Optimum Torque Operation of a Hybrid Cascaded Multilevel Converter-Fed Electric Vehicle Motor Drive

This paper describes a Hybrid Cascaded Multilevel Converter (HCMC) used in Electric Vehicles (EV) for motoring and extracting optimal power during regenerative braking operations. The HCMC converter includes a T-type inverter connected to an Interior Permanent Magnet Synchronous Motor (IPMSM) interfaced with a common DC link. A battery is connected to the DC link using a bi-directional boost converter. The control structure of the HCMC system includes two cascaded dual-loop control structures. The dual-loop control architecture of the IPMSM motor includes inner current control loops and an outer speed control loop. Further, the dual-loop structure of the battery-connected boost converter includes an inner average inductor/battery current control loop and an outer DC link regulator loop. A heuristic Maximum Torque Per Ampere (MTPA) Look-up-Table (LUT)-based methodology is adopted for the IPMSM inner control loops that generate optimized direct and quadrature-axes current references for the motoring mode. Further, optimum energy recovery is achieved with maximum regenerative torque during the braking mode. The IPMSM inverter is controlled using a three-level Space Vector Modulation (SVM) scheme for the T-type inverter. The direct axis current reference for the IPMSM inner loop is modulated based on the required reluctance torque using MTPA methodology. The technique proposed here is verified using PLECS simulation and presented in this paper.