JPH06105456A - Inverter overvoltage protection device - Google Patents

Abstract

PURPOSE:To delay the aging deterioration of an inverter device by continuously controlling operation of the inverter during the period from the start of operation of a cut-off circuit to the start of operation of a zero voltage discriminator. CONSTITUTION:When an overvoltage, which requires cutting-off of an AC input, circuit is generated, an AC input circuit is cut off with a circuit breaker 15, but the control for the inverter device 12 is continued. In this case, the frequency reference exceeding the actual number of rotation of an AC motor 16 is instructed to the inverter device 12. When a voltage of a DC main circuit becomes zero due to the power running of the AC motor 16, a zero voltage discriminator 1 operates, stopping operation of a control continuation circuit 2. Thereby, a frequency reference circuit 3 is disconnected from a throwing circuit 4 and a number of rotation reference circuit 24 is connected, returning to the ordinary speed control system. Thereby, an overvoltage of the DC main circuit is controlled within a short period, the time of voltage stress to be impressed to a power semiconductor element forming the inverter device 12 can be curtailed sufficiently and the aging deterioration of inverter device can also be delayed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter overvoltage protection device.

[0002]

2. Description of the Related Art In a variable speed drive device for an electric motor composed of a rectifier and an inverter device without a voltage control function and a power regeneration function, overvoltage protection of the inverter device is performed by detecting the overvoltage of the DC main circuit unit. The electric charge (energy) stored in the capacitor device is discharged by the resistor of the DC discharge circuit to suppress the overvoltage of the DC main circuit section.

When an overvoltage higher than the above overvoltage detection value occurs, the AC input power supply (circuit) is shut off to prevent damage to the inverter device, control of the inverter device is stopped, and the resistance of the DC discharge circuit is reduced. The energy stored in the capacitor device of the DC main circuit was discharged by the reactor.

[0004]

By cutting off the AC input circuit and stopping the control of the inverter device, a discharge circuit is formed by the capacitor of the DC main circuit section and the resistor of the DC discharge circuit, and the energy of this capacitor is reduced. discharge.

However, the resistors of the DC discharge circuit are limited due to handling a large amount of electric power and various restrictions related to the variable speed drive device. Therefore, the energy consumed by the resistor per unit time is small and the discharge time becomes extremely long.

With this long-time discharge, the overvoltage state of the inverter device also becomes long, and a long-term voltage stress is applied to the power semiconductor elements (transistor, thyristor, etc.) that form the inverter device.

The long-term voltage stress has a problem of accelerating the deterioration of the inverter device.

Further, when an overvoltage that cannot be suppressed only by the discharge capability of the DC discharge circuit occurs, there is a problem that the overvoltage exceeds the breakdown level of the power semiconductor element and the inverter device is suddenly damaged.

The present invention is to eliminate the above-mentioned problems, and an object of the present invention is to eliminate the above-mentioned problems when an overvoltage is generated which must shut off the AC input circuit and stop the inverter device. By increasing the overvoltage suppressing ability and shortening the voltage stress time of the power semiconductor element by a discharge method that does not rely on the DC discharge circuit, the inverter device has a delay in deterioration time and a sudden inverter device compared to the conventional one. Another object of the present invention is to provide an inverter overvoltage protection device for preventing damage to the inverter.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a rectifier for rectifying an AC input power source to a DC power source, an inverter device for rectifying the DC power source obtained by the rectification to an AC power source, and a DC power source. A DC discharge circuit connected between both poles of the main circuit to discharge overvoltage, a capacitor device connected between both poles of the main circuit and holding a DC voltage in parallel with this DC discharge circuit, and connected between both poles of the main circuit The voltage detector that detects the DC voltage of the DC main circuit, the discharge control circuit that controls the discharge of the DC discharge circuit by the overvoltage signal detected by this voltage detector, and the AC input power supply by the overvoltage signal of the voltage detector. A cutoff circuit that cuts off, a zero-voltage discriminator that determines that the DC voltage detected by the voltage detector is less than or equal to a preset voltage setting value, and a heavy overvoltage occurs in the DC main circuit section that activates the cutoff circuit. Or The frequency of calculating and outputting the frequency reference value that exceeds the actual rotation speed of the AC motor driven by the inverter device and the control continuation circuit that continuously controls the operation of the inverter device until the zero-voltage discriminator operates. An inverter overvoltage protection device comprising a reference circuit and a closing circuit which is connected to the frequency reference circuit when the control continuation circuit operates and outputs as a firing reference signal of the inverter device.

[0011]

In the inverter overvoltage protection device of the present invention, the AC input power supply is rectified into a DC power supply, the DC power supply obtained by the rectification is converted back to the AC power supply, and the DC voltage is applied between the two poles of the main circuit of the DC power supply. Connect the discharge circuit to discharge the overvoltage, connect the capacitor device between the main circuit both poles in parallel with the DC discharge circuit to hold the DC voltage, and the DC voltage of the DC main circuit connected between the main circuit both poles. Detected, the discharge of the DC discharge circuit is controlled by the overvoltage signal detected by the voltage detector, the AC input power is shut off by the heavy overvoltage signal of the voltage detector, and the DC voltage detected by the voltage detector is the predetermined voltage. It is determined that it is less than the set value, and the inverter device is continuously operated and controlled from the time when the overvoltage occurs in the DC main circuit section and the cutoff circuit operates until the zero voltage detector operates. On the device The frequency reference values above the actual rotational speed of the AC motor driven operation to output I, to connect the frequency reference circuit when the control continuation circuit operates to output a firing reference signal point of the inverter device.

[0012]

EXAMPLE An example of the present invention will be described below. In FIG. 1, 11 is a rectifier that rectifies an AC input power source to a DC power source, 12 is an inverter device that rectifies and converts the obtained DC power source back into an AC power source, and 13 is between both poles of the main circuit of the DC power source. DC discharge circuit connected to discharge overvoltage, 1
4 is a capacitor device connected in parallel with the DC discharge circuit 13 between both poles of the main circuit to hold a DC voltage; 5 is a voltage detector for detecting the DC voltage of the DC main circuit section connected between both poles of the main circuit; 6 is a discharge control circuit for controlling discharge of the DC discharge circuit 13 by the overvoltage signal detected by the voltage detector 5,
Reference numeral 7 is a cut-off circuit that cuts off the AC input power supply by the overvoltage signal of the voltage detector 5, 1 is a zero-voltage discriminator for discriminating that the DC voltage detected by the voltage detector 5 is less than or equal to a predetermined voltage setting 2 is a control continuation circuit that continuously controls the operation of the inverter device 12 from the time when the overvoltage is generated in the DC main circuit section and the cutoff circuit 7 operates until the time when the zero voltage discriminator 1 operates. The frequency reference circuit 4, which calculates and outputs a frequency reference value that exceeds the actual rotation speed of the AC motor 16 driven by the device 12, connects the frequency reference circuit 3 when the control continuation circuit 2 operates, and connects the inverter device 12 The DC main circuit that connects the rectifier 11 that rectifies the AC input power and the inverter device 12 that replaces the rectified DC power with the AC power again. Part, a DC discharge circuit 13 including a switching circuit and a resistor, a voltage detector 5 that detects the voltage of the DC main circuit part, and an overvoltage is detected from the detected value of the voltage detector 5 to control the DC discharge circuit. In the inverter overvoltage protection device including the discharge control circuit 6 that operates and the interrupting circuit 7 that determines the overvoltage and interrupts the AC input power by the interrupter 15 of the AC input circuit, the DC main circuit unit is detected from the detected value of the voltage detector 5. A zero voltage discriminator 1 for determining the zero voltage of
The control continuation circuit 2 for continuing the control of the inverter device 12 and the control continuation circuit 2 until the zero voltage discriminator 1 detects the zero voltage after the overvoltage is generated in the DC main circuit portion and the cutoff circuit operates. A frequency reference circuit 3 that calculates a frequency reference that exceeds the actual rotation speed of the AC motor 16 when operating.
And an input circuit 4 for inputting the frequency reference circuit 3, which is an inverter overvoltage protection device.

When an overvoltage that needs to interrupt the AC input circuit is generated, the AC input circuit is interrupted by the circuit breaker 15, but the control of the inverter device 12 is continued.

In this case, the AC motor 16 is in the state of free deceleration toward the complete stop, but the AC motor 16 at that time is
The inverter device 12 is instructed of a frequency reference that exceeds the actual number of revolutions (frequency), and positive powering operation is performed. As a result, the capacitor device 14 of the DC main circuit unit, the inverter device 12, and the AC motor 16 are connected to each other.
An AC discharge circuit for discharging the energy stored in is established, and it becomes possible to suppress the overvoltage of the DC main circuit section in a short time.

That is, FIG. 1 shows that the zero voltage discriminator 1 for determining the zero voltage of the DC main circuit portion and the zero voltage discriminator 1 detects the zero voltage after an overvoltage occurs in the DC main circuit portion and the interruption circuit operates. The control circuit 2 for continuing the control of the inverter device and the frequency reference circuit 3 and the frequency reference circuit 3 for calculating the frequency reference above the actual rotation speed of the electric motor when the control continuation circuit 2 is operating. It shows an inverter overvoltage protection device comprising a closing circuit 4 for closing.

The DC voltage of the DC main circuit portion between the rectifier 11 and the inverter device 12 is detected by the voltage detector 5. When the detected value of the DC voltage reaches a level (discharge level) that requires the discharge by the DC discharge circuit 13, the discharge control circuit 6 operates, and the DC discharge circuit 13 stores the energy stored in the capacitor device 14 of the DC main circuit unit. To suppress the overvoltage of the DC main circuit section.

Further, when the detected value of the DC overvoltage exceeds the discharge level and reaches a level (cutoff level) requiring protection of the inverter device 12, the cutoff circuit 7 operates and the breaker 15 causes the AC input circuit of the rectifier 11. Cut off.

At the same time when the cutoff level is reached, the control continuation circuit 2 operates and the inverter device 12 continues control, and the AC motor 16 operating before the cutoff level is reached.
The rotation speed reference circuit 24 for controlling the rotation speed is cut off by the closing circuit 4. Instead, the frequency reference circuit 3 is closed by the closing circuit 4.

The frequency reference circuit 3 calculates a speed reference that exceeds the detected speed value of the speed detector 17 attached to the AC motor 16, and inputs the calculated speed reference value to the speed control circuit 21. AC motor 16 due to interruption of AC power circuit
Becomes a state of free deceleration toward a complete stop, but since the speed control circuit 21, the current control circuit 22 and the inverter drive device 23 work based on the calculated value of the frequency reference circuit 3, the inverter device 12 always operates the exchange motor 16 The AC motor 16 operates so as to operate at a frequency higher than the actual rotation speed (actual frequency).

However, since it is premised that the AC motor 16 is stopped by the interruption of the AC input circuit, it is not necessary to strictly maintain the accuracy of speed control.

As a result, the inverter device 12 positively causes the AC electric motor 16 to perform a power running operation, so that an AC discharge circuit is established between the capacitor device 14 of the DC main circuit portion, the inverter device 12 and the AC electric motor 16. As a result, the energy stored in the capacitor device 14 is consumed by the power running operation of the AC electric motor 16.

When the energy of the capacitor device 14 is discharged by the power running of the AC electric motor 16 and the voltage of the DC main circuit section becomes zero, the zero voltage discriminator 1 operates to stop the operation of the control continuation circuit 2 and set the frequency reference. The circuit 3 is cut off by the closing circuit 4, and the rotation speed reference circuit 24 is closed to restore the normal speed control system.

As described above, the conventional inverter device 12
The overvoltage protection of (1) is performed by interrupting the AC input circuit of the rectifier 11 and stopping the control of the inverter to discharge the energy of the capacitor device 14 of the DC main circuit section by the DC discharge circuit 13.

On the other hand, according to the present invention, the AC input circuit of the rectifier 11 is cut off, and rather the AC electric motor 16 is positively driven by the inverter device 12,
The energy of the capacitor device 14 of the DC main circuit portion is consumed by the AC motor 16 in a short time.

As a result, the overvoltage of the DC main circuit portion can be suppressed in a short time, and the time of voltage stress applied to the power semiconductor elements (transistor, thyristor, etc.) that form the inverter device 12 can be sufficiently shortened.

[0026]

According to the present invention, it is possible to delay aged deterioration of an inverter device.

Further, according to the present invention, it is possible to prevent a problem in which the discharge capacity of the conventional DC discharge circuit cannot be suppressed and the DC overvoltage exceeds the breakdown level of the power semiconductor element to suddenly damage the inverter device. Is possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an inverter overvoltage protection device according to an embodiment of the present invention.

[Explanation of symbols]

 1 Zero Voltage Discriminator 2 Control Continuation Circuit 3 Frequency Reference Circuit 4 Closing Circuit 5 Voltage Detection Circuit 6 Discharge Control Circuit 7 Cutoff Circuit

Claims (1)

[Claims] 1. A rectifier for rectifying an AC input power source to become a DC power source, an inverter device for inversely converting the DC power source obtained by rectification into an AC power source, and a connection between both poles of a main circuit of the DC power source. A DC discharge circuit for discharging an overvoltage, a capacitor device connected in parallel to the main circuit poles for holding a DC voltage, and a DC main circuit section connected between the main circuit poles in parallel with the DC discharge circuit. Voltage detector for detecting the DC voltage of, a discharge control circuit for controlling the discharge of the DC discharge circuit by the overvoltage signal detected by the voltage detector, and shutting off the AC input power supply by the heavy overvoltage signal of the voltage detector And a zero-voltage discriminator for discriminating that the DC voltage detected by the voltage detector is equal to or less than a predetermined voltage setting value, and a shut-off circuit for generating a heavy overvoltage in the DC main circuit section. From the operation of the road to the operation of the zero-voltage discriminator, a control continuation circuit that continuously controls the operation of the inverter device, and a frequency that exceeds the actual rotation speed of the AC motor driven by the inverter device. An inverter comprising a frequency reference circuit that calculates and outputs a reference value, and a closing circuit that connects the frequency reference circuit when the control continuation circuit operates and outputs the firing reference signal of the inverter device. Overvoltage protection device.