Building Variable Frequency Drives for Fun and Profit
A variable frequency drive is actually a speed control method employed for regulating the speed of an alternating existing electric motor. The speed regulation is effected by varying the frequency of the electrical power supplied towards the motor. Variable frequency drives locate wide application in ventilation systems for significant buildings, conveyors, pumps, elevator, machine tool drives, etc.
An alternating existing induction motor draws as much as 6 occasions its rated present at the time of begin up. The current 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 plus a low voltage are applied to the motor. Generally, the start-up frequency is 2 Hz or less. As the frequency is low, the present flow at the time of beginning will also be low. When the motor is started employing 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 strategy of starting enables the motor to as a lot as 150% of its rated torque at much less than 50% of its rated current consumption.
The variable frequency drive program consists of an AC motor, a controller and an operator interface. A controller is really a solid state electronic energy conversion device. AC input power is converted to DC intermediate power making use of a three-phase bridge rectifier program. The DC power is then converted to quasi-sinusoidal AC power making use of an inverter switching circuit.
The positive aspects 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. As an example, AC motors used in ventilation systems aren’t required to always run at peak load. Variable frequency drives save power by controlling the volume of air necessary for a particular technique demand.
An induction motor using a variable frequency drive will last longer. The upkeep fees will also be lower. Although classic starters begin the motors abruptly, variable frequency drives gradually boost the speed to operating speed. This contributes to a reduction mechanical and electrical anxiety on the motor.
A variable frequency drive enables greater process manage. This really is due to the fact variable frequency drives may be programmed to run the motor in the necessary load, stop as per requirement and apply a specified quantity of torque.
You’ll find three sorts of variable frequency drives. These are constant voltage, continuous existing and cycloconverters. Essentially the most important section of a variable frequency drive could be the inverter circuit. These units help improve power factor and lessen harmonic distortion.