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

The paper contains an analysis of how the choice of energy optimal control of induction motors is influenced by motor construction, standard vs. high efficiency motors and by application, constant torque (CT) and 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. Energy optimal control strategies are reviewed and cos (/spl phi/) control, a model-based control and a search control are implemented in the laboratory in a vector and a scalar 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 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 (/spl phi/) control for HVAC applications.