Performance investigation on integrated controlled Z source inverter using modified modulation technique

Abstract

Z-source inverter has found wide spread applications and attracted the researchers in recent years. Z-source inverter overcomes the limitations and problems found in traditional voltage source inverters (VSI) and current source inverters (CSI). Z-source inverter based adjustable speed drive system (ASD) effectively uses the shoot-through state to boost DC bus voltage by simultaneously gating on both the upper and lower switches of a same phase leg. This research attempts at an integrated control technique (ICT) using modified modulation for the Z-source inverter fed three phase induction motor drives. Modified modulation provides a better DC link voltage boost by turning maximum period of the traditional zero state into shoot-through zero state with lowest voltage stress across the power switching devices, less Z-source capacitor voltage/inductor current ripples and with better harmonic profile of the motor terminal voltage/current waveforms. A detailed comparative analysis of modified modulation over the conventional modulation scheme has been presented in this research to validate the effectiveness of the proposed modulation scheme. MATLAB/SIMULINK simulations have been performed for different operating conditions of the induction motor drive and the results are given for Z-source inverter fed drive with constant load, during supply voltage sags and when step change is applied to the load. During supply voltage sags, the DC link capacitor voltage is boosted to the desired level by simply sensing the motor terminal voltage. The proposed controller strategy ensures better stability of the whole drive system. Torque pulsations are reduced during both light and heavy load operations, as the electromagnetic torque ripples are significantly minimized by proposed ICT using modified modulation. Performance of the drive is found to be very smooth during a constant supply/load operation, when a step change is applied to the load and during supply voltage sag/fluctuations. newline