JPS58151886A - Controller for alternating current motor - Google Patents

Abstract

PURPOSE:To enable stable operation even when output frequency is high by changing over the positive side thyristor and reverse side thyristor of a reverse side connected capacitor when the primary currents of the AC motor reach predetermined value or less. CONSTITUTION:The primary currents of the three-phase AC motor is compared with signals corresponding to the magnitude of primary current reference signals as an output from a vector control circuit 16 by comparison circuits 22U, 22V, 22W. Consequently, when said primary currents reach not more than the signals corresponding to the magnitude of said primary current reference signals, the ignition signals of thyristors are blocked, and the positive side thyristors and reverse side thyristors of antiparallel connected converters 3U, 3V, 3W are changed over by using phase control-positive reverse change-over circuits 23U, 23V, 23W. Accordingly, the delay of actual primary currents to a primary current reference is reduced, and stable operation is enabled even when output frequency is high.

Description

DETAILED DESCRIPTION OF THE INVENTION (&) Description of the Technical Field The present invention relates to a control device for an AC motor comprised of thyristors that output alternating current or direct alternating current.

(b) Description of Prior Art When driving a three-phase induction motor, a three-phase sine wave cycloconverter that can directly obtain alternating current from the above-mentioned alternating current is employed as a variable frequency drive device that flows three-phase sinusoidal current. ing.

Figure 1 is a circuit configuration diagram showing a sine wave cycloconverter. In the figure, 1 is a three-phase AC power supply, 2 is a power transformer,
v・2W is 3U・3v・
Two sets of 3W three-phase Graetz connection converters are connected in antiparallel to each other, each of which is capable of passing current in both forward and reverse directions.

4U, 4V, 4W is a shunt, 5 is a three-phase AC motor that is a load (hereinafter simply referred to as a motor), and 6 is the motor 5.
The anti-parallel connected converter 3U, 3V, 3W is connected to the U-phase winding, V-phase winding, and W-phase winding of the motor 5. Connected to the power transformer 202nd order**2U・2V・2
The commercial AC of W is the anti-parallel connection converter 3U/3V.
- Direct AC-RK conversion of a predetermined frequency is performed by 3W and applied to the electric motor 5.

10F of control circuit! a speed setter 11 for setting the speed of the electric motor 5; a rounding adder 11 that matches the speed reference signal set by the speed setter 10 with the speed feedback signal detected by the speed detector 6; , 12 is a speed/control circuit for amplifying the deviation signal of the output of the adder 11, 13
14 is a magnetic flux weakening control circuit which inputs a speed feedback signal and outputs a secondary magnetic flux reference signal, and 14 is a secondary magnetic flux reference signal output from the magnetic flux weakening control circuit 13 and a vector control circuit 1 to be described later.
15 is a magnetic flux control circuit that amplifies the deviation signal of the output of the adder 14. Reference numeral 16 indicates a torque current reference signal 11"1 output from the speed control circuit 12, a magnetic flux current reference signal iL output from the magnetic flux control circuit 15, and the speed detector 6.
speed feedback signal #m of the output of the motor 5.
Secondary magnetic flux, slip angular frequency ω8, torque current 1t, phase difference between magnetic flux current 1h - magnitude of 11th order current 1t#q
4", to the primary angular frequency = ωm + ms, and from these, the primary current reference 11u of the U-phase, ■-phase, W-phase windings of the motor 5 = 1IBin (6Iot+θ), icy
= 1lsin(a+et+θ-120°) 11w
This is a vector control circuit that calculates and outputs = 1tsln(a4t+θ-240°). 18U, 18V, 18
W is an addition that matches the primary current reference signal of each phase output from the vector control circuit 16 with the current feedback signal from the 17U/17V/17W current detector that amplifies the 4U/4V/4W signal. Equipment, 19U/19V/19W
22U is a current control circuit for amplifying the deviation signal of the output of the adder.

22V/22W is a comparison circuit that compares the signal set by the rheostat 21 and each phase current feedback signal which is the output of the 17U/17V/17W, and 20U/20V/20W is the current control circuit 19U/19V/ The phase control signal of the 19W output, the output signal of the comparator circuit 22U, 22V, 22W, and each phase primary current reference signal of the output of the vector control circuit 16 are inputted to the anti-parallel connected converter 3U, 3V.
・This is a phase control/forward/reverse switching circuit that creates switching signals and firing signals for the 3W positive and negative thyristors.

In this sine wave cycloconverter, switching from the positive side thyristor to the reverse side thyristor of the anti-parallel connected converter 3U, that is, switching from the positive direction current to the reverse direction current will be explained. The U-phase primary current of the motor 5 is connected to the rheostat 2.
When the value is below the value set in step 1, multiple signals from the comparison circuit 22U are output to the phase control/forward/reverse switching circuit 20U, and the firing phase of the positive side thyristor becomes the maximum filling phase. Sidesilisks are gate-blocked for a predetermined period of time;
It is then switched to the opposite thyristor. This situation is shown in FIG. The dash-dotted line is the primary current reference, and the solid line is the primary current. After time to, the primary current is set by the rheostat 21 and the force is below the predetermined value l, so the next 11≦t (
During a predetermined period of tl, the firing phase of the positive side risk becomes the squeeze phase, and then the next t! ≦1 <1. During a predetermined period of time, the gate of the positive thyristor is blocked, and at time t8, the reverse thyristor is fired to flow a reverse current.According to this method, switching from the positive side to the reverse side or vice versa occurs from t1 to 1. The primary current reference signal always lags behind the primary current reference signal by a predetermined period of time, and especially when the output frequency and primary current of a sine wave cycloconverter increase greatly, the proportion of this delay in one period increases, and the primary current reference vector There is a drawback that the primary current vectors that actually flow do not match, making stable operation impossible.

(e) Purpose of the Invention The present invention has been developed in view of the above points, and in a vector controlled sine wave cycloconverter, the delay of the actual primary current with respect to the primary current reference is reduced, and the output frequency is reduced. An object of the present invention is to provide a control device for an AC motor that can operate stably even when the primary current is high and the primary current is large.

(d) Structure of the Invention The present invention will be explained in detail below with reference to the drawings. FIG. 3 is a circuit diagram of an embodiment of a vector controlled sine wave cycloconverter according to the present invention. In the figure, the same reference numerals as in FIG. 1 indicate the same or equivalent parts.

23U/23V/23W is a phase control/forward/reverse switching circuit that outputs the primary current reference signal that is the output of the vector control circuit 16, the output signal of the comparator circuit 22U/22V/22W, and the output of the current control circuit 19U/19V/19W. It inputs the phase control signal and outputs switching and firing signals for the positive and reverse thyristors of the anti-parallel connected converter. Comparison circuit 22U
-22V-22W is current detector 17U-17V-17W
The current feedback signal from
When the magnitude of the next current reference signal 11 becomes less than a signal set to a predetermined magnitude by the variable resistor 24, a signal is output.

(6) Effect of the invention.

In this AC electric type control device, the switching knob from the positive side thyristor to the reverse side thyristor of the U-phase anti-parallel connected converter 3U will be explained with reference to FIG. 4. The dashed-dotted line in the figure is the primary current reference.
The solid line is the primary current. Since the primary current became less than the value l・1 set by the rheostat 24 after time 1o, t・
At <t, the gate of the positive side thyristor is blocked, and after a predetermined time, the gate is blocked until 9to<t<ts, and the exit side thyristor is fired to flow a reverse current.

FIG. 5 is a diagram showing how the positive thyristor is switched to the reverse thyristor when the value of the primary current is small, and shows the value l@! set by the rheostat 24. is smaller than the set value 1111 in Fig. 4 because the magnitude of the primary current reference is small, and the positive side thyristor is gate-blocked when the primary current becomes a smaller value t 〈t< tm At a predetermined time, the side risk on the exit side is ignited and current flows in the opposite direction.

In this way, when the primary current falls below a predetermined value, the gate of the positive side thyristor is immediately blocked, and after a predetermined time, all the reverse side thyristors are fired, or vice versa, thereby reducing wasted time during switching. Since the delay of the actual primary current with respect to the primary current reference can be reduced, stable operation can be achieved even when the output frequency becomes high, and the timing of gate blocking can be adjusted even if the magnitude of the primary current is large or small. Since the determining signal is a signal having the magnitude of the primary current reference, the dead time of switching is almost constant.

(f) Effects of the Invention As explained above, according to the AC motor control device of the present invention, the switching dead time of the forward and reverse thyristors of the anti-parallel connected converter is reduced, and the delay of the primary current with respect to the primary current reference is reduced. This enables stable operation even at high output frequencies, regardless of the magnitude of the primary current.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of a sine wave cycloconverter using anti-parallel connected converters, Fig. 2 is an output current waveform diagram when switching forward/reverse of the sine wave cycloconverter shown in Fig. 1, and Fig. 3 is a sine wave cycloconverter according to the present invention. FIGS. 4 and 5 are circuit configuration diagrams showing one embodiment of the wave cycloconverter, and are output current waveform diagrams when the sine wave cycloconverter shown in FIG. 3 is switched between forward and reverse directions. 1...3-phase AC power supply 2...Power transformer 2U/2
V-2W - Secondary winding of power transformer 3U, 3v, 3
W... Anti-parallel connection converter 4U・4■・4W・
...Shunt 5...3-phase AC motor 6...Speed detector 10...
・Speed setter 11, 14, 18U-18V-18W... Adder 12... Speed control circuit 13... Magnetic flux weakening control circuit 15... Magnetic flux control circuit 16... Vector control circuit 17U/17V・17W...Current detector 19U
・19V・19W...Current control circuit 21.24...
rheostat

Claims (1)

[Claims] In a sine wave cycloconverter in which a three-phase AC motor is connected to three sets of anti-parallel connected converters in which three-phase Graetz connected converters are connected in anti-parallel, three-phase primary current references each having a phase difference of 12,000, and the primary current The output signal of the comparison circuit that compares the signal corresponding to the reference magnitude and the primary current of the AC motor causes the primary current to be the same as the primary current.
An AC motor characterized in that when the signal becomes equal to or less than the magnitude of the next current reference, the firing signal of the thyristor is blocked and the positive side thyristor and the reverse side thyristor of the anti-parallel connected converter are switched. Control device.