JPS61150682A - Protecting system of inverter drive induction motor - Google Patents

Abstract

PURPOSE:To prevent the defect of a motor due to idling of the motor by detecting the overvoltage of a DC unit of a voltage type frequency converter for controlling the output for driving the motor to stop a converter drive signal, and flowing a brake current to the motor. CONSTITUTION:The voltage of a DC unit of an inverter for driving a motor is input from both ends of a main circuit capacitor 1, compared by a comparator 11 with a reference voltage 12, and when an overvoltage is detected, an alarm signal D is output. When a DC current B is examined by a detector 14 to detect an overcurrent, the pulse width of a duty ratio between the upper and lower limit values determined by a limiter 16 is generated from a unit 15 to output a DC brake signal. An output signal selector 17 switches a PWM signal fed with the base drive signals of power elements 2-7 so far from a pulse generator 15 to a DC brake signal, arbitrary 2-phase power elements are driven to flow a brake current to a motor 8. Thus, it prevents the motor from idling to protect the motor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a protection device for a motor and a load device when the motor is driven using a voltage-type frequency converter.

[Conventional technology]

When a voltage-type inverter device is used to drive an electric motor, a sudden deceleration of the motor or an abnormality in a load device may cause the device to become live, and the DC portion of the inverter device may become overvoltage.

Means for protecting the inverter device from this overvoltage include regeneration of regenerated power to the power source by a regenerative circuit, or, if the capacity of the device is relatively small, consumption of regenerated power by a regenerative power processing resistor. However, when power is regenerated that exceeds the processing capacity of the regeneration circuit or regenerative power processing resistor, the protection means cannot protect the inverter device from overvoltage.

For this reason, inverter devices generally detect the voltage of the device's DC section, compare it with a reference value, and if the detected voltage exceeds the standard, send an alarm signal, block the output drive signal, and output the device. There is an overvoltage protection circuit that prevents further regeneration by blocking the power element.

However, when this protection circuit is activated, the motor will coast. Further, the above-mentioned alarm signal is normally completely self-held and will not be released unless reset from the outside. In other words, in order for the electric motor to stop from the coasting state, a stopping time is required depending on the load state, etc., and during this time, the motor is in an uncontrolled state.

Therefore, if we consider, for example, the case where the above-mentioned inverter device is used to drive the main shaft, it is natural to judge that the above-mentioned activation of the protection device means that an abnormality has occurred in the load device. That is, in such a case, it is necessary to stop the electric motor immediately, but the above-mentioned protection circuit only protects the inverter device, as described above.
For example, there are problems such as requiring an external emergency brake device and complicating the circuit configuration. This emergency braking device generally consists of a DC power supply and a current limiting resistor, and when overvoltage is detected, it blocks the inverter operation signal, switches the motor terminal to the emergency braking device, and connects the motor to the DC voltage and current limiting resistor. Braking is performed by applying a DC current determined by the resistance used.

However, in a voltage source inverter drive system that is not equipped with a rotational speed detection device, the only way to confirm whether the motor has stopped is to use the human eye. Therefore, braking current continues to be applied until a person switches the brake device, causing heating of the electric motor or heating of the current limiting resistor.

In addition, in drive systems with limited movable ranges, for example when moving equipment on slide rails,
Although there is a movement limit point in the left-right (front-back) direction, a forced stop operation is not performed while the overvoltage protection is activated as described above, so a collision accident of the device is highly conceivable.

[Problem that the invention seeks to solve]

The present invention aims to protect the electric motor and its peripheral devices from accidents caused by coasting of the electric motor when the overvoltage protection circuit is activated as described above, and to optimize the application time of braking current. .

[Means for solving problems]

The present invention provides a voltage-type frequency converter for controlling output for driving an electric motor, an overvoltage detection means for a DC section of a converter, and a means for detecting overvoltage in a direct current section of a converter. The above-mentioned problem has been solved by providing an overvoltage protection means that protects the converter from overvoltage by applying the voltage.

〔Example〕

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 (al shows the basic configuration of a voltage source inverter. In this figure, the converter section is omitted.

FIG. 1(b) is a basic configuration block diagram of a protection device according to the present invention.

In FIG. 1+al, 1 is a main circuit capacitor, 2 to 7 are output power elements, 8 is an electric motor, and 9 is a base drive circuit. In addition, in FIG. 1(b), 10 is an isolation amplifier;
11 is a comparator, 12 is a reference voltage, 14 is a current detection section, 1
Reference numeral 5 indicates a pulse generating section, 16 a limiter section, and 17 an output signal selector section.

, Detection of overvoltage of the converter is performed using main circuit capacitor 1.
After detecting the voltage (A) across the terminal and insulating it from the main circuit with the isolation amplifier 10, the comparator 11 compares it with the reference voltage 12. If the detected voltage exceeds the reference voltage, the comparator II sends an alarm signal. Send out.

When the output signal selector section 17 receives the alarm signal, it switches the base drive signal from the PWM signal that had been sent out until then to the DC braking signal sent from the pulse generation section 15.

The phase to be switched by the DC braking signal can be arbitrarily selected from any combination such as the U phase (output element 2) and the V phase (output element 5), and can be set in advance.

The DC braking signal is a rectangular wave pulse train signal as shown in FIG. The duty of this pulse signal is a/b (%
) (where a is the on-time and b is the period), the braking force and braking current are changed. The braking current also changes depending on the inductance of the motor even if the duty of the pulse signal is the same. The larger the braking current, the greater the braking force, but it must be adjusted so as not to exceed the overcurrent rating of the converter.

Therefore, as shown in the block diagram of Fig. 1, the motor current (
Alternatively, overcurrent can be prevented by detecting the DC section current (B) and controlling the duty of the pulse signal according to the magnitude of the detected value.

Generally, the conversion device detects the motor current (or DC current) for its own overcurrent protection, so there is no need to add a new current detector, and you can just use the detection value described above. .

The limiter 16 provides an upper limit and a lower limit to the duty of the pulse signal, and prevents the braking current from becoming excessive when there is a mismatch between the converter and the motor capacity.

DC braking stops operation when the motor stops and a stop signal is applied.
The conversion device enters the standby state and the braking stop is completed.

Next, the motor stop signal generation circuit (stop detection circuit) will be explained.

FIG. 3 is a basic block diagram of the motor stop signal generation circuit. An alarm signal is sent out due to overvoltage detection, and the timer 19 starts counting at the same time as braking starts. timer 1
After counting the preset braking time, 9 sends an output select signal to the output signal select section and switches the base drive signal from the DC braking signal to the PWM signal. P.W.
The M signal is a very low speed (3 to 5 Hz) normal rotation driving pulse signal generated by the PWM signal generator 20. When such a normal rotation signal is applied to a motor that is coasting or stopped, depending on the relationship between the frequency of the motor and the signal, for example, if the motor frequency (rotation speed) is higher than the signal, the device will enter the regenerative state, and if it is lower, the device will enter the regenerative state. The device is in the operating state. During regeneration, the main current is so-called regenerative current that flows from the output side to the DC power supply side, and during drive, the main current flows from the DC power supply side to the output side, but these two currents are in opposite directions.
By detecting the direction of this direct current, the state of the motor can be determined. The sign determination circuit 18 performs this operation. The sign determination circuit 18 determines the sign (=direction) of the DC current based on the time amplifier signal of the timer 19 described above, and if the sign corresponds to the driving state, it is assumed that the motor has stopped or decelerated to an extremely low speed, and the aforementioned stop detection is performed. send out a signal,
Put the inverter into standby mode. If the sign corresponds to the regenerative state, the motor is assumed to have not decelerated sufficiently yet, and the timer 19 is set again. At the same time, the output select signal is operated to switch the base drive signal from the PWM signal to the DC braking signal, and the motor is set again. Continue braking for 41 times. Thereafter, the above procedure is repeated until it is determined that the electric motor has stopped.

Generally, there is a large difference between the motor rotation speed and the command signal; 衾-1
Is it warm spring I! ;Naedo's V/T;'L'Upper C)W■When an attack is applied, an overcurrent that is several times the rated value or more may flow, and this overcurrent activates the overcurrent protection circuit. There is a possibility that the original braking operation will be stopped. Therefore, the limiter 22 first detects the DC (motor) current,
Based on the detected value, the PWM pattern of the PWM generation circuit is adjusted and a limit is placed on the V/F of the PWM signal to prevent overcurrent from flowing. There is no need to add a new detector to detect the direct current (motor) current used in the limiter, and it is sufficient to use a detector that is generally provided in the inverter device for overcurrent protection.

When determining whether or not the motor has stopped, there is a method of detecting a change in the DC section voltage in addition to the method using the sign of the DC current as described above. That is, if the electric motor is still rotating at a high rotational speed when a driving command of 3 to 5 Hz is given as described above, the device enters a regenerative state and the DC section voltage increases. If the vehicle has already stopped or decelerated to an extremely low speed, the DC section voltage will either remain unchanged or decrease. There is also a method that utilizes this change to determine that if the DC power voltage rises, it is in a regenerative state, that is, that braking is required again, and if it does not change, it is determined that the vehicle has stopped or the speed has become sufficiently low and that braking is complete.

The method for realizing the braking circuit shown in the block diagram of FIG. 1 and the stop detection circuit shown in the block diagram of FIG. 3 is as follows.
Although various methods can be considered, for example, if a CPU is used as shown in FIG. 4, the signal generation function, duty control function, etc. can all be configured by software. In the same figure, 24 and 2
5 is a 4A/D converter that converts the detected voltage and current into digital signals, 26 is a microprocessor, and 27 is a signal selector that switches from an inverter PWM signal to a DC braking signal when an overvoltage occurs.

〔Effect of the invention〕

As described above, according to the present invention, when the overvoltage protection circuit is activated, without adding any other braking device or the like,
This has the effect of applying a DC braking current to the motor, preventing the motor from coasting, and protecting the motor.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the basic configuration of the voltage source inverter and the protection device according to the present invention, Fig. 2 is a waveform diagram of DC braking current, and Fig. 3 is a block diagram showing the basic configuration of the motor stop signal generation circuit of the present invention. 4 are block diagrams showing the basic configuration of the braking circuit and stop detection circuit according to the present invention, which are constructed using a microcomputer. 1: Main circuit capacitors 2 to 7: Output power element 8: Motor 9: Base drive circuit IO: Isolation amplifier 11: Comparison base 12: Reference voltage 14: Current detection section 15: Pulse generation section 16: Limiter section 17: Output Signal selector section 18: Sign determination circuit 19: Timer 20: PWM generator 21 = Output signal selector section 22: Limiter 24.25: A/D converter 26: Microprocessor 27: Signal selector Patent applicant Yasuyo Denki Seisakusho Co., Ltd. Type large
Masu Kobori (and 1 other person) Fig. 2 1 ----Motor electric 5It change 6 Fig. 3 Layer 8 Fig. 4

Claims (1)

[Claims] 1. A voltage type frequency converter for controlling the output for driving an electric motor, an overvoltage detection means for a DC section of a converter, and a converter drive signal that is stopped by the overvoltage detection. A protection method for an inverter-driven induction motor that includes an overvoltage protection means that applies a braking current to the motor to protect the converter from overvoltage. 2. In the overvoltage protection means, the braking current of the motor during braking is temporarily stopped, a low-frequency driving command is given, and the motor is placed in a regenerative state or a driving state depending on the polarity of the DC current or an increase or decrease in the DC voltage. determine whether
If the motor is in the regenerative state, the braking current is applied again to continue braking, and if the motor is in the driving state, it is determined that the motor has reached a stopped state or an extremely low speed state and the braking operation is stopped. A protection method for an inverter-driven induction motor according to item 1.