JPH1094268A - Inverter device with reduced power supply harmonic current - Google Patents

Abstract

(57) [Problem] To reduce harmonic current generated at the time of charging a capacitor at low cost. SOLUTION: A converter unit 2 which rectifies an output of a commercial AC power supply 1 by a diode bridge to obtain a DC voltage,
An inverter unit 4 for switching the DC voltage by a bridge composed of a first semiconductor switching element and applying a pulse-like waveform voltage to a load 5 including an inductance. A series circuit of capacitors 11 and 14 and second diodes 12 and 15 is connected between the negative electrode side and the neutral point 17 of the load 5, and the capacitors 11 and 14 are connected through the first semiconductor switching element and the load 5. 14 charges the output voltage of the converter unit 2 and supplies the charges charged in the capacitors 11 and 14 to the output side of the converter unit 2 through the diodes 13 and 16 when the battery is not charged, thereby reducing the power supply harmonic current. Inverter device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for applying a pulse voltage to a single-phase or three-phase electric motor or other inductance load by switching a single-phase or three-phase power supply, converting the DC voltage into a DC voltage, and then applying the pulse voltage. The present invention relates to an inverter device capable of supplying DC or AC power controlled by a computer.

[0002]

2. Description of the Related Art A conventional inverter device is as shown in FIG. Reference numeral 1 denotes a commercial AC power supply, which may be single-phase or three-phase. This is input to the diode bridge 2 and rectified. Reference numeral 3 denotes an electrolytic capacitor, which obtains a stable DC voltage by smoothing the output voltage of the diode bridge. This is supplied to the bridge circuit 4 of the semiconductor switching element. The bridge circuit 4 performs switching to apply a pulse voltage to a load 5 including an inductance such as a motor. The power and frequency supplied to the load are controlled by modulating the pulse width according to the purpose. Reference numeral 6 denotes a choke coil for reducing the harmonic current of the power supply frequency, and reference numeral 7 denotes a converter. This part may be constituted by an active filter as shown in FIG. 6, a high frequency inductance 8 and a semiconductor switching element 9 constitute a chopper circuit, and the semiconductor switching element 9 charges the electrolytic capacitor 3 through the diode 10 during the off period. In this example, it is known that the power supply harmonic current generated on the power supply side can be reduced by appropriately controlling the switching duty of the semiconductor switching element 9.

[0003]

However, in the prior art, the choke coil 6 is used for a low frequency (50 Hz or 6 Hz).
(Multiplication of 0 Hz), a large inductance is required, which is a bottleneck in miniaturization and cost reduction.
As a means for solving this problem, the method shown in FIG. 6 is adopted. However, a control circuit for controlling the semiconductor switching element 9 and its power supply are newly required, and low frequency harmonics for high frequency switching are required. Although the wave current can be reduced, high-frequency noise increases, so that it is necessary to newly strengthen a high-frequency noise filter, and it has been very difficult to reduce the cost. The problem to be solved by the present invention is
It is to reduce harmonic current generated when charging a capacitor at low cost.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention rectifies the output of a single-phase or three-phase commercial AC power supply by a first single-phase or three-phase diode bridge to obtain a DC voltage. And a converter for switching the DC voltage by a bridge made of a first semiconductor switching element and applying a pulse-shaped voltage to a single-phase or three-phase load including an inductance. In the device, a series circuit of a capacitor and a second semiconductor switching element or a diode is connected between a positive electrode side or a negative electrode side of the converter unit and a neutral point of the load, and the first semiconductor switching element and the Via a load, the capacitor was charged with the output voltage of the converter unit, and when not charged, the capacitor was charged. A load through the third semiconductor switching element or diode, in which a configuration supplied to the output side of the converter.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a capacitor is charged by using a load including an inductance and a first semiconductor switching element of an inverter. These are already provided in the present apparatus and do not increase the cost.
On the other hand, the first semiconductor switching element of the inverter is:
Switching is always performed to drive the load, and the following configuration is adopted to simultaneously perform capacitor charging. A second semiconductor switching element or diode connects between the neutral point of the load of the inverter and a capacitor connected to the output (positive side or negative side) of the converter. The reason for connecting to the neutral point of the load is that generally four or six semiconductor switching elements of the inverter are used, and the action from each switching element is made the same. A second semiconductor switching element or diode for connecting one of the capacitors connected to the positive side of the converter to the negative side of the converter or a capacitor of the capacitor connected to the negative side to supply the charged electric charge as the inverter power supply. A third semiconductor switching element or diode for connecting one to the positive side is provided. According to this configuration, charging of the capacitor is performed via the first semiconductor switching element for the inverter and the inductance of the load. Since the value is gradually implemented by the action of the load inductance, a low frequency component of about a multiple of the power supply frequency can be suppressed, and the power supply harmonic current can be reduced.

[0006]

FIG. 1 shows an embodiment of the present invention. A snubber capacitor and a noise filter are omitted. Electrolytic capacitors 11 and 14 are charged from a load 5 such as a motor through diodes 12 and 15, respectively.
Supplies the charge of the capacitor 14 to the bridge circuit 4. When the power supply voltage is lower than the voltages of the capacitors 11 and 14, the diode 2 is reverse-biased and no current flows from the power supply 1. Therefore, the capacitors 11 and 14 operate as a normal inverter in which the capacitors are parallel main circuit capacitors. Further, since the diodes 12 and 15 are reverse-biased, there is no operation for charging the capacitor. Therefore, a power supply current is generated only when the power supply voltage is higher than the capacitor voltage, and the operation at that time will be described with reference to FIG.

[0007] U, V and W in FIG. 2 are bridge circuits 4 in FIG.
The output waveform of FIG. f _C is a carrier frequency, and the similar state of FIG. Now U,
It is assumed that V and W are in the state of FIG. 2 and the current direction to the load is the direction of the arrow shown in FIG. At this time, the combinations of the states of the bridge circuit 4 are four as a to d as shown in FIG.
There are types. In a, all phases are at a high level, there is no power supply as a three-phase load, and the inverter operates in a so-called reflux mode. At this time, since the potential of the neutral point 17 of the load also tends to be the same as the potential of the power supply + side, if the terminal voltage of the electrolytic capacitor 14 is lower than that, a charging current is generated, and as shown in FIG. The capacitor 14 is charged through the diode bridge 2 and the load 5, and currents I1 and I4 shown in FIG. 2 flow. Next, in the section b, V and W
Is at a high level, U is at a low level, and there is a terminal voltage, so that energy is consumed. Therefore, I
_It is necessary to supply the current indicated by ₁ to the bridge circuit 4. However, since the capacitors 11 and 14 are lower than the voltage of the converter unit 2 due to the diode drop, they are supplied from the power supply 1 side. However, when the voltage drops due to the power supply impedance, part of the voltage is also supplied from the capacitor side. Therefore, I ₂ and I ₁ are as shown in FIG. In the section c, since V is at a low level, the current flowing to the negative side from the U-phase does not pass through the converter unit 2 but flows to the V-phase. I ₁ + I ₂ decreases.
During these periods b and c, the potential of the neutral point 17 becomes 2/3 and 1/3 of the power supply voltage, so that the diode 1
2 and 15 are reverse-biased and do not perform a charging operation. In the section d, all phases are at the low level contrary to the state a, and the capacitor 11 is charged through the diode 12.

The waveform in FIG. 2 is not intended for capacitor charging because it is a waveform of a normal inverter PWM, but is charged automatically because the above-mentioned reflux mode exists during each PWM cycle. since the charging current i.e. the supply current peak is suppressed as in I ₁ of FIG. 2, by increasing the flowing time, as shown in FIG. 4, it is possible to reduce the harmonic components of the source current. Since this current includes a ripple higher than the carrier frequency, it can be removed by a small high-frequency noise filter.

[0009]

As described above, according to the present invention, the power supply input current is changed to a high-frequency switching current similar to that of an active filter by utilizing the power switching element of the inverter device and the inductance of the load. Higher harmonic current can be reduced. A high-speed power switching element required for an active filter and a control circuit therefor are not required, and a low-cost and small-sized inverter can be realized in which power supply harmonic current generated when charging a capacitor is reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a three-phase output with a single-phase power supply according to the present invention.

FIG. 2 is a current waveform diagram per carrier in the embodiment of FIG.

FIG. 3 is an equivalent circuit diagram when a capacitor is charged.

FIG. 4 is a waveform diagram of a power supply voltage and an input current.

FIG. 5 is a circuit diagram showing an example of a conventional inverter including a harmonic current suppression circuit using a choke.

FIG. 6 is a circuit diagram of a conventional filter for suppressing harmonic current.

[Explanation of symbols]

1. Commercial AC power supply, 2. Diode bridge (converter part), 3. Electrolytic capacitor, 4. Bridge circuit, 5.
Load, 6 choke coil, 7 converter section, 8 high frequency inductance, 9 semiconductor switching element,
10 Diode, 11, 14 Electrolytic capacitor, 1
2,13,15,16 diode, 17 neutral point

Claims (1)

[Claims] A converter for obtaining a DC voltage by rectifying the output of a single-phase or three-phase commercial AC power supply with a first single-phase or three-phase diode bridge; An inverter unit that switches by a bridge made of elements and applies a pulse-shaped waveform voltage to a single-phase or three-phase load including inductance, wherein the positive electrode side or the negative electrode side of the converter unit and the load A neutral circuit between the capacitor and a second semiconductor switching element or a diode,
Via the semiconductor switching element and the load, the capacitor is charged with the output voltage of the converter section, and when not charged, the charge charged in the capacitor is passed through a third semiconductor switching element or a diode to the converter section. An inverter device with a reduced power supply harmonic current, characterized in that it is configured to supply to an output side.