A variable frequency drive is really a speed manage program employed for regulating the speed of an alternating current electric motor. The speed regulation is effected by varying the frequency of the electrical energy supplied towards the motor. Variable frequency drives discover wide application in ventilation systems for large buildings, conveyors, pumps, elevator, machine tool drives, et cetera.
An alternating current induction motor draws as much as 6 occasions its rated existing in 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 start the induction motor, a low frequency plus a low voltage are applied to the motor. Typically, the start-up frequency is two Hz or much less. When the frequency is low, the current flow in the time of beginning will also be low. As soon as the motor is began using the variable frequency drive, the applied voltage and frequency are elevated at a controlled rate to make sure that the motor will not draw excessive present. This approach of beginning enables the motor to as considerably as 150% of its rated torque at much less than 50% of its rated existing consumption.
The variable frequency drive system consists of an AC motor, a controller and an operator interface. A controller is actually 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 advantages of a variable frequency drive are the following:
~ Saving in electrical energy consumption is by far essentially the most important benefit of utilizing variable frequency drives. For instance, AC motors utilized in ventilation systems are not required to often run at peak load. Variable frequency drives save power by controlling the volume of air required for a particular method demand.
~An induction motor employing a variable frequency drive will last longer. The upkeep expenses will also be lower. Although classic starters start off 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 far better approach manage. This really is since variable frequency drives might be programmed to run the motor at the necessary load, quit as per requirement and apply a specified quantity of torque.
You will find three sorts of variable frequency drives. These are continuous voltage, constant current and cycloconverters. One of the most crucial section of a variable frequency drive may be the inverter circuit. These units aid increase power element and minimize harmonic distortion.
