Energy efficiency optimization of induction motors

Abstract

The high cost of energy, its ever-increasing consumption and the vital need to curb harmful energy related effects on the environment are strong incentives to reduce the energy losses and improve the operating efficiency of electric motor drive systems. Further more, reduced losses not only reduce operating cost but also reduce capital cost of utility systems supplying electric power to their consumers. Induction motors are dominant loads, they account for about 60 % of the electricity consumed, for this reason, it is important to concentrate on optimizing the efficiency of induction motors, in particular small and medium size motors below 52 kW, whose load are Heating, Ventilation and Air Conditioning (HVAC) application. In this work, two energy efficiency optimization techniques that minimize the total copper and core losses in a variable speed induction motor are studied and compared. The power factor efficiency optimizer is based on the calculation of induction motor displacement power factor from its complete per-phase equivalent circuit, and which leads to a maximum operating efficiency when it is kept constant throughout the range of speed variation. The model-based control technique, on the other hand, is based on induction motor loss model built in a d-q reference frame, where the optimization problem is solved by achieving a balance between the d- and q- loss components throughout the range of speed variation. Results are showing that the two control techniques for the induction motors population studied indicate an overall comparable level of performance for both controllers. Achievable efficiency improvement at partial loads can reach 18 %