JPS6018199B2 - Induction motor control device using cycloconverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for an induction motor that uses two sets of cycloconverters to supply current with few harmonic components to the induction motor, thereby reducing torque ripple. .

When driving an induction motor with a cycloconverter,
Since the induction motor has a lagging power factor, commutation on the load side of the cycloconverter is always performed after commutation on the power source side.

Therefore, when the output frequency of the cycloconverter is not synchronized with an integer fraction of the power supply frequency, the load-side commutation timing changes moment by moment, resulting in a phenomenon in which the output current phase and amplitude pulsate like a beat. Therefore, the method of driving the induction motor from the outside of the cycloconverter is to limit the operating frequency to an integer fraction of the power supply frequency. For example, if the power supply frequency is fa, the operating frequency is 2/2, fa/
A system is adopted in which the system operates at discrete frequencies, such as 3 and 4. FIG. 1 shows a block diagram of a typical cycloconverter induction motor control system.

In the same figure, 1 is an 18-arm thyristor RUP-TW
2 is an induction motor driven by the cycloconverter 1, 3 is a voltage detector that detects the terminal voltage of the induction motor 2, and 4 is a voltage reference signal A and a voltage. a voltage control amplifier that amplifies the deviation of the output signal of the detector 3; 5 a CT that detects the current supplied to the cycloconverter 1; 6 a current detector that converts the current detected by the CT 5 into a control signal;
7 is a current control amplifier that amplifies the deviation between the output signal of the voltage amplifier 4 and the output signal of the current detector 6; 8 is a phase controller that controls the phase of the thyristor according to the output signal of the current control amplifier 7; A step-down counter that converts the power supply frequency signal C to an integer fraction of the power supply frequency in accordance with the operating frequency command signal B; 10 is a step-down counter that uses the output signal of the phase controller 8 as a power supply side commutation command, and the output signal of the step-down counter 9; is input as a load-side commutation command, and is a gate logic circuit that outputs a firing pulse to be given to the thyristor of the cycloconverter 1. The system shown in Fig. 1 is called the V/F control method, which controls the ratio of the terminal voltage and primary frequency of the induction motor to a constant value. This is an open-loop speed control system that operates with a constant frequency ratio. FIG. 2 shows a time chart of the output current model of the cycloconverter according to this control system. A indicates the haze source commutation timing, and the commutation timing also changes as the ignition phase changes. B,C
shows the load side commutation timing and the output current model U phase when the output frequency is 1/2, and now, at time t. , even if the load side commutation command UP is received, the actual commutation is delayed until the power source side commutation timing RP, and at this point the thyristor RUP is fired, and a positive current flows to the U phase of the motor. . At the following times, thyristor SUP is fired, and at time t4, thyristor TVP is fired, and at the same time a positive current flows to the V phase, thyristor SUP is extinguished, and U
The phase positive current becomes 0. At time t5, load side commutation command U
During the N period, the power supply side commutation command SN is given and the thyristor SUN is fired, and at the time, the thyristor TUN is fired. Next, at time t7, the sirens evening RUN is turned on,
At the same time as the negative current flows into the V phase, the thyristor TUN is extinguished and the U phase current becomes zero. At the following time, a load-side commutation command for the U-phase positive current comes, but the thyristor TW has already been activated.
Since P is firing and the motor has a lagging power factor,
Load commutation from thyristor TWP to thyristor TUP (
Commutation due to the induced electromotive force of the motor is not performed, and the U-phase positive current waits until the dragon current commutation timing with a time ratio of 9, and then flows by firing the thyristor RUP. Therefore, as a result of the above explanation, the U-phase current model has an asymmetrical current waveform in which the zero current period is not uniform, as shown in FIG. 2C.

This is because, if 600 of the power supply phases are taken as one division, there are no current 0 periods other than odd-numbered periods. That is, only when the operating frequency has a load-side commutation command such as 1, 3, 5, 7, . . . for zero current periods, the output current waveform becomes a symmetrical waveform with equal zero current periods. In the case of /2, the current 0 period of the load side commutation command is 2, so the actual current 0 period is a repetition of 1 and 3, which is shown by the waveform in FIG. 2C. Figure 2 shows D and E' when the output frequency is /3, D shows the load side commutation timing, and E shows the output current model (U phase). In the case of /3, the current 0 period is 3, so the output current waveform becomes a symmetrical waveform. Fig. 2 F and G show when the output frequency is 0/4, F shows the load side commutation timing, and G shows the output current model (U phase). Ne/4
In this case, since the current 0 period is 4, the actual current 0 period is 3 and 5 repeatedly, and the output current waveform becomes an asymmetrical waveform. From the above, when the output frequency is an odd fraction of the power supply frequency, the output current has a symmetrical waveform, and it is an even fraction of the power supply frequency.
In this case, the output current waveform becomes an asymmetrical waveform. If an induction motor is driven by such an asymmetrical current waveform, there will be many harmonic components, which will lower the power factor of the power source and cause torque ripple. This invention was made to eliminate the above-mentioned drawbacks, and aims to reduce torque ripple by connecting two sets of cycloconverters to supply a current with few harmonic components to the electric motor.

Hereinafter, the control device of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a block diagram for explaining the present invention. In this figure, the same reference numerals as those in FIG. 1 are the same, so a description thereof will be omitted.

IA and IB are cycloconverters indicated by the reference numeral 1 in FIG. ), when the operating frequency command signal B is other than 1/5 or 7, the input signal phase is inverted by 1800, and when the operating frequency command signal B is 1/5 or 7, the input signal phase is reversed by 1800. 180
12 is a gate logic circuit 10 which inverts 0 and further shifts the phase by 180 degrees with the power supply phase;
Similarly, it is a gate logic circuit which inputs the output signal of the phase controller 8 and the output signal of the phase inversion shift circuit 11 and outputs a firing pulse to be given to the thyristor of the cycloconverter IB. The phase inversion shift circuit 11 can realize the above function with a delay circuit, a logic circuit, etc., and its circuit configuration can be easily inferred, so a description thereof will be omitted here. 4 to 7 are time charts for explaining this invention.

Among them, in Figures 4 to 6, the operating frequency is fa/5.
, in cases other than fa/7, Figures 4 and 5 show time charts where the operating frequency is an even fraction of the power supply frequency, taking examples of fa/2 and fa/4, and Figure 6. isfa/
This is the case of 3. A in FIGS. 4 to 6 corresponds to the output signal of the phase controller 8 in FIG. 3, B is the output signal of the step-down counter 9, C is the output signal of the phase inversion shift circuit 11, and B and C The symbols are 1800 out of phase. Therefore, the phases of the U-phase output currents combined from the cycloconverters IA and IB are reversed by 1800 degrees as shown in D and E in FIGS. 4 to 6. Furthermore, the polarity of the output current of the cycloconverter IB is reversed by the transformer IT, so the current supplied from the cycloconverter IB to the transfer motor is actually as shown in Figs.
It will look like F in the diagram. Therefore, the induction motor will be supplied with the sum of the power sources ○ and F, and as shown in G in Figures 4 to 6, this is of course not the case when the operating frequency is 1/3. However, even if the frequency is an even number, such as NN/2 or FA/4, 2 including the transformer
By combining a set of cycloconverters, it is possible to obtain a system in which the current waveform of the induction motor is symmetrical, the torque IJ pull is small, and the harmonic component is small and the power source power factor is good. In addition, Fig. 7 shows that the operating frequency is fa/5 and ha/7.
In the time chart for the case, B to G show the case of fa/5, and H to N show the case of fa/7.

Here again, A is the output signal of the phase controller 8 as in FIGS. 4 to 6, B and D are the output signals of the step-down counter 9, and C and J are the output signals of the phase inversion shift circuit 11. The operating frequency of the phase inversion shift circuit 11 is /5,
In the case of fa/7, it functions to invert the input signal by 1800 degrees and further shift the phase by 1800 degrees (3 sections) in the power supply phase, so the output signals are as shown in C and J described above. Therefore, the output current models (U phase) of the cycloconverters IA and IB have waveforms of ○, K and E, L due to the load side commutation command signals of B, day and C, J. However, the polarity of the output current of the cycloconverter IB is reversed by the transformer IT, so the current supplied from the cycloconverter IB to the transfer motor is actually as shown in Figure 7 F and M. become. Therefore, the induction motor is supplied with the sum of the currents D and F in the case of fa/5, and K and M in the case of fa/7, and the symmetrical currents such as G and N are supplied respectively. The waveform has fewer harmonic components. As explained above, in the present invention, a load-side commutation command signal suitable for each operating frequency is given to a transformer equipped with two sets of cycloconverters and a transformer for input/output polarity reversal, and the cycloconverter is By operating the converter, the torque ripple of the induction motor can be reduced, and the excellent effect of controlling the induction motor using a cycloconverter with less harmonics and a good power source power factor can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the conventional system, Fig. 2 is a time chart for explaining the conventional system, Fig. 3 is a block diagram of the control device of the present invention, and Figs. 4 to 7 are the control device of the present invention. It is a time chart for explaining. 1, IA, IB...cycloconverter, IT...
...Transformer (for polarity reversal), 2...Induction motor, 3...Voltage detector, 4...Voltage control amplifier,
5...C. T, 6...Current detector, 7...
・...Current control amplifier, 8... Phase controller, 9.
...Step down counter, 10, 12...
...Gate logic circuit, 1 1... Phase shift circuit. Figure 2 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 6 Figure

Claims (1)

[Claims] 1 Two sets of cycloconverters, a transformer installed on the output side of one of these cycloconverters to reverse the input/output polarity, and a transformer that is supplied with power from the two sets of cycloconverters including this transformer, In an induction motor control device that drives an induction motor with an output having a frequency of 1, when the induction motor is driven at a frequency other than 1/5 or 1/7 of the frequency, the input signals of the two sets of cycloconverters Reverse the phase by 180°,
Further, when driving at a frequency of 1/5 or 1/7 of the power supply frequency, a phase inversion shift circuit is provided which inverts the input signal phase by 180 degrees and shifts the power supply phase by 180 degrees. An induction motor control device using a cycloconverter that drives the induction motor using a load-side commutation command signal based on the output.