Simple computation techniques of online boundary to achieve constant switching frequency in any general n-level VSI fed IM drive using hysteresis current controller

Abstract

This paper proposes simple online current-error boundary computation techniques for a space phasor based hysteresis current controller. The proposed hysteresis current controller is capable of constant switching frequency operation for any general n-level VSI fed Induction Motor (IM) drive. The current-error boundary varies automatically depending on the operating points as well as the speed of the IM drive extending up to the over-modulation region. Theoretical analysis has been carried out to show the proposed online boundary is similar to that of a constant switching frequency space vector PWM (SVPWM) based multi-level VSI. This similarity is reflected in the current-error boundary shape and corresponding phase voltage FFTs between the proposed controller and SVPWM. All the online computations are easily achieved in DSP platform using the information of sampled three phase current errors and then referring the IM steady state circuit model. The proposed scheme ensures adjacent voltage vector switching and keeps all the inherent advantages like fast dynamic behaviour of a conventional hysteresis current controller. 5-level inverter fed IM drive is selected for simulation and experimentation to prove the generality of this scheme for any general n-level inverter.