JPH08149868A - Inverter - Google Patents

Abstract

PURPOSE: To reduce the burden of a mechanical brake in the braking of a motor which is caused by the generation of the fault of an inverter main circuit, and to simplify the processing and circuit for sensing the short-circuit faults of the respective phases and arms of the inverter main circuit. CONSTITUTION: By the sensing signals fed from an overcurrent sensing circuit 6, a control circuit 3 forces the respective arms of an inverter main circuit 1 to be in OFF-states. Thereafter, by the sensing signals fed from a faulty phase sensing circuit 7, the control circuit 3 discriminates between a faulty phase or faulty arm and other sound phases, and by the ON-OFF controls of the arms of the sound phases, it feeds DC currents to a motor 2, and by the application of a DC brake to the motor 2, it stops the motor 2. By the utilization of the fact that the output terminal voltage of the faulty phase whose arm is shorted approximates to the level of the positive or negative electrode of the DC voltage of the inverter main circuit 1, the sensing of the faulty phase is performed while the change of this level is compared with a reference voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter for driving an electric motor, and more particularly to detection of a failure in an inverter main circuit and braking control of the electric motor.

[0002]

2. Description of the Related Art In an apparatus for driving an induction motor or a synchronous motor by an inverter, a device for protecting a semiconductor element of an inverter main circuit from damage and failure is provided to prevent accidents from spreading to other elements and a motor serving as a load. To be

This protection means is generally an operation stop control by detecting an overcurrent. FIG. 5 shows a conventional protection device. The inverter main circuit 1 has a 6-arm configuration with a three-phase bridge connection of transistors U to Z, and the motor 2 has three arms.
Supply phase power.

The control circuit 3 having a microcomputer configuration or the like generates a gate control signal for each transistor of the main circuit 1 in accordance with a speed command of the electric motor 3 or the like. This control signal is distributed / amplified by the gate control circuit 4 into each phase, and is used as an on / off control signal for the transistors U to Z.

In the protective device, the U and W phase currents from the main circuit 1 to the electric motor 2 are detected by the detector 5, and the overcurrent detector 6 detects the overcurrent from this detection signal and transmits it to the control circuit 3. . The control circuit 3 outputs the overcurrent detection signal to the gate control circuit 4
The gate signal output of is forced to the off side, and all the transistors U to Z of the main circuit 1 are turned off.

In an inverter equipped with such a protection device, if the operation command is given again after the operation is stopped by the protection operation, the relevant phase is short-circuited when the arm paired with the failed arm is turned on.

For example, a U-phase upper arm transistor U
When the transistor X in the lower arm is turned on by restarting after short-circuit failure and overcurrent protection is performed, both transistors U and X are short-circuited, and the transistor X is also damaged by overcurrent.

In order to prevent such an accident from spreading, a circuit for detecting damage to the semiconductor element of each phase at the time of starting and restarting the inverter is provided, and means for prohibiting the operation of the inverter when there is damage is provided.

In this main circuit failure detection circuit, a series circuit of a resistor, a photocoupler and a detection transistor is provided in parallel with each element of the main circuit, and the detection transistor is turned on before the operation of the inverter. There is an output of the photocoupler that determines whether or not a current flows through the transistor for use (whether or not the main circuit element is short-circuited and damaged).

[0010]

In an inverter equipped with a conventional protection device, if a main circuit failure occurs during operation of the electric motor and an overcurrent stop occurs, the electric motor is integrated with the load or disconnected from the load and runs freely. It will be in the (idle) state, and it will be forced to stop by another mechanical brake, or it will wait until the idling is stopped by a slight friction loss and stops.

However, in an application to a transportation electric motor (for example, an elevator or an electric vehicle) in which it is not possible to wait until the idling is stopped, a mechanical brake is used to convert the rotational energy into heat and stop the rotation. Therefore, the load on the sliding material of the brake and the life of the brake are adversely affected.

Further, the conventional main circuit failure detection circuit needs to be provided for each arm of the main circuit, resulting in high cost. Furthermore, in order to detect a failure, detection software is required to apply an ON signal to the detection transistor for each phase and individually check the signal from each photocoupler.

It is an object of the present invention to provide an inverter that reduces the load on the mechanical brake when braking the electric motor due to the occurrence of a main circuit failure.

Another object of the present invention is to provide an inverter that simplifies the process / circuit for detecting a short circuit fault of each phase and each arm of the main circuit.

[0015]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an inverter main circuit having a bridge connection of semiconductor elements and an output end connected to an electric motor as a load, and a gate of the inverter main circuit. In an inverter having a control circuit for controlling and stopping the operation of the inverter main circuit when the current to the electric motor becomes an overcurrent, a failure detection for detecting a failure of an arm element of the inverter main circuit by arm or phase A circuit is provided, and the control circuit stores a sound phase and a failure phase or a failure arm with a failure detection signal from the failure detection circuit, and after the overcurrent is detected, the sound phase of the inverter main circuit is controlled to be constant to the electric motor. Is provided with a braking control means for supplying the DC current.

The failure detection circuit includes a reference voltage circuit that obtains a detection reference voltage that is an intermediate value of the DC voltage of the inverter main circuit, a detection reference voltage output of the reference voltage circuit, and a voltage of each phase output terminal of the inverter main circuit. And a voltage detection circuit for detecting a short-circuit failure of a semiconductor element connected to the terminal when the voltage of each phase output terminal is close to the positive or negative level of the DC voltage.

[0017]

[Action]

(First invention) When a main circuit element is broken, a DC brake is applied by controlling other sound elements to generate an electric braking force in the electric motor to quickly stop the electric motor.

(Second invention) For the short-circuit failure of each arm, the fact that the output voltage of the phase is close to the positive and negative electrode levels of the DC voltage is used to determine the intermediate value of the DC voltage and the voltage of each phase output terminal. By comparing, the failure of each phase or each arm of the inverter main circuit is detected.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention. The control circuit 3A stops the inverter operation by forcibly turning off each arm of the inverter main circuit 1 by the detection signal from the overcurrent detection circuit 6, similarly to the conventional operation stop. In the present embodiment, the electric motor is brake-controlled after the operation stop control.

The fault phase detection circuit 7 for this purpose detects a fault in each phase U, V, W of the inverter main circuit 1 for each arm. Further, the control circuit 3A performs braking control using the detection signal from the faulty phase detection circuit 7 and the current detection signal from the current detector 5.

The control circuit 3A stores the faulty arm, its faulty phase, and its sound phase by the detection signal from the faulty phase detection circuit 7 after the inverter main circuit 1 is turned off by the overcurrent detection.
Then, a DC brake is applied to the electric motor 2 by supplying a constant DC current to the electric motor by the ON / OFF control of the healthy phase of the inverter main circuit 1.

For example, when the failure arm is the transistor U, the failure phase is stored as U, and the sound phase is stored as V and W, and the transistor Y or Z is switching-controlled. At this time,
Since the transistor U serves as an upper arm of the U-phase and is short-circuited to the positive electrode side of the DC power supply, when the transistor Y or Z is ON-controlled, the transistor U passes through the armature coil (inductive reactance) of the motor 2 or the transistor Y or. An electric current flows through Z. This current causes the electric motor 2 to generate a braking force by a DC brake.

The braking force at this time can be controlled by the DC current supplied. In order to control this braking force to a constant value, the control circuit 3A sets the healthy phase transistor (Y in the above example) so that the detected current from the current detector 5 becomes a set value.
Alternatively, the on / off ratio of Z) is controlled.

FIG. 2 shows a current control waveform at the time of braking. At the start of the braking, the ON control of the transistor Y or Z in the normal phase is performed (time t ₀ ), and this ON causes the motor current to start rising. A transistor that turns off the transistor when this current reaches a certain value (upper limit) (time t ₁ ), and turns on the transistor when the current drops from a certain value to a certain value (up to the lower limit) due to this off The motor current is controlled to a constant value by repeatedly turning on and off. Note that both the transistors Y and Z may be on / off controlled.

Therefore, according to the present embodiment, the faulty phase or the faulty arm is stored when the overcurrent is detected, and a constant DC current is passed through the motor by using the faulty arm and the sound phase to apply the DC brake to the motor. The load on the mechanical brake can be reduced, and the electric motor can be stopped quickly.

In this embodiment, the DC brake can be applied using only the sound phase. For example, when the failure phase detection circuit 7 has a failure detection function for each phase (does not have an arm-specific detection function), the transistor V is ON-controlled and the transistor Z is ON / OFF-controlled for the U-phase failure detection. By doing so, the DC brake can be applied.

FIG. 3 shows an embodiment of the fault phase detection circuit 7. The resistors R1 and R2 divide the DC voltage of the inverter main circuit 1 to obtain a detection reference voltage having an intermediate value of the DC voltage. The capacitors C1 and C2 are for stabilizing the voltage divided by the resistors R1 and R2.

Between the reference voltage circuit composed of these resistors and capacitors and the output terminals of each phase of the inverter main circuit 1, voltage detection circuits VD1 to VD3 for each phase are provided.

The voltage detection circuits VD1 to VD3 are shown in FIG. 4 as one of them. Each phase terminal voltage of the inverter main circuit 1 is applied as a comparison input to the reference voltage of the reference voltage circuit, and a pair of photocoupler PC is provided between them.
Input elements (light emitting diodes) of A and PCB are connected in anti-parallel, and a current limiting resistor R3 is connected in series to this.

A control power supply is connected to the output element (photodetection transistor) of the photocoupler through collector resistors R4 and R5, and the on / off operation signal of the output element is taken out as a failure detection signal.

In this embodiment, for example, when the transistor U of the inverter main circuit 1 has a short circuit fault, the voltage of the U phase becomes a value close to the positive level of the DC voltage, and the photocoupler PCA of the voltage detection circuit VD1 keeps on. , The failure of the transistor U is detected. On the contrary, when the transistor X has a short circuit failure, the voltage of the U phase becomes a value close to the negative electrode level of the DC voltage, the photocoupler PCB of the voltage detection circuit VD1 keeps on, and the failure of the transistor X is detected.

These faults can be detected both while the inverter main circuit 1 is operating and when it is stopped.

According to the present embodiment, the conventional failure detection circuit requires the failure detection control signal for providing the check signal for each phase, whereas the signal processing is not necessary and the failure for each arm can be detected. .

If the failure detection for each phase is sufficient, the photocoupler PCA and the output element of the PCB are common, that is, the photocoupler has two input elements and one output element.
With the integrated structure, it is possible to detect the phase failure when the upper arm or the lower arm of the phase fails. In this case, the circuit configuration can be simplified.

Further, when the failure detection of the inverter main circuit 1 is sufficient, the logical sum of the output elements of all the photocouplers can be taken and taken out as one detection signal.

[0036]

As described above, according to the present invention, the failure detection circuit detects each arm or phase of the inverter main circuit, and from this failure detection, the failure arm or the failure phase and the sound phase are discriminated, and the sound element is detected. Since a constant DC current is supplied to the electric motor by the control, when a failure occurs, an electric braking force is generated in the electric motor, the load on the mechanical brake is reduced, and the electric motor can be stopped quickly.

Further, according to the present invention, the failure detection circuit of the inverter main circuit has a reference voltage circuit for obtaining a detection reference voltage which is an intermediate value of the DC voltage of the inverter main circuit, and the detection reference voltage output of the reference voltage circuit and the inverter. With a voltage detection circuit that uses the voltage of each phase output terminal of the main circuit as a comparison input and detects as a short-circuit fault of the semiconductor element connected to the terminal when the voltage of each phase output terminal is close to the positive or negative level of the DC voltage Since the configuration is adopted, control / processing for detecting a failure is unnecessary. In addition, the circuit configuration can be simplified for the failure detection for each phase and the failure detection for the main circuit.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention.

FIG. 2 is a current control waveform during braking in the embodiment.

FIG. 3 is a fault phase detection circuit in the embodiment.

FIG. 4 is a voltage detection circuit according to an embodiment.

FIG. 5 is a block diagram of a conventional protection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inverter main circuit 2 ... Load electric motor 3, 3A ... Control circuit 4 ... Gate control circuit 5 ... Current detector 6 ... Overcurrent detection circuit 7 ... Fault phase detection circuit VD1, VD2, VD3 ... Voltage detection circuit

Claims (2)

[Claims] 1. An inverter main circuit configured by bridge connection of semiconductor elements and having an output end connected to an electric motor that serves as a load, and an inverter main circuit that controls the gate of the inverter main circuit and causes an overcurrent in the electric motor. In an inverter having a control circuit for stopping the operation of the circuit, a failure detection circuit for detecting a failure of an arm element of the inverter main circuit is provided for each arm or each phase, and the control circuit is provided with a failure detection signal from the failure detection circuit. And a braking control unit for storing a constant DC current to the electric motor by ON / OFF control of the healthy phase of the inverter main circuit after detection of the overcurrent, Inverter to do. 2. The failure detection circuit includes a reference voltage circuit that obtains a detection reference voltage that is an intermediate value of a DC voltage of the inverter main circuit, a detection reference voltage output of the reference voltage circuit, and each phase output terminal of the inverter main circuit. And a voltage detection circuit for detecting as a short-circuit fault of a semiconductor element connected to the terminal when the voltage of each phase output terminal is close to the positive or negative level of the DC voltage. Inverter.