Motor Control Techniques: VFDs, ECMs, and More, Part 1
An in-depth look at induction motors with voltage/frequency controlled variable frequency drives, induction motors with vector-controlled VFDs, and electronically commutated motors.
The topic of motors and motor control techniques is wide and varied. Part one of this two-part article will cover the principles of alternating-current (AC) motor operation and control. Part two will cover design considerations for AC motors with variable speed drives and electronically communicated variable-speed direct-current (DC) motors (ECMs), followed by a comparison table of suggested advantages and disadvantages and design considerations for each type, and concluded with a case study comparing the use of AC motors with variable speed drives (VSDs) with ECMs.
The most common type of motor used in HVAC fan and pump applications is the three-phase AC induction motor (IM). DC motors also have applications in the building and HVAC systems — in particular, many elevator designs employ DC motors. Compared to DC motors, AC motors are simpler in design, are more rugged, and have a longer life under normal operating conditions.