The Essential Components of An Electric Drive

Power electronics deals with the applications of solid-state electronics for the control and conversion of electric power. The conversion techniques require switching power semiconductor devices ON and OFF.

The block diagram below shows the essential components of an electric drive controlled by a power semiconductor converter.

The converter regulates the flow of power from the source to the motor in such a way that the motor speed-torque and speed-current characteristics become compatible with the load requirements.

The low-voltage control unit, which may consists of integrated transistorized circuits or a microprocessor, is electrically isolated from the converter-motor circuit and controls the converter.

The sensing unit, which is required for closed-loop operation or protection or both, is used to sense the power circuit’s electrical parameters such as converter current, voltage and motor speed.

The command signal forms an input to the control unit, adjusting the operating point of the drive.

The motors commonly used in variable-speed drives are Induction motors, DC motors, and Synchronous motors. A variable speed drive can use a single converter or more than one. All converters have harmonics in their inputs and outputs. You might find some converters with a problem of poor factor especially at low output voltages.

Related: Key Facts about Thyristor DC Motor Drives Operation

The main merits of converters are:

• High efficiency
• Fast response
• Reliability
• Flexibility of control
• Easy to maintain them
• Low weight and volume
• Have less noise and long life

Generally the drive specifications are determined by the load requirements, which in turn depend on normal running needs, transient operational needs and requirements related to the location and environment. Other specifications depend on the available source and its capacity, as well as other aspects like harmonics, power factor, reactive power, regenerated power and peak current.