A Novel Modified AC/AC Z-Source Converter for Starting Current Reduction for Three-phase Induction Motor

Induction motors inherently have very high current in order to provide sufficient power and torque for the loads when started. This very high current can cause the damage for the motors and other components. Therefore, an additional electronic soft starter such an AC/AC converter is commonly used to reduce this current but the reduced current is still high and relatively has high harmonics. This paper proposes a novel electronic soft starter, a modified AC/AC Z-Source converter for the three-phase induction motor. The proposed soft starter could directly convert AC voltage from a three-phase power supply with constant voltage and frequency by adjusting voltage together with the additional impedance source. The performance in terms of starting current reduction capacity and harmonic reduction capacity of the proposed starter with/without the overlap switching state implementation was examined and evaluated in comparison to the conventional starter with an AC/AC converter. These starter circuits were simulated via the computer program by operating at 3 load torque conditions: without load, half load and full load. The test results showed that the proposed starter with overlap switching state implementation provided the lowest starting current and lowest current harmonic distortion at the full load, following by the proposed starter without the overlap switching state implementation and a conventional starter, respectively. In turn, the proposed starter without the overlap switching state implementation provided the fastest settling times.