JPH01148069A - Power converting circuit - Google Patents

Abstract

PURPOSE:To obtain a power converting circuit with a small power loss by using an auto-transformer having a necessary minimum capacity as an output transformer. CONSTITUTION:As to a three-phase load, the required capacity per phase of a three phase auto-transformer Tb is expressed by the equation I. When a secondary side phase voltage V2P is a little larger than a primary side phase voltage V1P, V2P V1P, that is, the required capacity W1P may be sufficiently smaller than the product of the secondary side phase voltage V2P and a three-phase balanced load phase circuit I3. As to a single-phase load, on the other hand, there is a small unbalance in load capacities between respective phases, because load equipment groups are distributed and connected between respective phases. Said auto-transformer Tb works as a reactor having a neutral-point for the load and each phase capacity W1l is expressed by the equation II. Therefore, the total capacity W1 per phase of the auto-transformer Tb is expressed by the equation III and the capacity per phase of the auto-transformer Tb may be a little larger than the required capacity.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improvements in power conversion circuits.

[Prior Art] A three-phase AC power supply, for example, a three-phase 200 V rms AC power supply, is connected to a three-phase four-wire type 200 Vrms AC power supply having a frequency different from that of the power supply.
When converting to a Vr■S power source, the input power source is first 3-phase full-wave rectified and smoothed to obtain a 270V DC power source, and then this is converted into a 3-phase constant frequency power source using a 3-phase bridge type power switching circuit and an LC smoothing circuit. It is usually obtained by converting it to alternating current. The three-phase alternating current thus obtained is a three-phase, three-wire type with a maximum line voltage of about 175 V rms. Therefore, to obtain a 3-phase 4-wire output of 200/115 Vrss, use a 3-phase transformer from the above 3-phase 3-wire output, step up the voltage, and connect the secondary side of the 3-phase transformer to a Y-connection. A method of obtaining a neutral point has been adopted.

Figure 3 shows an example of a conventional power conversion circuit, in which 1 is a three-phase full-wave rectifier power supply circuit, 2 is a bridge type switching circuit, and 3 is a reactor Lu=Lv and a Yabashita Cu-Cv.
This is a smoothing circuit consisting of:

As shown in the figure, the DC voltage rectified by the three-phase full-wave rectifier power supply circuit 1 is transferred to the power switching circuit 2.
- Pulse width modulation is performed by high frequency chopper operation by transistors Qup-Qvn to generate a three-phase AC voltage.

This three-phase AC voltage is smoothed by a smoothing circuit 3 and a sine wave 3 is generated.
Obtain the phase AC voltage.

Ta in the figure is a three-phase transformer that boosts the three-phase AC voltage to obtain a predetermined voltage between the lines, and also obtains a neutral point from the connection point of the Y connection. Further, the inverter control circuit 4 feeds back the output voltage to the power switching circuit 2 and sends a chopper operation signal to each switching element of the power switching circuit 2.

Next, the operation will be explained. For example 200 to input power supply
When a three-phase power supply of V rtrs is supplied, a DC voltage of approximately 270V is generated in the three-phase full-wave rectified power supply circuit 1. Note that this power supply circuit is omitted when a DC voltage of 270 V is provided as a bus bar of the power distribution system. The power switching circuit 2 includes U-phase power transistors Qup and Qu.
nSV phase Q vpSQ vn.

It is composed of a diode connected anti-parallel to the W-phase QV[)SQwn and each power transistor,
A high frequency chopper operation is performed by a drive signal from the inverter control circuit 4, and the pulse width is modulated so that the smoothed value between each line becomes a sine wave.

The smoothing circuit 3 forms a low-pass filter, smoothes the pulse width modulated output voltage from the power switching circuit 2, and extracts a fundamental sine wave.

This sine wave voltage has an input power supply voltage of 3-phase 200V r
In the case of a voltage obtained by full-wave rectification of ms or a DC voltage of 270 V, the maximum three-phase line voltage is 175 V.
It will be about r+ms. Also, the output from smoothing circuit 3 is 3
It is a phase 3-wire system. Therefore, a transformer Ta is provided to boost the line voltage to 200 V rags, and the secondary side of the transformer Ta is Y-connected to obtain a neutral point.
200V/115Vrms of 3-phase 4-wire system is obtained, and this output is converted to 3-phase 200V rms and single-phase 115V.
Can be used as r+ms power supply.

The inverter control circuit 4 detects the output voltage as a feedback value, controls each pulse width in pulse width modulation using the feedback value, and sends this to the power switching circuit 2 as a drive signal, so that the output voltage value is set to a predetermined value. It functions so that it is maintained.

[Problems to be Solved by the Invention] In the power conversion circuit configured as described above, the capacity of the transformer Ta must be equal to or greater than the output of the power conversion circuit. 9, the shape and weight of the transformer Ta increase, and the transformer Ta
A loss of [output VAX (1-η)] occurs in the part. Note that η is the efficiency of the transformer Ta.

This is not desirable for power converters for vehicles and aircraft.

The present invention has been made in order to solve the above-mentioned problems of conventional devices, and aims to provide a power conversion circuit that requires a small transformer capacity and reduces power loss within the transformer.

[Means for Solving the Problems] In order to achieve the above object, in the power conversion circuit according to the present invention, an autotransformer having the minimum required capacity is used for the output transformer.

[Function] Since the power conversion circuit is configured as described above, the capacity of the autotransformer is basically only the step-up capacity, which allows the transformer to be made smaller and lighter, and reduces the loss within the transformer. It also requires less. It is also possible to use an autotransformer as a neutral point forming actor to obtain the neutral point.

[Embodiment of the Invention] FIG. 1 is a block diagram of a power conversion circuit showing an embodiment of the present invention, in which numerals 1 to 4 are the same parts as in the conventional device, and Tb is an autotransformer. Further, FIG. 2 is a configuration diagram showing the load state of the autotransformer Tb.

In FIG. 2, Vll is the output terminal U' of the smoothing circuit 3,
Line voltage of v', W', V tp 3 (7) Single s
V2p is the voltage between the input terminal of the three-phase half-turn transformer Tb and the neutral point N, that is, the primary phase voltage, and V2p is the voltage between the output terminal of the transformer Tb and the neutral point N. voltage i.e. 2
The next phase voltage, also V2e, is the line voltage at the output terminals U, V, W. Figure smell.

The three-phase loads Z 3u, Z 3v, and Z 3w are three-phase balanced loads, which include a balanced load connected between each line and a phase voltage balanced load. Note that Zlu is a phase voltage load.

In FIG. 1, for example, the input power supply voltage is 200v ru
ns, the output voltage Vll of the smoothing circuit 3 is about 175Vra+s, as in the case of FIG.

The required capacity Wlp for each equivalent of the three-phase half-wound transformer Tb for a three-phase load is expressed as follows. This means that when V2p is slightly larger than vlp, V2pS? V lp , and Wlp may be a value sufficiently smaller than V2p-13. Note that 13 indicates a phase current for a three-phase balanced load, and V2p·13 indicates a phase output.

When the input voltage is 200 V rms, when the output voltage is 200 V ris, this is 10, 125 x 115 x I3 Therefore, the capacity of the autotransformer Tb for the three-phase balanced load can be 0.125 in this example. It is shown that.

On the other hand, for single-phase loads, load equipment groups are distributed and connected between each phase as much as possible, so the imbalance in load capacity between each phase is reduced. Zlu indicates this unbalanced load. For this load, the autotransformer Tb acts as a neutral point forming actor.

Each customer as this reactor = Wt+ is Wll-V2p
@I l is sufficient. Note that 1 is the current flowing through the load Zlu.

Therefore, the total capacity Wl for each equivalent of the autotransformer Tb
is W I −W 1p+ W 11 , and since Wll is usually much smaller than Wlp, the capacity of each equivalent of transformer Tb only needs to be slightly larger than wtp.

Furthermore, since the efficiency of this autotransformer Tb is equivalent to that of the ordinary transformer shown in FIG. 3, the loss Wl·η generated therein is sufficiently small.

As described above, the autotransformer Tb can be of small capacity and the loss generated by the transformer can be reduced, so that the overall efficiency of the power conversion circuit according to the present invention can be increased. .

[Effects of the Invention] Since the present invention uses an autotransformer in the power conversion circuit, it is possible to make the power conversion circuit smaller and lighter, and to obtain a highly efficient three-phase three-wire power source. Ta.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a power conversion circuit showing an embodiment of the present invention, FIG. 2 is a block diagram showing the load state of an autotransformer, and FIG. 3 is a block diagram of a conventional device. In the figure, 1 is a three-phase full-wave rectified power supply circuit, 2 is a bridge type power switching circuit, 3 is a smoothing circuit, 4 is an inverter control circuit, Tb is an autotransformer, and Vll is the line voltage between the output terminals of the smoothing circuit. , Vlp is the voltage between the output terminal of the autotransformer and the neutral point, V2p is the line voltage between the output terminals, Z
3u, Z 3vSZ 3v is a three-phase balanced load, and Zlu is a phase voltage load. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Patent Attorney Muneharu Sasaki Procedural Amendment (Voluntary) June 13, 1932

Claims (1)

[Claims] Consisting of a 3-phase full-wave rectifier circuit, a bridge type power switching circuit, a smoothing circuit, a 3-phase transformer, an inverter control circuit, etc., the 3-phase AC power source is rectified to become a DC power source, and then the DC power source is converted into a DC power source. In a power conversion circuit that converts the three-phase AC power supply into a three-phase four-wire AC power supply having the same voltage value and a different constant frequency, the three-phase transformer is
The three-phase three-wire AC voltage output obtained from the power switching circuit and smoothing circuit is connected to the low-voltage input side terminals of the three autotransformers, and the three autotransformers are connected to A power conversion circuit characterized in that a three-phase four-wire power source having a predetermined voltage value can be output by connecting the common terminals of the autotransformers to form a neutral point.