JPH084370B2 - Uninterruptible power system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an uninterruptible power supply device using an inverter, and particularly to an uninterruptible power supply device suitable for supplying power to a load such as a computer that does not like an instantaneous power failure. .

[Conventional technology]

2. Description of the Related Art Conventionally, an uninterruptible power supply device using an inverter has been widely used as a power supply device for a load such as a computer that does not allow an instantaneous power failure.

In addition, in this type of uninterruptible power supply, the power supply to the load by the inverter is supplied to the load by the commercial power supply by the bypass power supply, and the switching between the inverter and the commercial power supply is called the bypass switching. In the conventional device, a semiconductor switch element with a forced commutation circuit is mainly used as a circuit for this bypass switching, as described in Japanese Patent Application Laid-Open No. 61-32900. .

[Problems to be solved by the invention]

In the above prior art, since the semiconductor switch element with the forced commutation circuit is used for the bypass switching circuit, there is no concern about the generation of the circulating current between the bypass power supply and the inverter at the time of bypass switching, Since the forced commutation circuit is required, there is a problem that it is difficult to increase the cost and downsize the device.

On the other hand, if a semiconductor switch element that does not have a self-extinguishing function, such as a triac, is used, even if the control signal is turned off, the arc is not extinguished until the current in the main circuit of the inverter reaches zero, so high-speed operation is possible. Moreover, as a switch element for bypass switching of an uninterruptible power supply that requires bypass switching without instantaneous interruption, it is difficult to apply as it is. That is,
In a bypass switching circuit that uses a triac as a switch element, it is necessary to apply a reverse bias voltage to the triac in order to avoid circulating current between the bypass power supply and the inverter. Since it is necessary to provide an off time for bypass switching of more than one cycle, bypass switching without instantaneous interruption of output cannot be performed, and thus it is difficult to apply.

On the other hand, as a method of suppressing this circulating current, there is a method of inserting a reactor between the inverter output and the bypass power supply, but in this case, this reactor must be large enough to withstand the flow of the main circuit current. However, there are problems such as an increase in size of the device, an increase in weight, and an increase in cost.

According to the present invention, when a semiconductor element having no self-extinguishing function such as a triac is used as the switch element of the bypass switching circuit, when the bypass switching is performed without taking the output off time at the time of the bypass switching, the bypass power supply and the inverter are connected. It was made in view of the problem that a circulating current appears in the.The purpose is to use a semiconductor device without a self-extinguishing function such as a triac as a switching device of a bypass switching circuit. It is to provide an uninterruptible power supply that enables the above.

[Means for solving problems]

The above object is achieved by controlling the switch element of the main circuit of the inverter to be off at the time of bypass switching.

[Work]

By turning off all the switch elements of the inverter main circuit, current does not flow from the inverter side to the bypass power supply side.

On the other hand, conversely, the flow of current from the bypass power supply side to the inverter side may occur via the flywheel diode of the inverter main circuit, but at this time, if the DC power supply voltage of the inverter is higher than the rectified voltage of the bypass power supply. ,
This current flow does not occur.

Therefore, even if a switch element such as a triac that does not have a self-extinguishing function is used as it is, a circulating current can be prevented.

〔Example〕

Hereinafter, the uninterruptible power supply according to the present invention will be described in detail with reference to the illustrated embodiment. Prior to this, first, a commonly used inverter will be described with reference to FIG.

In FIG. 2, 1 is a DC power supply, 2A, 2B, 2C and 2D are semiconductor switches composed of transistors and thyristors that form the main switch element of the inverter, and 3A, 3B, 3C and 3D.
Is a flywheel diode, 4 is an inverter circuit, 5
Is an AC filter, 6 is a reactor, and 7 is a capacitor.

The semiconductor switches 2A to 2D are pulse width controlled to be turned on and off, and the output voltage of the main circuit 4 has a waveform obtained by performing pulse width modulation (PWM) on the voltage of the DC power supply 1. Therefore, the output of the inverter circuit 4 is passed through a filter 5 to attenuate the harmonic components and obtain the output of the inverter.

FIG. 1 is an embodiment of the present invention, the inverter part of which is as described in FIG. 2, and a bypass switching circuit 8 is added to this to construct an uninterruptible power supply.
Is a triac, 10 is a bypass power supply consisting of a commercial power supply,
11 is a load.

 Next, the operation of this embodiment will be described.

First, in a normal state, the triac 9A of the bypass switching circuit 8 is controlled to be on and the triac 9B of the bypass switching circuit 8 is controlled to be off by a control device (not shown), so that power is supplied from the inverter side to the load 11. At this time, the inverter circuit 4 is controlled by a control device (not shown).
The operation is controlled in synchronization with the bypass power supply 10.

Next, when switching to the bypass power supply state due to a failure of the inverter or the like, first, the semiconductor switch 2A of the inverter circuit 4 is controlled by the control device (not shown).
2D are all controlled to be off, and at the same time, the triac 9A and 9B of the bypass switching circuit 8 are controlled to be off and on, respectively.

At this time, the triacs 9A and 9B are connected to the input side voltage V ₁ ,
The state of V ₂ and the output voltage V ₃ to the load 11 side will be described with reference to FIG.

In FIG. 3, until time t ₀ , there is no problem in the power supply by the inverter and the operating state is as it is, but at this time t ₀
Shows the case where some abnormality occurs in the inverter and it is necessary to switch to the power supply by the bypass power supply 10 here.First, the triac 9A is on and 9B is on until time t _0.
Are controlled to be off, and the inverter circuit 4 is operated in synchronization with the bypass power supply 10.

Next, at time t ₀ , switching to bypass power supply 10 is performed,
First, all the semiconductor switches 2A to 2D of the inverter circuit 4 are turned off, and at the same time, the triac 9B of the bypass switching circuit 8 is controlled to be turned on and the bypass power supply 10 switches the power supply state.

In FIG. 3, the hatched portions in the waveforms of the inverter output voltage V ₁ and the bypass power supply voltage V ₂ indicate the states in which power is being supplied to the load 11, respectively. Then, at this time, the time t ₀ of the inverter output voltage V ₁
The part shown by the broken line thereafter indicates that the triac 9A, which is the switching switch on the inverter side, has not been turned off after time t ₀ . That is, the triac 9A does not turn off until the output voltage of the inverter becomes zero even after the gate signal turns off at time t ₀ .
This is because the voltage V ₂ of the bypass power supply 10 appears during this period.

From this, it is sufficient to supply the gate signal of the triac 9A on the inverter side between the timing (t ₀ ) at which switching is performed and the timing at which the voltage V ₁ next crosses the zero phase. In the embodiment, in order to simplify the control logic, the gate signal is turned off at time t ₀ .

Next, the circulating current between the inverter circuit 4 and the bypass power supply 10 will be described.

First, in this embodiment, since the semiconductor switches 2A to 2D of the inverter circuit 4 are all controlled to be off at the time of bypass switching, no circulating current appears from the inverter circuit 4 to the bypass power supply 10 side.

Next, considering the circulating current from the bypass power supply 10 side to the inverter 4 side, even if all the semiconductor switches 2A to 2D of the inverter circuit 4 are turned off, at this time, the triac 9B of the bypass switching circuit 8 is turned on. Yes, as a result, the flywheel diode 3A of the inverter circuit 4
A circulating current from the bypass power supply 10 to the DC power supply 1 appears via ~ 3D. Then, this phenomenon continues for a maximum of 1/2 cycle from the timing of bypass switching to the next zero crossing point.

However, the voltage E of the DC power supply 1 at this time
And the output voltage V ₁ (vms) of the bypass power supply 10 are: E × K · Sin θ = (square root of 2) · V ₁ where K; control rate of semiconductor switch (K = 0 to 1.0) ), And therefore the voltage of bypass power supply 10 is diode 3A
Even if it appears through 3D, the voltage does not become higher than the voltage E of the DC power supply 1, and there is no fear of becoming a circulating current.

Next, FIG. 4 shows an embodiment of a control signal generating circuit for realizing the above control.

In FIG. 4, reference numeral 40 is an inverting circuit and 41 to 46 are NAND circuits. Then, a signal for switching between inverter power feeding and bypass power feeding is input to the inverting circuit 40 and the NAND circuit 41, and the output of the inverting circuit 40 is supplied to the remaining NAND circuits 42 to 46.

Therefore, in the case of inverter power feeding, the gate signal of the triac 9B on the bypass power supply side is off, and the triac 9A on the inverter side and the semiconductor switch 2A of the inverter circuit 4 are
The ~ 2D gate signal is turned on, and in the case of bypass power supply, the above operation is reversed to obtain the predetermined control.

In the above embodiments, the triac is used as the switch element of the bypass switching circuit, but it goes without saying that an antiparallel thyristor without a forced commutation circuit may be used.

〔The invention's effect〕

According to the present invention, by adding a simple logic circuit, a bypass switching circuit can be configured by using a triac, a thyristor, or the like that does not have a self-extinguishing function as it is. There is an effect that the power supply device can be sufficiently reduced in size, weight, and cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an uninterruptible power supply according to the present invention, FIG. 2 is a circuit diagram showing an example of a general inverter, FIG. 3 is a waveform diagram for explaining the operation, and FIG. It is a circuit diagram which shows one Example of a control signal generation circuit. 1 ... DC power supply, 2A-2D ... Semiconductor switch, 3A-3D ...
... flywheel diode, 4 ... inverter circuit,
5 ... AC filter, 6 ... Reactor, 7 ... Capacitor, 8 ... Bypass switching circuit, 9A, 9B ... Triac, 10 ... Bypass power supply (commercial power supply), 11 ... Load.

Claims (2)

[Claims] 1. An inverter operated by a DC power supply, a first switch means connected between a commercial AC power supply and the load, and a second switch connected between the load and the output of the inverter.
An uninterruptible power supply comprising: a switch means for controlling the first switch means and a control means for simultaneously controlling the on-control of the first switch means and the off-control of the second switch means when an abnormality occurs. Is composed of a semiconductor switching element to which a forced commutation circuit is not added and which does not have a self-extinguishing function, and the control means is ON control of the first switch means and OFF control of the second switch means. At the same time, an uninterruptible power supply characterized in that at the same time, all the switching elements of the inverter are controlled to be turned off. 2. The uninterruptible power supply device according to claim 1, wherein the semiconductor switching element having no self-extinguishing function is either a triac or an antiparallel connection thyristor.