JP2645144B2 - Motor control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a power conversion circuit for supplying AC power of an arbitrary frequency to a motor when an AC input power supply temporarily drops in voltage due to a momentary power failure or the like. The present invention relates to a control device for an electric motor having a function of controlling the power conversion circuit to start operation promptly when power is restored and power is restored.

(Prior Art) For example, when controlling by supplying AC power of an arbitrary frequency to an induction motor, a forward converter for converting AC power to DC power, a DC reactor for smoothing this DC power, and A power conversion circuit including an inverter that converts DC power into AC power of an arbitrary frequency is used. The control system of the forward converter is a voltage controller that obtains a voltage signal from the difference between the speed reference and the terminal voltage of the induction motor, and current control that generates a current signal from the difference between this voltage signal and the input current of the forward converter. And a phase controller for controlling the phase of the forward converter based on the current signal, and the control system of the inverter is a frequency controller for generating an output current phase signal from a speed reference and the output current phase. , And a pulse controller for controlling the pulse phase of the inverse converter in accordance with. Since the details of the basic operation of these control systems are already known, their description is omitted here.

By the way, in such an induction motor control device, when the AC input power of the forward converter temporarily drops due to an instantaneous power failure or the like, the operation of the forward converter and the inverse converter is temporarily stopped, and the operation is started when the power is restored. Then, the induction motor is restarted.

FIG. 3 shows an example of a system configuration having an instantaneous power failure restart capability when a current source inverter is used as an inverter. In FIG. 3, 1 is an AC power supply, 2 is a forward converter for converting the AC power of the AC power supply 1 into DC power,
Reference numeral 3 denotes a DC reactor for smoothing the DC power, and 4 denotes an inverter which converts the smoothed DC power to AC power of an arbitrary frequency and supplies the AC power to the induction motor 5, and these constitute a power conversion circuit. .

The control system of the forward converter 2 includes a voltage controller 6 and a current controller 7
And a phase controller 8. The control system of the inverse converter 4 includes a frequency control circuit 9 and a pulse converter 10. In the control system of the forward converter 2, the voltage controller 6 outputs a voltage signal when a deviation between the speed reference set by the speed setting unit 11 and the terminal voltage of the induction motor 5 detected by the transformer 12 is input. When a deviation between the voltage signal and the AC input current of the forward converter 2 detected by the current transformer 13 is input, the current controller 7 outputs a current signal, and outputs a current signal.
When this current signal is input, the phase of the forward converter 2 is controlled by the output. In the control system of the inverter,
When the speed reference is input, the frequency control circuit 9 converts the phase and outputs an output current phase signal. When the output current phase signal is input, the pulse converter 10 changes the current phase of the inverter 4 based on the output. Perform pulse control.

In the control system of the induction motor having such a power conversion circuit, the control function of the restart at the time of the instantaneous power failure is as follows. That is, the power failure detector 15 connected to the AC power supply 1 via the transformer 14 detects whether the input voltage of the forward converter 2 has dropped to a predetermined value or less, and outputs the detection signal to the frequency control circuit 9. To enter. Further, the input current of the forward converter 2 detected by the current transformer 13 is supplied to the reference correction circuit 16, the speed reference signal is corrected by the output signal, and the corrected signal is input to the frequency control circuit 9. Further, an operation command signal is input to the frequency control circuit 9.

On the other hand, as shown in FIG. 4, the frequency control circuit 9 includes an AND circuit 9a that outputs an operation command signal when no power failure is detected by the power failure detector 15, and a flip-flop 9b that is set when no power failure is detected by the power failure detector 15. When the flip-flop 9b is set and an operation command signal is output from the AND circuit 9a, an AND circuit 9c for giving an operation command to the phase controller 8 and the pulse converter 10, and a motor input via the transformer 12 Detects whether the terminal voltage has dropped below a predetermined value, and resets the flip-flop 9b when the terminal voltage has dropped below the predetermined value. Container 10
Is provided with a phase converter 9e.

Here, the operation when the AC power supply 1 momentarily loses power will be described. When a power failure is detected by the power failure detector 15, the AND circuit 9a,
Since the AND condition of 9c is not satisfied and the operation command given to the phase controller 8 and the pulse converter 10 is blocked,
These control operations stop. When the AC power supply 1 is restored and the power failure detector 15 detects that power is restored, the AND condition of the AND circuit 9a in the frequency control circuit 9 is satisfied.
In the circuit 9c, the AND condition of the AND circuit 9c is not satisfied until the flip-flop 9 is reset by the voltage drop detector 9d. That is, the control of the phase controller 8 and the pulse converter 10 does not immediately start even after the AC power supply 1 is restored, and the voltage drop detector 9d detects that the terminal voltage of the induction motor 5 has dropped to a sufficiently low value. Then, when the flip-flop 9b is reset, the AND condition of the AND circuit 9c is satisfied, and the control of the phase controller 8 and the pulse converter 10 is started.

However, such restart control at the momentary power failure has the following disadvantages.

After the power is restored, the operation cannot be restarted until the terminal voltage of the induction motor 5 is sufficiently reduced. Therefore, the time until the restart is long, and the induction motor 5 applies a load, such as a pump, whose deceleration time due to free-run is very short. In the case of driving, a decrease in speed becomes too large, which may lead to a system down.

Since the operation is restarted after the terminal voltage of the induction motor 5 becomes almost zero, the terminal voltage of the induction motor 5 becomes a normal value and the time until the induction motor 5 outputs a torque corresponding to the load is long. Become.

When the operation is restarted with the terminal voltage of the induction motor 5 remaining to some extent, the voltage and current oscillate, and in some cases, an overvoltage, an overcurrent, and the like are generated, damaging the control device and the induction motor.

The characteristics of the induction motor 5 vary depending on the capacity, the number of poles, and the like, and the time until the restart is different for each induction motor 5.

After the restart, the rotation speed of the induction motor 5 and the output frequency of the inverter 4 are corrected by the input current signal of the forward converter 2 until the rotation speed of the induction motor 5 and the output frequency of the inverter 4 are synchronized. Time becomes longer.

(Problems to be Solved by the Invention) As described above, in the conventional motor control device, the restart control at the momentary power failure is performed by the induction motor 5 even if the power is restored.
Cannot be restarted until the terminal voltage of the induction motor is sufficiently reduced, so that the restart time is not constant for induction motors having different characteristics depending on the capacity and structure. Further, since the correction of the output frequency of the inverter 4 with respect to the free-run speed of the induction motor is performed after the restart, the rotation speed of the induction motor 5 is reduced by this time. Thus, no matter how short the power outage time, there is a problem that the time until the restart is determined by other factors.

The present invention provides a highly reliable motor that can be restarted immediately after power is restored, regardless of its characteristics, even if the motor temporarily stops due to a temporary voltage drop such as an instantaneous power failure of an AC power supply. It is an object of the present invention to provide a control device.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a forward converter for converting an AC voltage to a direct current, a reactor for smoothing a direct current supplied from the forward converter, and The DC converter converts the DC current into an AC current of an arbitrary frequency based on a first current phase command and supplies the AC current to the AC motor. A voltage controller for controlling, a signal converter for outputting the current phase command according to the speed reference, and a detector for detecting a terminal voltage and a voltage phase of the AC motor, wherein the AC voltage is equal to or less than a predetermined voltage. , The operation of the forward converter and the inverse converter is stopped, the speed (frequency) of the AC motor is obtained from the voltage phase detected by the detector, and the speed and the speed detected by the detector are determined. End of AC motor A voltage correction signal is output so that a ratio with the slave voltage becomes a predetermined value, a second current phase command is obtained by adding the phase correction signal to the voltage phase, and the first current phase command is changed to the second current phase command. , The input of the signal converter is switched to the speed of the AC motor, and the output signal of the signal converter and the second
The deviation from the current phase command is monitored, and when the AC voltage is restored, the operation of the forward converter and the inverse converter is restarted, and when the deviation becomes a predetermined value or less, the signal converter Means for returning an input to the speed reference and returning the first current phase command to an output signal of the signal converter to resume normal operation.

(Operation) Therefore, in the motor control device having such a configuration, when a decrease in the input voltage of the forward converter is detected and the operation of the forward converter and the inverse converter is stopped, during the power failure period, A voltage correction signal is output so that the ratio between the terminal voltage of the motor and the speed becomes a predetermined value, the phase correction signal is added to the voltage phase to obtain a second current phase command, and the first current phase command is 2, the input of the signal converter is switched to the speed of the AC motor, the deviation between the output signal of the signal converter and the second current phase command is monitored, and the terminal voltage phase of the motor and the inverter are switched. The operation is resumed by the power recovery, and when the deviation becomes equal to or less than a predetermined value, the input of the signal converter is returned to the speed reference and the first current phase command is issued. Return to the output signal of the signal converter,
By restarting the normal operation, the restart can be performed immediately after the power is restored regardless of the characteristics of the electric motor.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a system configuration of a motor control device according to the present invention. The same parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. Only different points will be described here. In the present embodiment, as shown in FIG. 1, a phase detector 17 to which the terminal voltage of the induction motor 5 detected by the transformer 12 is input is provided, and the voltage phase detected by the phase detector 17 is converted into the following. It is input to the frequency control circuit 90 having such a configuration.

FIG. 2 is a block diagram showing an example of the internal configuration of the frequency detection circuit 90. In FIG. 2, the operation command signal is input to the AND circuit 91a together with the output of the power failure detector 15. The AND circuit 91a receives an operation command signal and outputs an operation command to the phase controller 8 and the pulse converter 10 when a power failure is not detected by the power failure detector 15. Speed reference is changeover switch
A phase converter 94 is input to a phase converter 94 via an integration circuit 93 comprising a resistor R1 and a capacitor C1 for suppressing a sudden change in the speed reference 92a, and the phase converter 94 converts the speed reference into a phase and outputs a current phase reference signal. . The voltage phase signal detected by the phase detector 17 is input to a differentiator 95, which differentiates the voltage phase signal to obtain the rotation speed of the induction motor, and outputs the output signal to a changeover switch 92a. And input to the power factor angle detector 96a. The power factor angle detector 96a calculates a voltage correction signal from the rotation speed of the induction motor and the terminal voltage of the motor obtained by the differentiator 95 so that the ratio between the rotation speed and the terminal voltage of the AC motor becomes a predetermined value. The output signal is given to the proportional integrator 96b. This proportional integrator 9
The output signal of 6b is corrected by adding to the voltage phase signal detected by the phase detector 17, and one of the output and the current phase reference signal output from the phase converter 94 is switched.
It is selected by 92b and output to the pulse converter 10 as the output current phase. Further, the deviation between the output signal of the proportional integrator 96b, the sum signal of the voltage phase signal detected by the phase detector 17 and the current phase reference signal output from the phase converter 94 is input to the absolute value circuit 97a, The value is output to a phase difference detector 97b. When detecting that the output signal of the absolute value circuit 97a has reached a predetermined phase, the phase difference detection circuit 97b inputs the detection signal to one input terminal of the AND circuit 91c. On the other hand, the above-described power failure detection signal is input to the set terminal of the switching circuit 91d and is input to the on-delay circuit 91b, and its output signal is input to the other input terminal of the AND circuit 91c. When the AND condition is satisfied, a reset signal is input to the switching circuit 91d. This switching circuit 9
1d is set by a detection signal when a power failure is detected by the power failure detector 15, and switches so that a switching command is given to the changeover switch 92a to output a rotation speed signal of the induction motor obtained by the differentiator 95, The output voltage phase detected by the phase detector 17 by the changeover switch 92b and the proportional integrator
Switching is performed so that an addition signal with the 96b output is output.
Further, when a predetermined time elapses after the power failure is detected by the power failure detector 15, the on-delay 91b operates, and the phase difference detector 9 operates.
When it is detected by 6b that the output of the absolute value circuit 96a has reached a predetermined phase, it is reset by the output of the AND circuit 91c, and switches the changeover switches 93a and 93b to return to the state before the power failure.

Next, the operation of the motor control device configured as described above will be described.

Now, when the input voltage drop is detected by the power failure detector 15, the inverted signal of the power failure detection signal is input to the AND circuit 91a in the frequency control circuit 90, so that the AND condition is not satisfied, and the phase controller 8 and the pulse converter The operation of the container 10 stops. At the same time, the switching circuit 91d is set by the power failure detection signal, and the changeover switches 92a and 92b are switched to the signal path corresponding to the power failure side. As a result, the output phase signal, which is the output of the frequency control circuit 90, is obtained from the current phase reference signal by the phase detector.
The signal is switched to the sum signal of the output signal of 17 and the output signal of the proportional integrator 96b, and the input signal of the pulse converter 10 follows the voltage phase of the induction motor 5. In this case, the power factor angle detector 96a
Is a differentiator between the terminal voltage of the motor and the output signal of the phase detector 17.
A voltage correction signal is output so that a ratio with a speed signal obtained by differentiating at 95 becomes a predetermined value. Further, the input signal of the phase converter 94 is also used for differentiating the voltage phase detected by the phase detector 17 into a differentiator 95.
Is switched to the rotation speed signal of the motor, which is differentiated and output by the motor, and the charging voltage of the capacitor C1 is also changed to the induction motor 5
Follow the rotation speed of Thus, the current phase reference can reliably follow the rotation speed of the induction motor even if the load characteristics change.

In such a state, when the power failure detector 15 detects the restoration of the input power, the AND condition of the AND circuit 91a is satisfied, and the phase controller 8 and the pulse converter
10 starts driving immediately. At this time, since the ratio of the rotation speed of the induction motor 5 to the terminal voltage does not match the ratio of the rated rotation speed of the induction motor 5 to the terminal voltage, the power factor angle detector 96
In a, a signal is output so that the ratio between the rotation speed of the induction motor 5 and the terminal voltage becomes a predetermined value. The signal output from the power factor angle detector 96a calculates a phase correction signal by the proportional integrator 96b, and adds this signal to the output voltage phase signal detected by the phase detector 17, thereby obtaining the final inverse signal. Converter 4
Is determined.

As a result, the output phase of the inverter 4 is corrected, so that the input current phase of the induction motor 5 changes and the terminal voltage also changes. This operation makes the ratio of the rotation speeds of the induction motor 5 constant. Thereafter, the absolute value of the deviation between the output signal of the phase converter 94 and the output signal of the proportional integrator 96b corrected by the output voltage phase signal detected by the phase detector 17, that is, the phase difference between the two signals is detected. When the output of the AND circuit 91b is within the predetermined value, the AND condition of the AND circuit 91c is satisfied, and the switching circuit 91d is reset. Accordingly, the inverting operation of the switching circuit 91d causes the switches 92a and 92b to return to the contact state before the power failure, the input signal of the phase converter 94 becomes the speed reference by the speed setting device 11, and the output current of the frequency control circuit 90 The phase signal is switched to the output signal of the phase converter 94, and returns to the normal control state.

From the above operation, the present embodiment can provide the following operation and effect.

(1) Since the phase signal that is the input signal of the pulse converter 10 is made to follow the voltage phase of the induction motor 5 during the power failure period,
Restart is possible immediately after the power is restored, and the operation stop time of the control device due to the power failure can be minimized.

(2) Since the restart is started by synchronizing the terminal voltage phase of the induction motor 5 and the pulse phase of the inverter 4, the torque of the induction motor 5 can be established in the shortest time.

(3) Since the control device is automatically corrected based on the terminal voltage phase and the rotation speed determined by the motor and the load characteristics during the power failure period, no special adjustment by the load characteristics or the like is required.

(4) Since the rotational speed and the phase match the induction motor 5 at the start of re-operation, no abnormal current or voltage is generated, and stable and safe switching can be performed.

The present invention is not limited to the embodiment described above and shown in the drawings, and can be implemented with various changes without departing from the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, restarting can be performed ignoring the residual voltage and load characteristics of the motor, so that the motor is very effective even for loads such as pumps having a short deceleration time. A motor control device that can implement an instantaneous power outage measure, greatly improve the reliability of system operation, and eliminate the stress on restarting the machine side by controlling the phase and rotation speed in synchronization. Can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a system configuration of an embodiment of a motor control device according to the present invention, FIG. 2 is a block diagram showing an internal configuration of a frequency control circuit in the embodiment, and FIG. FIG. 4 is a circuit diagram showing a configuration example of a control device, and FIG. 4 is a block diagram showing an internal configuration of a frequency control circuit of the control device. 1 AC power supply 2 Forward converter 3 DC reactor 4 Inverter 5 Induction motor 6 Voltage controller 7 Current controller 8 Phase Controller, 11 Speed setting device, 12, 14 Transformer, 13 Current transformer, 15 Power failure detector, 17 Phase detector, 90 Frequency control circuit
91a, 91c …… AND circuit, 91b …… On delay circuit, 91d…
... Switching circuit, 92a, 92b ... Switch, 93 ... Integrating circuit, 94 ... Phase converter, 95 ... Differentiator, 96a ... Power factor detector, 96b ... Proportional integrator, 97a ... Absolute Value circuit, 97b…
... Phase difference detector.

Claims (1)

(57) [Claims] 1. A forward converter for converting an AC voltage into a direct current, a reactor for smoothing a direct current supplied from the forward converter, and an optional converter for converting the smoothed direct current into a predetermined current based on a first current phase command. An inverter that converts the frequency into alternating current and supplies the alternating current to the AC motor, a voltage control unit that controls the forward converter by comparing a speed reference and the voltage of the AC motor, and the current according to the speed reference. A signal converter that outputs a phase command, and a detector that detects a terminal voltage and a voltage phase of the AC motor, and operates the forward converter and the inverse converter when the AC voltage falls below a predetermined voltage. Is stopped, the speed (frequency) of the AC motor is obtained from the voltage phase detected by the detector, and the ratio of this speed to the terminal voltage of the AC motor detected by the detector is set to a predetermined value. Output voltage correction signal Then, a second current phase command is obtained by adding the phase correction signal to the voltage phase, the first current phase command is switched to the second current phase command, and the input of the signal converter is connected to the AC motor. And the deviation between the output signal of the signal converter and the second current phase command is monitored to synchronize the terminal voltage phase of the motor and the phase of the control signal of the inverter, and When the power is restored, the operation of the forward converter and the inverse converter is restarted. When the deviation becomes equal to or less than a predetermined value, the input of the signal converter is returned to the speed reference and the first current phase is returned. A control device for an electric motor, comprising: means for returning a command to an output signal of the signal converter and restarting normal operation.