JP2000069754A - Converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve conversion efficiency by reducing current-carrying loss in conducting conversion into single-phase alternating current/three-phase alternating current. SOLUTION: This converter circuit consists of AC switches S1 to S6 and two wiring reactors L1, L2 as compared with a conventional one consisting of a high power-factor converter and a three-phase inverter. By taking two energized AC switches, for example, S1 and S4, S2 and S5 or S3 and S6 to reduce current-carrying loss, it is possible to improve conversion efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC / AC for converting a single-phase AC voltage into a three-phase AC voltage having different frequencies.
The present invention relates to a converter (converter circuit), and more particularly to a converter circuit for converting an AC input current into a sine wave having a high power factor while reducing the number of conversion stages to reduce the size and the loss.

[0002]

2. Description of the Related Art FIG. 3 shows a conventional example of this type of circuit. That is, the input of the rectifier bridge circuit composed of the diodes D1 to D4 is provided to the single-phase AC input power supply E via the input terminals 1 and 2, and the output of the rectifier bridge circuit is composed of the transistor Qc and the diode Dc via the reactor L2. The boosted chopper circuit has a capacitor C2 at the output of the boosted chopper circuit, and a three-phase inverter composed of switches Qu to Qz in which transistors and diodes are connected in parallel to the capacitor C2 in antiparallel to the output of the three-phase inverter. Is connected to a three-phase AC load (for example, a motor M) via output terminals U, V, and W, respectively.

The operation will be described below. Now, when the transistor Qc of the converter section is turned on, a current flows through the path of the single-phase AC power supply E → rectifier bridge circuit → reactor L2 → transistor Qc → rectifier bridge circuit → single-phase AC power supply E. Next, when the transistor Qc is turned off, the current flowing through the reactor L2 is reduced to the reactor L2.
2 → Diode Dc → Capacitor C2 → Rectifier bridge circuit → Single-phase AC power supply → Rectifier bridge circuit → Reactor L2
And the capacitor C2 is charged.

In the circuit as described above, the transistor Qc
By turning on, even when the input AC voltage is low,
A current can flow through the reactor L2. For this reason,
By adjusting the on / off ratio of the transistor Qc,
The input current can be sinusoidal. Further, the voltage of the capacitor C2 can be made constant. Next, the DC voltage of the capacitor C2 is adjusted by adjusting the on / off ratios of the switches Qu to Qz constituting the inverter unit by, for example, a well-known sine wave-triangle wave comparison (PWM) method or the like. A three-phase AC voltage whose frequency can be freely adjusted is output. With such a circuit, it is possible to output a three-phase AC voltage whose voltage and frequency can be freely adjusted while the input current is a current having a high power factor close to a sine wave.

[0005]

In the circuit of FIG. 3, current flows through two diodes (D1, D4 or D2, D3) and one transistor Qc or diode Dc in the converter section. Further, in the inverter section, from the capacitor C2 to the load, for example, Qu → load → Qy (or Qz), Qv → load → Qz (or Qx), Qw →
In the case where current flows through the path of load → Qx (or Qy) and the current of the load circulates, also Qu → load → Qv (or Q
w), current flows through the path of Qx → load → Qy (or Qz). Therefore, a current flows through at least two switches in the inverter section.

As described above, in the conventional circuit, two diodes and three transistor or diode semiconductor elements are energized in the converter section, and two semiconductor elements are energized in the inverter section, for a total of five semiconductor elements. The element will be energized. Since a semiconductor element has an on-state voltage, a conduction loss occurs, which causes a problem such as a decrease in conversion efficiency. There is also a problem that the number of parts is large, such as 11 diodes and 7 transistors, resulting in an increase in cost. Accordingly, it is an object of the present invention to reduce the number of parts, reduce conduction loss, increase conversion efficiency, and reduce the size and cost.

[0007]

In order to solve such a problem, the invention according to claim 1 is a converter circuit for converting a single-phase AC voltage into a three-phase AC voltage having different frequencies. It comprises a sixth alternating current (AC) switch and a two-winding reactor, short-circuits one terminal of each of the first to third AC switches, and connects the other terminal of each of the first to third AC switches to a three-phase load. , And the fourth to sixth AC
One terminal of the switch is short-circuited, the other terminals of the fourth to sixth AC switches are respectively connected to terminals of a three-phase load, and the short-circuited terminals of the first to third AC switches are connected to one of the two-winding reactors. Connected to one of the single-phase AC inputs via a winding, and connected the short-circuited terminals of the fourth to sixth AC switches to the other of the single-phase AC inputs via the other winding of the two-winding reactor; The other of the single-phase AC inputs is connected to the neutral point of the three-phase load, and a capacitor is connected between the neutral point and the three-phase load. In the first aspect of the present invention, one of the capacitors can have a larger capacitance than the other capacitors (the first aspect of the invention).

That is, by turning on two of the first to sixth AC switches connected on the three-phase load side, the single-phase AC voltage is short-circuited by two via the reactor, To store energy. As a result, even when the single-phase AC voltage is low, a current can flow through the reactor, so that the input current can be a current having a high power factor close to a sine wave. Next, if only the first switch turns on the energy stored in the reactor, one side winding of the reactor → the first switch → a star-connected capacitor → a neutral point → a path of the AC power supply, the first switch, Only the connected phases can be charged. On the other hand, in the case of discharging, by turning on only the first switch and, for example, the fourth switch connected on the three-phase load side, the other winding of the reactor L → neutral point → star-connected capacitor →
The capacitor charge is discharged through the path of the fourth switch. Also, if you want to charge and discharge the capacitor of another phase, turn on and off the switch connected to that phase,
A similar operation is performed.

Therefore, when energy is stored in the reactor at the converter section, only two switches are energized, and at the time of inverter operation, operation is performed by energizing one switch. In addition, by using a single star-connected capacitor as an electrolytic capacitor to increase the capacitance and accumulating DC voltage, when the single-phase input voltage is low, the electrolytic capacitor → the switch connected to the electrolytic capacitor → reactor → neutral point Since energy can be supplied to the reactor through the path, the energy pulsation due to the single-phase AC input voltage can be eliminated.

[0010]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. That is, the single-phase AC input terminal 1
The input of the N1 winding of the reactor L, the input of the AC switches S1 to S3 to the output of the N1 winding of the reactor L,
The output of the AC switch S1 has a three-phase output terminal U via a terminal of a capacitor Cu, the output of the AC switch S2 has a three-phase output terminal V via a terminal of a capacitor Cv, and the output of the AC switch S3 has a capacitor. 3 via the terminal of Cw
The phase output terminal W is connected to the single-phase AC input terminal 2 by the reactor L.
The output of the AC switch S1 is the output of the AC switch S4, the output of the AC switch S2 is the output of the AC switch S5, the output of the AC switch S3 is the output of the AC switch S6, the capacitor Cu, The other terminals of Cv and Cw are connected to each other and connected to the single-phase AC input terminal 2 respectively.

In such a circuit, for example, by turning on the AC switch S1 and the AC switch S4, the single-phase AC power supply E → the N1 winding of the reactor L → S1 → S4 →
A current is accumulated in the reactor L through a path from the N2 winding of the reactor L to the single-phase AC power supply E. As a result, current can flow through the reactor even when the single-phase AC voltage is low, and the input current can be a high power factor current close to a sine wave.
Also, instead of turning on the switches S1 and S4, the same operation as described above is performed by turning on S2 and S5 and turning on S3 and S6.

Next, by turning on only the energy stored in the reactor S1 (turning off S4),
Only the capacitor Cu can be charged through the route of the reactor N1 winding → S1 → capacitor Cu → neutral point → AC power supply → reactor N1 winding. At this time, the current flowing in N2 of the reactor is transferred to N1. On the other hand, when discharging the capacitor Cu, only the switch S4 is turned on, so that the capacitor Cu is discharged through a route from the N2 winding of the reactor → the neutral point → the capacitor Cv → S4. Further, when it is desired to charge / discharge a capacitor of another phase, the same operation can be performed by turning on / off a switch connected to that phase. Therefore, the converter section of FIG. 1 needs only to energize two switches when accumulating energy in the reactor, and operates only by energizing one switch when operating the inverter. Therefore, the energization number of the element is
Even when the number is large, the number is two, and the number of current-carrying elements is greatly reduced as compared with the conventional case.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. The difference from FIG. 1 is that the capacitor Cu is an electrolytic capacitor Cuo having a large capacitance.
By doing so, when the single-phase input voltage is low, electrolytic capacitor Cuo → S3 → N1 winding of reactor L →
Since energy can be supplied to the reactor L at the neutral point,
The pulsation due to the single-phase AC input voltage can be eliminated. It goes without saying that the same operation is performed even if the switches S2 to S6 are turned on instead of the switch S1.

[0014]

According to the present invention, a conversion circuit for obtaining a three-phase AC voltage of an arbitrary frequency and voltage with an input current of a sine wave having a high power factor is provided with two current-conducting elements and a conventional five-circuit. Since it can be constituted by half or less, the power loss is reduced and the conversion efficiency is improved. As a result, the number of cooling bodies can be reduced, and the size and cost of the device can be reduced. In addition, the number of constituent elements is smaller than that of the conventional 11 diodes and 7 transistors by the AC switch 6.
Since the number of parts and the number of parts can be reduced to half or less, advantages such as downsizing of the apparatus and reduction in cost can be achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

E: single-phase AC power supply, S1 to S6: AC (AC) switch, L, L1, L2: reactor, Cu, Cv, Cw,
Cuo: capacitor, D1 to D4, Dc: diode,
Qu to Qz: switches, Qc: transistors, M: three-phase loads.

Claims (2)

[Claims] 1. A converter circuit for converting a single-phase AC voltage into a three-phase AC voltage having a different frequency, comprising a first to sixth AC (AC) switches and a two-winding reactor. To short-circuit one terminal of the third AC switch, connect the other terminals of the first to third AC switches to terminals of the three-phase load, and short-circuit one terminal of the fourth to sixth AC switches. , The other terminals of the fourth to sixth AC switches are respectively connected to terminals of a three-phase load, and the short-circuited terminals of the first to third AC switches are connected to a single-phase reactor via one winding of the two-winding reactor. Connect to one of the AC input,
The short-circuited terminals of the fourth to sixth AC switches are connected to the other of the single-phase AC inputs via the other winding of the two-winding reactor, and the neutral point of the other of the single-phase AC input and the three-phase load is connected. A converter circuit, wherein a capacitor is connected between the neutral point and the three-phase load. 2. The converter circuit according to claim 1, wherein one of the capacitors has a larger capacitance than another capacitor.