This paper designs a hybrid speed controller in which a Sine Triangle PulseWidth Modulated (SPWM) inverter is used below the\nbase speed and a square wave inverter is employed above the base speed. The two inversion techniques complement each other\nfor their advantages and disadvantages below and above the base speed. This paper proposes a unique strategy for the transition\nbetween SPWMand square wave by simply setting the frequency of the carrier signal equal to zero.Theproposed methodology in a\nway uses only one inversion technique and realizes a seamless transition fromthe SPWMto square wave compared to conventional\nmethod in which modes are simply switched from SPWM to square wave and vice versa when the speed changes above and below\nthe base speed, respectively. Computer simulations show that the proposed technique has smoother torque transition and thus a\nbetter speed response compared to conventional approach of inverter mode switching around the base speed.The performance of\nproposed hybrid approach is also validated on a small prototype induction motor through experimental results.
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