JPH0327793A - Controller for motor - Google Patents

Abstract

PURPOSE:To immediately restart a motor even if the motor is once stopped by correcting a power factor angle obtained by a terminal voltage and rotating speed of the motor during a power interruption period with a voltage phase detected by a phase detector, and outputting it as a phase control signal of an inverter. CONSTITUTION:When a power interruption detector detects recovery of an input power source, the AND condition of an AND circuit 9a is satisfied. Accordingly, a phase controller and a pulse converter immediately start according to its output signal. In this case, since the ratio of the rotating speed to the terminal voltage of an induction motor does not coincide with the ratio of the rated rotating speed to the rated terminal voltage of the motor, a power factor angle detector 96a so outputs a signal that the ratio of the rotating speed to the terminal voltage of the motor becomes a predetermined value. A phase correction signal is calculated by a proportional integrator 96b with a signal output from the detector 96a to determined the final output phase of an inverter.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention provides a power conversion circuit that supplies AC power of any frequency to a motor when the AC input f4R temporarily drops in voltage due to a momentary power outage, etc. The present invention relates to a control device for an electric motor, which has a control function such that a power converter circuit is once stopped and then the operation of a power conversion circuit is promptly started when the power is restored.

(Prior art) For example, when controlling an induction motor by supplying AC power of an arbitrary frequency, a forward converter converts AC power to DC power, a DC reactor smoothes this DC power, and a DC reactor smoothes this DC power. A power conversion circuit is used that includes an inverse converter that converts DC power to AC power of an arbitrary frequency.

The control system of the forward converter consists of a voltage controller that obtains a voltage signal from the deviation between the speed reference and the terminal voltage of the induction motor, and a current control that generates a current signal from the deviation between this voltage signal and the input current of the forward converter. The control system of the inverse converter includes a frequency control device that controls the output current phase signal from the speed reference, and a phase controller that controls the phase of the forward converter based on this current signal. It consists of a pulse controller that controls the pulse phase of the inverter according to the current phase. Since the details of the basic operations of these control systems are already known, their explanation will be omitted here.

By the way, in such an induction motor control device,
When the AC input power supply of the forward converter temporarily drops in voltage due to a momentary power outage, etc., the operation of the forward converter and reverse converter is temporarily stopped, and when the power is restored, the operation is started and the induction motor is restarted. There is.

FIG. 3 shows an example of a system configuration having 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 that converts the AC power of this AC power supply 1 into DC power, and 3
4 is a DC reactor that smoothes this DC power, and 4 is an inverter that converts the smoothed DC power into AC power of an arbitrary frequency and supplies it to the induction motor 5. These constitute a power conversion circuit.

The control system of the forward converter 2 includes a voltage controller 6, a current controller 7, and a phase controller 8, and the control system of the inverse converter 4 includes a frequency control circuit 9 and a pulse converter 10. There is. In the control system of the forward converter 2, the voltage controller 6 outputs a voltage signal when the deviation between the speed reference set by the speed setting device 11 and the terminal voltage of the induction motor 5 detected by the transformer 12 is input. When the current controller 7 receives the deviation between this voltage signal and the AC input current of the forward converter 2 detected by the current transformer 13, it outputs a current signal, and the phase controller 8 outputs a current signal. When input, the phase of the forward converter 2 is controlled by its output. In the control system of the inverse converter, when the speed reference is input, the frequency control circuit 9 performs phase conversion and outputs an output current phase signal, and the pulse converter 10
When this output current phase signal is input, the current phase of the inverter 4 is pulse-controlled by its output.

In a control system for an induction motor equipped with such a power conversion circuit, the restart control function in the event of a momentary power outage is as follows. That is, a power failure detector 15 connected to the AC power supply 1 side via a transformer 14 detects whether the input voltage of the forward converter 2 has decreased below a predetermined value, and transmits the detection signal to the frequency control circuit 9. Enter.

Further, the input current of the forward converter 2 detected by the current transformer 13 is given to the reference correction circuit 16, and the speed reference signal is corrected by the output signal thereof and input to the frequency control circuit 9. Further, a driving 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 outage is detected by the power outage detector 15, and a flip-flop 9b that is set when no power outage is detected by the power outage detector 15. , this flip-flop 9b is set, and the AND circuit 9a
AND circuit 9 which gives a driving command to the phase controller 8 and pulse converter 10 when a driving command signal is output from
c. A voltage drop detector 9d that detects whether the motor terminal voltage input via the transformer 12 has fallen below a predetermined value, and resets the free-sov flop 9b when the voltage has fallen below the predetermined value, and a speed reference. a phase converter 9 which converts the phase of the output current and provides the output current phase to the pulse converter 10;
It is equipped with e.

Here, to describe the operation when there is a momentary power outage in the AC power supply 1, when a power outage is detected by the power outage detector 15, the AND condition of the AND circuits 9a and 9c in the frequency control circuit 9 is not satisfied due to the power outage detection signal. , phase controller 8
Since the operation command given to the pulse converter 10 is blocked, these control operations are stopped. Furthermore, when the AC power supply 1 is restored and this is detected by the power outage detector 15, the AND condition of the AND circuit 9a in the frequency control circuit 9 is satisfied, but the AND circuit 9C has the flip-flop 9 connected to the voltage drop detector. AND until reset by 9d
The AND condition of circuit 9C is not satisfied. That is, even if the AC power supply 1 is restored, the control of the phase controller 8 and the pulse converter 10 is not started immediately, and the voltage drop detector 9d detects that the terminal voltage of the induction motor 5 has decreased to a sufficiently low value. When the flip-flop 9b is reset, the AND condition of the AND circuit 9C is satisfied and control of the phase controller 8 and pulse converter 10 is started.

However, such restart control in the event of a momentary power outage has the following drawbacks.

■ After the power is restored, restarting cannot be performed until the terminal voltage of the induction motor 5 drops sufficiently, so it takes a long time to restart the operation. When driving, the speed drop may become too large and the system may go down.

■ Since the operation is restarted after the terminal voltage of the induction motor 5 becomes almost zero, it takes a long time until the terminal voltage of the induction motor 5 returns to a normal value and the induction motor 5 outputs torque commensurate with the load. become longer.

(2) If the induction motor 5 is restarted with a certain amount of terminal voltage remaining, the voltage and current will oscillate, and in some cases overvoltage or overcurrent may occur, damaging the control device and the induction motor.

(2) The characteristics of the induction motor 5 vary depending on the capacity, number of poles, etc., and the time until restart differs depending on each induction motor 5.

■ After restart, the rotation speed of the induction motor 5 and the output frequency of the inverse converter 4 are synchronized because the rotation speed of the induction motor 5 and the output frequency of the inverse converter 4 are corrected by the input current signal of the forward converter 2. It will take longer.

(Problems to be Solved by the Invention) As described above, in the conventional electric motor control device, restart control in the event of a momentary power outage restarts the induction motor 5 until the terminal voltage drops sufficiently even after the power is restored. Therefore, restart time is not constant for induction motors with different characteristics depending on capacity and structure.

In addition, an inverse converter 4 for the free run speed of the induction motor
Since the correction of the output frequency is performed after the restart, the rotational speed of the induction motor 5 decreases during this time. As described above, there is a problem in that no matter how short the power outage time is, the time until restart is determined by other factors.

The present invention provides a highly reliable electric motor that can restart the electric motor immediately after power is restored, regardless of its characteristics, even if the electric motor temporarily stops due to a temporary voltage drop such as a momentary power outage of an AC power supply. The purpose is to provide a control device for.

(Means for Solving the Problems) In order to achieve the above object, the present invention converts AC power into DC power using a forward converter, smoothes this DC power using a DC smoothing circuit, and then converts it into DC power using an inverse converter. It includes a power conversion circuit that converts AC power of an arbitrary frequency to supply it to the motor, obtains a voltage signal from the deviation between the speed reference and the terminal voltage of the motor, and combines this voltage signal with the input current of the forward converter. a forward converter control system that obtains a current signal from the deviation of the forward converter to control the phase of the forward converter; and an inverse converter control system that obtains an output current phase signal from the speed reference and controls the phase of the inverse converter using this output current phase signal. A motor control device comprising a converter control system, a voltage drop detector for detecting a drop in input voltage of the forward converter, a phase detector for detecting an output voltage phase of the inverse converter; , operation command means for stopping the operation of the forward converter and reverse converter by blocking an operation command given to the forward converter and reverse converter control system when a voltage drop is detected by the voltage drop detector; Frequency detection means for detecting the rotational speed of the electric motor from the output voltage phase signal detected by the phase detector, and calculating the power factor angle of the electric motor from the rotational speed detected by the frequency detection means and the terminal voltage of the electric motor. a power factor angle calculation means that outputs a current phase reference obtained from the speed reference as a phase control signal of the inverse converter when the input voltage of the forward converter is normal; When a drop in the input voltage of the converter is detected, the power factor angle calculated by the power factor angle calculating means is corrected by the output voltage phase detected by the phase detector and output as a phase control signal of the inverter. When a voltage drop is detected by the switching means and the voltage drop detector, a phase difference determined by a signal obtained by correcting the power factor angle by the output voltage phase and the rotational speed detected by the frequency detection means is detected. and a frequency control circuit comprising a switching command means that gives a switching command to the switching means to return to the original state when the phase difference reaches a predetermined value after the AC power supply is restored.

(Function) Therefore, in a motor control device with such a configuration, when a drop in the input voltage of the forward converter is detected and the operation of the forward converter and the reverse converter is stopped, the The power factor angle obtained from the terminal voltage and rotational speed of the motor is corrected by the voltage phase detected by the phase detector and output as a phase control signal of the inverter, thereby inversely converting the terminal voltage phase of the motor. The phase of the inverter is controlled so that the pulse phase of the inverter is synchronized with the pulse phase of the inverter, and when operation is resumed due to power restoration, the phase of the inverter is controlled so that the ratio of the terminal voltage of the motor and the output frequency of the inverter is constant. It is possible to restart immediately after power is restored, regardless of the situation.

(Example) 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 control device for an electric motor according to the present invention. The same parts as in FIG. 3 are given the same symbols, and the explanation thereof will be omitted, and only the different points will be described here. In this embodiment, as shown in FIG. 1, a phase detector 17 is provided to which the terminal voltage of the induction motor 5 detected by the transformer 12 is input, and the voltage phase detected by this phase detector 17 is The signal 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 fatigue number detection circuit 90. In FIG. 2, the operation command signal is input together with the output of the power failure detector 15 to an AND circuit 91a. This AND circuit 91a receives an operation command signal and outputs an operation command to the phase controller 8 and pulse converter 10 when a power failure is not detected by the power failure detector 15. The speed reference is input to a phase converter 94 via a selector switch 92a and an integrating circuit 93 consisting of a resistor R1 and a capacitor C1 that suppress sudden changes in the speed reference, and this phase converter 94 converts the speed reference into a current phase. Outputs the reference signal. Further, 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 inputs the output signal to the changeover switch 92a. At the same time, the power factor angle detector 96a
Enter. This power factor angle detector 96a determines the power factor angle of the load from the rotational speed of the induction motor determined by the differentiator 95 and the motor terminal voltage, and its output signal is given to a proportional integrator 96b.

The output signal of the proportional integrator 96b is corrected by adding it to the voltage phase signal detected by the phase detector 17, and either the output of the output signal or the current phase reference signal output from the phase converter 94 is selected by the switch 92b. is selected and outputted to the pulse converter 1o as an output current phase. In addition, the deviation between the output signal of the proportional integrator 96b, the voltage phase signal detected by the phase detector 17, and the current phase reference signal output from the phase converter 94 is inputted into the absolute value circuit 97a. The output signal is converted into a value and applied to the phase difference detector 97b. This phase difference detection circuit 97b is an absolute value circuit 97.
When it is detected that the output signal of m has a predetermined phase, the detection signal is inputted to one input terminal of the AND circuit 91c. On the other hand, the aforementioned power failure detection signal is input to the set terminal of the switching circuit 91d and also input to the on-delay circuit 9lb, and its output signal is input to the other input terminal of the AND circuit 91c. When the AND condition is satisfied, the AND circuit 91c inputs a reset signal to the switching circuit 91d. This switching circuit 91d is set by a detection signal when a power outage is detected by the power outage detector 15, and a switching command is given to the changeover switch 92a so that the rotational speed signal of the induction motor obtained by the differentiator 95 is output. Switch to
Further, the changeover switch 92b is switched so that a sum signal of the output voltage phase detected by the phase detector 17 and the output of the proportional integrator 96b is output. In addition, power outage detector 1
When a predetermined period of time has elapsed after a power outage was detected by 5, the on-delay 9lb operates, and when the phase difference detector 96b detects 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. is,
The changeover switches 93a and 93b are switched to restore the state before the power outage.

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

Now, when the power failure detector 15 detects a drop in the input voltage, the inverted signal of the power failure detection signal is input to the AND circuit 91a in the frequency control circuit 90, so the AND condition is not established, and the phase controller 8 and The operation of the pulse converter 10 is stopped. At the same time, the switching circuit 91d is set by the power outage detection signal, and the changeover switches 92g and 92b are switched to the signal path corresponding to the power outage side. Thereby, the output phase signal which is the output of the frequency control circuit 90 is changed from the current phase reference signal to the output signal of the phase detector 17 and the proportional integrator 96b.
The pulse converter 1 is switched to a sum signal with the output signal of
An input signal of 0 follows the voltage phase of the induction motor 5. Further, the input signal of the phase converter 94 is also switched to the motor rotation speed signal which is output by differentiating the voltage phase detected by the phase detector 17 by the differentiator 95, and the charging voltage of the capacitor C1 is also changed to the motor rotation speed signal which is output by differentiating the voltage phase detected by the phase detector 17. Follows the rotation speed of 5.

This allows the current phase reference to reliably follow the rotational 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 supply, the AND condition of the AND circuit 91a is satisfied, so the phase controller 8 and the pulse converter 10 immediately start operating based on the output signal. do. At this time, the ratio of the rotational speed and terminal voltage of the induction motor 5 does not match the ratio of the rated rotational speed and rated terminal voltage of the induction motor 5, so the power factor angle detector 96a detects the rotational speed and terminal voltage of the induction motor 5. A signal is output so that the ratio of the two becomes a predetermined value. The signal output from the power factor angle detector 96a is processed by a proportional integrator 96b to calculate a phase correction signal, and by adding this signal to the output voltage phase signal detected by the phase detector 17, the final inverse The output phase of converter 4 is determined.

As a result, the output phase of the inverse converter 4 is corrected, so
The input current phase of the induction motor 5 changes, and the terminal voltage also changes. This operation makes the ratio of the rotational speeds of the induction motor 5 constant. After that, 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,
In other words, when the phase difference detector 97b detects that the phase difference between both signals is within a predetermined value, the output signal
The AND condition of the ND circuit 91c is satisfied, and the switching circuit 91d
is reset. Therefore, due to the inverting operation of the switching circuit 91d, the switching circuit 92a. 92b returns to the contact state before the power outage, the input signal of the phase converter 94 becomes the speed reference for the speed setter 11, and the frequency control circuit 9
The output current phase signal of 0 is switched to the output signal of the phase converter 94, and the normal control state is restored.

From the above-mentioned effects, the following effects can be obtained in this embodiment.

(1) During a power outage, the phase signal that is the input signal of the pulse converter 10 follows the voltage phase of the induction motor 5, so it can be restarted immediately after power is restored, minimizing the time when the control device stops operating due to a power outage. Can be done.

(2) Since 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 possible time.

(3) During a power outage period, the control device is automatically corrected based on the terminal voltage phase and rotational speed determined by the motor and load characteristics, so no special adjustment based on load characteristics or the like is required.

(4) Since both the rotational speed and the phase match the induction motor 5 at the time of restarting the operation, no abnormal current or voltage is generated, and stable and safe switching is possible.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various changes within the scope of the gist thereof.

[Effects of the Invention] As described above, according to the present invention, it is possible to restart the motor ignoring the residual voltage and load characteristics, which is very effective even for loads such as bombs that have a fast deceleration time. A motor control device that can implement instantaneous power outage measures, greatly improve the reliability of system operation, and eliminate stress on the machine when restarting by synchronizing phase and rotational speed control. can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the system configuration of an embodiment of the electric motor control device according to the present invention, FIG. 2 is a block diagram showing the internal configuration of the frequency control circuit in the same embodiment, and FIG. FIG. 4 is a circuit diagram showing an example of the configuration of the control device. FIG. 4 is a block diagram showing the internal configuration of the frequency control circuit of the control device. 1... AC power supply, 2... Forward converter, 3... DC reactor, 4... Inverse converter, 5... Induction motor, 6
... Voltage controller, 7... Current controller, 8... Phase controller, 11... Speed setting device, 12.14... Transformer, 13... Current transformer, 15.・・Power outage detector, 17・
...Phase detector, 90...Frequency control circuit, 91a,
91c...AND circuit, 9lb...on delay circuit, 91d...switching circuit, 92a, 92b...switching 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)

[Claims] A power conversion circuit that converts AC power into DC power using a forward converter, smoothes this DC power using a DC smoothing circuit, converts it into AC power of an arbitrary frequency using an inverse converter, and supplies the converted AC power to the motor. Forward converter control that obtains a voltage signal from a deviation between a speed reference and a terminal voltage of the motor, and obtains a current signal from a deviation between this voltage signal and an input current of the forward converter to control the phase of the forward converter. and an inverse converter control system that obtains an output current phase signal from the speed reference and controls the phase of the inverse converter using this output current phase signal. a voltage drop detector that detects a drop in input voltage; a phase detector that detects the output voltage phase of the inverse converter; and when a voltage drop is detected by the voltage drop detector, the forward converter and the inverse converter operation command means for stopping the operation of the forward converter and the reverse converter by blocking an operation command given to the control system;
Frequency detection means for detecting the rotational speed of the electric motor from the output voltage phase signal detected by the phase detector, and calculating the power factor angle of the electric motor from the rotational speed detected by the frequency detection means and the terminal voltage of the electric motor. a power factor angle calculating means for outputting a current phase signal obtained from the speed reference as a phase control signal of the inverse converter when the input voltage of the forward converter is normal; When a drop in the input voltage is detected, the power factor angle calculated by the power factor angle calculation means is corrected by the output voltage phase detected by the phase detector and output as a phase control signal of the inverse converter. When a voltage drop is detected by the switching means and the voltage drop detector, a phase difference determined by a signal obtained by correcting the power factor angle by the output voltage phase and the rotational speed detected by the frequency detection means is detected. and a frequency control circuit comprising a switching command means for giving a switching command to the switching means to return to the original state when the phase difference reaches a predetermined value after the AC power supply is restored. A control device for an electric motor.