A Five-Level Inverter Scheme With Increased Linear Modulation Range

In this paper, the method to extend linear modulation range till full base speed irrespective of the load power factor (p.f.) is presented using a 5-Level inverter scheme. Using this method, inverter can be operated linearly till peak phase fundamental voltage of 0.637Vdc (i.e. till full base speed) without exceeding machine phase voltage rating. The 5-level inverter is realized by a dual-fed inverter scheme for Open-End Induction Motor (OEIM) drive. A 2-Level inverter cascaded with a HBridge inverter acts as primary inverter and feeds the drive from one end whereas capacitor fed 2-Level inverter acts as secondary inverter and feeds the drive from another end. A single DC source is connected with primary 2-Level inverter. The ratio of the DC-link voltage to the primary H-Bridge inverter capacitor voltage is 4:1 and the DC-link to the secondary inverter capacitor voltage is maintained at 2:1 ratio for proper 5-Level inverter operation. Simulation and experimental results for inverter operation till full base speed are presented in this paper for OEIM and resistive load under steady state and dynamic conditions.