Sizing of Modular Cascade Machines System for Electric Vehicles

Modular cascade machines (MCM), as a new multi-machine system, are expected to be applied for electric vehicles (EVs). This paper focuses on the sizing of MCM systems. Expanding MCM high-efficiency area and reducing MCM mass are selected as optimization targets for sizing. The proposed machine efficiency map and MCM mass evaluation methods are the means to achieve this goal without machine pre-design. The efficiency evaluation method enables to evaluate machines efficiency maps only with four basic design specifications (rated speed, rated torque, overload factor, and speed expansion ratio). Neither finite element (FE) nor experimental data (inductance and resistance) are used. Its calculation is fast and can be finished within several milliseconds. The method is validated by comparisons with the experimental efficiency maps of two prototypes. The proposed methods are proven having an accuracy that is acceptable for the MCM definition and pre-design. The exemption of machine pre-design saves a lot of time during sizing stage. The sizing optimization is realized by genetic algorithm. And the comparisons of different sizing are conducted with the same vehicle model. Moreover, general sizing rules for the similar EVs are proposed. For the studied EV, the number of machines is proposed as a function of traction power. The sized specifications could be used for more accurate machine design by the FE method in future. The sizing method could be extended for the other kind of multi-machine systems.