RU2418356C1 - Electric drive with three-phase asynchronous motor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: electric drive includes three-phase rectifier bridge to which ends of stator windings of asynchronous motor are connected. Polar outputs of rectifier bridge are connected through transistors to neutral wire of supply voltage. Connection points of stator windings to the bridge are also connected to neutral wire through RC-chains.

EFFECT: decrease of voltage on switches and switching overvoltages occurring during the operation; providing possibility of implementing dynamic braking mode.

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Description

The invention relates to electrical engineering, which is used in an asynchronous electric drive.

It is known that the direct start of an induction motor (HELL) is accompanied by an inrush current in the stator windings, which is many times higher than the nominal value. This creates significant difficulties in the operation of blood pressure. The easiest way to implement the current limitation involves limiting the rate of rise of voltage of the stator windings during acceleration of the motor (see Petrov L.P. Control of starting and braking of asynchronous motors. M: Energoatomizdat, 1981). Despite the decrease in the electromagnetic moment and the speed of the drive, this method satisfies the requirements of mechanisms having a fan mechanical characteristic with a small starting torque. Implementation of soft start is most often carried out using a thyristor voltage regulator, performed on three (in terms of the number of phases of the supply voltage) pairs of in-parallel connected thyristors. The disadvantage of this solution is that during phase control the level of higher harmonics is high, and the thyristor turns off naturally.

A technical solution is known (see A.S. 817677 (USSR). Switching voltage stabilizer. / Autobiography: M.E. Kutsko, V.N. Gruzdev, O.A. Tomigas. - Published in BI, 1981 , No. 12), in which it is proposed to partition the primary winding and control each individually. The disadvantage of this solution is the difficulty of manufacturing such a winding and an increase in the number of transistors.

A technical solution is known (see patent 2294592 (RU). A device for smooth starting of an asynchronous motor. / Auto-image: DS Sidorov, SN Sidorov. - Published on February 27, 2007), which proposes to introduce into the circuit three-phase booster transformer, which is controlled by a special electronic circuit. The disadvantage of this technical solution is the introduction of a transformer, a diode bridge and an additional transistor into the circuit, which significantly complicates the circuit.

The closest technical solution is a circuit in which a three-phase diode bridge is connected in series with the motor windings, the polar outputs of which are closed by a transistor operating in pulse-width mode (PWM). This transistor closes the DC circuit at the output of a three-phase bridge (see. Shuvaev Yu.N., Vilenkin A.G. Switching voltage stabilizer. - Semiconductor devices in the telecommunication technique. / Ed. By I.F. Nikolayevsky. - M .: Communication , 1974, issue 13, p. 26-36). The disadvantage of this circuit is the high voltage on the key and switching overvoltage that occurs during operation.

A common feature of the prototype and the proposed solution is the presence of a three-phase bridge circuit in the power circuits, to which the terminals of the motor windings that connect the star are connected.

The technical result of the proposed device is to reduce the voltage on the transistors and switching overvoltages that occur during operation, in addition, it is possible to implement the dynamic braking mode. To this end, the regulator is proposed to be made in the form of a three-phase rectifier bridge, to which the ends of the stator windings of the AD connected to the star connection are connected. The polar outputs of the three-phase rectifier bridge through transistors are connected to the neutral wire of the supply voltage. The connection points of the stator windings to the three-phase rectifier bridge are also connected to the neutral wire via RC circuits.

The invention is illustrated by drawings, where figure 1 shows a diagram of an asynchronous electric drive equipped with the proposed device, figure 2 shows a diagram of the signals on transistors.

The input alternating voltage is supplied through the stator windings of the motor (1) HELL to a three-phase rectifier bridge (2), the polar outputs of which through transistors T1 and T2 operating in the PWM mode are connected to the zero wire of the supply voltage. The connection points of the stator windings to the three-phase rectifier bridge are also connected to the neutral wire through RC circuits (3). The proposed device reduces the inrush due to a smooth increase in the voltage of the stator windings according to any possible law of its change in time.

The device operates as follows. When the stator winding of the motor (1) is connected to the supply voltage at the output points of the three-phase rectifier bridge (2), a constant voltage appears, applied to two transistors (T1 and T2), which are controlled by the PWM signals U1 and U2.

When synchronous and equal in duration to the PWM signals, a soft start is performed (Fig. 2, a).

When synchronous and not equal in duration signals, dynamic braking is performed (Fig.2, b).

RC circuits (3) are used to reduce switching overvoltages.

The achieved technical and economic effect is due to the reduction of voltage on transistors and switching overvoltages that occur during operation, and also provides the possibility of implementing a dynamic braking mode.

Claims (1)

An electric drive with a three-phase asynchronous motor, comprising a three-phase rectifier bridge, to which the ends of the stator windings of the asynchronous motor are connected, characterized in that the polar outputs of the three-phase rectifier bridge through transistors are connected to the neutral wire of the supply voltage, the connection points of the stator windings to the three-phase rectifier bridge are also connected to the zero wire through the RC circuit.

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