IMPROVED MODULATION TECHNIQUES FOR PWM-VSI DRIVES

PWM-VSI based ac-drives have two main problems. The inverter is nonlin ear which causes instability problems in some specific working points of the ac-machine and it emits acoustical noise due to the switching f requency, Nonlinearities like dead-time in the inverter, a load depend ent de-link voltage ripple and the voltage drop across the switches ar e modelled and compensated by improved modulation techniques in order to obtain an almost ideal inverter, Different feedback and feedforward techniques are proposed. The acoustic noise Is reduced by using a ran dom modulation strategy, Measurements show a significant improvement b y using feedforward and feedback techniques for linearizing the invert er, As well an improvement in reduction of the acoustic noise emission is achieved by using random modulation, It is concluded that a combin ation of a random modulation strategy and feedforward/feedback techniq ues gives an almost ideal ac-drive system.