SU520683A1 - Device for controlling three-phase asynchronous electric motor - Google Patents

Description

(54) DEVICE FOR MANAGING THREE-PHASE

An ASYNCHRONOUS MOTOR element and a parrot resistor of the indicated element, while the control transition of the thyristor is connected to the control unit, to the input of which is fed back slip on the slide. FIG. Figures 1 and 2 show two variants of the proposed mustache (images; Fig. 3 is a vector diagram 1a of an asynchronous motor circuit, built on the first harmonics of voltage and current; Fig. 4 is an control circuit diagram. Asynchronous motor 1 is fed power supply phase, and the third phase of the motor through a phase-shifted capacitor 2 and damping resistor 3 is connected to one of two network terminals depending on the given direction of rotation of the mechanism. The damping resistor 3 is asth or completely determined when p counting the parameters of the phase-shifting device, is shunted by one semiconductor gate (thyristor) 4 controlled, for example, by a semiconductor pulse generator 5. The generator 5 operates in the standby mode, and is started up by node 6 in combination with a sinusoidal voltage source 7. Relay the mode of operation of the system as a whole is provided by a semiconductor relay 8 and an adjustable return coefficient (R,). At the input of the relay element, two signals are compared: the driving voltage (U-) removed from the sensor soon 9, and the feedback voltage (and wasp) taken from potentiometer 10 or takhomashina 11 (Fig. 2). The feedback signal (in Fig. 1), taken out of the output e: a common magnetic amplifier 12, is determined by the system voltage variables: on the phase-shifting capacitance 2, to which the transformer 13 is connected, top 15) and current in the main phase of the engine. A signal, proportional to this current, through l lp, p 16, feed i to the winding P. The control windings 14 and 17 are turned on so that their magnetizing forces are directed oppositely. The bias winding is used to form the desired output characteristic of the magnetic amplifier during circuit tuning. The engine is started as follows. When the phases are connected to the mains supply, the voltage is applied to the third phase via a phase-decoupling capacitor 2. The level of this voltage subsequently changes depending on the slip of the motor. The effect of the signal, which is proportional to this voltage, is especially manifested with a sliding slip, when the stress increases approximately 1.5-2 times. The signal from the current feedback is maximum in the region of large slip, the main phase A flowing the largest current of the motor. Therefore, at the first moment of launch at the input of a magnetic amplifier, an approximate value of us spinning forces takes place. Therefore, magnetically magnify;). 12 is locked, and the signal and its output, i.e., the signal UQ is minimal. This signal. And in the circuit with tachomasch is zero- Ecjm I set-; CRS signal -UBX is absent, then a negative voltage is applied to the base of the transistor 18 (Fig. 4) of the relay element, it is opened; and the starting transistor 19 is blocked by the bias voltage, the capacitor 20 is charged, which subsequently provides the shift of the trigger pulse in the direction of his-; stavashsh compared with the voltage of phase C on the threshold). The pulse generator 5 does not work, the thyristor 4 is locked, the resistor 3 is turned on completely, which aggravates the start of the motor due to the current limiting in the capacitor phase. For a normal start-up of the motor to the desired speed, the generator 9 applies a positive voltage difference (11, to the base of the transistor 18 of the relay element, the latter is closed, which causes the switching of the relay element 8. As a result of this switching to the base of the start-: the turning transistor 19 is given a signal compensating bias voltage. Thus by sensing a sinusoidal voltage of a sinusoidal pulse generator 7, the triggering transistor 19 generates triggering pulses differentiable by a capacitor 21 supplied to the input of the pulse generator 5. At the same time, the transistor 22 is unlocked and the capacitor 20 discharges, which prevents the transistor 23 from closing quickly. This provides a temporary change in the pulse shear angle of the pulse generator relative to the phases of the motor. The thyristor 4, by opening, shunts the damping 1) resistor 3, ensuring at the same time a smooth variation of the voltage (current) in the capacitor phase of the engine from the minimum to its maximum value. Starting engine 1, having a short-circuit resistance H, occurs at the maximum .. ". the most equivalent capacitance of the phase-shifting element b. . Providing the estimated starting torque of the engine (Fig. 3). As the speed of rotation of the rotor increases, the regulating speed increases. with. biasing the magnetic amplifier 12 (or the voltage at the terminals of the tachomachine 11), causing it to increase. Now the signal at the input of the relay element 8 U, determined by the difference Ug.jj - UQ,, decreases, i As soon as you reach; {and this difference tells us the insensitivity of the relay element Ci, - UQj, AU5iO), it overturns, and the thyristor 4 closes , enters the resistor 3 into the capacitor phase of the motor. This ensures the redistribution of the voltage between the resistor 3 and the condensate rum 2, thereby realizing a gradual decrease in its level per phase, the motor winding. In this state of the circuit, the further increase in engine speed is stopped. Reducing the speed leads to an increase of 5i5 yarns at the input of the relay element and to unlocking the taristor 4. Later, this process repeats and, as the set speed is reached, it switches to the auto-oscillatory mode. A stable on and off mode of the resistor 3 is set, thereby maintaining the required capacitance phase capacitance and the set speed of the motor. i With a change in the setpoint of the engine installed soon (AND „v) or its load on, -,,,. At a given speed, the switching frequency of the shunting 1 thyristor 4 is changed, IITO leads to a decrease or increase in the equivalent capacitance of the phase-shifting element and thereby contributes to the maintenance of the balanced mode of the engine. The diagrams of FIG. 1 the following equilibrium voltages and currents are valid:

them

,

A b

to.

j The solution of these equations with respect to the currents, taking into account their direct (1) and reverse (1 sequences and subsequently joint solution of these currents, allows to obtain the dependence of the vector of the complex phase-shifting element:

one

),

TO

one;

Lt

18

one"

 The selected resistance is calculated on the equivalent phase current of the motor.

The average speed on the section of the on and off state of the cell electromotor is determined as follows:

sixteen

., (JU, tt) Jdt,

t,

I The damping resistance is adjusted to the engine at operating speed; V2r Xj.CaS - 1 e fr - 1 iP, p is the module of the motor impedance for the working slip, SS; p-, the shear angle between the current and the voltage at the working slip .v Thus, about the known starting capacity of the available equivalent working capacity Phasic device is determined by damping; resistance R p. Its value is taken into account, taking into account the switching frequency K VF .. 1 p - - «sp; - frequency of shunt thyristor inclusions,

Where

the engine impedance complex of a straight sequence at a given slip;

i JT turning vector.

The graphic interpretation of the complex coefficient for the vector b is illustrated in FIG. 3 in the third quadrant, and the impedance in the fourth. From the vector diagram of FIG. 3 it follows that the automatic regulation of the equivalent capacitance is coupled with the simultaneous compensation of the required reactive power for the cpc asynchronous in the scheme under consideration: 1 Engine.

The calculation of the phase-dropping element is carried out on two conditions: starting and working.

The choice of phase-shifting capacity according to the conditions; start is as follows:

)

. B.

the full impedance of the phase-shifting element during the engine start;

- engine impedance module

sk at S - 1;

H

angle of shear between current and voltage

SI, engine.

 where is the corresponding time of switching on and disconnecting of the resistance of thyristors; lnipU uUjCO - change of speed during start-up and deceleration of the engine;

uUj - (l - the value of the speeds at which the thyristor is unlocked and locked.

 use the equation

 runway water

,,,.,. dour MM to Ji for the retardation section

dujs "i-M, J

c - dt

where M, M is the electromagnetic moment of the engine i and the moment of resistance of the mechanism.

be

: M "M,

  Respectively, the nominal power supply of the engine and its components are direct and bypass the sequence), then the average speed with sufficient accuracy for practice will be:

Uj I 12 W -

 t. g t.

sh

G -

- “- t.

and the accuracy of the mechanical characteristics of AMD-y ai., x where y is the coefficient of speed; „JT

where and is the phase voltage of the engine when it is about O j in relative units; i I

B is the moment of inertia of the systeriol electric drive ;;

Mts is the motor boundary moment developed in the natural / switching circuit and nominal power feed rate.

The analysis of the obtained basic relations shows that increasing the steady-state speed to a speed close to the engine idling speed, or unloading the engine at a given speed at a given speed leads to a decrease in the switching frequency of the damping resistor, which is the same to a decrease in the equivalent capacitance of the phase-shifting element. With the reverse change of these variables, the frequency increases, it means that the equivalent capacitive conpo-j volume increases and the circuit automatically adjusts itself.

eight :

520683 К ,, - non-uniformity coefficient in a fast way the engine to the mode close to the balanced one.

Claims (1)

Invention Formula A device for controlling a three-phase asynchronous electric motor connected to a single-phase one, containing an active-capacitive element in the free phase of the motor and a thyristor, is because the thyristor is connected in series with the phase-shifting capacitor aTHTH to ensure a balanced operation of the electric motor against its sliding. -eMKOcTHoiY element and parallel to the resistor of the specified element, wherein the control transition of the thyristor is connected to the control unit, to the input of which # 1 is given a feedback signal on splitting zheniyu. 1h-K 1-k with negative feedback i (MH-MC) C -ui-ji --- rj-sf MjjMgT (.) Ll-0,2L5Ci-U) .. Mg Frequency of self-oscillations will depend on a constant time relay -phase control unit j 0. device.- T: I A f jf ti // g Ua x % .