Field-oriented control of an induction motor using random pulse width modulation

The principle of field-oriented control (FOC) is a well-established means to obtain a high-performance drive, but the de facto standard FOC does not solve an important secondary problem for inverter-fed motors: the acoustic noise emitted from the motor is tonal due to the constant switching frequency operation. This may be very annoying, even if the exposure time is short. On this background, this paper proposes a classic FOC synchronized to a current-controlled PWM inverter operating with a random switching frequency. This implies that the sampling frequency of both the current controller and the flux estimator is nonuniform, but nevertheless, it is shown that the good dynamic response inherited from the FOC can be maintained while lowering the subjective acoustic annoyance to a great extent due to the random switching frequency operation. Besides laboratory test results documenting the dynamic and steady-state characteristics of the proposed system, design considerations are presented.