MODELING AND SIMULATION OF SPACE VECTOR CONTROLLED MLI FED INDUCTION MOTOR DRIVE

Abstract

Multilevel inverters have drawn tremendous interest in the field of high voltage and high power applications field. In the researches of multilevel inverters, its corresponding PWM control strategies are one of the research hot points. In high power and high voltage applications, the two level inverters, however, have some limitations in operating at high frequency mainly due to switching losses and constraint of the power device ratings. For high voltage applications, two or more power devices can be connected in series/parallel in order to achieve the desired voltage/current ratings. However, the characteristics of devices of the same type are not identical. For the same OFF/ON state current, their OFF/ON state voltages differ, the unbalance in device characteristics can damage the power devices. The above problem can be prevented by using multilevel inverters. Multilevel inverters can increase the power by (in-]) times than that of two-level inverter through the series connection of power semiconductor devices. Comparing with two-level inverter system having the same power, multilevel inverters have the advantages that the harmonic components of line-to line voltages fed to motor and switching frequency of the devices problem could be much decreased. Due to those merits, many studies about multilevel inverters have been performed. The multilevel topologies are classified into three categories: Diode Clamped Inverters, Flying Capacitor Inverters, and Cascaded Inverters. Diode clamped inverters, particularly the three-level one, are used in motor drive applications because it needs only one common voltage source and many simple and efficient PWM algorithms have been developed, even if it has inherent unbalanced DC-link capacitor voltage problem. However, it would be a limitation to applications beyond four-level diode clamped inverters for the reason of reliability and complexity considering DC-link balancing and more number of clamping diodes. On the other hand flying capacitor inverters need the more number of capacitors. Cascaded inverters have structurally not any problem of DC-link voltage unbalancing but have another problem it requires many separated DC sources in motor drive applications. The cascaded inverter has been largely studied and used in the fields of SVCs (Static VAR Compensators), stabilizers, I-IVDC trans missions.