Intelligent Motor Controls

All you could want to know

First, a definition

A motor controller is a device or group of devices that serves to govern (in some predetermined manner) the performance of an electric motor.

It might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, changing and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.

Applications

of Motor Controls

(AC Induction Motors)

Every electric motor should have some sort of intelligent control. The motor controller will have differing features and complexity depending on the task that the motor will be performing.

 Typically, if the speed of the motor can afford to be reduced, a VSD or VFD (Variable Speed or Frequency Drive) will provide energy and operational savings in several ways. It will provide the motor with a PLC-controlled Soft Start and reduce inrush current.

This means that rather than the motor starting Direct-On-Line (DOL) and causing the motor to draw a very high current upon start-up, it gradually increases the voltage supply to the motor (and applied torque by the motor) in a manner which gently ramps up the current draw as the speed of the motor increases until it reaches the rated speed (RPM) or the pre-set speed and the required voltage is met. 

The main benefit to this feature is to increase the longevity of the motor and prevent costly unscheduled downtime and maintenance.

 

Most electric utilities will not charge their client for current spikes since their impact on the kW demand and electrical grid is negligible. Another way in which a VFD can provide savings is by reducing the speed of the motor if little to no-load condition is met. In doing this, the VFD effectively reduces the size of the motor to dynamically satisfy the required load resulting in significant Demand (kW), Energy (kWh), Power Factor, and operational savings.

 VFDs can also facilitate overload and overcurrent protection by providing the option to limit the operating current of the motor. If a motor is overloaded for an extended period of time, the drive has the ability to interrupt the current to the motor and thus preventing a mechanical breakdown, acting similar to an overload contactor. 

PLC based Motor Controllers can be manually, remotely or automatically operated. They may include the means for starting and stopping the motor or they may include other functions such as Signal Optimization for constant speed applications. In this process, the controller is married to Thyristors which instantaneously chop the Amplitude of the AC Voltage Sine Wave resulting in the optimization of kW, kVAR-L, and KVA components of Power, improve Power Factor, and thus lower electricity and operating costs.