Loss minimization control of an induction motor drive

A practical method for operating an inverter-fed induction motor drive at the point of maximum efficiency while maintaining any particular torque-speed load point is presented. The design and operation of an economical, microprocessor-based adaptive controller used to modify a commercially available six-step inverter for minimum loss operation of an induction motor are described. Experimental results are presented in graphical form, giving comparison of overall drive system efficiencies between loss minimization control and constant volts/hertz control operation for a standard-efficiency induction motor with a 10 hp rating. The greatest potential for energy savings is found to exist for the case of loads with nonlinear torque-speed characteristics, such as a fan or pump load