Thyristor Electric Drive

an electric drive in which the operating conditions of the actuating motor or some other actuating mechanism are controlled by a converter that incorporates thyristors (seeCONVERSION TECHNOLOGY).

In AC thyristor electric drives, asynchronous or synchronous three-phase electric motors are frequently used as actuating motors. The operating conditions of such motors can be controlled by changing the frequency and amplitude of the voltage supplied to the stator; in the case of a synchronous motor, the operating conditions can also be controlled by changing the current in the field winding. When thyristor electric drives of this type are supplied with power from an AC source, a thyristor frequency converter usually functions as the control converter. Such frequency converters are built either with an AC or DC intermediate unit or in a direct-coupling design. When thyristor electric drives of this type are supplied with power from a DC source, a free-running inverter is used as the converter. In AC thyristor electric drives, the actuating motor is reversed by changing the phase-alternation sequence of the voltage supplied to the stator (seeREVERSING ELECTRIC DRIVE).

In DC thyristor electric drives, DC motors with series, shunt, compound, or separate excitation are used. The operating conditions of such motors can be controlled through either the armature-winding circuit or the field-winding circuit. In thyristor electric drives of this type that are supplied with power from an AC source, a thyristor rectifier functions as the converter. If thyristor electric drives of this type are supplied with power from a DC source, the converter consists of a pulsed DC regulator or an inverter-rectifier system with an AC intermediate unit operated at a stepped-up frequency. In DC thyristor electric drives, the actuating motor is reversed by changing the direction of the current in the armature winding or the field winding of the motor. In this case, a second converter is connected antiparallel to the first converter with respect to the circuit of the actuating motor.

A transformer is used in a thyristor electric drive for galvanic decoupling of the supply and load circuits and to match the voltage of the power supply to the operating voltage of the actuating motor. This transformer is connected to the input of the converter if the thyristor electric drive is supplied with power from an AC source, or to its intermediate unit if the power supply is a DC source. The energy flow through the converter is controlled by a manual or automatic control and regulation system. Such a system includes units that supply the power, regulate the frequency and voltage, form the control pulses for the thyristors in the power circuits of the converter, and provide protection against short-circuit currents, overloads, and overvoltages. The control and regulation systems in current use incorporate standard logic units (seeLOGIC ELEMENT) and integrated circuits, which are small, fast-operating, and reliable. Heat is removed from the thyristors and actuating motors by natural or forced air or liquid cooling.

Thyristor electric drives are used in various industries and in transportation. The power rating of thyristor electric drives, which depends on their intended use, ranges from a few kilowatts to 10 megawatts or more.