PERFORMANCE EVALUATION OF MULTILEVEL INVERTER FED INDUCTION MOTOR DRIVE

Abstract

Multilevel inverters are increasingly being used in high-power medium voltage applications due to their superior performance compared to two-level inverters, such as lower common-mode voltage, lower dv/dt, lower harmonics in output voltage and current, and reduced voltage on the power switches. Especially for use in high power applications, some medium voltage motor drives and utility applications require medium voltage and megawatt power level. For a medium voltage grid, it is troublesome to connect only one power semiconductor switch directly. As a result, a multilevel power converter structure has been introduced as an alternative in high power and medium voltage situations. All the matters are that minimize the THD in conventional two level voltage source inverter (VSI) is towards various PWM techniques. However , this trend invited problems, like the increase of switching frequency increased the switching loses, generating a common mode voltage which becomes significant at high power levels. Multi level power converters have gained much attention in recent years due to the proven mitigation of various problems sited above. The general structure of the multi level inverter is such as to synthesize a sinusoidal voltage from several levels of DC voltage. Increasing the number of levels produces a fine staircase wave form approaching close to a sinusoidal wave with minimum harmonic distortion. In this simulation of various inverters Two level and Three Level NPC Inverter is carried out and the performance of these Inverters with different Modulation Control Schemes and under various operating conditions by changing the load and output frequencies are Investigated. The work mainly focuses on the improvement in THD of both voltage and current wave forms from normal VSI PWM inverter to Three Level Neutral Point Clamped inverter. Space Vector Modulation Scheme for both Two and NPC Inverter have been implemented, from this observed that as THD Values are reduces to very desired values, and the performance is highly superior to other Modulation Schemes, inverters in reduced harmonic distortion, lower EMI (Electro Magnetic Interference) and higher dc link voltages The performance of scalar v/f control of the 3-phase induction motor drive fed from both conventional three phase inverter and neutral point clamped inverter is investigated in closed loo