JPH0442740A - Uninterruptible power supply - Google Patents

Abstract

PURPOSE:To improve power factor and to deal with higher harmonics through a simple constitution by converting an normally inputted AC power through a converter circuit into a DC power which is then smoothed and stored in a storing unit, and inverting the DC power stored in the storing unit into a stabilized AC power upon power interruption and outputting thus inverted AC power to an AC output terminal. CONSTITUTION:An AC switch B is normally turned ON to feed AC power directly from a single phase power supply S to a load L. Thus inputted AC power is converted through a rectifying element 10 in a converter circuit C into a DC power which is then smoothed through a smoothing circuit D and stored in a storing unit E. Upon power interruption, the AC switch B is turned OFF to start power supply operation through an inverter circuit F which inverts the DC power stored in the storing unit E into a stabilized sine wave AC power through PWM control. Thus produced AC power is then outputted through the reactor 14 and the capacitor 6 in a lowpass filter A to an AC output terminal 2 thence fed to the load L.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an uninterruptible power supply (hereinafter referred to as UPS) used for computers, electromagnetic switches, variable speed motors, etc. The present invention relates to technology for improving power factor and countermeasures against harmonics in UPS.

[Prior art] (1) U of the conventional inverter regular power supply system shown in Fig. 3
PS is a converter circuit #I that converts AC power input from the single-phase AC power supply S through the AC input terminal 1 into DC power.
C, a power storage device E that stores this DC power, and an AC output terminal 2 that converts the DC power converted by the converter circuit F1!1c or the DC power stored in the power storage device E into AC power.
The bypass 3 connects the inverter circuit iF that outputs to the AC input terminal 1 and the AC output terminal 2, and the bypass 3 is always shut off and the inverter circuit F is opened, and the bypass 3 is opened only when the UPS fails. and an AC switch B that cuts off the inverter circuit F.

This type of UPS operates as follows.

First, during normal times, AC power input through AC input terminal 1 is converted to DC power by converter circuit C, and this DC power is charged to power storage device E (charging may be performed by a dedicated charging circuit). ), the inverter circuit F converts it into stable AC power, and supplies it to the load.

Next, in the event of a power outage, the DC power stored in the power storage device E is converted into stable AC power by the inverter circuit F, and is supplied to the load.

In the unlikely event that the UPS itself malfunctions,
The AC switch B opens the bypass 3 without momentary interruption, and the AC power from the single-phase AC power supply S is directly supplied to the load.

(2) Conventional inverter standby type UPS shown in Figure 4
The bypass 3 connects the AC input terminal 1 and the AC output terminal 2, and the bypass 3 is opened during normal operation to shut off the inverter circuit #1F, and the bypass 3 is closed during a power outage and the inverter circuit F is opened. The AC switch B, the converter circuit C that converts the AC power input from the AC input terminal 1 into DC power, and the power storage device E that stores this DC power are in a standby state or a no-load operating state under normal conditions, and are on standby in case of a power outage. Sometimes, the power storage device E includes an inverter circuit F that converts the DC power stored in the power storage device E into AC power and outputs the AC power to the AC output terminal 2.

This type of UPS operates as follows.

First, under normal conditions, the AC switch B opens the bypass 3, and AC power from the single-phase AC power supply S is directly supplied to the load. At the same time, AC power input from AC input terminal 1 is converted into DC power by converter circuit C, and power storage device E is charged with this DC power. At this time, the inverter #IF is in a standby state or in a no-load operating state.

Next, in the event of a power outage, AC switch B instantly switches to bypass 3.
At the same time, the inverter circuit F instantly starts operating, converts the DC power stored in the power storage device E into stable AC power, and supplies the power to the load.

[Problems to be Solved by the Invention] (1) According to the UPS of the inverter regular power supply system shown in Fig. 3, the distortion rate of the AC output voltage can be suppressed by the inverter frequency F@F during normal times, but on the other hand, the following problems occur. There was a problem.

■During normal times, there is power loss due to inverter iF, etc., which reduces efficiency and increases heat generation.

■ Since inverter circuit meters, etc. operate continuously during normal times, devices with sufficient capacity are required, which increases costs and tends to be larger and heavier.

■ The input current is a peak-like current that contains many harmonic components, and the power factor is poor.

■ If the above-mentioned harmonic components enter the AC input current, there is a risk of causing noise generation or malfunction of other electrical equipment.

Here, if only to improve the problems of ■ and ■ above, it would be possible to use a high power factor converter circuit that converts the input current into a sine wave, but the problems of ■ and ■ above remain unresolved. Ta.

(2) According to the inverter standby type UPS shown in FIG. 4, the above-mentioned problems (1) and (2) can be solved and improved.

That is, since AC power is directly supplied to the load from the bypass 3 during normal times, there is little power loss, high efficiency, and less heat generation. In addition, the inverter circuit F only during a power outage
Because it operates, there is no need to consider a margin in terms of temperature, and a small device can be used with the minimum capacity suitable for the load.
In addition, the cooling fins can be made smaller, making it possible to reduce costs, size, and weight. However, the above-mentioned problem (■) remained unresolved.

Therefore, in order to improve the power factor and take measures against harmonics, is it possible to consider a method of inserting a separate active filter circuit G as shown by the chain line in Figure 4, or is it possible to reduce the cost as described above? , there is a contradiction that leads to high costs.

The purpose of the present invention is to develop an inverter standby type UPS that can achieve higher efficiency, lower heat generation, lower cost, smaller size and lighter weight, etc.
By improving the
The object of the present invention is to provide a new UPS that can improve the power factor and take measures against harmonics with a simple configuration.

[Means for Solving the Problems] In order to achieve the above object, the uninterruptible power supply of the present invention has a bypass that connects an AC input terminal and an AC output terminal, and a bypass that is open during normal times and An AC switch that sometimes cuts off the bypass, a converter circuit that converts AC power input from the AC input terminal into DC power, a smoothing circuit that smoothes this DC power, a power storage device that stores this DC power, and a power storage device that stores this DC power. The DC power smoothed by the circuit is converted into a compensation current to cancel the harmonic components of the load current, and in the event of a power outage, the DC power stored in the power storage device is converted to AC power for powering the load, and each AC output terminal The configuration includes an inverter circuit that outputs output to the

[Operation] First, under normal conditions, the AC switch is turned on and the bypass is opened, so the AC power input from the AC input terminal is directly supplied to the load. Further, the input AC power is converted to DC power by a converter circuit, and the DC power including this ripple is smoothed by a smoothing circuit, and is charged to the power storage device. At this time, the inverter circuit converts the DC power smoothed by the smoothing circuit into a compensation current for canceling harmonic components of the load current, and outputs this compensation current to the AC output terminal. That is, the inverter circuit operates as an active filter. Therefore, the system current from the AC input terminal becomes a sine wave without harmonic components flowing into it.

Next, in the event of a power outage, the AC switch is turned off and the bypass is instantly cut off. Simultaneously with this interruption, the power supply operation by the inverter circuit starts, converting the DC power stored in the power storage device into stable AC power, and outputting this AC power to the AC output terminal to power the load.

[Example] Hereinafter, an example of a UPS embodying the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, one of the AC input terminals 1 to which the single-phase AC power source S is connected and one of the AC output terminals 2 to which the load is connected are connected by a bypass 3, and the inlet of the bypass 3 is A switch 15 is provided. In addition, connection 4 is connected between the other AC input terminal 1 and the other AC output terminal 2.
! 4, and the connecting wire 4 is grounded.

A is a low-pass filter inserted between the AC input terminal 1 and the AC output terminal 2, and is composed of a reactor 5 and a capacitor 6. The reactor 5 may be as small as, for example, several hundred μH, and the capacitor 6 may be as small as, for example, several tens of μF.

B is an AC switch inserted in the middle of the bypass 3, which opens the bypass 3 during normal times and cuts off the bypass 3 during a power outage. This alternating current switch B is a known one constructed of two switching elements 7 using bipolar transistors. Of course,
This AC switch B can also be constructed using other switching elements such as FET, IGBT, and SI thyristor.

C connects the reactor 5 and resistor 9 to one of the AC input terminals 1.
This is a converter circuit connected through a series circuit of the AC input terminal 1 and converts AC power input from the AC input terminal 1 into DC power. This converter circuit C is composed of two rectifying elements 10 such as diodes connected in series,
The resistor 9 is connected to the intermediate portion thereof.

D is a smoothing circuit connected to the converter circuit C,
This is to smooth the DC voltage containing a large ripple component converted by the converter circuit #IC.

This smoothing circuit is composed of two smoothing capacitors 11 connected in series, and the intermediate portion thereof is connected to the connecting line 4.

E is a power storage device connected to the converter circuit C,
It stores the DC power converted by the converter circuit C. This power storage device E is constituted by a storage battery 12 such as a lead storage battery or an alkaline storage battery, but other means (for example, a flywheel type power storage device, etc.) may also be used.

F is an inverter circuit connected to the converter circuit Hc, and under normal conditions, DC power smoothed by a smoothing circuit is converted into a harmonic component i[ of the load current i. Compensation current i to cancel. In the event of a power outage, the DC power stored in the power storage device E is converted into AC power for load power supply, and the AC power is output to the AC output terminals 2, respectively. This inverter circuit F
is composed of two switching circuits 13 connected in series, and is connected to one of the AC output terminals 2 via a low-pass filter A consisting of an axle 14 and a capacitor 6 in the middle thereof. The two switching circuits 13 are I
It is composed of a switching element 13a using a GBT and a flywheel diode 13b connecting each collector-emitter. Of course, this switching circuit 13 is a bipolar transistor, FET, GTO.
, SI thyristor, and other switching elements may also be used.

The operation of the UPS configured as above will be explained.

First, under normal conditions, the AC switch B is turned on to open the bypass 3. Since the connection line 4 is always open and held at a predetermined potential by grounding, the AC power input from the single-phase AC power supply S through the AC input terminal 1 is directly supplied to the load. The system current from this single-phase AC power supply S is assumed to be i3.

When there are harmonics superimposed on the single-phase AC power source S, they are removed by the reactor 5 and capacitor 6 of the low-pass filter A. In addition, the input AC power is converted into converter circuit C
The rectifying element 10 converts the DC power into DC power, and the DC power including this ripple is smoothed by the smoothing circuit JiI! It is smoothed at D and is charged to power storage device E.

At this time, the inverter circuit F is operated as follows.

In other words, if the load is a nonlinear load such as shown in FIG. 2 in which the load current i[ flows, the load current i[
are the fundamental wave component 11 and the harmonic component i. It can be considered in two parts.

i[=i1+i[.

Therefore, this harmonic component i,. is detected, and the inverter circuit F is PWM-controlled based on the detection, thereby generating a compensation current IC having a polarity opposite to that of the harmonic component 'Ln.
This compensation current IC is transferred to reactor 1 of low-pass filter A.
4 and the harmonic component i, by outputting it to the AC output terminal 2 via the capacitor 6. to cancel out.

That is, the inverter circuit IF operates as an active filter. As a result, the system current is from the single-phase AC power supply S becomes a clean sine wave with no harmonic components flowing in, improving the power factor and preventing noise generation in other electrical equipment due to the harmonic components flowing out. Malfunctions and the like can also be prevented. In addition, in the inverter circuit F, it is also effective to generate a fundamental wave component in a superimposed manner to supply the loss in the UPS.

Next, in the event of a power outage, the AC switch B is turned off to instantly cut off the bypass 3. At this time, the current from the reactor 5 passes through the resistor 9 and the rectifying element 10 and slowly charges the smoothing capacitor 11 of the smoothing circuit (inrush prevention). At the same time as the bypass 3 is cut off, the power supply operation by the inverter circuit F is started, and the DC power stored in the power storage device E is converted into stable sine wave AC power by, for example, PWM control, and the reactor 14 of the low-pass filter A and the capacitor are 6 to the AC output terminal 2 to supply power to the load.

The UPS of this embodiment described in detail above has the following advantages.

■ Under normal conditions, the current passing through the inverter circuit iF, etc. is small, so there is little power loss. Therefore, it is possible to maintain high efficiency and low heat generation that are substantially equivalent to the conventional inverter standby system.

(2) In addition, the devices used for the inverter circuit iF and the like can be of small capacity, making it possible to reduce costs, size, and weight.

■ As mentioned above, even if a nonlinear load is connected, the power factor does not decrease because the harmonic components of the load current can be canceled out.

■ Also, since harmonic components flowing into the system current of the single-phase AC power supply are eliminated, there is no risk of causing noise generation or malfunction of other electrical equipment.

(2) When the switch 15 is turned on, the charging current of the smoothing capacitor 11 can be suppressed by the resistor 9 and the diode 10.

(2) The switching element 7 used in the AC switch B may be a low-speed bipolar transistor and is inexpensive.

It should be noted that the present invention is not limited to the configuration of the above-mentioned embodiments, and can be modified and embodied as desired without departing from the spirit of the invention.

[Effects of the Invention] Since the UPS of the present invention is configured as described above, it maintains the advantages of an inverter standby type UPS, which allows for higher efficiency, lower heat generation, lower cost, smaller size and lighter weight, etc. It has an excellent effect of improving the power factor and taking measures against harmonics with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of a UPS embodying the present invention,
FIG. 2 is a diagram showing the current flowing through each part of the circuit, FIG. 3 is a block diagram of a conventional inverter regular power supply type UPS, and FIG. 4 is a block diagram of a conventional inverter standby type UPS. 1... AC input terminal, 2... AC output terminal, 3...
・Bypass, 7... Switching element, 10.
... Rectifying element, 11... Smoothing capacitor, 12...
Storage battery, 13... Switching circuit, 13a...
Switching element, 13b... Flywheel diode, A... Low pass filter, B... AC switch, C... Converter circuit, D... Smoothing circuit, E... Power storage device, F...
...Inverter circuit, S...Single-phase AC power supply, L...
Load, i...Load current, 11...Fundamental wave component,'
Ln...harmonic component, j. ... Compensation current, i, ...
- Grid current.

Claims (1)

[Claims] A bypass connecting an AC input terminal and an AC output terminal, an AC switch that opens the bypass during normal times and shuts off the bypass during a power outage, and converts AC power input from the AC input terminal into DC power. A smoothing circuit smoothes this DC power; A power storage device stores this DC power; Under normal conditions, the DC power smoothed by the smoothing circuit is converted into a compensation current to cancel the harmonic components of the load current. An uninterruptible power supply equipped with an inverter circuit that converts DC power stored in a power storage device into AC power for load power supply in the event of a power outage, and outputs the AC power to each AC output terminal.