JPH0775459B2 - Power converter - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a power converter that has a function of an uninterruptible power supply using a battery and performs AC-AC power conversion.

[Prior art]

Figure 8 shows, for example, Fuji Bulletin Vol58, No11 (issued in 1985) 68.
It is a charging circuit block diagram which shows the conventional power converter shown on page 4, In the figure, 1 is an AC input power supply, 2 is a 1st diode rectifier connected to this AC input power supply 1,
3 is a capacitor connected to the output side of the first diode rectifier 2, 4 is a chopper connected to the output side of the first diode rectifier 2, and 5 and 6 are the chopper 4
Of the reactor and a capacitor connected to the output side of the battery, 7 is a battery connected in parallel to the capacitor 6, 8 is a first inverter connected to the battery 7 and the capacitor 6, and 9 is a battery of the first inverter 8. A first transformer connected to the output side, 10 is a second diode rectifier connected to the output side of the first transformer 9, and 11 and 12 are connected to the output side of the second diode rectifier 10. A reactor and a capacitor, 13 is a second inverter connected to the capacitor 12, and 14 and 15 are the second inverter 13
Is a reactor and a capacitor connected to the output side of the capacitor, and 16 is an AC load connected to the capacitor 15. Next, the operation will be described. First, the AC voltage of the AC input power supply 1 is rectified by the first diode rectifier 2,
It is smoothed by the capacitor 3 to obtain a DC voltage.
The chopper 4 performs DC-DC power conversion, and its DC output controls the voltage of the battery 7 via the reactor 5 and the capacitor 6 that act as a filter. Next, the first inverter 8 is a so-called voltage type inverter, which converts the DC voltage of the battery 7 into an AC voltage, and converts the DC voltage into a DC voltage again by the second diode rectifier 10 via the first transformer 9. Convert. The DC output voltage of the second Diode rectifier 10 is smoothed by the reactor 11 and the capacitor 12 which act as a filter.
Then, the second inverter 13 causes the capacitor 12
AC voltage is converted into AC voltage, and AC power is supplied to the AC load 16 via the reactor 14 and the capacitor 15 which act as a filter. Here, the first transformer 9
Has a function of insulating between the AC input power supply 1 and the AC load 16. A power MOSFET is used as a switching element of the chopper 4, the first and second inverters 8 and 13, and the reactors 5, 11, 14 and the capacitors 6, 1 acting as a filter are operated by switching operation at high frequency.
2, 15 and the first transformer 9 are downsized. Further, the second inverter 13 performs PWM control to supply an AC output voltage with a small waveform distortion to the AC load 16. Then, during steady operation, the chopper 4 charges the battery 7 via the first diode rectifier 2 while
It operates so as to supply power to the AC load 16 via the inverters 8 and 13. When the AC input power supply 1 fails, the chopper 4 stops operating and operates to supply power from the battery 7 to the AC load 16 via the first and second inverters 8 and 13.

[Problems to be Solved by the Invention]

Since the conventional power converter is configured as described above,
The distortion of the current of the AC input power source is large, the power capacity of the chopper 4 is large, and the AC power is obtained through a large number of power converters during steady operation, so the efficiency is reduced, and the filter There were problems such as the large number of components. The present invention has been made to solve the above problems, and can reduce the current distortion of an AC input power supply, have a power factor of 1, and improve the conversion efficiency of a power transformer. An object of the present invention is to obtain a relatively large-capacity power converter that generates an uninterruptible three-phase AC output from a three-phase AC power supply.

[Means for solving problems]

In the power converter according to the present invention, the first diode rectifier is connected in a three-phase bridge, the conventional chopper and the battery are connected in parallel to the main circuit through a filter, and the first inverter is provided in two stages. A current control type connected in series, and connected to a three-phase AC power source via a three-phase AC switch from a DC side intermediate point of the first inverter, and as a discharge path of a battery charged by the chopper. It is connected to the output terminal of the first diode rectifier through a discharging diode.

[Action]

In the power converter according to the present invention, the first inverter controls the instantaneous waveform of the input current to control the current of the three-phase AC power supply in a sine wave shape, and the chopper charges the battery to stop the operation of the chopper during a power failure. Power is supplied from the battery to the AC load by the first inverter and the second inverter via the discharging diode.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In the figure, the same parts as in FIG.
In the figure, 2a is a first diode rectifier connected to a three-phase bridge, 20P and 20N are reactors connected to the output terminals P and N of the first diode rectifier 2a, and 8a and 8b are first inverters. And, it is connected to a single-phase bridge and is connected in series between the reactors 20P and 20N. 26 is 3
Phase alternating current switch, wherein the first inverters 8a, 8a
It is connected between the intermediate connection point O of b and the three-phase AC power supply. 9
a and 9b are isolation transformers, and the first inverters 8a and 8a
It is connected to the output side of b. Reference numerals 10a and 10b denote second diode rectifiers, which rectify the outputs of the insulating transformers 9a and 9b and convert them into DC power. Reference numeral 13 is a second inverter, which is connected to a three-phase bridge and converts the DC power into three-phase AC power. Reference numeral 22 is a reactor for connecting the output of the first diode rectifier 2a to a capacitor.
The capacitor 23 is configured to be supplied to the capacitor 23, and the capacitor 23 constitutes a filter circuit. A chopper 24 is composed of a transistor which is a main switching element and a flywheel diode, and lowers the voltage of the capacitor 23 and supplies it to the battery 7 through the reactor 25. Reference numeral 26 is a three-phase AC switch, and 27 is a discharging diode, which is constructed by connecting in antiparallel to the series body of the transistors of the reactors 22 and 25 and the chopper 24. Next, the operation will be described. First, the operation of the power converter portion including the first diode rectifier 2a, the first inverters 8a and 8b, the isolation transformers 9a and 9b, the second diode rectifiers 10a and 10b, and the AC switch 26 is a conventional example. Since it is the same as, the description will be omitted. Therefore, description will be given below with reference to the operation waveforms in FIG. First, the first inverters 8a and 8b operate as current type inverters.
Instantaneous waveform control of each input current I _P , I _{N is performed} by high frequency switching. For example, the operation of each arm switch 81, 82, 83, 84 of the first inverter 8a is as follows. Turn on the arm switches 81 and 83 at the same time to input the input current Ip of the reactor 20P.
Then, the arm switches 81 and 84 are turned on at the same time to convert the input current Ip of the reactor 20P to the capacitor 12 side through the insulating transformer 9a and the second diode rectifier 10a, and the input current Ip rises. Go down. Next, the arm switches 82 and 84 are turned on to raise the input current Ip again. Next, the arm switches 82 and 83 are turned on to convert the input current Ip to the capacitor 12 side again. By repeating the above switching mode by high frequency switching, the input current Ip of the reactor 20P is controlled following the current reference. FIG. 2 shows the current waveforms of each part, and the input currents I _P and I _{N of the} reactors 20P and 20N are shown.
Is controlled to a current wave shape similar to the positive and negative three-phase half-wave rectified voltage of the three-phase AC power supply voltage. At this time, the current I _{O at} the intermediate point between the two inverters 8a and 8b becomes a difference current between the input current I _P and the output current I _N, and has a triangular waveform as shown in FIG. By switching the current I _O at this intermediate point every 60 ° and returning it to the AC power source side through the three-phase AC switch 26, it is combined with the input current of the first diode rectifier 2a, and as shown in the figure. Three-phase sinusoidal AC power supply currents Iu, Iv, Iw are obtained. Next, the charging operation of the battery 7 will be described with reference to the voltage waveforms of the respective parts in FIG. e _u, e _v, e _w denotes the phase voltage of the three-phase AC power _{source, e p, e n, e} o each output P of the first diode rectifier 2a, N and the first inverter 8a, 8b of The potential at the midpoint 0 is applied. V _po and V _on are the first diode rectifiers
2a shows the voltage waveform between the output terminals P and N and the intermediate point 0 of the first inverters 8a and 8b, where V _pn is the first diode rectifier 2
The voltage waveform between the output terminals P and N of a is shown. Furthermore, | Vsu
|, | Vsv |, and | Vsw | represent the waveforms of the absolute values of the applied voltages of the AC switches Su, Sv, and Sw, respectively. Terminal voltage of capacitor 23
Vc becomes the average value of the output voltage V _pn of the first diode rectifier 2a, and if the effective line value of the AC power supply voltage is Es, become. Battery voltage V _B is 90% if the lower limit of allowable AC power supply voltage fluctuation is Becomes That is, if the AC power supply voltage drops within 10%, the inverters 8a, 8a, 8
Supply power to b. Chopper 24 is the voltage V of capacitor 23
The operation of charging the battery 7 by lowering the voltage of c is performed, and Vc> V _B
Is. Therefore, if the AC power supply voltage drops to within 10%, the battery 7 can be charged by the chopper 24. Here, the reactors 22 and 22 are provided to reduce ripple components of the charging current of the capacitor 23 and the battery 7, respectively. Next, when the AC power supply fails, the AC switch 26 and the chopper 24 are stopped and the battery 7 discharges the diode.
Power is supplied to the first inverters 8a and 8b via 27.
At this time, the input currents I _p and I _n of the first inverters 8a and 8b must be controlled to be the same. This is because the current I _{o at} the midpoint 0 of both inverters 8a and 8b becomes zero because the three-phase AC switch 26 is stopped.
For this reason, the first inverters 8a and 8b perform switching operations at exactly the same timing, or
Either one of 8a and 8b is operated in the DC short-circuit mode (for example, the arm switches 81 and 83 or the arm switches 82 and 84 of the first inverter 8a are simultaneously turned on). In addition,
In the latter case, the first inverters 8a and 8b may be periodically operated alternately in the DC short circuit mode. In the above embodiment, the mechanical switch is shown as the three-phase AC switch 26. However, as shown in FIG. 4, it is composed of a diode bridge circuit and a bidirectional semiconductor switch 26a composed of a self-extinguishing type semiconductor device. Alternatively, the surge voltage generated when the semiconductor switch is turned off may be returned to the capacitor 23 via the snubber diode 30 and clamped. Further, the reactor 22 may be divided and reactors 22a and 22b may be provided on the output terminals P and N sides of the first diode rectifier 2a, respectively. Furthermore, diodes 28a and 28b may be connected in series with the reactors 22a and 22b. The capacitor 23 may be inserted and connected in the charging direction, and in this case, the current of the first diode rectifier 2a can be prevented from joining via the snubber diode 30 and the semiconductor switch 26a.
Further, the discharging diode 27 of the battery 7 is divided into 27a and 27b, and the output terminals P and N of the first diode rectifier 2a are respectively divided.
May be inserted and connected to the side, in this case, in a large capacity system in which a plurality of power converters in FIG. It is possible to prevent the current from circulating between the power converters. In addition, L. is connected to the AC input terminal of the first diode rectifier 2a.
A filter composed of C or L, C, R may be provided to absorb the high frequency current ripple component generated by the first inverters 8a, 8b. In the above embodiment, the case where the capacitor 23 is charged from the output side of the first diode rectifier 2a has been described, but as shown in FIG.
It may be charged via the snubber diode 30 of. The snubber capacitor 40 is connected to the output side of the snubber diode 30, and the terminal voltage Dcc of the snubber capacitor 40 is, as shown in FIG.
It becomes a voltage waveform obtained by rectifying Sv, Sw voltages | Vsu |, | Vsv |, | Vsw |, and its average value is approximately 0.966Es. The voltage Vc of the capacitor 23 is smoothed by the reactors 31a and 31b. In this case, the voltage V _B of the battery 7 is V _B 0.9 × Vcc average = 0.9 × 0.966 Es = 0.87 considering the 10% decrease in the power supply voltage.
It becomes Es. Therefore, the voltage V _B of the battery 7 in the case of FIG.
The voltage level is 79% compared to (≈1.1Es). Further, in the above embodiment, the first inverters 8a and 8b are shown to be bridge-connected, but the switch element may be composed of two arms as shown in FIG. The arm switches 85 and 86 are alternately controlled to be turned on and off, and when the arm switch 85 is turned off and the arm switch 86 is turned on, the second diode rectifier is connected via the isolation transformer 9c.
The power is converted to the capacitor 12 side by 10c, and the arm switch 8
When 5 is on and arm switch 88 is off, the isolation transformer 9c is reset via the second diode rectifier 10c. FIG. 7 (a) shows the diode of the second diode rectifier 10c with two arms, and FIG. 7 (b) shows the diode with four arms, both of which perform the same operation. In the latter case, the applied voltage of each diode becomes smaller. The secondary side of the insulation transformer 9c is unequally divided in order to increase the voltage at the time of resetting and accelerate the resetting operation. Further, in the above embodiment, the first inverters 8a, 8b, the second inverter 13, the chopper 24, and the AC switch 26 are constituted by transistors as switching elements, but other self-extinguishing semiconductor elements (for example, , MOSFET, B
IMOS, GTO, GTO, SIT, IGBT, etc.), and the same effect as the above-mentioned embodiment is obtained.

【The invention's effect】

As described above, according to the present invention, the charging path of the battery of the power converter is stepped down via the filter from the output side of the first diode rectifier or the rectified output side of the voltage across the three-phase AC switch. The charging circuit is configured to be charged by a chopper, and the discharging path of the battery is configured to be discharged to the output side of the first diode rectifier via the discharging diode, and the first inverter is configured to be a current source inverter, and high frequency Since the instantaneous waveform control is performed by switching, the power factor on the side of the AC power supply can be made almost 1, the high frequency current component can be reduced, and the chopper is configured to be used only for charging the battery. The efficiency of the converter can be improved, and the capacitor of the input filter of the chopper is also used as the voltage clamp circuit of the AC switch. Since the, the effect obtained is that by reducing the breakdown voltage of the AC switch of three-phase.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing a power converter according to an embodiment of the present invention, FIGS. 2 and 3 are operation waveform diagrams of the power converter of FIG. 1, FIG. 4, FIG. 5 and FIG. FIG. 6 is a circuit configuration diagram of a power converter showing another embodiment of the present invention, FIG. 6 is an operation waveform diagram of the power converter of FIG. 5, and FIG. 8 is a circuit configuration diagram showing a conventional power converter. is there. In the figure, 1 is an AC input power source, 2a is a first diode rectifier, 8a and 8b are first inverters, 9a, 9b and 9c are isolation transformers, 10a, 10b and 10c are second diode rectifiers, and 13 is 2nd inverter, 7 is a battery, 24 is a chopper, 26, 26a
Is an AC switch. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (5)

[Claims] 1. A first diode rectifier for converting a three-phase AC power supply into DC power, and a first diode rectifier connected in series to the output side of the first diode rectifier in two stages via a reactor. A first inverter for individually controlling the positive and negative output currents into positive and negative polarity three-phase half-wave rectified waves; an intermediate point of the first inverters connected in series in the two stages; A three-phase AC switch that is connected between the three-phase AC power supplies and returns a difference current between the positive-side and negative-side output power supplies of the first diode rectifier to the three-phase AC power supply, and the output of the first inverter. Power conversion including an insulation transformer connected to the side, a second diode rectifier that rectifies the output of the insulation transformer, and a second inverter that converts the DC output power of the second diode rectifier to AC In the bowl, A chopper for stepping down a voltage obtained by rectifying a voltage applied to the output side of the first diode rectifier or the three-phase AC switch through a filter, and a battery charged by the chopper, A power converter comprising: a discharge diode connected in a forward direction from a positive side of the battery to a positive side of the first diode rectifier. 2. When the power of the three-phase AC power supply is interrupted, the operation of the chopper and the AC switch is stopped, and the inverters connected in series in the two stages are operated at exactly the same switching timing, or one of them is alternately operated. The power converter according to claim 1, wherein only the inverter is operated in the DC short-circuit mode. 3. A diode rectifier in which each phase of the three-phase AC switch is bridge-connected, and a semiconductor switching element connected between the DC ends of the diode rectifier, the terminal voltage of the semiconductor switching element being a snubber. The power conversion according to claim 1, wherein the voltage is rectified by a diode and returned to a filter capacitor on the input side of the chopper to clamp a voltage generated when the semiconductor element is switched. vessel. 4. The effective value of the lower limit of the three-phase AC power supply voltage which is allowed when the charging voltage of the battery charged by the chopper is charged from the output side of the first diode rectifier. The power converter according to claim 1, wherein the power converter is configured as follows. 5. When the charging voltage of the battery is charged from the voltage obtained by rectifying the applied voltage of the AC switch, the effective value of the lower limit of the allowable three-phase AC power supply voltage is set.
The power converter according to claim 1, wherein the power converter is 0.966 times or less.