RU2014721C1 - Process of phase control over asynchronous motor with thyristor voltage regulator - Google Patents

Abstract

FIELD: electric motor drives. SUBSTANCE: salient feature of invention lies in control over angles of switching on and off of thyristors of fully controlled thyristor keys as function of ctgφ between current and voltage of stator of asynchronous motor. Positive signal of feedback proportional to ctgφ acts on switching-on angle and negative one - on switching-off angle so that stabilization of power factor, of asynchronous motor and its compensation both under motor and generator braking mode are provided. Most advantageous field of application of proposed process is asynchronous drive of vehicles of freight and passenger transport of continuous action working in lifting and lowering of freights under conditions of periodically changing load. EFFECT: improved operational characteristics and reliability. 3 dwg

Description

 The invention relates to an automated AC electric drive with a thyristor voltage regulator, and in particular to automatic voltage regulation of asynchronous motors operating under conditions of periodically changing load, and can be used in the electric drive of continuous passenger and freight transport mechanisms (metro escalators, conveyors, cable cars, etc. .) to save electricity.

 There are a number of methods for regulating the voltage of an induction motor, providing rational energy consumption. They all boil down to the direct or indirect identification of one of the five parameters of an induction motor (speed, slip, power factor, efficiency of the coefficient of static overload) and the construction of a stabilization system for this parameter to maintain high values of power factors and the efficiency of the induction motor with a deep change in load.

 However, regardless of which parameter the voltage of the motor is regulated, the efficiency of electric power consumption in the motor mode and the energy generation efficiency in the braking modes of the asynchronous machine is determined primarily by the method of phase regulation of AC voltage.

 A known method of regulating an alternating voltage, made in the form of two counter-parallel connected thyristors included in each phase of the stator winding of an induction motor and a device for implementing a method for controlling the turning angle of thyristors, for example, as a function of motor speed or as a function of motor power factor.

 The disadvantage of this method is that when controlling the motor operation modes of an asynchronous machine, voltage regulation is carried out with a lagging phase shift of the first harmonic relative to the mains voltage, and in generator braking mode with a leading shift of the first harmonic, which reduces the power factor of the network in both motor and in generator modes of operation of an asynchronous electric drive.

 For the prototype, a method was chosen for regulating the voltage with the inclusion angle α and the rotation angle β of thyristors of fully controlled thyristor switches with two-sided conductivity, at which the switching angles of the thyristors are related by the expression β = π - α.

 With this method, it is possible to control the supply voltage of an induction motor without shifting the first harmonic with respect to the mains voltage during stabilization of the angle φ of the motor with positive and negative slip, using, for example, a control system with indirect measurement of slip through the current and voltage of the stator.

 As a result, the thyristor switch does not degrade the cos φ of the network. However, it does not improve it, since with this method of regulation compensation of the reactive power of the network is not achieved.

 The purpose of the invention is to improve the power factor of the network.

The essence of the invention lies in the fact that the relationship between the angles of turning on α and turning off β of the thyristors of the controller, interconnected by the expression β = π - α, is set in the idle speed of the engine, in which the angles and α = α _o , β = β _o and α _o <β are fixed so that the engine speed is maintained at its nominal value, and in the motor mode it is carried out by changing the angle α in the range from "+" α _o to "-" β, and in the generator braking mode by changing the angle β in the range from β _o to π + α _o , while the angle α is changed in accordance with the mismatch of signals proportional to ctg φ and _ctg φ _n1 , and the change in angle β in accordance with the mismatch of negative signals proportional to ctg φ and _ctg φ _n2 , where φ, φ _н1 and φ _н2, respectively, the current value of the angle between the current and voltage of the winding stator and its values with positive and negative nominal slip of the motor.

In FIG. 1 shows a diagram of one of the possible devices that implement the proposed method; in FIG. 2 and 3 are time diagrams of two variants of the method for α _o <π / 2 and α _o > π / 2 radians, which illustrate the principle of the method when the asynchronous machine operates in motor mode, respectively (Fig. 2a and 3a), in reactive mode power (Fig. 2b and 3b) and in the generator braking mode (Fig. 2c and 3c).

 The device consists of a three-phase thyristor switch 1, made on three single-phase fully controlled thyristor switches with two-sided conductivity, a system of pulse-phase thyristor control, consisting of the first and second blocks 2 and 3, respectively forming pulses with an angle of on α and off angle β of the thyristors completely controlled thyristor keys, two comparison elements 4 and 5, first and second diodes 6 and 7, two single-phase current transformers 8 and 9, sensor 10 cotangent of the angle between current and voltage asynchronous motor 11.

 For the implementation of the first variant of the method in the diagram (Fig. 1), the connections between the comparison elements 4 and 5 and the control units 2 and 3 are shown by solid lines, and for the second variant, by dashed lines.

 The principle of the method is as follows.

In the mode of consumption of reactive power by the asynchronous motor 11 (Fig. 2b and 3b), the switching angles are related by the expression β = π - α and, respectively, are equal to α = α _o and β = β _o , at which the minimum voltage close to zero is applied to the motor 11, in order to minimize reactive power. This mode occurs when the asynchronous machine switches from idle to generator braking, when mechanical energy W _{о is} supplied to the shaft of the engine 11. This energy maintains the rotation of the machine at a speed close to the ideal idle speed even at minimum voltage, and creates the opportunity to reduce to a minimum the reactive power consumed from the network.

The change of mechanical energy on the shaft of the engine 11 in the direction of decreasing (increasing) from the value of W _about transfers the machine to the motor of FIG. 2a, FIG. 3a (generator FIGS. 2c and 3c), the mode in which the signal from the feedback sensor 10, which is proportional to the cotangent of the angle φ between the current and voltage of the motor 11 from a value equal to zero (φ = π / 2), increases and has a positive (negative) sign, since φ <π / 2 (φ> π / 2). The signal from the feedback sensor 10 with a positive (negative) sign and proportional to ctg φ is compared on element 4 (element 5) of comparison with a given value _ctg φ _н1 ( _ctg φ _н2 ), which correspond to the ratio of active power to reactive at nominal positive (negative) slip of the machine, and the resulting signal proportional to the difference ctg φ- _ctg φ _n1 ( _ctg φ- _ctg φ _n2 ), in the first version of the method is fed to block 2 (block 3) of the control system of the angle α (angle β) β of fully controlled thyristor thyristors bite 1-phase switch it.

 The detection of a positive (negative) feedback signal and its effect on the turn-on angle α (turn-off angle β) of the thyristors can be carried out, for example, using diode 6 (diode 7), turned on in the forward (reverse) direction, as shown in FIG. 1.

 In the second embodiment of the proposed method in the process of voltage regulation (see Fig. 3), the switching angles α and β change roles. In the diagram (Fig. 1) this is shown by dashed lines.

With this control, the amplitude of the current of the motor with a constant phase φ _n1 in the motor (φ _n2 in the generator) mode of the machine is regulated, forming the stator current vector tangentially to the family of pie diagrams, as well as compensating the reactive power of the network due to the lead (lag) of the first harmonic the supply voltage of the induction motor relative to the mains voltage and, accordingly, decrease (increase) in this case, the angle φ ¹ between the current and the mains voltage in the motor (generator) mode, bringing it closer to 0 radians (to π radians). The result is the stabilization of the power factor of the induction motor and its compensation during operation of the drive to lift and lower the load.

The first and second variants of the method require adjustment of the drive, namely: setting the angles α = α _o and β = β _o (see Fig. 2b and 3b), controlling, for example, zero the signal taken from the feedback sensor 10, the consumption mode reactive power. This can be done under operating conditions of the drive when, for example, escalators are used to lower passengers, and mountain conveyors-bramsbergs to lower rocks or in bench conditions with an additional racing engine, which complicates setup.

 To simplify the adjustment of the drive control system while providing the device with a high value of the network power factor, another variant of the method is proposed in which the connection between the switching angles should be established when the device operates on an engine disconnected from the mechanism, since the engine is idle at 20 -40%.

 When implementing the method, a signal proportional to ctg φ is used as a feedback signal. This is not the only solution. As a feedback signal, a signal proportional to slip, power factor, etc. can be used, which when the machine switches from the motor mode to the generator braking mode changes its sign to the opposite and does not have an intermittent character.

 The use in the inventive method of feedback actually on ctg φ is preferable because of the simplification of implementation and increase the accuracy of regulation.

 The application of the invention is most appropriate for asynchronous electric drives of continuous transport vehicles operating both on lifting and lowering the load under conditions of periodically changing load.

Claims (1)

METHOD FOR PHASE CONTROL OF AN ASYNCHRONOUS ENGINE WITH A THYRISTOR VOLTAGE REGULATOR, in which the angle of turn-on α and the turn-off angle β of the thyristors of the controller are interconnected by the expression β = π-α, characterized in that, in order to increase the power factor of the network, the connection between the angles α and β are set in the engine idle mode, in which the angles α = α ₀ ; β = β ₀ ; α ₀ <β _{0 is} fixed so that the engine speed is maintained at its nominal value, and in the motor mode it is carried out by changing the angle α in the range from "+" α ₀ to "-" β ₀ and in the generator braking mode by changing the angle β in the range from β ₀ to π + α ₀ , while the change in the angle α is made in accordance with the mismatch of signals proportional to ctgφ and ctg φ _n1 , and the change in the angle β is made in accordance with the mismatch of signals proportional to ctgφ and ctgφ _n2, where φ, φ _n1 and φ _n2 are, respectively, the current value of the angle between current and voltage we have stator windings and its values with positive and negative nominal slip of the motor.

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