JPH07154986A - Control method of electric motor - Google Patents

Abstract

PURPOSE:To prevent an overvoltage in an inverter part by a method wherein, when an electric motor is driven in a regenerative mode, a converter part and the inverter part are controlled in such a way that they are interlocked. CONSTITUTION:The regenerative electric power of an electric motor 29 is regenerated in a three-phase input power supply 1. In this case, it is detected that the DC voltage of a converter part 4 has become a prescribed voltage or higher, and the converter part 4 is started. Then, a dynamic braking signal from a dynamic braking circuit 11 is turned off, an inverter part 8 is driven, and the electric motor 29 is operated. Then, the drive of the inverter part 8 is stopped, the dynamic braking signal from the dynamic braking circuit 11 is turned off, the drive of the converter part 4 is then stopped, and the operation of the electric motor 29 is stopped. Thereby, it is possible to prevent an overvoltage in the inverter part 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric motor control method useful for a large-capacity drive device or an electric motor application field operated in a continuous regenerative mode. The present invention relates to a motor control method capable of protecting an inverter unit that drives a motor.

[0002]

2. Description of the Related Art As a main circuit of a conventional converter capable of regenerating power, a dual converter in which thyristors are connected in anti-parallel, or, for example, Japanese Patent Laid-Open No. 62-2881.
There is a circuit in which a diode of a three-phase full-wave rectifier circuit is connected in parallel with a power switching element that can self-extinguish, as shown in Fig., Etc., and the motor is driven by the inverter section connected to the output of this inverter section. .

[0003]

In the conventional example, the converter section and the inverter section are independently controlled, and a large-capacity smoothing capacitor is connected to the DC voltage output section of the converter section. Therefore, since the output impedance of the converter is very small, the converter is short-circuited in the power regeneration mode. for that reason,
The three-phase input power supply unit required a three-phase reactor. If the converter is cut off carelessly when the smoothing capacitor is removed, the stored energy discharge path may be lost depending on the operating conditions of the motor connected to the inverter, causing excessive voltage to be generated in the inverter, It destroys the switching element. INDUSTRIAL APPLICABILITY According to the present invention, when an inverter unit connected to a converter unit drives a load that operates in a power running or regenerative mode such as an electric motor, power can be regenerated by controlling the converter unit and the inverter unit in an interlocking manner. It is an object of the present invention to provide a control method capable of further simplifying the configuration of the converter section and preventing the occurrence of overvoltage in the inverter section.

[0004]

In order to solve the above problems, the present invention is directed to a converter section for converting a three-phase input power supply voltage into a DC voltage, a snubber capacitor connected between the output terminals of the converter section, and a snubber. A motor control method comprising an inverter unit for inputting a DC voltage across a capacitor to control an electric motor, wherein the regenerative electric power of the electric motor is regenerated to the three-phase input power source, wherein the DC voltage of the converter unit is equal to or higher than a predetermined voltage. After that, the converter unit is started, the dynamic brake signal is turned off, the inverter unit is driven to operate the electric motor, and the drive of the inverter unit is stopped. After the signal is turned on, the driving of the converter unit is stopped to stop the operation of the electric motor.

[0005]

According to the present invention, by removing the smoothing capacitor on the output side of the converter unit, the winding impedance of the motor, which is the load of the inverter unit, is connected to the converter unit in series even during the power regeneration operation of the converter unit. Therefore, the current of the converter unit basically does not exceed the current controlled by the inverter unit.

[0006]

EXAMPLES Examples of the present invention will be described below. FIG. 1 is an overall configuration diagram of the present invention. In the figure, 1 is a three-phase input power supply, 2 and 3 are ACCTs (AC current transformers), 4 is a converter section, 5 is a reactor, and high frequency current is smoothed in the PWM controlled inverter section, but this is not provided. Can be controlled. A snubber capacitor 6 absorbs a transient surge voltage when the switching element of the inverter section is turned off. 7 is a resistor for detecting an overcurrent in the inverter, 8 is an inverter, 9 and 10 are DC
CT (DC current transformer), 11 is a DB (dynamic brake) circuit, 12 is an overcurrent detection circuit on the input side of the converter section, 13 is a phase discrimination circuit of a three-phase input power supply, and 14 and 15 are a converter section and an inverter section, respectively. Is a base drive circuit that controls on / off of a transistor, which is a power switching element of. However, the power switching element is not limited to the transistor, and the MO
Any element capable of self-extinguishing, such as SFET, IGBT, and GTO, may be used. Reference numeral 16 is an overcurrent detection circuit that detects an overcurrent in the inverter unit 8 based on a terminal voltage drop of the resistor 7. The overcurrent detection circuit 16 may be an insulating type using a Hall element instead of the resistor 7, or a DC / DC converter type. Reference numeral 17 is a voltage detection circuit for detecting whether the DC input voltage of the inverter section is in a low voltage state or an overvoltage state. 18 is a protection sequence circuit, 19
Is a PWM (pulse width modulation) circuit, 20 is a current detection circuit for giving a feedback signal of a current minor loop, 21
Is a speed amplifier when forming a speed control loop, 22 is a speed detection circuit for giving a speed feedback signal, and 23 is a current command circuit. In addition, this circuit configuration is a drive motor,
For example, the circuit configuration differs depending on the synchronous motor, the induction motor, the DC motor, or the like, but is not particularly limited. However, when the DC motor is driven, the configuration of the inverter unit 8 changes, but since the configuration method is well known, it will not be particularly mentioned here. Reference numerals 24, 25 and 26 are current amplifiers, 27 and 28 are inverting amplifiers, and 29 is an electric motor which is a load of the inverter. As the electric motor, a synchronous electric motor, an induction electric motor, a direct current electric motor or the like is also used. Reference numeral 30 is a detector that outputs a signal necessary for speed control, position control, vector control of an AC motor, or the like. FIG. 2 is a detailed diagram of the protection sequence circuit 18. 31 is a set / reset circuit, 32 is an OR circuit, 33 is a sequential circuit, 34 is an AND circuit, and 63 is an inverter gate. Next, the circuit operation will be described. In FIG. 1, diodes 41, 42, 43 and 4 of the converter section are included.
4, 45 and 46 form a three-phase full-wave rectifier circuit. The transistors 35, 36, 37 and 38, 39, 40 provide an energizing path for the regenerative current when the electric motor, which is the load of the inverter unit, is operated in the regenerative mode. As shown in FIG. 3, these transistors are supplied with on / off signals in a 120 ° conduction phase of a three-phase input power supply. The case where each signal in FIG. 3 is at the H level is an ON signal. For example, the transistor 35 is turned on when the voltage phase of the R phase of the three-phase input power supply in FIG. 3 is between 30 ° and 150 °. The current path in the regenerative mode has the maximum voltage phase of the three-phase input voltage among the transistors connected to the P side of the converter and the minimum voltage phase of the transistors connected to the N side. Are sequentially controlled by switching. FIG. 4 shows a time chart of the protection sequence circuit 18. (A) of the same figure shows a sequence when the three-phase input power is turned on and off. First, when the power is turned on, the phase discrimination circuit 13 shown in FIG.
The signal N is output. After the time t1, the converter unit 4
When the DC output voltage rectified by the three-phase full-wave rectifier rises and the low voltage detection signal UV of the voltage detection circuit 17 is released,
Which is the output signal of the set / reset circuit 31 of
The Y signal turns on. The reset signal is prioritized in the set / reset circuit 31, and when the set signal and the reset signal are turned on at the same time, the reset signal becomes valid.
When the READY signal turns on, the P (ON) signal becomes valid, and the phase determination circuit 13 supplies the signal shown in FIG. 3 for controlling the transistor of the converter unit 4 to the base drive circuit 14 to drive the transistor. Further, after the time t2, the DB (OFF) signal is turned on, the DB circuit 11 is released, and the connection between the DB circuit 11 and the electric motor 29 is released. The PWM signal of the inverter unit 8 is INV (O) after the DB circuit 11 is released, that is, after the time t3.
When the N) signal is turned on, the signal is given to the base drive circuit 15, and the electric motor 29 can be operated. Next, when the power is cut off, first, the operation of the inverter unit 8 is turned off, and at the same time, the DB circuit 11 is turned on. t4 is the time from turning off the inverter to turning on DB. afterwards,
After the time t5, the P (ON) signal is turned off, and the operation of the switching element of the converter unit 4 is stopped. t6 is ACO
This is the time from when the N signal is turned off until the low voltage detection signal UV of the main circuit DC voltage is activated. However, as the worst condition when the power is cut off, it is assumed that the power is turned off while the inverter unit 8 is operating, for example, at the time of power failure. In this case, it is necessary to stop the operation of the inverter unit 8 and immediately turn on the DB circuit at the timing shown by the dotted line (abnormal) of the ACON signal in FIG. During this time 1
It has to be controlled in a short time of about 0 μsec. t
Reference numeral 7 indicates the time during which the AC input power is shut off before the INV (ON) signal when an abnormality such as a power failure occurs. In particular, when the power is suddenly turned off when the electric motor 29 is in the regenerative mode, the snubber capacitor having a capacity of several μF to 10 μF is charged rapidly because the regenerative current bypasses only the snubber capacitor of 6. It leads to overvoltage. Even in such an emergency, the power is turned off and DB
If the period up to the operation is executed in a short time, breakdown due to overvoltage can be avoided. FIG. 4B shows a typical example of the protection sequence during normal operation. In the figure, the BB signal is a base block signal for turning off the inverter unit 8 at an arbitrary timing. When the BB signal is turned on, the operation of the inverter unit 8 is stopped. The IOC (I) signal is one of typical abnormality detection signals and represents the overcurrent detection signal of the inverter unit 8. The abnormality detection signal is not limited to this, and includes signals used in servo amplifiers and general-purpose inverters. The addition can be easily performed by the OR circuit 32 of FIG. Here, the case where the IOC (I) signal is generated will be described as a typical example. At this time as well, similarly to the case where the power is cut off, first, the inverter unit 8 is turned off (INV (O
N) signal is turned off), and then the DB circuit 11 after time t4
Is turned on (the DB (OFF) signal is turned off). After that, after time t5, the P (ON) signal is turned off. Incidentally, as a backup measure in case of a power failure, it is possible to suppress the generation of an excessive voltage by separately providing a protection circuit as shown in FIG. In the figure, 59 is a resistor, 60 is a transistor, 61 is an inverter gate, and 62 is a base drive circuit. When the three-phase input power is off, the DC input terminal of the inverter unit 8 is short-circuited via the resistor 59.

[0007]

According to the present invention, it is not necessary to provide a reactor in the three-phase input power source section, the smoothing capacitor in the converter output section is not necessary, and the control of the converter is simple. Cost reduction is possible.
It is necessary to add a DB circuit to protect the inverter from overvoltage.
Generally, it has a built-in circuit. Therefore,
By appropriately controlling the operation timings of the converter section, the inverter section, and the DB circuit, it is possible to realize a motor control device capable of regenerating power with a simple configuration.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a motor control device for implementing the present invention.

FIG. 2 is a protection sequence circuit.

FIG. 3 is a signal time chart of the phase determination circuit.

FIG. 4 is a time chart of a protection sequence circuit.

[Fig. 5] Overvoltage protection circuit in case of emergency such as power failure.

[Explanation of symbols]

1 Three-phase input power supply 2, 3 ACCT 4 Converter part 5 Reactor 6 Snubber capacitor 7, 59 Resistor 8 Inverter part 9, 10 DCCT 11 DB circuit 12, 16 Overcurrent detection circuit 13 Phase discrimination circuit 14, 15, 62 Base drive Circuit 17 Voltage detection circuit 18 Protection sequence circuit 19 PWM circuit 20 Current detection circuit 21 Speed amplifier 22 Speed detection circuit 23 Current command circuit 24, 25, 26 Current amplifier 27, 28 Inversion amplifier 29 Electric motor 30 Detector 31 Set / reset circuit 32 OR circuit 33 Sequential circuit 34 AND circuit 35, 36, 37, 38, 39, 40, 47, 48, 4
9, 50, 51, 52, 60 Transistors 41, 42, 43, 44, 45, 46, 53, 54, 5
5, 56, 57, 58 Diode 61, 63 Inverter gate

Claims (2)

[Claims] 1. A converter unit for converting a three-phase input power supply voltage into a DC voltage, a snubber capacitor connected between converter unit output terminals, and an inverter unit for inputting a DC voltage across the snubber capacitor to control a motor, In the electric motor control method for regenerating the regenerative power of the electric motor to the three-phase input power source, it is detected that the DC voltage of the converter unit is equal to or higher than a predetermined voltage, and the converter unit is started, After turning off the dynamic brake signal, the inverter unit is driven to operate the electric motor, the driving of the inverter unit is stopped, and then the driving of the converter unit is stopped by turning on the dynamic brake signal. An electric motor control method, characterized in that the operation of the electric motor is stopped. 2. A converter unit for converting a three-phase input power supply voltage into a DC voltage, a snubber capacitor connected between converter unit output terminals, and an inverter unit for inputting a DC voltage across the snubber capacitor to control the electric motor. In a motor control method adapted to regenerate the regenerative power of the motor to the three-phase input power supply, any one of an overcurrent input, an overvoltage output, a low voltage output of the converter unit or an inverter overcurrent output is detected. Then, the driving of the inverter unit is stopped, the dynamic brake signal is turned on, and then the driving of the converter unit is stopped to stop the operation of the electric motor.