JP2006345647A - Uninterruptible power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an uninterruptible power supply that has less loss and is compact in size, highly efficient, and cost effective. <P>SOLUTION: This invention deals with the uninterruptible power supply that, when an input power source voltage except a power failure fluctuates, adjusts a voltage of a secondary winding of a transformer by the power conversion operation of a first DC-AC converter to stabilize an AC output voltage and applies and receives DC electric power converted by the first DC-AC converter between a second DC-AC converter and an AC bus line as a first operation mode, and during a power failure of an input power source, that converts the DC electric power of an electricity storing means into AC electric power by the second DC-AC converter to supply stable AC electric power to a load as a second operation mode. A switch 10 is connected between an AC terminal of the first DC-AC converter 24 and that of the second DC-AC converter. In a first operation mode where the input power source is sound, the switch 10 is opened. In a second operation mode of the power failure, the switch 10 is closed to operate the first and second DC-AC converters 24, 25 in parallel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an uninterruptible power supply that supplies stable AC power to a load even when the input commercial power supply fluctuates. More specifically, to reduce the size, cost, and efficiency of a series voltage compensated uninterruptible power supply. Related to technology.

FIG. 3 is a diagram showing a circuit configuration of a conventional series voltage compensated uninterruptible power supply.
In FIG. 3, a thyristor type AC switch 4 and a secondary winding 1b of a transformer 1 are connected in series to an AC bus 31 between an AC input terminal u and an AC output terminal U. An AC terminal of a first DC / AC converter 24 composed of semiconductor bridges 20 and 21 is connected to the line 1 a via a reactor 9. Reference numeral 7 denotes a filter capacitor.

Further, the AC terminal of the second DC / AC converter 25 composed of the semiconductor bridges 22 and 23, which has a direct current unit in common with the first DC / AC converter 24, is connected to the AC output terminals U and U via the reactor 6. In addition to being connected to V, a filter capacitor 8 is connected between the AC output terminals U and V. In addition, a storage battery 3 as a power storage unit is connected to the direct current portions of the DC / AC converters 24 and 25. Reference numeral 32 denotes an AC bus between the AC input / output terminals v and V.
Here, the semiconductor bridges 20 to 23 are configured by connecting in series two semiconductor switching elements such as IGBTs, each having a reverse diode connected in reverse parallel.

  In the above configuration, when the power supply voltage of the input power supply (commercial power supply) connected to the AC input terminals u and v fluctuates within a range that is not determined as a power failure, the first DC / The secondary voltage can be adjusted by operating the AC converter 24 to control the primary voltage of the transformer 1. That is, by compensating the fluctuation of the input power supply voltage in series with the voltage of the secondary winding 1b of the transformer 1, a stable voltage can be supplied to the load via the AC output terminals U and V. .

Here, if the fluctuation of the input power supply voltage is a voltage drop, the transformer 1 performs voltage addition to compensate for the voltage drop. When a load current flows through the AC buses 31 and 32 in this state, power is injected from the first DC / AC converter 24 to the AC buses 31 and 32 via the transformer 1.
The energy required at that time is supplied from the AC buses 31 and 32 by performing the converter operation (rectifier operation) of the second DC / AC converter 25 having a common DC section.

  On the contrary, if the fluctuation of the input power supply voltage is a voltage increase, the transformer 1 performs voltage subtraction to compensate for the voltage increase. When a load current flows through the AC buses 31 and 32 in this state, the first DC / AC converter 24 absorbs DC power via the transformer 1. This direct current power (energy) is regenerated to the alternating current buses 31 and 32 side by causing the second DC / AC converter 25 having a common direct current section to operate as an inverter.

FIG. 4 shows the power supply voltage, the secondary voltage of the transformer 1, and the output voltage of the uninterruptible power supply for each of the normal period, the decrease period, and the increase period of the input power supply voltage.
As is clear from FIG. 4, it is possible to output a constant voltage from the uninterruptible power supply device in both the decrease period and the increase period of the input voltage as in the normal period.

When the input power supply fails, as a second operation mode, the thyristor AC switch 4 in FIG. The AC / AC converter 25 can convert to AC power and supply stable power to the load.
The detailed operation of such a series voltage compensated uninterruptible power supply is disclosed in Patent Documents 1 and 2.

US Pat. No. 4,651,265 (FIG. 6A, etc.) Japanese Patent No. 3390007 (FIG. 1 etc.)

Now, in the uninterruptible power supply, improvement of device efficiency and reduction in size and price are major issues.
In the prior art, when the rating of the uninterruptible power supply shown in FIG. 3 is 100%, the capacities of the second DC / AC converter 25 and the reactor 6 are the device ratings for the case where the input power supply fails. The same 100% capacity is required. Moreover, the capacity | capacitance of the 1st DC / AC converter 24 and the reactor 9 assumes 15% or more which is the range requested | required of the general uninterruptible power supply device for the voltage fluctuation compensation range before the input power supply fails. If 20% is set, 20% of the device rating is required.
Therefore, in the prior art, the total capacity of the first and second power converters 24 and 25 requires 120% of the apparatus rating, and similarly, the total capacity of the reactors 6 and 9 also needs 120% of the apparatus rating. ing.

In addition, among the loss generated in the conventional uninterruptible power supply, the loss occurring in the range where the input power source does not become blackout occupies the most time, and the DC / AC converter 24 and the reactor 9 have a capacity of 20%. And the no-load loss of the DC / AC converter 25 and the reactor 6 that are in the standby operation state with a capacity of 100%.
Here, it is assumed that the operating loss of a general DC / AC converter is 3% of its variable capacity and the no-load loss is 0.5%. Similarly, the operating loss of the reactor is 1% of the reactor capacity, no load Assuming that the loss is 0.5% and other losses such as thyristor type AC switch 4 and transformer 1 are 1%, the efficiency of the uninterruptible power supply shown in FIG.
100% − {20% × (3% + 1%) + 100% × (0.5% + 0.5%) + 1} ≈97.2%.

As described above, in the prior art shown in FIG. 3, the apparatus efficiency is about 97.2%, and it is difficult to further increase the efficiency because of the inherent characteristics of the circuit configuration.
SUMMARY OF THE INVENTION Accordingly, the problem to be solved by the present invention is to provide an uninterruptible power supply device that is smaller, more efficient, and less expensive than the prior art.

In order to solve the above-mentioned problem, the invention described in claim 1 includes a transformer in which a secondary winding is connected in series to an AC bus between AC input and output terminals, and an AC terminal is connected to the primary winding of the transformer. A second direct current section for sharing power between the first DC / AC converter and the first DC / AC converter, and the alternating current terminal is connected to the alternating current output terminal. An uninterruptible power supply comprising a DC / AC converter and power storage means connected to the direct current section,
At the time of fluctuation of the input power supply voltage excluding power failure, as a first operation mode, the voltage of the secondary winding is adjusted by the power conversion operation of the first DC / AC converter to stabilize the AC output voltage, Direct current power converted by the first DC / AC converter is exchanged with the alternating current bus via the second DC / AC converter, and at the time of power failure of the input power source, as a second operation mode, In the uninterruptible power supply that converts the DC power of the power storage means into AC power by a second DC / AC converter and supplies stable AC power to the load,
An opening / closing means is connected between the AC terminal of the first DC / AC converter and the AC terminal of the second DC / AC converter;
In the first operation mode in which the input power is sound, the opening / closing means is opened, and in the second operation mode in which the input power is interrupted, the opening / closing means is closed and the first and second DC / AC converters are operated in parallel. It is something to be made.

According to the present invention, in the second operation mode in which the input power supply is interrupted, the AC terminals of the first and second DC / AC converters are connected by the switching means to operate both in parallel and supply power to the load. By doing so, the capacity required for the second DC / AC converter can be made smaller than in the conventional case. As a result, the entire uninterruptible power supply can be reduced in size and price.
Further, since the capacity of the second DC / AC converter can be reduced, the no-load loss of the second DC / AC converter when the input power supply is healthy is reduced, and the efficiency of the entire uninterruptible power supply is improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram of this embodiment. The same components as those in FIG. 3 are denoted by the same reference numerals, and the description thereof is omitted. Hereinafter, different portions will be mainly described.

  In FIG. 1, a switch 10 is provided between both ends of the primary winding 1a of the transformer 1 and the AC output terminals U and V (between the AC terminals of the first and second DC / AC converters 24 and 25). Are connected, and the DC / AC converters 24 and 25 are operated in parallel by closing the switch 10, whereby the output of the first DC / AC converter 24 is changed to that of the second DC / AC converter 25. Along with the output, the load can be supplied from the AC output terminals U and V.

  In the circuit configuration described above, when the input power supply is healthy and the input power supply voltage varies except for a power failure, the thyristor AC switch 4 is turned on and the same operation as in the prior art is performed in the first operation mode to output the output voltage. Stabilize. At that time, the switch 10 is open.

  Next, in the second operation mode in which the input power supply has failed, the thyristor type AC switch 4 is turned off, the switch 10 is closed, and the first and second DC / AC converters 24 and 25 are operated in parallel. Thus, the DC power of the storage battery 3 is converted into AC power by both the first and second DC / AC converters 24 and 25, and the sum is supplied from the AC output terminals U and V to the load. For this reason, stable AC power can be supplied to the load in the same manner as when the power supply is healthy.

  At this time, the current sharing ratio between the second DC / AC converter 25 and the first DC / AC converter 24 is approximately proportional to the capacity of the reactor 6 and the reactor 9 connected to each of them (inversely proportional to the impedance). ). Therefore, the total capacity of the first DC / AC converter 24 and the second DC / AC converter 25 is set to 100%, which is the same as the device rating, and the total capacity of the reactor 9 and the reactor 6 is the same ratio. Therefore, it may be set to 100% which is the same as the device rating.

  An example of the relationship between each current and capacity at this time is shown in FIG. As shown in FIG. 2, by closing the switch 10 and operating the first and second DC / AC converters 24 and 25 in parallel at the time of a power failure of the input power supply 30, the capacity is, for example, 80% of the device rating. A current of 80% of the device rating is supplied to the load 40 from the second DC / AC converter 25 and the reactor 6 side, and a current of 20%, which is a shortage of the device rating, has a capacity of 20% of the device rating. It is supplied from the first DC / AC converter 24 and the reactor 9 side.

  In the conventional device, the voltage compensation range in the normal range where the input power supply does not cause a power failure is 15%, and the capacity of the first DC / AC converter 24 and the reactor 9 is set to 20% of the device rating with a margin. , The total capacity of the DC / AC converters 24 and 25 and the total capacity of the reactors 6 and 9 are 120%, respectively, but according to the present embodiment, 100% is sufficient for both. As a whole, downsizing and price reduction are possible.

  In the present embodiment, as described above, when the capacities of the first DC / AC converter 24 and the reactor 9 are set to 20% of the device rating, the second DC / AC converter 25 and the reactor 6 are Each of them is 80% of the device rating, and the second DC / AC converter 25 and the reactor 6 can be reduced in size and cost compared to the case where 100% of each is conventionally required.

Here, it is assumed that the operation loss of a general DC / AC converter is 3% of the converter capacity and the no-load loss is 0.5%. Similarly, the operation loss of the reactor is 1% of the reactor capacity and no load loss. When the load loss is 0.5% and the other losses of the thyristor AC switch 4 and the transformer 1 are 1%, the efficiency of the uninterruptible power supply according to this embodiment is
100% − {20% × (3% + 1%) + 80% × (0.5% + 0.5%) + 1} = 97.4%, which can be more efficient than the prior art shown in FIG. Become.

  In the above embodiment, the single-phase device has been described as shown in FIG. 1, but it is apparent that the present invention can achieve the same effect even in a multi-phase uninterruptible power supply such as a three-phase.

It is a circuit block diagram which shows embodiment of this invention. It is a figure which shows the relationship between each part capacity | capacitance and electric current sharing in embodiment of this invention. It is a circuit block diagram of the conventional series voltage compensation type | formula uninterruptible power supply. It is a wave form diagram which shows the operation | movement of FIG.

Explanation of symbols

1: Transformer 1a: Primary winding 1b: Secondary winding
3: Storage battery 4: Thyristor type AC switch 6, 9: Reactor 7, 8: Filter capacitor 10: Switch 20, 21, 22, 23: Semiconductor bridge 24, 25: DC / AC converter 30: Input commercial power supply 31, 32: AC bus 40: Load u, v: AC input terminal U, V: AC output terminal

Claims (1)

A transformer having a secondary winding connected in series to an AC bus between the AC input / output terminals, a first DC / AC converter having an AC terminal connected to the primary winding of the transformer, and a first DC / A second DC / AC converter in which a DC unit for transmitting and receiving power to and from the AC converter is shared and an AC terminal is connected to an AC output terminal, and an electric power storage connected to the DC unit An uninterruptible power supply comprising:
At the time of fluctuation of the input power supply voltage excluding power failure, as a first operation mode, the voltage of the secondary winding is adjusted by the power conversion operation of the first DC / AC converter to stabilize the AC output voltage, Direct current power converted by the first DC / AC converter is exchanged with the alternating current bus via the second DC / AC converter, and at the time of power failure of the input power source, as a second operation mode, In the uninterruptible power supply that converts the DC power of the power storage means into AC power by a second DC / AC converter and supplies stable AC power to the load,
An opening / closing means is connected between the AC terminal of the first DC / AC converter and the AC terminal of the second DC / AC converter;
In the first operation mode in which the input power is sound, the opening / closing means is opened, and in the second operation mode in which the input power is interrupted, the opening / closing means is closed and the first and second DC / AC converters are operated in parallel. An uninterruptible power supply that is characterized by

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