Building Variable Frequency Drives for Fun and Profit

A variable frequency drive is actually a speed manage system utilised for regulating the speed of an alternating present electric motor. The speed regulation is effected by varying the frequency of the electrical power supplied towards the motor. Variable frequency drives discover wide application in ventilation systems for huge buildings, conveyors, pumps, elevator, machine tool drives, etc.

An alternating present induction motor draws up to 6 occasions its rated current in the time of start up. The existing continues to remain high till the motor approaches the full speed. When a variable frequency drive is employed to begin the induction motor, a low frequency plus a low voltage are applied towards the motor. Normally, the start-up frequency is 2 Hz or less. As the frequency is low, the existing flow at the time of beginning will also be low. When the motor is started using the variable frequency drive, the applied voltage and frequency are elevated at a controlled rate to ensure that the motor does not draw excessive present. This approach of starting enables the motor to as significantly as 150% of its rated torque at much less than 50% of its rated existing consumption.

The variable frequency drive technique consists of an AC motor, a controller and an operator interface. A controller is really a solid state electronic power conversion device. AC input energy is converted to DC intermediate power employing a three-phase bridge rectifier system. The DC power is then converted to quasi-sinusoidal AC power making use of an inverter switching circuit.

The rewards of a variable frequency drive are the following:

Saving in electrical energy consumption is by far the most important benefit of utilizing variable frequency drives. For instance, AC motors used in ventilation systems are not required to constantly run at peak load. Variable frequency drives save power by controlling the volume of air required for a specific technique demand.

An induction motor using a variable frequency drive will last longer. The maintenance expenses will also be lower. Whilst classic starters begin the motors abruptly, variable frequency drives gradually improve the speed to operating speed. This contributes to a reduction mechanical and electrical anxiety on the motor.

A variable frequency drive enables far better procedure manage. This is simply because variable frequency drives could be programmed to run the motor at the necessary load, stop as per requirement and apply a specified quantity of torque.

You’ll find three varieties of variable frequency drives. These are constant voltage, continuous current and cycloconverters. Essentially the most crucial section of a variable frequency drive could be the inverter circuit. These units assist boost energy factor and decrease harmonic distortion.