PERFORMANCE INVESTIGATION OF THREE LEVEL Z-SOURCE NPC INVERTER FOR INDUCTION MOTOR DRIVE

Abstract

Conventional inverters are incapable of boosting input dc voltage, so two stage conversion is required for boost operation. To overcome this drawback Z—source inverter can be used. Z-Source inverter implies unique X shape L-C impedance network which uses shoot through states to boost output voltage. This provides single stage dc-ac conversion with high reliability. For high voltage applications two level inverters cannot be used because of high voltage stress on switching devices. Multilevel inverters have many advantages like low voltage stress on switching devices, low harmonic contents in output voltage, less EMI effect etc. So unique X shape L-C network is used with three level NPC inverter to form three level Z-Source NPC inverter. This dissertation work starts with analysis of impedance network and principle operation of three level Z-Source NPC inverter. Different PWM control schemes are discussed in detail. Performance of three level Z-Source NPC inverter is evaluated for R, R-L and induction motor load and close loop operation of induction motor for indirect field oriented control (IFOC) method is done in MATLAB SIMULINK. Hardware has been implemented in the laboratory and is checked with different control schemes for R, R-L and induction motor load. Also performance of three level Z-Source NPC inverter is evaluated using V/f control of induction motor. SPARTAN 3 kit is used for implementation of control scheme in hardware.