JPH10271823A - Power factor improved three-phase converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a factor improved three-phase power converter which can satisfy harmonic control and phase current balance concurrently by commonizing the control circuit of the converter in three-phase four-line AC feeding. SOLUTION: In three-phase four-line AC feeding, series circuits of booster choppers 1, 17, 18, and DC-DC converters 8, 9, 20 are disposed respectively between respective phases U, V, W, and a neutral N, and their outputs are connected in parallel to be supplied to a load 21. The circuit is formed so that respective switching elements may repeat ON and OFF with the same driving signal, by setting the output voltages V1, V2, V3 of the respective boosting choppers 1, 17, 18 so as to be DC voltage of the same value, and controlling the respective DC-DC converters 8, 9, 20 with one control circuit 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type stabilized DC power supply for suppressing a harmonic current in a three-phase four-wire AC power supply.

(2)

2. Description of the Related Art In a three-phase four-wire AC power supply, three converters having a single-phase harmonic suppression function are connected between a neutral point and each phase, and respective outputs are connected in parallel to form a power supply circuit. There are known ways to do this. In this method, if the current flowing through each phase is a sine wave of the same value, the current flowing through the neutral line becomes zero.

[0003]

However, in the conventional configuration, since each converter has its own control circuit, the harmonic component of each phase current is reduced, but the balance of each phase current, ie, each converter The loads to be shared are not necessarily the same, and a slight difference in the output voltage setting of each control circuit causes a large difference between the respective phase currents, and a large current flows through the neutral line. For this reason, it has been difficult to realize a power supply circuit with a conventional configuration without the load balance function.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a three-phase power factor improving converter in which phase currents are balanced by a circuit configuration similar to that of the prior art and by a simple method.

[0005]

FIG. 1 shows an embodiment of the present circuit. In the three-phase four-wire AC power supply, first, the boost chopper circuit 1 is connected between the U phase and the N phase. This step-up chopper circuit 1 includes a full-wave rectifier 2, an inductor 3, a switch element 4, a rectifier element 5,
The control circuit 7 is controlled by a capacitor 6 so that the phase current of the U-phase is proportional to the voltage waveform between the U-phase and the N-phase, and the output voltage V1 is a constant DC voltage.

[0006] (3) Next, the output V1 of the step-up chopper circuit 1 is input to D
The C-DC converter 8 is connected. The DC-DC converter 8 includes switch elements 9 and 10, a transformer 11,
Rectifier elements 12 and 13, inductor 14, capacitor 1
The on / off timing of the switch elements 9 and 10 is controlled by the control circuit 16 so as to output the DC voltage output V0 in the forward type converter constituted by 5. Note that the forward converter is a method of supplying power to an output when a switching element is turned on, and a half-bridge or full-bridge converter is also included in this range.

The circuit configurations of the boost chopper circuit 1 connected between the U-phase and the N-phase, the boost chopper circuit 17 connected between the V-phase and the N-phase, and the boost chopper circuit 18 connected between the W-phase and the N-phase are as follows. The same applies to each output voltage V
The respective control circuits are set such that V1, V2, and V3 satisfy V1 = V2 = V3 under certain input / output conditions.

Further, each of the output voltages has a regulation characteristic such that the voltage decreases as the load increases. DC-DC converters 8, 19 and 20 are connected to the outputs of the boost chopper circuits, respectively. These DC-D
The C converter has the same circuit configuration, and its outputs are connected in parallel and supplied to the load 21. The DC voltage V0 supplied to the load 21 is kept constant by the control circuit 16.
Also, the control circuit 16 sends the DC-DC converters 8, 1
The drive signals sent to the switching elements 9 and 20 are the same.

In such a circuit configuration, if the input voltages of the DC-DC converters 8, 19, and 20 have the same value and the same output voltage and the same drive signal for the main switch as described above, DC-DC converters 8, 19,
The load shared by 20 is also the same (4). That is, each of the DC-DC converters 8, 19, 2
Boost chopper circuits 1, 1 supplying an input voltage to 0
The powers converted by the power converters 7 and 18 are the same, and if there is no voltage imbalance in the three-phase four-wire AC power supply, the phase currents of the U, V, and W phases are also the same.

Even if the load of the boost chopper circuit of a certain phase is higher than that of another boost chopper circuit, the output voltage of the boost chopper circuit has a regulation characteristic in which the voltage decreases as the load increases. When the input voltage of the converter falls, the load currents shared by the DC-DC converters 8, 19, and 20 work in a direction to balance.

With the above-described method, it has become possible to simultaneously satisfy the harmonic suppression and current balance of each phase current, which cannot be achieved by the conventional configuration.

[0012]

According to the present invention, in a three-phase four-wire AC power supply, the suppression of the harmonic component of the phase current and the balance of each phase current are simultaneously satisfied with a very simple circuit configuration.

[Brief description of the drawings]

FIG. 1 is a harmonic suppression power supply circuit in a three-phase four-wire AC power supply.

[Brief description of reference numerals]

 1,17,18 Step-up chopper circuit 2 Full-wave rectifier 3,14 Inductor 4,9,10 Switch element 5,12,13 Rectifier element 6,15 Capacitor 7,16 Control circuit (5) 8,19,20 DC-DC Converter 11 Transformer 21 Load

Claims (4)

[Claims] 1. A three-phase four-wire AC power supply having a neutral point between each phase and
In a circuit configuration in which three sets of single-phase converters having a harmonic suppression function are connected, a boost chopper circuit is used as a single-phase input power supply between the neutral point and each phase, and an isolated DC-DC having this output as an input. Converters, each output of the isolated DC-DC converter is connected in parallel, and the DC-DC converter
-A three-phase power factor correction type converter characterized by driving a main switch of a DC converter. 2. The three-phase power factor improvement converter according to claim 1, wherein the output voltages of the respective boost chopper circuits have the same value. 3. The three-phase power factor correction type converter according to claim 2, wherein a current of each of said isolated DC-DC converters is balanced by regulation of an output voltage of each of said step-up chopper circuits. Features a three-phase power factor improving converter. 4. The three-phase power factor correction type converter according to claim 1, wherein each of the isolated DC-DC converters is a forward type DC-DC converter. converter.