A variable frequency drive is really a speed control system utilized for regulating the speed of an alternating current electric motor. The speed regulation is effected by varying the frequency of the electrical energy supplied to the motor. Variable frequency drives locate wide application in ventilation systems for large buildings, conveyors, pumps, elevator, machine tool drives, and so on.
An alternating present induction motor draws up to 6 times its rated current at the time of commence up. The present continues to remain high till the motor approaches the full speed. When a variable frequency drive is used to begin the induction motor, a low frequency and a low voltage are applied to the motor. Normally, the start-up frequency is 2 Hz or less. As the frequency is low, the current flow at the time of starting will also be low. As soon as the motor is started utilizing the variable frequency drive, the applied voltage and frequency are increased at a controlled rate to ensure that the motor doesn’t draw excessive present. This technique of beginning enables the motor to as significantly as 150% of its rated torque at less than 50% of its rated existing consumption.
The variable frequency drive method consists of an AC motor, a controller and an operator interface. A controller can be a solid state electronic power conversion device. AC input energy is converted to DC intermediate energy making use of a three-phase bridge rectifier method. The DC power is then converted to quasi-sinusoidal AC energy making use of an inverter switching circuit.
The benefits of a variable frequency drive are the following:
Saving in electrical power consumption is by far the most crucial benefit of using variable frequency drives. For instance, AC motors utilised in ventilation systems are not necessary to often run at peak load. Variable frequency drives save energy by controlling the volume of air required for a specific technique demand.
An induction motor utilizing a variable frequency drive will last longer. The upkeep expenses will also be lower. Whilst standard starters commence the motors abruptly, variable frequency drives gradually improve the speed to operating speed. This contributes to a reduction mechanical and electrical pressure on the motor.
A variable frequency drive enables better method manage. This really is simply because variable frequency drives might be programmed to run the motor at the required load, quit as per requirement and apply a specified amount of torque.
You will find three varieties of variable frequency drives. These are constant voltage, continuous existing and cycloconverters. Probably the most critical section of a variable frequency drive may be the inverter circuit. These units support increase power factor and lessen harmonic distortion.
