JPH0763233B2 - Synchronous motor control method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a synchronous motor control method capable of improving operating characteristics in a low speed region of a thyristor motor drive system that performs load commutation.

[Technical Background of the Invention and Problems Thereof] Thyristor motor drive systems are used in various fields as motor drive systems for variable speed operation of synchronous motors. In particular, load commutation of the inverter of the thyristor motor is performed using the back electromotive force of the synchronous motor, so the main circuit configuration is simple, the high voltage of the main circuit is easy, and highly efficient operation is possible. Ideal for variable speed driving. An example of the configuration of this thyristor motor drive system is shown in FIG.

In this figure, 11 is an input AC power supply, 12 is a rectifier, 13 is a DC reactor, 14 is an inverter, 15 is a synchronous motor, 16 is a speed reference, 17 is a position detector that detects the position of the magnetic field of the synchronous motor 15, Reference numeral 18 is a speed controller, 19 is a current controller, 20 is a current detector, 21 is a phase controller, 22 is a β controller, and 23 is a current interrupt commander. The thyristor motor drive system shown in FIG. 3 is a known drive system, the outline of which will be described below. The AC power of the input AC power supply 11 is converted into DC power by the rectifier 12, the DC power is smoothed by the DC reactor 13, and the DC power is inversely converted into AC power of variable frequency by the inverter 14. This inversely converted AC power is applied to the synchronous motor 15
To drive the synchronous motor 15 at a variable speed. Synchronous motor
The operating speed of 15 is set by the speed reference 16, and the operation speed signal of the synchronous motor 15 detected by the signal of this speed reference 16 and the position detector 17 is compared and controlled by the speed controller 18, and the current reference is made by the speed controller 18. Is output. The current controller 19 compares and controls the current reference signal and the detection signal of the current detector 20, and the DC power output from the rectifier 12 is adjusted via the phase controller 21. If this DC power is increased, the generated torque of the synchronous motor 15 increases and the speed is increased, and if the DC power is decreased, the synchronous motor 15 is similarly decelerated. The synchronous motor 15 detects the position of the magnetic field by the position detector 17, inputs this position signal to the β controller 22, and the β controller 22 controls the load commutation timing of the inverter 14 by this position signal, Reference numeral 14 performs load commutation using the counter electromotive voltage of the synchronous motor 15.

Although the speed control of the synchronous motor 15 is performed as described above, since the counter electromotive voltage is low in the low speed region of the synchronous motor 15,
The inverter 14 cannot perform the load commutation described above in the low speed operation region. Therefore, in such a low speed operation region, the inverter corresponding to the position detection signal of the position detector 17
The current controller 19 is controlled by the current interrupting command device 23 for each commutation timing of 14, thereby controlling the DC current output by the rectifier 12 to zero, and the current of the inverter 14 is also zero at each commutation timing. The synchronous motor 15 is accelerated while sequentially repeating such operations. This kind of commutation method is called intermittent start in the thyristor motor drive system,
Intermittent start is commonly used at speeds below about 10% of rated speed.

The waveform of the DC current flowing through the DC reactor 13 at the time of intermittent start is shown in FIG. 4 (a), and the torque generated by the synchronous motor 15 at this time is shown in FIG. 4 (b). When the operating speed is low, such as immediately after the synchronous motor 15 is started, the period in which the DC current is reduced to zero can be relatively ignored. For example, in FIG. 4A, the direct current Id1 is supplied from time t11 to time t12, and the direct current is made zero from time t12 to time t21. Further, the direct current Id1 is supplied from time t21 to time t22. Similarly, the synchronous motor 15 is accelerated while continuing the current in sequence, the direct current is passed from time t51 to time t52, and the direct current is made zero from time t52 to time t61. Furthermore, the inverter 14 switches to load commutation at time t81 at which the synchronous motor 15 accelerates to reach a predetermined operating speed, so that the DC current becomes continuous. The time from time t12 to time t21 and time t52 to time t61 at which the DC current at the intermittent start is zero is constant because it is determined by the condition of the inverter 14. Therefore, from time t11 to time t21, time t5
Comparing the average currents from 1 to time t61, the average value of the DC current is significantly smaller in the latter period.

Therefore, since the torque generated by the synchronous motor 15 corresponds to the average value of the direct current described above, as shown in FIG.
As the driving speed of 15 increases, it decreases. Rectifier 12 at this time
Since the DC reactor 13 tries to suppress the rise of the output current of the above, this tendency becomes more and more intense as the operating speed of the synchronous motor 15 increases. Therefore, the generated torque is drastically reduced in the vicinity of time t81 as compared with in the vicinity of time t11.

The conventional thyristor motor drive system that operates as described above has the following technical problems.

As a result of the torque generated by the synchronous motor 15 decreasing as shown in FIG. 4B, the operating speed of the synchronous motor 15 increases and the acceleration of the synchronous motor 15 and its load becomes difficult. As a result, if a thyristor motor drive system is used to drive an extruder or the like in the chemical industry that has a relatively large load reaction torque even in the low-speed operation range, the inverter 14
However, there was a problem that smooth operation and acceleration could not be performed in the vicinity of switching from intermittent start to load commutation.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a method for controlling a synchronous motor that can prevent a decrease in torque generated by the synchronous motor during intermittent start. I am trying.

[Summary of the Invention] The reason why the torque generated by the synchronous motor decreases during intermittent start is that the average value of the DC current decreases with the lapse of time after intermittent start. In the present invention, when the inverter intermittently starts in the low speed region of the synchronous motor in which load commutation cannot be performed, the input current of the rectifier is detected to obtain the average value of the output current of the rectifier in each intermittent period, and the current average of each intermittent period. Synchronous by increasing the peak value of the output current of the rectifier sequentially by increasing the limit value of the current reference signal during intermittent start so that the value becomes a constant value with a predetermined relationship as the operating speed of the synchronous motor increases. It is characterized in that the torque generated by the electric motor is averaged.

Embodiment of the Invention An embodiment of the present invention is shown in FIG. In this figure, the circuit components given the same numbers as in FIG. 3 are circuit components having the same function, and therefore their explanation is omitted here.

In FIG. 1, when the inverter 14 intermittently starts the synchronous motor 15, the current limiter 24 detects the input current of the rectifier 12 via the current detector 20 and the average value of the DC current output by the rectifier 12. Is calculated. The average value of the DC current is constantly calculated during the intermittent start, and the timing at time t81 when the inverter 14 switches from the intermittent start to the load commutation is input from the current interrupt commander 23. The current limiter 24 can limit the magnitude of the current reference signal output by the speed controller 18. Synchronous motor
If 15 increases operating speed during intermittent start, current limiter 24
The average value of the direct current output by the rectifier 12 is calculated moment by moment, and the magnitude of the current reference signal is regulated by the current limiter 24 so that the average value becomes a certain magnitude or a predetermined magnitude or more. Increase the size.

The above-described embodiment of the present invention will be described with reference to FIG. 2 for comparison with FIG. FIG. 2A shows a DC current waveform, and FIG. 2B shows the torque generated by the synchronous motor 15. The operating speed of the synchronous motor 15 is higher on the time t81 side than the time t11. Therefore, the period from time t12 and time t21 when the DC current becomes zero, and from time t52 to time t61
Are equal to each other, the period in which the DC current flows is relatively longer from time t11 to time t12 than from time t51 to time t52. Therefore, the peak value of DC current Id1
Conventionally, Id5 is equal, but in the present invention, the current limiter 2
By the action of 4, the peak value Id1> Id5 of the direct current is controlled by the action of the current limiter 24. In this way, the synchronous motor is increased by increasing the operating speed of the synchronous motor 15 and sequentially increasing the limit value of the current reference signal during intermittent start.
It is possible to reduce the decrease in the generated torque of 15.

As described in the embodiments of the present invention, the reduction of the torque generated by the synchronous motor 15 can be reduced, so that smooth operation and acceleration can be performed even if the load torque of the synchronous motor 15 is large during intermittent start.

In the present invention, the circuit configuration shown in FIG. 1 is shown as an example, but the configuration is not limited, and the present invention can be applied to a thyristor motor drive system having a 12-pulse configuration without changing the gist of the present invention.

The present invention does not limit how to control the magnitude of the DC current after the inverter 14 switches to load commutation after time t81, but limits the current reference signal within the rated overload current of the rectifier 12. Anything can be done.

Besides, various modifications can be configured without changing the gist of the present invention.

EFFECTS OF THE INVENTION According to the present invention, it is possible to reduce the decrease in the torque generated by the synchronous motor by the action of the current limiter during the period from the intermittent start to the switching to the load commutation in the thyristor motor drive system. . Therefore, even if the load torque of the synchronous motor is relatively large, smooth operation and acceleration during intermittent start can be realized, and sudden changes in the torque generated by the synchronous motor immediately after switching to load commutation from intermittent start can be reduced. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of DC current and generated torque in the low speed operation region of FIG. 1, FIG. 3 is a block diagram of a conventional device, and FIG. It is the figure which showed the waveform of the direct current and generated torque by the conventional apparatus corresponding to FIG. 11 ... Input AC power supply, 12 ... Rectifier, 13 ... DC reactor,
14 ... Inverter, 15 ... Synchronous motor, 16 ... Speed reference, 17 ...
Position detector, 18 ... Speed controller, 19 ... Current controller, 20 ... Current detector, 21 ... Phase controller, 22 ... β controller, 23 ... Current interruption commander, 24 ... Current limiter.

Claims (1)

[Claims] 1. A method of controlling a synchronous motor in which alternating current power is converted into direct current power by a rectifier, and this is again converted by a load commutation type inverter to drive a synchronous motor. When the motor is intermittently started in the low speed region, the input current of the rectifier is detected to obtain the average value of the output current of the rectifier in each intermittent period, and the average value of the current in each intermittent period is set to a constant magnitude. The limiting value of the current reference signal during intermittent start is increased in a predetermined relationship as the operating speed of the synchronous motor is increased to sequentially increase the peak value of the output current of the rectifier, thereby averaging the torque generated by the synchronous motor. A method for controlling a synchronous motor, comprising: