A constant switching decoupled space vector PWM scheme for a four-level open-end winding induction motor drive

In this paper, decoupled space-vector based PWM strategy is described, which is used to synthesize a four-level inversion with dual two-level inverters feeding an open-end winding induction motor. Each inverter is capable of producing 8-states independently of the other. A combination of two 2-level inverters with the DC-link voltages of 2V_dc/3 and V_dc/3 employed to produce a total of 64 space vector combinations spread over 37 space vector locations. Some of the space vector combinations overcharge the DC link voltage of inverter-2 which can be avoided by employing Decoupled space vector PWM strategy. Proposed Space Vector PWM employs 1 KHz constant switching frequency to maintain constant switching loss in the entire range of modulation index. The instantaneous three phase reference voltages are employed to eliminating the need of sector identification or lookup tables. The gating pulses are generated to both of the inverters without using look-up tables. The zerosequence currents are not allowed to flow in this circuit as isolated DC power supplies are employed to feed individual inverters. The scheme is implemented using a 3-HP open-end winding induction motor drive and Experimental results are presented.