Field Oriented Control of Induction Motors

Induction motors have always been known for their simple rugged construction, but until lately were not suitable for variable speed or servo drives due to the inherent complexity of the controls. With the advent of field oriented control (FOC), however, the induction motor has become an attractive option for these types of drive systems. At NASA Lewis Research Center, we are currently working with an FOC system which utilizes the pulse population modulation method to synthesize the motor drive frequencies. This system allows for a variable voltage to frequency ratio and enables the user to have independent control of both the speed and torque of an induction motor. A second generation of the control boards have been developed and tested at NASA with the next point of focus being the minimization of the size and complexity of these controls. Many options have been considered with the best approach being the use of a Digital Signal Processor (DSP) due to its inherent ability to quickly evaluate control algorithms. This paper will discuss the present test results of the system and the status of the optimization process using a DSP.