1, so it is necessary to use a selector switch. , 9, the direct commercial power supply 1 shares most of the load current to the load 8, and the output current of the inverter 5 increases only after the changeover switch 9 is turned off. An output voltage fluctuation almost equivalent to a sudden change in load occurs.

In order to reduce this voltage fluctuation, there are methods to install an inverter device with a larger capacity than necessary, or to install a PWM inverter with complex can control as an inverter device with small internal impedance. There is a problem with sexuality.

[Purpose of the invention]

The object of the present invention has been made in view of the above-mentioned points, and the object of the present invention is to provide frequency control in which the output ends of an inverter and another AC power source are connected by a changeover switch, and the output phase of the inverter is controlled to match the phase of the AC power source. An object of the present invention is to provide an inverter control system that does not cause fluctuations in output voltage when switching from an AC power supply to an inverter using the changeover switch in a device equipped with a circuit.

[Summary of the invention]

To achieve this objective, the present invention suppresses fluctuations in the output voltage by controlling the output phase of the inverter so that it gradually increases during switching until the output current of the inverter matches the load current. It is something to do.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described with reference to FIG. In Fig. 2, the same reference numerals as in Fig. 1 represent the same parts as in Fig. 1, so the explanation thereof will be omitted.
1 is a CT that detects the inverter output current, 22 is a CT that detects the load current, 2j is a changeover switch control circuit, 24 is a CT according to a command from the changeover switch control circuit 23, 2
2, CT, a proportional integrator that proportionally integrates the deviation between the inverter output current and the load current detected at 23; 25 provides the deviation between the output of the phase difference detector 11 and the output of the proportional integrator to the low-pass filter 12; It is an analog adder.

The polarity of the proportional integrator 24 and the analog adder 25 are selected so that they operate in a direction that advances the inverter output phase by (inverter output current) and (load current).

A specific example of the proportional integrator 24 is shown in FIG. 3
1 is an operational amplifier 1.32 is an analog switch (usually O
N, 0FF due to integration start command) 33, 34° 35
is a resistor, and 36 is a capacitor.

Next, the operation of the embodiment shown in FIG. 2 will be explained. FIG. 4 is a time chart for explaining the operation of each part of the embodiment shown in FIG. Changeover switch 7 is OFF.

When the changeover switch 9 is in the ON state, the output of the proportional integrator 24 is zero, and the output phase of the inverter 5 is the direct feed commercial [rff
! It is controlled to match the phase of 1. When the selector switch 7 of the inverter 5 is turned on at the next turn, at the same time, the selector switch control circuit 23 gives a command to start integration to the proportional integrator 24, and the proportional integrator 24 outputs the inverter output as shown in FIG. , starts integrating the deviation between the current and the load current, and the output of the proportional integrator 24 is applied to the low-pass filter 12 through the analog adder 25. As the output of the proportional integrator 24 interrupts the PLL circuit that controls the output phase of the inverter 5 in this way, the output phase of the inverter 5 shifts in the leading direction. It is well known that in a parallel system of AC power supplies, the load sharing is determined by the phase of each power supply, and during the wrap period of the changeover switch 7.9 (t1 to t2 in FIG. 4), the output of the proportional integrator 24 is As the output phase of the inverter 5 gradually increases, the output current of the inverter 5 gradually shifts from the direct commercial power supply 1 to the inverter 5, and as shown in Fig. 4, the output current of the inverter 5 gradually increases. To increase.

Since the output voltage control system of the inverter 5 responds at a speed sufficiently faster than the slope of the increase in output current, almost no fluctuation in the output voltage occurs. The output of the proportional integrator 24 becomes balanced when the deviation between the load current and the inverter output current reaches zero and remains at a constant level, and the tW force phase of the inverter 5 also becomes constant at θH. In other words,
A kind of constant current control loop is formed based on the load current.

At time t, when the load transfer from the direct commercial power supply l to the inverter 5 is completed, the selector switch 9 is turned off, and the proportional integrator 2 is turned off.
4 and reset the output of the proportional integrator 24 to zero, the PLL circuit operates so that the output phase of the inverter 5 matches the phase of the direct commercial power supply 1, and the normal inverter 5 Move to load power supply 1 state.

Also, the slope where the inverter output phase gradually advances and the final value θ
Since H is based on the load current, it is optimally controlled according to the load current so that no cross current occurs between the direct current 1 and the inverter 5.

In the embodiment shown in FIG. 2, a case has been described in which a commercial power source is used as the other AC power source, but similar effects can be obtained by using various power sources as the other AC power source. For example, the other AC power source may be a commercial power source via an automatic lightning regulator (AVR), a private generator, or an inverter.

〔Effect of the invention〕

As explained above, according to the present invention, a high-quality power supply device in which the output ends of an inverter and other AC power sources are supplied with a changeover switch, which does not cause voltage fluctuations when switching from an AC power source to an inverter, is provided. Power supplies can be configured.

Furthermore, it is advantageous in terms of economy because it is only necessary to add a simple configuration of a current transformer and a proportional integrator.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a conventional uninterruptible power supply device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a specific example of the configuration of the proportional integrator in Fig. 2. The circuit diagram shown in FIG. 4 is a time chart illustrating the operation of each part of the embodiment shown in FIG. 1... Direct commercial power supply, 2... Commercial power supply for inverter, 3... Rectifier, 4... Storage battery, 5... Inverter, 6... AC filter, 7.9... Changeover switch,
8...Load, 11...Phase difference detector (PHD),
12...Low pass filter (LPF), 13...
・Voltage controlled oscillator (VCO), 14... gate control circuit, 15, 23, , changeover switch control circuit, 21
, 22...CT, 24...proportional integrator, 25...
Analog adder, 31... operational amplifier, 32... analog switch, 33, 34. 35... resistor, 36...
...Capacitor. (7317) Agent Patent Attorney Noriyuki Chika (1 person) Figure 2 Figure 3 J, 5 Figure 4

Claims (1)

[Claims] In a power supply device in which the output end of an inverter and another AC power source are connected by a changeover switch, when the changeover switch switches the load from the AC power supply to the inverter without interruption, the load current, current, and output of the inverter are changed. An inverter control system, characterized in that the output phase of the inverter is controlled so that the output current of the inverter matches the load current using an output obtained by proportionally integrating the deviation from the current.