JPS6012878B2 - Control method of induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling an induction motor using two sets of cycloconverters, which supplies current with few harmonic components to the induction motor and reduces 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 oscillation pulsate like a beat. For this reason, as a method of driving an induction motor using a cycloconverter, the operating frequency is limited to an integer fraction of the power supply frequency.For example, if the power supply frequency is pua, the operating frequency is na a/2, na a/3, na a/4
,... A method of operating at discrete frequencies is used. FIG. 1 shows a block diagram of a typical cycloconverter induction motor control system.

In the figure, 1 is a cycloconverter consisting of 18-arm thyristors RUP to TWN and DC reactors LA to LC, 2 is a concession motor driven by the cycloconverter 1, and 3 detects the terminal voltage of the induction motor 2. 4 is a voltage control amplifier that amplifies the deviation between the voltage reference signal A and the output signal of the voltage detector 3; 5 is a current transformer (5) that detects the current V supplied to the cycloconverter 1; 6 is a current detector that converts the current detected by the CT 5 into a control signal; 7 is a current detector that amplifies the deviation between the output signal of the voltage control amplifier 4 and the output signal of the current detector 6. A current control amplifier; 8 is a phase controller that controls the firing phase of the thyristor according to the output signal of the current control amplifier 7; 9 is a phase controller that sets the power supply frequency signal C to an integer fraction of the power supply frequency in accordance with the signal of the operating frequency command B; a step-down counter; 10 is the phase controller 8;
The output signal of the step-down counter 9 is input as a power-side commutation command, and the output signal of the step-down counter 9 is input as a load-side commutation command, and the gate logic circuit outputs a firing pulse to be given to the thyristor of the cycloconverter 1. This figure 1 shows the V
This is called the /F control system, and is an open room speed control system that uses a voltage reference signal A and an operating frequency command signal B to drive the induction motor while keeping the ratio of voltage and frequency constant. FIG. 2 shows a time chart of the output current model of the cycloconverter according to this control system. In FIG. 2, 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 output current model (U phase) when the output frequency is 〆a/2, and now the time ratio,
Even if the load side commutation command UP is received, the actual commutation is delayed until time t2 of the power source side commutation timing RP, at which point the thyristor RUP is fired, and a positive current flows to the U phase of the motor. At the subsequent time Ut3, the thyristor SUP is fired, and at the same time, the thyristor TVP is fired and a positive current flows to the V phase, and at the same time, the thyristor SUP is extinguished and the U phase positive current becomes zero. At the time, the power supply side commutation command SN is given during the load side commutation command UN period, and the thyristor SUN
is fired, and at time t6, thyristor TUN is fired. Next, at time t7, thyristor RVN is fired, and at the same time, the load current flows to the V phase, and at the same time, thyristor TUN is extinguished, and the U-phase current becomes 0. At the following time, a load-side commutation command for the U-phase positive current comes, but the thyristor TWP has already fired, and since the induction motor has a lagging power factor, the thyristor TWP
Load commutation (commutation due to the induced electromotive force of the motor) from to the thyristor TUP is not performed, and the U-phase positive current waits until the instantaneous power supply commutation timing and flows when the thyristor RUP is fired. 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 due to the fact that the current 0 period does not exist other than the parsimonious period when 60° of the power supply phase is taken as one section. That is, the current 0 period is 1, 3, 5,
Only when the operating frequency has a load-side commutation command such as 7, the output current waveform becomes a symmetrical waveform with equal zero current periods.
In the case of a/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, as shown in the waveform of FIG. 2C. Figure 2 D and E are when the output frequency is 〆a/3, D is the load side commutation timing, and E
shows the output current model (U phase). In the case of a/3, the current 0 period is 3, so the output current waveform becomes a symmetrical waveform. Figure 2 F and G show when the output frequency is a/4, F shows the load side commutation timing, and G shows the output current model (U phase). Therefore, the actual current 0 period is a repetition of 3 and 5, and the output current waveform becomes an asymmetrical waveform.From the above, when the output frequency is a fraction of the power supply frequency, the output current becomes a symmetrical waveform.
In the case of 1/even number, 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. The purpose of the present invention was to eliminate the above-mentioned drawbacks, and it is an object of the present invention to
It is an object of the present invention to provide a control method for a transfer motor that can supply a current with less harmonic components to the motor and reduce torque ripple by combining and combining the motors. FIG. 3 is a block diagram showing one embodiment of the present invention, and the same reference numerals as those in FIG.

In FIG. 3, IA and IB are the cycloconverters shown with reference numeral 1 in FIG. 1, and IT is the cycloconverter I.
A power transformer supplies power with a 600 phase difference to A and IB; 11 is a phase controller that controls the firing phase of the thyristor of the cycloconverter IB according to the output signal of the current control amplifier 7; has a phase difference of 60° from the output signal of the phase controller 8 in terms of the power supply phase. 12
inputs the output signal of the step-down counter 9 (load side commutation command), and the operating frequency command signal B becomes 〆a/5,
〆Only when giving a no 7, change the power phase to 18
00 (3 sections) A phase shift circuit that shifts the phase and locks the phase shift function when other operating frequency command signals are given; The phase shift circuit 1
2, the cycloconverter I
This is a gate logic circuit that outputs the firing pulse to be applied to the thyristor of B.

The phase shift circuit 12 shifts the power supply phase by 180 degrees through logical processing of the delay circuit or the power supply frequency logic signal and the output signal (load side commutation command) of the step-down counter 9. FIG. 4 is a time chart for explaining the present invention, and A to G are for the case where the operating frequency is a/5.

A and B correspond to the output signals of the phase controllers 8 and 11 in FIG. 3, and the phase difference between them is 60° in terms of the power supply phase. C and D correspond to the output signals of the step-down counter 9 and the phase shift circuit 12 in FIG. The output current model (U phase) of the cycloconverter IB looks like F, which is shifted in phase by a. Therefore, the phase current model of the induction motor 2 has a symmetrical waveform like G, and by shifting the load side commutation command signal by 1800, the waveform has fewer harmonic components. Similarly, HM indicates the case where the operating frequency is 7. Figure 4 F
Alternatively, as shown in M, according to the present invention, a step waveform current can be supplied to the induction motor 2. Therefore, the low-order harmonic current components (fifth order, seventh order) included in this staircase waveform are reduced. As a result, the low-order harmonic current component that causes large torque ripple is reduced, so the torque ripple of the induction motor 2 is reduced. Figure 6 shows the case where the operating frequency is other than Na a/5 and Pu a/7, and Figure 5 shows the operating frequency when it is an even fraction of the power supply frequency, taking Na a/2 and Na A/4 as examples. Fig. 6 shows the case of Na A/3. A and B in FIGS. 5 and 6 are the output signals of the phase controllers 8 and 11 as in FIG. 4, and C
is the output signal of the step-down counter 9 and the phase shift circuit 12. Since the function of the phase shift circuit 12 is locked, the load side commutation command signal of the same phase is given to the gate logic circuit, so the cycloconverters IA, IB The U-phase output current supplied from the power supply phase is shifted by 600 as shown in D, E, J, J in Fig. 5, and D, E in Fig. 6, and is shifted by 600 in terms of the power supply phase. Like F Cyclo Converter I
The sum of the currents A and IB is supplied to the induction motor 2. The same goes for Figures 5 and 6.
The waveform becomes a staircase waveform, and lower harmonic current components decrease. As a result, the low-order torque ripple generated by the induction motor 2 is also reduced. Even if the operating frequency is an even fraction of the power supply frequency, if two sets of cycloconverters are combined, the current waveform in the induction motor 2 will be symmetrical, there will be less torque ripple, and there will be less harmonic components and the power factor will be lower. A good system can be obtained. As explained above, the present invention provides two sets of cycloconverters connected to a power supply with 600 phases, and when the output frequency is a/5 or a/7, load side commutation commands are sent in current phase with each other. ] By operating two sets of cycloconverters with an 80° shift, and by operating the two sets of cycloconverters with load-side commutation commands of the same phase at operating frequencies other than main a/5 and na a/7. Therefore, it is possible to provide a method for controlling an induction motor that is free from external cycloconverters, which reduces the torque ripple of the induction motor, has few harmonics, and has a good power source power factor.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional device, FIG. 2 is a time chart for explaining the operation of the conventional device, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIGS. 4 to 6 are a diagram of the present invention. This is a time chart for explaining the operation of the invention. 1, IA, IB...cycloconverter, IT...power transformer, 2...induction motor, 3...voltage detector, 4.
... Voltage control amplifier, 5... Current transformer, 6... Current detector, 7... Current control amplifier, 8, 11... Phase controller, 9... Step down counter, 10, 13...
Gate logic circuit, 12...phase shift circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. 2 connected to power sources with a phase difference of 60° from each other.
In an induction motor control device comprising a set of cycloconverters and an induction motor that is powered by the two sets of cycloconverters and driven at a frequency that is an integer fraction of the power supply frequency, the induction motor is driven at 1/5 and 1/5 of the power supply frequency. When driving at a frequency of 7, a load side commutation command with a phase difference of 180° is given in the power supply phase, and the induction motor is driven at 1/1 of the power supply frequency.
A method for controlling an induction motor using a cycloconverter, characterized in that when driving at a frequency other than 5 and 1/7, two sets of cycloconverters are operated by giving load-side commutation commands of the same phase.