JPH1189259A - Operating system of synchronous motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an operating system which can directly actuate a synchronous motor, by making any dynamic brake circuit unnecessary. SOLUTION: A controller 16 discriminates the actuation of a first synchronous motor 2 by means of circuits 13-15 from the output current of an inverter 1 and, after discriminating the actuation, detects that the DC voltage of the inverter 1 rises to a voltage which is close to an overvoltage level due to regenerated energy by means of circuits 11 and 12. Upon detecting the DC voltage approaching the overvoltage level, the controller 16 adjusts the phase of the inverter 1 so that the first synchronous motor 2 may be set to a driving mode and, after the motor 2 is pulled in by the phase adjustment, returns the inverter 1 to a normal operating state. The regenerated energy form a second motor 3 and after the second motor is absorbed by the first motor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronous motor operation system in which a plurality of synchronous motors are operated in parallel by one inverter, and each synchronous motor is inserted directly into the inverter and started.

[0002]

2. Description of the Related Art As shown in FIG. 4, this type of equipment operates an inverter 1 and a magnet contactor (MC) provided between each of the synchronous motors 2, 3 and the inverter 1.
The synchronous motors are sequentially started by sequentially turning on the switches 4 and 5 which become the motors and breakers (MCCB), and the synchronous motors are synchronously operated at the operating frequency of the inverter by pulling in the synchronous motors.

[0003] Thus, it is possible to start a plurality of synchronous motors directly and to operate them in parallel by using a single inverter having a constant output frequency.

When the speed of the synchronous motor increases and approaches the synchronous speed at the start of the direct drive of the synchronous motor, as shown in FIG. 5, the synchronous motor repeats pull-in and step-out of the synchronous motor, and vibration appears in the speed. Due to this vibration, the synchronous motor repeatedly drives and regenerates according to the speed, and then converges to the inverter frequency by pulling in the synchronization.

[0005] In the above-described straight-on start, the inverter has very good power conversion efficiency and low internal loss. For this reason, the regenerative energy from the synchronous motor is supplied to the path A in FIG.
As shown by, the main capacitor 6 of the inverter is charged. For this reason, the voltage of the main capacitor increases during regeneration,
When the regenerative amount is large, the voltage rise also becomes large, and the overvoltage protection circuit of the inverter may operate to stop the inverter.

In order to prevent this overvoltage stop, a dynamic brake (DBR) circuit 7 is provided in the DC circuit of the inverter.
Is provided. When the DC voltage rises, the DBR circuit 7 connects the discharge resistor to the DC circuit by turning on the semiconductor element to discharge the regenerative energy through the resistor.
Suppress DC voltage rise.

[0007]

In the conventional apparatus, 2
When the synchronous motors subsequent to the first motor are started, a vibration state occurs due to repetition of driving and regeneration at the time of the start, similarly to the first motor. In the second and subsequent start-ups, unlike the first start-up, the regenerative energy is consumed by the first synchronous motor as shown by the path B in FIG.

Therefore, the dynamic brake circuit 7
Is used only when the first synchronous motor is started. Although it is used at a low rate, it is necessary on the circuit, which increases the cost and reliability of the device, and further complicates maintenance. There is.

An object of the present invention is to provide an operation system in which a synchronous motor can be started directly without requiring a dynamic brake circuit.

[0010]

SUMMARY OF THE INVENTION According to the present invention, overvoltage is determined by determining the start and voltage rise of the first synchronous motor from the DC voltage and output current of the inverter, and controlling the output phase of the inverter in this determination. This is characterized by the following method.

In a synchronous motor operating system in which a plurality of synchronous motors are sequentially inserted directly into one inverter and operated in parallel, means for judging the activation of the first synchronous motor from the output current of the inverter, Means for adjusting the phase of the inverter so that the first synchronous motor is in the drive mode when it is detected or predicted that the DC voltage of the inverter has risen to near the overvoltage level after the determination; and Means for returning the inverter to a normal operation state after the first synchronous motor has been brought into synchronization.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an apparatus configuration diagram showing an embodiment of the present invention, and portions equivalent to FIG. 4 are denoted by the same reference numerals.

The voltage detector 11 detects the voltage of the main capacitor 6. Comparator 12, the voltages V ₁ which is slightly lower than the overvoltage detection level of the inverter 1 as a comparison reference, the voltage detected by the voltage detector 11 detects that exceeds the voltages V _1.

The current detector 13 detects the output current of the inverter 1. The AC-DC converter 14 includes the current detector 1
The current detected in step 3 is converted to direct current. A / D converter 15
Samples the detection signal from the current detector 13 and converts it into a digital signal.

The control device 16 has a microcomputer configuration and includes software for controlling the start / stop of the inverter 1, controlling the output frequency and voltage to be constant, and generating control signals for generating a PWM waveform and the like. I have.
This configuration is equivalent to the conventional device.

Here, the control device 16 controls the comparator 1
2 and software for performing start control of the synchronous motor from the DC voltage and output current of the inverter obtained from the A / D converter 15.

This control will be described with reference to FIG. After power-on of the time t _1, the no-load output current by operation of the inverter 1 stores retained. Thereafter, were charged the switch 4 at time t _2, the starting current flowing when starting the first unit of the synchronous motor 2 uptake, compares the current and no-load current, no-load current of several tens% (e.g. 30%), it is determined that the first synchronous motor 2 is started (time t ₃ ).

After this start-up determination, when a detection signal indicating that the voltage rise of the capacitor 6 has approached the overvoltage level is obtained from the comparator 12 (time t ₄ ), the gate signal phase of the inverter 1 is adjusted.

This phase adjustment lowers the output frequency by delaying the output phase angle of the inverter by a predetermined parameter. As a result, the first synchronous motor 2 which has been in the regenerative mode is in the drive mode, in which the DC voltage of the capacitor 6 is suppressed from rising and smooth synchronization is achieved. This synchronization pull-in waveform is shown in FIG.
Shown in

When the synchronization is completed (time t ₅ ), the voltage of the capacitor 6 returns to the normal level, and the comparator 12
, The phase processing for returning the output frequency of the inverter to the normal frequency ends, and the processing completion flag is set.

With the above processing, a function equivalent to that of the conventional dynamic brake circuit 7 is obtained. After the subsequent start of the synchronous motor 3 (time t ₆ ), the phase adjustment is not performed from the setting of the processing completion flag. In this case, as in the conventional case, the first synchronous motor consumes energy and suppresses the voltage rise of the capacitor.

In the phase adjustment, since the output frequency of the inverter fluctuates instantaneously, there may be a case where the inverter cannot be used depending on the application. However, this operation can be prohibited by a parameter.

In the embodiment, the case where the rise of the capacitor voltage is detected by the comparator 12 or the like has been described. However, this is omitted, and the voltage rise due to the regenerative energy is predicted from the time integration of the current detected by the current detector 13. The same operation and effect can be obtained by a configuration in which the determination process is performed by software, such as by estimating the voltage rise from the method or the time after the determination of the start of the first synchronous motor.

[0024]

As described above, according to the present invention, the start and voltage rise of the first synchronous motor are determined from the DC voltage and output current of the inverter, and the output phase of the inverter is controlled by this determination. Since the overvoltage is suppressed, the following effects are obtained.

(1) The conventional dynamic brake circuit is not required, the circuit configuration is simplified, and the reliability of the device can be improved.

(2) Maintenance of the dynamic brake circuit becomes unnecessary.

(3) The cost of the inverter can be reduced.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an embodiment of the present invention.

FIG. 2 is a control time chart in the embodiment.

FIG. 3 is a waveform diagram of synchronization pull-in according to the embodiment.

FIG. 4 is a configuration diagram of a conventional parallel operation system.

FIG. 5 is a waveform diagram of a conventional synchronization pull-in.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inverter 2, 3 ... Synchronous motor 4, 5 ... Switch 6 ... Capacitor 7 ... Dynamic brake circuit 12 ... Comparator 15 ... A / D converter 16 ... Control device

Claims (1)

[Claims] 1. A synchronous motor operation system in which a plurality of synchronous motors are sequentially inserted directly into one inverter and operated in parallel, means for judging start-up of a first synchronous motor from an output current of the inverter; Means for adjusting the phase of the inverter so that the first synchronous motor is in the drive mode when it is detected or predicted that the DC voltage of the inverter has risen to near the overvoltage level after the start determination; Means for returning the inverter to a normal operation state after the synchronization of the first synchronous motor has been completed by the adjustment.