JPH07219660A - Uninterruptible power supply control method - Google Patents

Abstract

PURPOSE:To provide the control method which improves the power factor of the load of the noninterruptive power unit to a commercial power source to 1, suppresses a higher harmonic current, and also suppresses Ferranti effect in a light load state. CONSTITUTION:The noninterruptive power unit 1 normally supplies AC electric power from the commercial power source 2 to the load 5 through an AC switch 4 and supplies AC electric power from a battery 6 to the load 5 through an inverter main circuit 8 in case of the power failure of the commercial power source 2; and an inverter control circuit 20 performs control by inputting the detection value of a current detector 13 detecting the current of the load 5 and the detection value of a current detector 21 detecting a filter capacitor current and supplies a gate signal to the inverter main circuit 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention supplies AC power from a commercial power source to a load via an AC switch when the commercial power source is healthy (hereinafter referred to simply as "normal time"), and a storage battery when the commercial power source fails. The present invention relates to a control method for an uninterruptible power supply that supplies AC power to a load via an inverter.

[0002]

2. Description of the Related Art FIG. 3 shows a configuration example of a conventional uninterruptible power supply. In FIG. 3, reference numeral 1 is an uninterruptible power supply, 2 is a commercial power supply, and 6 is a storage battery. The uninterruptible power supply 1 includes a circuit breaker 3, an AC switch 4, an electromagnetic contactor 7, an inverter main circuit 8, and a transformer. It is composed of a container 9, an AC reactor 10, a filter capacitor 11, an inverter control circuit 12, and a current detector 13. Further, the filter capacitor 11 is a filter that removes switching noise generated along with the switching operation of the inverter main circuit 8.

The uninterruptible power supply 1 operates as follows. First, in normal times, AC power is supplied from the commercial power source 2 to the load 5 via the circuit breaker 3, the AC switch 4, and the current detector 13, and the inverter main circuit 8 charges the storage battery 6 and performs fundamental wave operation. A reactive current compensation operation and an active filter operation are performed. Among the operations of the inverter main circuit 8, the fundamental wave reactive current compensation operation is an operation for setting the load power factor (cos φ) to the commercial power source 2 to 1, and the active filter operation is the harmonic current of the load 5. It is an action to absorb.

Next, when the commercial power source 2 fails, the commercial power source is cut off from the circuit, and the load 5 is passed from the storage battery 6 through the electromagnetic contactor 7, the inverter main circuit 8, the transformer 9, the AC reactor 10, and the filter capacitor 11. Supply AC power to. Here, the inverter main circuit 8 includes the current detector 1
It is controlled by a gate signal output from the inverter control circuit 12 on the basis of the detected value of the load current detected by 3.

[0005]

According to the above conventional control method, the current of the filter capacitor for removing the switching noise generated by the switching operation of the inverter main circuit is not controlled.
A current also flows into the filter capacitor from the commercial power source, and as a result, the load power factor (cosφ) of the commercial power source does not become 1 (cosφ = 1), but rather the advanced power factor (cosφ).
However, there is a problem that the ratio becomes 0.98 to 0.99).

Further, when the load becomes light during normal operation and at night, the magnitude of the current of the filter capacitor cannot be ignored, and the ferrant effect (Fe
There is also a problem that the terminal voltage applied to the load becomes high due to the occurrence of r-ranti effect. An object of the present invention is to provide a control method for an uninterruptible power supply that solves the above problems.

[0007]

According to the first aspect of the present invention, when the commercial power source is healthy, AC power is supplied from the commercial power source to the load via the AC switch, and the inverter charges the commercial power source to the storage battery. In addition, the fundamental wave reactive current compensation operation that improves the load power factor of the commercial power supply and the active filter operation that absorbs the harmonic current of the load are performed.When the commercial power supply is cut off, the storage battery transfers the load to the load via the inverter. In a control method of an uninterruptible power supply for supplying AC power, when a commercial power source is healthy, a current of a load and a current of a filter capacitor of the inverter are detected to detect a fundamental wave reactive current of the inverter, and an active filter. Control movements.

In the second aspect of the invention, when the commercial power source is sound and the load is light, the inverter is controlled so as to suppress the current of the filter capacitor.

[0009]

According to the first and second aspects of the invention, in addition to the conventional load current detection, the current of the inverter capacitor of the inverter is detected to control the inverter in consideration of the influence of the filter capacitor.

[0010]

1 is a block diagram of an uninterruptible power supply device showing an embodiment of the present invention. In FIG. 1, reference numeral 20 is an inverter control circuit, 21 is a current detector, the other elements having the same functions as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. The function will be mainly described.

FIG. 2 is a control block diagram of the inverter control circuit 20, in which 201 is a load compensation current command value calculation circuit, 202 is a capacitor compensation current command value calculation circuit, 203 is an adder circuit, and 204. Is an inverter gate signal generation circuit. In the load compensation current command value calculation circuit 201, the current value (negative overcurrent) flowing through the load 5 detected by the current detector 13 and the commercial power supply 2 not shown
Is input, and the fundamental wave compensation current value and the harmonic compensation current value of the load current are calculated. Further, the current value flowing through the filter capacitor 11 detected by the current detector 21 and the voltage waveform of the commercial power supply 2 are input to the capacitor compensation current command value calculation circuit 202, and the fundamental wave compensation current value of the filter capacitor current is calculated. To be done.

The output of the load compensation current command value calculation circuit 201 and the output of the capacitor compensation current command value calculation circuit 202 are combined by an adder circuit 203 and led to an inverter gate signal generation circuit 204, and the inverter gate signal generation circuit 20.
4 adjusts the output of the adder circuit 203 to a desired gate signal,
It is converted and given to the inverter main circuit 8. The inverter main circuit 8 performs a switching operation based on the gate signal output from the inverter gate signal generating circuit 204, thereby performing a fundamental wave reactive current compensation operation and a harmonic current of the load 5 in consideration of the influence of the filter contenter 11. Active filter operation that absorbs

Further, when the load current detected by the current detector 13 is smaller than a predetermined value, the filter capacitor current is suppressed to reduce the rise of the terminal voltage in the load 5.

[0014]

According to the present invention, the current of the filter capacitor is canceled as a function of the fundamental wave reactive current compensation function by detecting the load current and the current of the filter capacitor of the inverter to control the inverter. As a result, the load power factor of the commercial power supply can be improved to 1, and the current of the filter capacitor can be detected and the current of the filter capacitor can be suppressed even when the ferrant effect occurs. By doing so, it is possible to reduce the rise in the terminal voltage applied to the load, so that it is possible to provide an uninterruptible power supply device suitable for a commercial power supply and a load.

[Brief description of drawings]

FIG. 1 is a block diagram of an uninterruptible power supply showing an embodiment of the present invention.

FIG. 2 is a control block diagram of the inverter control circuit of FIG.

FIG. 3 is a configuration diagram of an uninterruptible power supply device showing a conventional example.

[Explanation of symbols]

 1 Uninterruptible Power Supply 2 Commercial Power Supply 3 Circuit Breaker 4 AC Switch 5 Load 6 Storage Battery 7 Magnetic Contactor 8 Inverter Main Circuit 9 Transformer 10 AC Reactor 11 Filter Capacitor 12 Inverter Control Circuit 13 Current Detector 20 Inverter Control Circuit 21 Current Detector 201 Load compensation current command value calculation circuit 202 Capacitor compensation current command value calculation circuit 203 Adder circuit 204 Inverter gate signal generation circuit

Claims (2)

[Claims] 1. When the commercial power source is healthy, AC power is supplied from the commercial power source to the load through an AC switch, and the inverter improves the charging operation from the commercial power source to the storage battery and the load power factor of the commercial power source. Controls the uninterruptible power supply that supplies a reactive current compensation operation for the fundamental wave and an active filter operation that absorbs the harmonic current of the load, and supplies AC power to the load from the storage battery via the inverter during a power failure In the method, when the commercial power source is healthy, the load current and the inverter capacitor current of the inverter are detected to control the fundamental wave reactive current compensation operation of the inverter and the active filter operation. Power supply control method. 2. The control method for an uninterruptible power supply according to claim 1, wherein when the commercial power source is healthy and the load is a light load, the inverter is controlled so as to suppress the current of the filter capacitor. An uninterruptible power supply control method comprising: