JPH0823682A - Surge voltage suppression deevice - Google Patents

Abstract

PURPOSE:To suppress overvoltage applied to an electric motor by adding only simple circuit, easily select a circuit constant, and extend the life of the insulation of electric motor coil winding. CONSTITUTION:The AC terminal of a three-phase diode bridge circuit 5 is connected to the input terminal of an AC electric motor 2 which is connected to a voltage-type PWM inverter 1 with a relatively long cable and is driven by an inverter 1 and a capacitor 6 and a resistor 7 are connected in parallel across the DC terminal. A surge voltage energy is absorbed by the capacitor 6 and at the same time the impedance of a cable 3 and resonance phenomenon by the capacitor 6 are stopped by half cycle by a diode 5. A voltage increase due to energy absorbed by the capacitor is consumed by connecting the resistor 7 in parallel with the capacitor or the positive/negative DC terminals of the diode bridge 5 are connected to the DC bus of the inverter body 1 directly or via reactor for collection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surge voltage suppressor in a voltage type PWM (pulse width modulation) inverter for driving a motor at a variable speed.

[0002]

2. Description of the Related Art FIG. 4 shows a basic electric motor drive system. In the figure, 1 is a voltage type PWM inverter, 2 is an AC electric motor, and 3 is a cable connecting them. A resistance component and an inductance component are present in the length direction of the cable, and an electrostatic capacitance is present between the lines or between the earth and the ground, forming a distributed capacitance network. On the other hand, the PWM inverter 1
Has a configuration as illustrated in FIG. 5, and controls the output voltage by turning on / off a bridge circuit (generally using a transistor) at the output stage with a high frequency carrier signal.
Here, in order to reduce the loss of the transistor at the time of switching, it is desirable to make the voltage change as steep as possible. In the circuit configuration of FIG. 4, when a steep voltage is applied to the entry side of the cable, when the cable 3 is long (for example, 10
0m or more), high voltage change rate (dv /
Due to the resonance caused by dt) and the L, C, and R constants of the cable 3, a high voltage is applied to the motor terminals, resulting in shortening the insulation life. When a transformer is installed at the output of the inverter to boost the voltage, this phenomenon may become more remarkable.

As a countermeasure against this, in many cases, a method of insulating the electric motor to a higher voltage specification (about twice) is adopted, but it is unavoidable that the cost becomes high and the size of the electric motor becomes large. There is also. Especially, when the existing electric motor is driven by an inverter, it becomes more difficult. Figure 6
Inserts a suitable filter 4 into the output of the inverter 1,
It is intended to reduce the rate of change of the voltage applied to the cable 3 and the electric motor 2 to suppress vibration. In this method, it is necessary to select the optimum filter constant depending on individual conditions, and if the selection of the filter constant is wrong, there is a possibility that it may have an adverse effect, so it cannot be a universal measure. Further, the surge voltage suppressor disclosed in Japanese Patent Laid-Open No. 59-25584 reduces the surge voltage by the configuration of the tapped reactor, the capacitor and the clamp diode, but the current stored in the reactor due to resonance is reduced. Even after the resonance is clamped by the diode, there is a problem that the reactor-diode-main circuit element continues to circulate, resulting in an increase in generated loss, and the burden on the main circuit element becomes large especially when the switching frequency is high.

[0004]

The problem to be solved by the present invention is to suppress the overvoltage applied to the electric motor by simply adding a simple circuit, to easily select the circuit constant, and to insulate the electric motor winding. Is to extend the life of the.

[0005]

In order to solve the above problems, a first surge voltage suppressor of the present invention is an AC motor driven by the inverter, which is connected to a voltage type PWM inverter with a relatively long cable. An AC terminal of a three-phase diode bridge circuit is connected to the input terminal, and a capacitor and a resistor are connected in parallel at both ends of the DC terminal of the three-phase diode bridge circuit. The second surge voltage suppressor of the present invention is a voltage-type PW with a relatively long cable.
An AC motor connected to the M inverter and driven by the inverter is connected to an input terminal of a three-phase diode bridge circuit, and a capacitor is connected to both ends of a DC terminal of the three-phase diode bridge circuit. Three
The positive and negative terminals of the phase diode bridge and the positive and negative terminals of the DC bus of the inverter body are connected to each other via a reactor. A third surge voltage suppressor of the present invention is connected to a voltage type PWM inverter with a relatively long cable, and connects an AC terminal of a three-phase diode bridge circuit to an input terminal of an AC motor driven by the inverter, A capacitor is connected to both ends of the DC terminal of the three-phase diode bridge, and the positive and negative terminals of the three-phase diode bridge are connected to the positive and negative terminals of the DC bus of the inverter body.

[0006]

In the present invention, the AC terminal of the three-phase diode bridge is connected to the input of the electric motor, and both ends of the DC terminal are connected.
Connect a capacitor. The energy of the surge voltage is absorbed by this capacitor, and the impedance of the cable and the resonance phenomenon due to this capacitor are stopped in a half cycle by the diode. The voltage rise due to the energy absorbed by the capacitor is consumed by connecting a resistor in parallel with the capacitor or by connecting the positive and negative DC terminals of the diode bridge to the DC bus of the inverter body directly or via a reactor, Try to collect. This suppresses the voltage overshoot caused by the steep voltage change of the PWM inverter and the L, C, and R constants of the cable. In particular, since the diode bridge and the capacitor are connected in the immediate vicinity of the motor terminal, they are not easily affected by the cable constant and the like.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. In this embodiment, an AC terminal of a three-phase diode bridge 5 is connected to the electric motor 2. A capacitor 6 and a resistor 7 are connected in parallel to the DC side of this diode bridge 5. Capacitor 6 is normally charged to the maximum value of the inverter output voltage (inverter DC bus voltage). When the motor voltage is going to rise due to the resonance of the cable 3, the diode of the diode bridge 5 causes the capacitor 6
A current flows through the device, and the voltage rises only in proportion to the energy of the surge and the capacitance of the capacitor. When the voltage of the capacitor 6 peaks and the current is about to be reversed, the diode of the diode bridge 5 is blocked, and the continuation of the transient phenomenon is stopped. In FIG. 1, the energy of the surge accumulated in the capacitor is consumed by the resistor 7,
This is energy that originally did not contribute to the output of the motor and does not significantly affect the efficiency of the entire system.
However, the power consumed by the resistor includes a portion due to the constant output voltage. Therefore, there is a constant heat generation, which also affects the overall efficiency.

FIG. 2 shows a second embodiment for improving the drawbacks of the first embodiment. Instead of connecting the resistor 7 in parallel with the capacitor 6, the positive and negative terminals of the diode bridge 5 are connected to the reactor 8. , 9 are respectively connected to the positive and negative DC bus terminals of the inverter body 1.
The inductances of the reactors 8 and 9 are selected so that the natural frequency with the capacitor 6 is sufficiently longer than the resonance frequency of the cable 3 so that a gentle current is fed back to the inverter body 1. FIG. 3 shows a third embodiment in which the reactors 8 and 9 are omitted from the embodiment of FIG. In this case, part of the surge current will flow through the elements of the inverter body 1. Although the repetition frequency is high, the flow period is extremely short, so the inverter body 1
If there is a spare capacity, the circuit can be simplified.

[0009]

As described above, the present invention has the following effects. (1) The high voltage applied to the electric motor can be suppressed simply by adding a simple circuit. (2) Selection of circuit constants is relatively easy, and there is no need to set constants for each driving device. (3) Efficiency can be improved by returning the surge energy to the power supply. (4) Since the diode bridge and the capacitor are connected in the immediate vicinity of the motor terminal, the influence of the cable constant and the like is small.

[Brief description of 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 third embodiment of the present invention.

FIG. 4 is a configuration diagram of a system to which the present invention is applied.

FIG. 5 is a circuit diagram showing an example of a main circuit configuration of a voltage type PWM inverter.

FIG. 6 is a circuit diagram showing an example of a conventional voltage suppression device.

[Explanation of symbols]

1 voltage type PWM inverter, 2 AC motor, 3 cable, 4 filter network, 5 3 phase diode bridge, 6 capacitor, 7 resistor, 8 and 9 reactor

Claims (3)

[Claims] 1. A three-phase diode bridge circuit is connected to a voltage-type PWM inverter with a relatively long cable, and an AC terminal of a three-phase diode bridge circuit is connected to an input terminal of an AC motor driven by the inverter. A surge voltage suppressor characterized in that a capacitor and a resistor are connected in parallel at both ends of a DC terminal. 2. A voltage-type PWM inverter connected by a relatively long cable, and an AC terminal of a three-phase diode bridge circuit connected to an input terminal of an AC electric motor driven by the inverter. A surge voltage suppressor characterized in that a capacitor is connected to both ends of a DC terminal, and the positive and negative terminals of the three-phase diode bridge and the positive and negative terminals of a DC bus of the inverter body are connected to each other via a reactor. 3. A direct current of said three-phase diode bridge, wherein a three-phase diode bridge circuit is connected to an input terminal of an AC electric motor driven by said inverter, which is connected to a voltage type PWM inverter with a relatively long cable. A surge voltage suppressor characterized in that a capacitor is connected to both ends of the terminal, and the positive and negative terminals of the three-phase diode bridge are connected to the positive and negative terminals of the DC bus of the inverter body.