The variable speed drive is an electro-mechanical piece of machinery whose function is to regulate the speed and torque output of the specific electric motor it is attached to. There are three basic configurations for variable speed drives in use today.
- PWM design. This variable speed drive design has a working range between ½ and 500 horsepower. This is one the most popular types of variable speed drives as it has high reliability, affordability and environmentally safe. In this design, the AC line is connected to the input section and into the converter section. The converter section utilizes a diode bridge converter that creates a stable DC voltage output. The resulting DC output is nearly wave like.
- CSI design. This variable speed drive design allows the incoming AC power to be converter to DC voltage via a converter section which produces a variable DC bus voltage. This configuration is limited in reliability but has the power to regenerate power due to variable DC output.
- VSI design. This variable speed drive design is similar to the CSI configuration due to the use of SCR converters in regulating DC output voltage. In this design, the VSI utilizes transistors as well as thyristors that create adjustable frequency output to the connected motor. This configuration works best with multiple motor operations as the operation is not dependent on the load.
- Flux Vector PWM design. This is the newest design as it utilizes smart 32 bit microprocessors in its power switching function. Instead, the drive uses a closed loop control mechanism from the motor direct to the microprocessor. This is considered as the most efficient of all the variable speed drives but is the most expensive.
There are many options for a variable speed drive and opting for one can only help in increasing efficiency in both the work process and energy consumption.