On the energy optimized control of standard and high-efficiency induction motors in CT and HVAC applications

This paper contains an analysis of how the choice of energy optimal control of induction motors is influenced by motor construction, standard versus high-efficiency motor, and by application, constant torque (CT) and heating, ventilation, and air conditioning (HVAC) (interpreted as vector and scalar motor drives). The analysis is made with a 2.2 kW voltage-source-inverter-fed squirrel-cage motor drive as an example throughout the paper, but through statistics on the use of motors and their efficiencies, the conclusions are widened to a broader range (0-50 kW). Energy optimal control strategies are reviewed and cos(ϑ) control, a model-based control, and a search control are implemented in the laboratory in a vector and a scalar motor drive. The convergence speed for the strategies and their ability to reject disturbances are investigated by experiments. It is also shown experimentally that, for both standard and high-efficiency motors, motor energy-efficiency improvement is achievable by energy optimal control below 60% load torque. The energy savings using energy optimal control strategies are measured on a pump system with a certain load cycle. Model-based control is recommended for CT applications and cos(ϑ) control for HVAC applications