JPS5915278B2 - Induction motor speed control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device that operates an induction motor as a two-speed motor and is suitable for positioning and stopping a load machine.

5. In recent years, in order to improve the stopping accuracy of loaded machines, a method of switching to low-speed operation immediately before stopping and then braking has been frequently used.

The electric motor used for this purpose needs to be able to easily obtain at least two high and low speeds, and for this reason, the induction motor is operated directly and easily with a frequency of 10 to operate at a low speed, so-called "thinned energization". control has been used. There are various methods for "thinning energization" control, but in Fig. 1 a and b, the three-phase induction motor M is controlled by 1/6n-1 or 1/6n+1, respectively.
(n is an integer) The main circuit connection diagram when controlling 5.S, T, R are three-phase AC power supply THI3TH23TH
3 is a bidirectional switching element, and MC is a contactor.

In Figure 1a, the 1/6n-1 low frequency voltage component applied to the motor M due to thinning energization has a phase rotation direction opposite to the power supply voltage. It is necessary to switch between two phases when energizing and operating at low speed. Therefore, in order to use the contactor MC and prevent short circuits during switching, it is necessary to start thinning energization at a time interval of 0.2.5 to 0.3 seconds after opening the contactor MC. This time is wasted time that hinders speeding up of control. However, in the case of 1/6n+1 deceleration control, the low frequency voltage component has the same phase rotation direction as the power supply voltage, so there is no need to change the phase connection when switching speeds, and the circuit and operation are simple. Become.

In addition, in order to prevent loads from collapsing, conveyors, etc., are often required to start and stop slowly without causing shock when switching speeds, but with the connection shown in Figure 1b, the purpose can be easily achieved with ignition 15 phase control. This makes it more versatile than in the case of FIG. 1a.

Therefore, an object of the present invention is to propose a speed control device for an induction motor that performs 1/6n+1 deceleration control. Embodiments of the present invention will be described below with reference to the drawings.

Figure 2 shows the block circuit of the present invention, where R, S, and T are three-phase AC power supplies, M is a three-phase induction motor, N, V, and W are electric windings, and Tl, T2, and T3 are triax, etc. It is a bidirectional switching element (hereinafter referred to as a thyristat). A is a synchronization signal generator that outputs six synchronization signals a corresponding to the positive and negative line voltages of the power supply, and B is a reference signal b by logically processing the synchronization signal a and the output d of a hexadecimal ring counter D. A reference signal generating device to output, C is a 1/n frequency divider that divides the reference signal b and operates a hexadecimal ring counter (hereinafter simply referred to as a counter) D by the divided output, and E is a counter D.
a phased reference signal generating device which logically combines the outputs of the two to output three phased reference signals e having a width of 240 degrees and a phase difference of 120 degrees, with one cycle being 6n+1/2 cycles of the power supply voltage; G is the phase-specific reference signal e and the output f of the ignition phase adjuster F.
The ignition pulse g of thyristors T1 to T3 is obtained by logically processing
This is an ignition pulse generator that gives

FIG. 3 shows details of the ignition control circuit of FIG.

The synchronous signal generator A consists of three circuits of the same configuration connected between each line of the power supply. To explain the circuit between the power supplies T and R, the photocoupler 1 and the low resistors 2 and 3 are connected to the line voltage V.
(Fig. 4) and generates a signal having the same phase as the inverted voltage of the line voltage, and transmits this signal to the resistors 4 and 5 and the inverter 6.
The waveform is shaped by the Schmitt circuit configured in , 7,
A synchronizing signal A3 having a phase difference of 180 degrees from the line voltage T-R is generated, and the inverter 8 converts the signal A3 to the line voltage T-R.
It is converted into a synchronization signal A6 that is in phase with R. Line voltage R-S,
Similarly, for ST, synchronization signals A2, al and in-phase synchronization signal A5 having opposite phases to the corresponding line voltages are generated.
, a4 are generated. FIG. 4 shows the signal waveforms of each part when n=2, and al to A6 are rectangular wave signals corresponding to the positive and negative lines of the line voltage.

In FIG. 3, the reference signal generator B includes six AND
It has elements 9 to 14, 0R elements 15 and 16, a differentiation circuit 17, and a mono-multivibrator 18, and AND elements 9 to 14.
14 is a synchronizing signal al~A according to the change in the contents of the counter D.
6, the differentiating circuit 17 mono multivibrator 18 and 00R gate 16 output the selected synchronizing signal as the reference signal b from the 0R element 16 without interruption before and after the selection.

Next, the integrated operation of the reference signal generator B, the 1/n frequency divider C (n=2, that is, the reduction ratio 13), and the counter D will be described in detail with reference to the operational waveform diagram of FIG.

Now, suppose that the content of counter D is 0 at a certain point, the output of terminal 0 is at H level, and the other terminals 1 to 5 are at L level. In this case, only AND element 10 is open, so signal A4
passes through the element 10 and the 0R element 15, and the differential circuit 17
outputs a differential pulse (B2) at time t1 to trigger the mono multivibrator 18. Now, if the output pulse width of the mono multivibrator 18 is adjusted so that it is larger than 60 degrees and smaller than 180 degrees in terms of the phase width of the power supply voltage, the output b of the 0R element 16 becomes H. L at t2 b1
The pulse has the same width as signal A4. This pulse is 1/2
Since this is the first input signal to frequency divider C, frequency divider C does not output and the contents of counter D do not change. Therefore, the signal A4 passes through the AND element 15 even after T2. When the signal A4 becomes H again at time T3, it becomes 0R as before.
Element 16 outputs a second signal to frequency divider C, causing it to operate.

As a result, the counter D is shifted by 1, terminal 0 becomes L level and terminal 1 becomes H level, AND element 10 is closed, AND element 13 is opened, and signal A3 is output from now on. Since the phase is delayed by 60 degrees from A4, it is at L level at time T3, and becomes H level at time T4, which is 60 degrees later than that. Therefore, the output (b1) of the 0R element 15 temporarily goes to the H level at time T3, then immediately drops to the L level as a pulse, and then goes to the high level by the signal A3 at time T4. As a result, the differentiating circuit 17 outputs differential pulses at times T3 and t4, and after being triggered by the differential pulse at T3, the mono-multivibrator 18 continues to output for a predetermined period without being affected by the differential pulse at T4 (B3) . Therefore, the output b of the 0R element 16 is at H level from time T3 to T. Thereafter, at times T6, t7, t8, t9, etc., the same operations are repeated at times Tl, t2, t3, t4, etc., and the power supply voltage is output from the 0R element 16. With the phase of 180 degrees and 240 degrees H level period is 180 degrees L
A reference signal b that appears alternately with a level period is output.

Letters A3, a4, etc. written on the upper side of the waveform diagram in Fig. 4 b1
・represents the selected synchronization signal, and the number 1 written at the bottom
, 2, . . . represent the contents of the counter D. As described above, when the contents of the counter D are shifted, the circuit BS including the 0R element 16, the differentiating circuit 17, and the monomultivibrator 18 receives the synchronization signal (in the above description) selected before and after the shift, respectively. This is a signal continuation circuit that continues the H level periods of A4 and A3) without interruption during shifting.

In addition to the above-described embodiments, the circuit may employ other known means, such as delaying the transition of the AND elements 9 to 14 from open to closed during the shift by a time corresponding to a phase width of 60 degrees. can. Furthermore, although the reference signal b is synchronized with the power supply voltage at the rising time and the falling time v of the pulse, it is practically sufficient if either one of the time points is synchronized with the power supply voltage.

Figure 4c shows the output pulse of frequency divider C, and the figure DO-D
5 indicates output signals of terminals 0 to 5 of the counter D.

The phase-specific reference signal generator E includes three 0R elements 19, 20,
21, and the 0R element 19 receives the signals DO, dld3, d4.
The 0R element 20 converts the OR signal el into the signals DO, d2,
0R element 21 outputs the OR signal E2 of d3 and d5 as the signal D
A logical sum signal E3 of l, d2, d4, and d5 is output, respectively.

As shown in FIG. 4, the signals e1 to E3 are pulses with a width of 240 degrees, each of which has a pulse width of 12
It has a phase difference of 0 degrees. The ignition phase regulator F consists of an inverter 22, a mono multivibrator 23, a variable resistor 24, a resistor 25, a capacitor 26, an inverter 27, and an AND element 28. input, producing an output F2 of width determined by resistor 24.

F2 remains at L level for a period determined by variable resistor 24 from the time when f1 changes from L to H level. Further, the inverter 27 outputs an inverted signal F3 delayed from F2 by a time determined by the resistor 25 and the capacitor 26, and
D element 28 outputs an AND signal F4 of F2 and F3. Therefore, F4 becomes a pulse signal delayed by the phase α determined by the variable resistor 24 from the point in time when the reference signal b changes in level from H to L. The ignition pulse generator G includes AND elements 29, 30, and 31, and a resistor 291 connected to each element.
, a transistor 292, and an amplifier consisting of a pulse transformer 293. AND elements 29, 30, and 31 output logical product signals Gl, g2, and g3 of signals e1 and F4, E2 and F4, and E3 and F4, respectively.

These signals are applied to the thyristors T1 to T by valving the amplifiers.
3 respectively, the electric motor M has Hl, h2, h
A thinning voltage of 3 is applied. The fundamental wave of the voltages hl to H3 is a low frequency three-phase AC voltage of the power supply frequency m, and rotates the electric motor M at a low speed approximately ≠ the rated speed.
Figures 5 and 6 are operating waveform diagrams when the frequency division ratio n of the l/n frequency divider C in Figure 3 is set to 1 or 3, respectively, and the same symbols as in Figure 4 are The corresponding signal is shown.

The phase-specific reference signals el to E3 shown in FIG.
A pulse with a width of 240 degrees, with one cycle being one period, and a pulse of 1
It has a phase difference of 20 degrees, and the fundamental wave of the thinned-out voltages h1 to H3 is a low frequency three-phase AC voltage of ten times the power supply frequency,
The phase reference signals e1 to E3 shown in FIG. 6, which rotate the motor at a low speed that is approximately one of the rated speed, are set at 120 degrees with a width of 240 degrees, with one cycle being η cycles of the power supply voltage. It is a pulse having a phase difference of , and the thinning voltage hl~H3
The fundamental wave causes the V1 motor, which is the same as the power supply frequency, to rotate at a speed approximately ρ lower than the rated speed.

The present invention is based on the above, and when operating a motor at low speed with a low frequency voltage of 1/6 n+l of the power supply frequency, the speed control device can be used by simply changing n of the l/n division. , other circuits can be used in common,
In addition to having the advantage of being highly flexible, the ring counter has the effect of greatly simplifying the circuit configuration because it uses a hexadecimal ring counter with a small number of stages.

Furthermore, in the present invention, the contents of the counter are fed back,
A reference signal is generated by selecting a power synchronization signal according to the content, so even if the power is turned on at any time, the damping device can immediately enter the operating state as it is, unlike conventional methods. This eliminates the need for an initial setting device when the power is turned on, as in the case of the device, and has the effect of significantly simplifying the entire device.

[Brief explanation of drawings]

FIGS. 1A and 1B show connection diagrams of the main circuit of a motor using the conventional thinning-out energization method, and FIG.

Claims (1)

[Claims] 1. In a speed control device for a three-phase induction motor that is supplied with power from a three-phase AC power source via a bidirectional switching element,
6 operated by the output of the (1/n) frequency divider (n is an integer)
Generate a reference signal by sequentially selecting a plurality of periodic signals corresponding to the positive and negative states of the line voltage of the power supply based on the output of the leading ring counter, and at the same time, generate a reference signal to operate a (1/n) frequency divider using the reference signal. a firing phase adjuster for generating a firing phase adjustment signal having an adjustable phase lag with respect to said reference signal; Power supply 6n+1/
a phased reference signal generation device that outputs three phased reference signals having a phase difference of 120 degrees in a width of 240 degrees with two cycles as one period; and the phased reference signals and the ignition phase adjustment signal. 1. A speed control device for an induction motor, comprising: a firing pulse generating device that outputs an AND signal of the two-way switching element as a firing signal for a bidirectional switching element.