A variable frequency drive is actually a speed manage system used for regulating the speed of an alternating present 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 significant buildings, conveyors, pumps, elevator, machine tool drives, and so on.
An alternating present induction motor draws as much as 6 times 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 start the induction motor, a low frequency along with a low voltage are applied to the motor. Normally, the start-up frequency is two Hz or less. As the frequency is low, the present flow at the time of starting will also be low. When the motor is started utilizing the variable frequency drive, the applied voltage and frequency are elevated at a controlled rate to make sure that the motor does not draw excessive present. This method of starting enables the motor to as significantly as 150% of its rated torque at much less than 50% of its rated current consumption.
The variable frequency drive method consists of an AC motor, a controller and an operator interface. A controller is a solid state electronic energy conversion device. AC input energy is converted to DC intermediate power making use of a three-phase bridge rectifier technique. The DC power is then converted to quasi-sinusoidal AC energy 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 the most important benefit of employing variable frequency drives. For instance, AC motors employed in ventilation systems are not needed to usually run at peak load. Variable frequency drives save energy 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 costs will also be lower. Whilst conventional starters start off 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 better procedure control. This really is because variable frequency drives can be programmed to run the motor in the necessary load, cease as per requirement and apply a specified amount of torque.
You’ll find 3 types of variable frequency drives. These are continuous voltage, constant existing and cycloconverters. Essentially the most critical section of a variable frequency drive is the inverter circuit. These units support increase power factor and lessen harmonic distortion.