JPS5923199B2 - Three-phase induction motor speed control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When a three-phase induction motor is used as a two-speed motor, the present invention can speed up the deceleration from high speed to low speed and make it suitable for positioning and stopping a loaded machine. Regarding a control device.

Conventionally, a two-speed control system has been proposed in which a three-phase induction motor is switched to a low speed having a speed ratio of 1/6n±1 (n is an integer) by thinning energization using a bidirectional thyristor.

This method has the advantage of being inexpensive and applicable to general-purpose motors, so it is often used to control two-speed motors that position and stop load machines, and speed ratios such as 1/11 and 1/13 are often used. ing. However, the above method
Because the regenerative braking force generated when switching to low speed is weak,
The disadvantage was that it took a long time to transition from high speed to low speed.

For example, Fig. 1 is a rotation speed-torque characteristic diagram of an induction motor with energization thinned out so that the speed ratio is 1/11, curve a is the characteristic when full voltage is applied, and curves b and c are 1/1 with energization thinned out. This is the characteristic when operating at a low speed with a speed ratio of 11. Generally, when operating a motor at low speed by thinning energization, phase control is used to prevent a decrease in the load time factor due to a large current flowing due to a decrease in motor impedance, and to reduce vibration and noise. Control the applied voltage to be as low as possible. Curve b shows the characteristics when the applied voltage is large, and curve c shows the characteristics when the applied voltage is small. In both cases, the regenerative braking torque is small when switching to low-speed operation, and especially when the load inertia is large, the regenerative braking torque is small. It takes a considerable amount of time to shift to low speed. Therefore, conventionally, when shifting from high speed to low speed, phase control is applied so that the maximum voltage is applied during deceleration range d, and then the minimum voltage sufficient to generate the low speed torque required to drive the load is applied. A control method was used.

As a result, the purpose of increasing the braking force during the deceleration period and at the same time suppressing vibration and noise at low speeds was achieved to a certain extent, but in thinning energization, the braking torque remains on the curve even when the full voltage is applied. It is at the level of b, which is insufficient. An object of the present invention is to shorten the transition time from high speed to low speed by switching from high speed operation to low speed operation with thinned-out energization by first switching to a medium level with large braking torque and then switching to low speed. The object of the present invention is to provide a speed control device for a three-phase induction motor that can be shortened to a much larger width than the previous one. FIG. 2 shows the rotation speed/torque characteristics of the electric motor according to the present invention, curves A and c are the same as those in FIG. 1, and curve e shows the torque characteristics during medium speed operation of the speed ratio.

As can be seen from the figure, the braking force for deceleration from speed n1 to speed N2 is considerably larger on average for curve e than for curve c. Therefore, by decelerating from n1 to N2 by medium-speed operation and decelerating from N2° to N3 by low-speed operation, it is possible to quickly decelerate even a load with a considerably large inertia. Since the deceleration time from n1 to N2 can be considered to be approximately constant for each load, according to the present invention, by appropriately determining the speed ratio during medium-speed operation and the time point for switching from medium to low speed. The best deceleration control can be performed. Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 shows a block circuit diagram of the present invention for low speed operation with a speed ratio of 1/6n-1. R, S, T are three-phase AC power supplies, M is a three-phase induction motor, U, v, w are Y-connected armature windings, MCl, MC2 are magnetic contactor contacts for high-speed operation and low-speed operation, respectively. be. When switching from high-speed operation to low-speed operation, a low-speed command signal opens MCl and closes MC2, and energizes the electric motor M in a reduced manner through bidirectional switching elements (hereinafter referred to as thyristors) TH1, TH2, and TH3. When decelerating to a speed ratio of 1/6n-1, the power supply voltage and phase rotation of the three-phase low-frequency torque component applied to the motor M due to thinning energization are reversed, so the circuit of thyristors THl to TH3 is as shown in the diagram. Swap the two phases and connect.

A is six synchronization signals a corresponding to the positive and negative line voltages of the power supply.
B is a reference signal generator that sequentially selects synchronization signals a according to the output d of a hexadecimal ring counter (hereinafter simply referred to as counter) D and outputs a reference signal b; C is a reference signal generator that outputs a reference signal b; It is a 1/n frequency divider that divides the frequency, and when the speed ratio is set to 1/11, it is a Σ frequency divider. E logically combines the output d of the counter D to form the thyristors THl to TH3.
A phase-specific reference signal generator that outputs a phase-specific reference signal e that determines the ignition possible period, F is a mode switch, and a counter is activated for a predetermined time (the deceleration time) after the low-speed command signal is input to S. D is activated by the reference signal b, and thereafter, the counter D is activated by the output signal of the frequency divider C. The predetermined time is adjusted by a variable resistor 17. G is the reference signal b
An ignition phase adjuster that outputs an ignition phase adjustment signal g at a time delayed by a phase α from the rising or falling point of the phase α.
is adjusted by a variable resistor 27. H is an ignition pulse generator that logically processes and amplifies the signal e (5g) to provide an ignition pulse h to the thyristors THl to TH3. Fig. 4 shows the main points of Fig. 3 when n=2. Show details.

The synchronizing signal generator A consists of three circuits having the same configuration and connected between the power supply lines R, S, and T. To explain the circuit connected to power supplies R and T, photocoupler 1, resistor 2,
3 generates a signal having a phase opposite to that of the line voltage (FIG. 5v), and a Schmitt circuit constituted by resistors 4 and 5 and inverters 6 and 7 shapes this signal and outputs a synchronizing signal A3. Furthermore, the inverter 8 converts the signal A3 into the line voltage and the synchronization signal A6.
Convert to Similarly, synchronizing signals Al, a2 of opposite phases and synchronizing signals A4, a5 of the same phase are output for the line-to-line tortoise pressures R-S and S-T, respectively.

FIG. 5 shows the signal waveforms of each part in FIG. 4, and a1 to A6 are rectangular wave signals corresponding to the positive and negative of the line voltage of the main source.

Reference signal generator B includes six AND elements 9 to 14 and 0R.
AND elements 9 to 14 receive a synchronizing signal a.
One signal from 1 to A6 and the output DO of counter D, which will be described later.
- Each logical product signal with one output of D5 is output, and when the counter D is shifted as described later by the output, the next synchronizing signal whose phase is advanced by 60 degrees among the synchronizing signals a1 to A6 is sequentially generated for each shift. It is selected and output from the 0R element 15.

This is the reference signal b. - Frequency divider C is J in this embodiment
This is a -K flip-flop, and if terminals J and K are fixed at H level, the output level of terminal Q will be inverted every time a signal is input to terminal C, and once for every two input signals. produces a pulse output of

The mode switch F is a mono multivibrator 16, . It consists of a variable resistor 17, an inverter 18, AND elements 19, 20, and an 0R element 21.

In the case of high-speed operation, the mono-multivibrator 16 is inactive and its Q output is at L level, so the AND element 19 is open and the AND element 20 is closed. Counter D is therefore shifted by the output of frequency divider C. However, when the low-speed command signal is input to point S, the mono-multivibrator 16 becomes active, and the Q output becomes H level only for a time T determined by the variable resistor 17, closing the AND element 19 and opening the AND element 20. . As a result, counter D is shifted by reference signal b. Next, the relational operation between the reference signal generator B and the counter D will be explained.

(1) When counter D is shifted by the output of frequency divider C (Fig. 5) At a certain point in time, the contents of counter D are O, terminal 01 is at H level, and other terminals 1 to 5 are at L level. If so, only the AND element 13 is opened and selects the signal A3, and the output of the 0R element 15 is at H level from time T to T2 and at L level from T2 to T3, as shown in FIG. 5B.

This signal is input to frequency divider C, but since it is the first signal, frequency divider C does not output it, and the contents of counter D do not change.
Next, at T3, when the signal A3 becomes H level again, the frequency divider C outputs an output to set the contents of the counter D to 1. As a result, terminal 0 becomes L level and terminal 1 becomes H level. Therefore, AND element 13 is closed and AND element 10 is opened to select signal A4. This signal A4 becomes L level at T4 and becomes H level again at Jt5, but the frequency divider C does not output it.When the signal A4 becomes L level at T6 and becomes H level again at T7, the frequency divider C outputs it. and set the contents of counter D to 2.

As a result, terminal 1 becomes L level, terminal 2 becomes H level, AND element 10 is closed, AND element 11 is opened, and signal A2
Select. These operations proceed one after another until 0R.
From element 15, the phase angle of the power supply voltage is 180 degrees and 120 degrees.
A reference signal b is output in which H level periods of 180 degrees alternate with L level periods of 180 degrees.

Figure 5c is the output of the frequency divider C, DO~D5 are the outputs of the counter D, the letters A3, a4, etc. attached to the waveform diagram b represent the selected synchronization signals, and the letters A3, a4, etc. attached to the waveform diagram c The number represents the contents of counter D. 2) When the counter D is shifted by the reference signal b (Fig. 6) Similarly to (1), if the content of the counter D is O at a certain point in time and the signal A3 is selected, then the value shown in Fig. 6 b The output of the 0R element 15 is T
, and at the same time the counter D is shifted to set the content to 1.

As a result, AND element 13 closes and AND element 10 opens to select signal A4. Therefore, A4 is output from the 0R element 15 and becomes L level at T2. Next T3
When signal A4 becomes H level again, counter D shifts to content 2, AND element 10 closes and AND element 11 opens.

Therefore, signal A2 is output from 0R element 15, and T4
It becomes L level. Similarly, from the 0R element 15, an H level period of 120 degrees and a 18
A reference signal b is output in which L level periods of 0 degrees appear alternately.

DO to D5 in FIG. 6 are the outputs of the counter D in this case. The phase-specific reference signal generator E includes three 0R elements 22, 2.
3, 24, and the 0R element 22 receives the signals DO, dl, d3.
, d4, the 0R element 23 outputs the logical sum signal e1 of the signals Dl,
OR signal E2 of d2, d4, d5, and 0R element 2
4 outputs the OR signal E3 of the signals D2, d3, d5, and dO as phase-specific reference signals.

The signals El, e2, e3 are as shown in FIG. 5 when the counter D is shifted by the output of the frequency divider C.
As shown in Fig. 11, one cycle of the power supply voltage is one period, and the pulses have a width of 240 degrees and a phase difference of 120 degrees, and when the counter D is shifted by the reference signal b, as shown in Fig. 6. Thus, one cycle of the power supply voltage is one period, and the pulses have a width of 240 degrees and a phase difference of 120 degrees.

The ignition phase adjuster G includes inverters 25 and 30, a mono-multivibrator 26, a variable resistor 27, a resistor 28, a capacitor 29, and an AND element 31.

Mono multivibrator 26 has clamp terminal CDb3L
Does not operate while at level. However, the clamp terminal is H.
When the level is reached, it operates when the inverted signal b of the reference signal b is input from the inverter 25, and connects the Q terminal to the resistor 2.
A signal g1 having a width determined by 7 is output. The signal g1 is L for a width α from the time when the signal b changes its level from L to H.
level. Further, the inverter 30 outputs an inverted signal G2 delayed from g1 by a time determined by the resistor 28 and the capacitor 29, and the AND element 31 outputs a logical sum signal G3 of g1 and G2.

Therefore, G3 becomes a pulse signal delayed by the phase α determined by the variable resistor 27 from the time when the reference signal Bb5H changes to the L level. Ignition pulse generator H is AND
It consists of elements 32, 33, 34 and an amplifier 321 etc. connected to these, and each AND element receives a signal e.
Each AND signal Hl of 1 and G3, e2 and G3, e3 and G3
, h2, h3 are output.

The signals h1 to H3 are amplified to the thyristors TH1 to TH3.
If the ignition signal is , the thinned out voltages Vl, v2, v3 shown in FIG. 5 or 6 are applied to the electric motor M. Voltage V
The fundamental waves of l, v2, and v3 are: (1) When counter D is shifted by frequency divider C (Fig. 5), it is a low frequency three-phase AC voltage of one power supply frequency, and the motor M is rated. speed(
High speed) 1)
(2) When the counter D is shifted by the reference signal (Fig. 6), the motor M is rotated at a medium speed of τ of the rated speed with a three-phase AC voltage at the cross of the power supply frequency. Rotate it.

It will be easily understood that by expanding the above principle, it is generally possible to rotate the electric motor M at a low speed of 1/6n-1 of the rated speed using the one-frequency divider NC.

Next, the operation of the present invention will be explained.

Contact MC2 is open during high-speed operation, but since there is no low-speed command signal, the output of the delay circuit 35 is at L level, and the mono-multivibrator 26 of the ignition phase regulator G is closed.
is inactive.

Therefore) G3 does not output, and ignition pulse generator H also does not output.

When contact MCl opens and MC2 closes due to the low speed command signal, mono multivibrator 16 of mode switch F also operates and its Q output remains at H level for time T.

Therefore, the reference signal b is the AND element 20 and the 0R element 21.
is input to counter D via , and this is shifted. However, while the output of the delay circuit 35 is still at L level, the ignition phase regulator G is inactive, so the thyristor THl
~TH3 is not fired. When the output of the delay circuit 35 reaches H level after a predetermined delay time, the ignition phase regulator G is activated, the thyristors THl to TH3 are ignited, and the electric motor M is switched to low speed operation.

As mentioned above, since the input and output terminals of the thyristors THl to TH3 are connected in reverse phase, there is a risk of short-circuiting when the contacts MCl and MC2 are opened and closed, but this risk is avoided by providing the delay time. be able to. Delay time is 0
．． Approximately 1 second is sufficient and does not adversely affect the transition from high-speed operation to low-speed operation. If the speed ratio at low speed is 1/6n+1, thyristors THl to TH3
Since the input and output terminals of the circuit are in-phase connected (FIG. 7), the delay time described above is unnecessary. When the delay time elapses, the reference signal b is input to the counter D, so the electric motor M enters a medium-speed operation state, and is brought to a high speed by the large braking torque shown on the axis e in Fig. 2. N, and rapidly decelerates to medium speed N2. Set time T of multivibrator 16 to N
, the output of the multivibrator 16 becomes L level after a time T, and the counter D is shifted by the output of the division period C. Therefore, the electric motor M is switched to a low speed operation of 1/11, and thereafter is decelerated by the large braking torque shown by the curve c in FIG. 2, and finally reaches the low speed N. By making the set time T approximately equal to the deceleration time until the curve e crosses the curve c after passing the negative maximum torque, the average braking torque can be maximized.

Since the motor drive torque at low speeds can be changed by the variable resistor 27 of the ignition phase adjuster G, by adjusting this and the time T, the transition time of the motor M to low speed operation can be minimized. .

FIG. 7 is a block circuit diagram of an embodiment in which the motor is operated at a low speed of 1/6n+1 of the rated speed, and FIG. 8 is a detailed circuit diagram of its main parts.

In the drawings, the same reference numerals as in FIGS. 3 and 4 indicate the same components. In this practical example, since the thinned-out voltage applied to the motor M at low speed has the same phase rotation as the power supply voltage, the input and output ends of the thyristors TH1 to TH3 are connected in the same phase. This embodiment differs from the previous practical example in that an auxiliary circuit Bs consisting of a differentiating circuit 36, a multivibrator 37, and an 0R element 38 is added to the reference signal generator B, and that the reference signal generator B and the counter The only difference is that the connection between D and the phase reference signal generator E is slightly different.

The operation of this practical example will be explained with reference to FIGS. 9 and 10.

(1) When the counter D is shifted by the output of the frequency divider C (Fig. 9) If the content of the counter D is O at a certain point, only the AND element 10 is opened and the signal A4 becomes 0R.
After passing through the element 15, the differentiating circuit 36 outputs a differentiating pulse B2 at time t1 in FIG. 9, and triggers the mono-multivibrator 37.

If the output pulse width of the mono multivibrator 37 is adjusted so that the phase width of the power supply voltage v is greater than 60 degrees and smaller than 180 degrees, the output b of the 0R element 38 becomes H at t1.
, t2 becomes L, and becomes a pulse with the same width as signal A4. Since this pulse is the first input signal to frequency divider C, frequency divider C does not output it, 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, a second signal is output from the 0R element 38 to the frequency divider C to activate it, and the contents of the counter D are set to 1 in the same manner as described above.

As a result, AND element 10 is closed and AND element 13 is opened to select signal A3. Signal A3 has a phase of 60 compared to A4.
Since it is delayed by 60 degrees, it is at L level at T3, and becomes H level at time T4, which is 60 degrees later than that. Therefore 0
The output b1 of the R element 15 becomes a high level pulse at T3, then immediately becomes an L level, and at time T4.
When the signal A3 goes high, the overall deceleration time can be much shorter than in the past. In the above embodiment,
Although automatic switching from medium speed to low speed was performed, it is of course possible to perform manual switching if the timing of the switching is good.

[Brief explanation of the drawing]

FIG. 1 is a rotation speed-torque characteristic diagram during two-speed switching operation of a three-phase induction motor according to the conventional method, FIG. 2 is a rotation speed-torque characteristic diagram similar to FIG. 1 according to the present invention, and FIG. FIG. 4 is a logic circuit diagram of an embodiment of the invention, FIG. 5 and FIG. 6 are operation waveform diagrams of each part of FIG. 4, and FIG.
This figure is a block circuit diagram of another practical example of the present invention, FIG. 8 is a logic circuit diagram of the main part, and FIGS. 9 and 10 are operation waveform diagrams of each part of FIG. THl, TH2, TH3... Bidirectional switching element, M... Three-phase induction motor, B...
・・Reference signal generator, C・・1 frequency divider, D・
...Hex ring n counter, E...Phase-specific reference signal generator, F...Mode switch, G...
...Ignition phase adjuster, H...Ignition pulse generator, U, V, W...Three-phase AC power supply.

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,
a reference signal generator that generates a reference signal by sequentially selecting a plurality of synchronization signals synchronized with the power supply voltage using the output of a hexadecimal ring counter;
an n frequency divider (n is an integer), a mode switch that switches the input signal of the hexadecimal ring counter from the output of the 1/n frequency divider to the reference signal, and an adjustable delay phase with respect to the reference signal. a firing phase adjuster for generating a firing phase adjustment signal;
By ORing the outputs of the leading ring counters, one period is 6n-1/2 (or 6n+1/2) cycles of the power supply voltage, and three cycles have a phase difference of 120 degrees with a width of 240 degrees.
a phase-specific reference signal generator that outputs phase-specific reference signals;
an ignition pulse generator that generates an AND signal of the phase-specific reference signal and the ignition phase adjustment signal to provide a ignition pulse to a bidirectional switching element; The speed of the motor is 1/1 of the rated speed.
5 (or 1/7) speed ratio to 1/11 (or 1/13)
A speed control device for a three-phase induction motor, characterized in that the speed is reduced to a speed ratio of ).