Building Variable Frequency Drives for Fun and Profit
A variable frequency drive can be a speed control technique used for regulating the speed of an alternating present electric motor. The speed regulation is effected by varying the frequency of the electrical power supplied to the motor. Variable frequency drives uncover wide application in ventilation systems for large buildings, conveyors, pumps, elevator, machine tool drives, and so on.
An alternating current induction motor draws up to 6 occasions its rated present at the time of start off up. The present continues to stay high till the motor approaches the full speed. When a variable frequency drive is employed to start the induction motor, a low frequency plus a low voltage are applied to the motor. Normally, the start-up frequency is 2 Hz or less. As the frequency is low, the present flow in the time of starting will also be low. Once the motor is started utilizing the variable frequency drive, the applied voltage and frequency are elevated at a controlled rate to ensure that the motor does not draw excessive existing. This strategy of starting enables the motor to as much 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 actually a solid state electronic power conversion device. AC input energy is converted to DC intermediate power making use of a three-phase bridge rectifier method. The DC energy is then converted to quasi-sinusoidal AC power employing an inverter switching circuit.
The benefits of a variable frequency drive are the following:
Saving in electrical energy consumption is by far probably the most critical benefit of utilizing variable frequency drives. As an example, AC motors used 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 employing a variable frequency drive will last longer. The maintenance expenses will also be lower. While traditional starters begin the motors abruptly, variable frequency drives gradually increase the speed to operating speed. This contributes to a reduction mechanical and electrical pressure on the motor.
A variable frequency drive enables better procedure control. This is because variable frequency drives might be programmed to run the motor at the required load, cease as per requirement and apply a specified amount of torque.
You will find three kinds of variable frequency drives. These are continuous voltage, continuous present and cycloconverters. The most essential section of a variable frequency drive could be the inverter circuit. These units aid improve energy factor and decrease harmonic distortion.