JPH04217896A - Controller for ac motor - Google Patents

Abstract

PURPOSE:To quickly restart an AC motor by immediately turning on a main switch when the charged voltage of a smoothing capacitor between a power source side PWM converter and load side PWM becomes higher than a prescribed value by turning on an auxiliary switch which is connected in series with a resistance before turning on the main switch. CONSTITUTION:A series circuit of a charging resistance 5 and auxiliary switch 4 is connected in parallel with a main switch 2 which connects three-phase AC power source 3 to a power source side PWM inverter 1. By charging a smoothing capacitor 7 with the direct current outputted from the inverter 1, a load side PWM inverter 6 is driven. An AC motor 8 is driven by means of the VVVV outputted from the inverter 6. The terminal voltage of the capacitor 7 is inputted to a control circuit 17 after detection and, when the terminal voltage is higher than a prescribed value, the main switch 2 is turned on and the auxiliary switch 4 is turned off. Therefore, the anxiety of passengers can be reduced, since the AC motor 8 can be restarted quickly after the power supply is restored from a momentary break.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] The present invention relates to a control device for an AC motor, and in particular, the present invention relates to a control device for an AC motor, and in particular, it uses a pulse width modulation type inverter (hereinafter referred to as a "power supply side PWM inverter") on the power supply side to convert an AC power supply into direct current. The DC current is transferred to the load side pulse width modulation inverter (hereinafter referred to as ``load side PWM inverter'').
The present invention relates to a control device for an AC motor that converts the AC voltage into AC with variable voltage and variable frequency to drive the AC motor.

0002

2. Description of the Related Art An example of a conventional control device for an AC motor of this type is an elevator control device disclosed in Japanese Patent Application Laid-Open No. 2-17865. This control device estimates in advance the time required to complete charging of the smoothing capacitor as a delay time, and closes the main switch after the delay time has elapsed after closing the auxiliary switch. Therefore, when turning on the main switch or igniting the PWM inverter,
Rapid charging of the smoothing capacitor due to inrush current is suppressed,
This is designed to prevent damage to the smoothing capacitor and the gate turn-off thyristor constituting the power supply side PWM inverter.

0003

[Problem to be Solved by the Invention] Conventional elevator control devices are configured to delay the closing of the main switch by the delay time as described above, so the auxiliary switch is closed by the control circuit. When the smoothing capacitor starts charging, the motor is started only after the delay time has elapsed. Therefore, the elevator car does not start moving up or down immediately, and if an elevator car carrying passengers stops due to a momentary power outage, the elevator car will not start moving up or down immediately after power is restored, making the passengers inside feel uneasy. There was a possibility.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a control device for an AC motor that can start the motor immediately after stopping while preventing damage caused by rush current.

[0005]

[Means for Solving the Problems] The control device for an AC motor according to the present invention converts the AC power supplied by the main switch into DC using a PWM inverter on the power supply side, and converts the DC power into DC using a PWM inverter on the load side. In a device that converts into alternating current and supplies it to an alternating current motor, when the charging voltage of the smoothing capacitor detected by the voltage detection means is less than a predetermined value when the auxiliary switch is closed prior to closing the main switch, Closing control means is provided which delays closing of the main switch and immediately closes the main switch when the charging voltage is equal to or higher than a predetermined value.

[0006]

[Operation] In the present invention, when the charging voltage of the smoothing capacitor is less than a predetermined value, the closing of the main switch is delayed by the delay time to prevent the generation of rush current, and when the charging voltage is higher than the predetermined value, the closing of the main switch is delayed by the delay time. Since there is no risk of inrush current occurring, the main switch is immediately turned on and the AC motor is started.

[0007]

[Examples] Examples of the present invention will be described below. FIG. 1 is a block diagram showing an elevator control device according to an embodiment of the present invention.

In the figure, 1 is a power supply side PWM inverter connected to a three-phase AC power source 3 via a main switch 2, 4 is an auxiliary switch connected in parallel to the main switch 1 together with a charging resistor 5, 6 is a load side PWM inverter connected to the output of the power supply side PWM inverter 1, 7 is a smoothing capacitor provided between the series circuit connecting the power supply side and load side PWM inverters 1 and 6, and 8 is a load side PWM inverter. An AC motor 9 connected to the output of the inverter 6 for raising and lowering the elevator car is a sheave that is rotationally driven by the AC motor 8 and raises and lowers the elevator car 11 and the counterweight 12 via a rope 10.

Further, 13 is a gate circuit that outputs a gate signal to the power supply side PWM inverter 1, 14 is a gate circuit that also outputs a gate signal to the load side PWM inverter 6, and 15 is a gate circuit that detects the voltage of the smoothing capacitor 7. a voltage detection circuit as a voltage detection means detected by the device 16;
Reference numeral 17 denotes a control circuit comprising a microcomputer as input control means. Note that this control circuit 17 inputs the detection signal from the voltage detection circuit 15 via the signal line 18, and outputs a PWM signal to the gate circuits 13 and 14 via the signal lines 19 and 20. line 21,
22, the main switch 2 and the auxiliary switch 4 are controlled to open and close.

FIG. 2 is a block diagram showing the configuration of a control circuit 17 of an elevator control device according to an embodiment of the present invention.

In the figure, 23 is a central processing unit (hereinafter referred to as
24 is a read-only memory (hereinafter referred to as R
25 is a readable and writable memory (hereinafter referred to as "RAM"), 26 is an A/D converter, 27, 2
8 is a D/A converter, 29 and 30 are interfaces, 3
1 is a bus. The ROM 24 stores various programs for operating the elevator control device, and the CPU 23 executes various processes in accordance with these programs. Note that the RAM
25 is designed to temporarily store data for processing performed by the CPU 23.

Next, the operation of the elevator control device of this embodiment constructed as described above will be explained. FIG. 3 is a flowchart showing the processing of the control circuit 17 of the elevator control device according to one embodiment of the present invention.

Now, if the system is started up by turning on the control power, etc., the control circuit 17 performs step S1.
The auxiliary switch 4 is turned on to charge the smoothing capacitor 7 with power from the three-phase AC power supply 3, and the voltage of the smoothing capacitor 7 detected by the voltage detection circuit 15 is inputted in step S2. Since the smoothing capacitor 7 has not been charged in advance, the voltage at this point is approximately "0", and since the voltage of the smoothing capacitor 7 is less than a predetermined value in step S3, the process moves to step S4.

[0014] Then, in step S4, the process waits until a preset delay time has elapsed, and when the delay time has elapsed, the voltage phase is calculated in step S5 to determine the firing timing of the power supply side PWM inverter 1. Next, in step S6, the main switch 2 is turned on, and the power source side PWM inverter 1 is ignited according to the ignition timing determined in step S7. As a result, the AC motor 8 is activated and the elevator car 11 starts moving up and down. Since the main switch 2 is turned on after the smoothing capacitor 7 is charged in this manner, rapid charging of the smoothing capacitor 7 due to rush current is suppressed.

On the other hand, in the case where the elevator car 11 is stopped due to a momentary power outage, charging of the smoothing capacitor 7 has already been completed before the stop, so that the voltage of the smoothing capacitor 7 is higher than the predetermined value in step S3. Therefore, there is no possibility that an inrush current will occur, and the process directly proceeds to step S5. Therefore, the processing from step S5 to step S7 is performed without waiting for the delay time, and the main switch 2 is immediately turned on, the AC motor 8 is started, and the elevator car 11 is turned on.
lifting and lowering will resume.

As described above, the elevator control device of the above embodiment has a power supply side PW that converts the three-phase AC power supply 3 into DC.
M inverter 1, a load side PWM inverter 6 that converts the DC converted by the power source side PWM inverter 1 into variable voltage variable frequency AC and supplies it to the AC motor 8;
A smoothing capacitor 7 provided in a DC circuit connecting the power source side and load side PWM inverters 1 and 6 to each other, and a smoothing capacitor 7 provided between the three phase AC power source 3 and the power source side PWM inverter 1, and a three phase AC power source 3 A main switch 2 that turns on and off the voltage, an auxiliary switch 4 that is turned on before the main switch 2 is turned on and that charges the smoothing capacitor 7 with a charging resistor 5, and a main switch 4 that controls the voltage of the smoothing capacitor 7. When the charging voltage of the smoothing capacitor 7 detected by the voltage detection circuit 15 is less than a predetermined value when the voltage detection circuit 15 and the auxiliary switch 4 are turned on, a predetermined delay time elapses. A control circuit 17 is provided which later closes the main switch 2 and immediately closes the main switch 2 when the charging voltage of the smoothing capacitor 7 is equal to or higher than a predetermined value.

Therefore, in the above embodiment, when the charging voltage of the smoothing capacitor 7 is less than a predetermined value, such as when the system is started up, the closing of the main switch 2 is delayed by the delay time to prevent damage due to inrush current. This can be prevented. Furthermore, when the charging voltage of the smoothing capacitor 7 is higher than a predetermined value, such as when the elevator car 11 is stopped due to a momentary power outage, the main switch 2 is immediately turned on and the AC motor 8 is started. the result,
Even if the elevator car 11 stops due to a momentary power outage, the elevator car 11 immediately resumes its ascent and descent, and it is possible to prevent the passengers inside from feeling uneasy.

By the way, although the above embodiment is embodied as a control device for an elevator, it may be embodied in a control device for any type of equipment as long as it controls the drive of an AC motor 8 by an inverter using an AC power source 3. It's okay.

[0019]

As described above, the AC motor control device of the present invention includes a power supply side PWM inverter that converts AC power to DC when the main switch is turned on, and a power supply side PWM inverter that converts the DC to AC and converts the AC power to AC motor. a load-side PWM inverter to supply; an auxiliary switch that is turned on prior to turning on the main switch and charges a smoothing capacitor connected between both the inverters; and a voltage detection means when the auxiliary switch is turned on. When the charging voltage of the smoothing capacitor detected at is less than a predetermined value, the closing of the main front switch is delayed by a delay time, and when the charging voltage of the smoothing capacitor is equal to or higher than the predetermined value, the main switch is immediately closed. Since it is equipped with a closing control means, when the charging voltage of the smoothing capacitor is less than a predetermined value, closing of the main switch is delayed to prevent damage caused by the generation of inrush current. In the event of a momentary power outage during operation, the main switch is immediately turned on and the AC motor can be started because the charging voltage of the smoothing capacitor is above the specified value and there is no risk of inrush current. .

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an elevator control device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a control circuit of an elevator control device according to an embodiment of the present invention.

FIG. 3 is a flowchart showing the processing of the control circuit of the elevator control device according to the embodiment of the present invention.

[Explanation of symbols]

1 Power supply side PWM inverter 2
Main switch 3 Three-phase AC power supply 4 Auxiliary switch 5 Charging resistor 6 Load side PWM inverter 7
Smoothing capacitor 8 AC motor

Claims (1)

[Claims] 1. A power source side PWM inverter that converts an alternating current power source into direct current; a load side PWM inverter that converts the direct current converted by the power source side PWM inverter into variable voltage variable frequency alternating current and supplies it to an alternating current motor. , a smoothing capacitor provided in a DC circuit connecting the power supply side and load side PWM inverters to each other, and the AC power supply and the power supply side PWM inverter.
a main switch that is provided between the WM inverter and turns on/off the AC power; an auxiliary switch that is turned on prior to turning on the main switch and charges the smoothing capacitor via a charging resistor; a voltage detection means for detecting the voltage of the smoothing capacitor, and when the auxiliary switch is turned on,
When the charging voltage of the smoothing capacitor detected by the voltage detection means is less than a predetermined value, the main front switch is closed after a predetermined delay time has elapsed, and the charging voltage of the smoothing capacitor is higher than the predetermined value. 1. A control device for an AC motor, sometimes comprising a closing control means for immediately closing a main switch.