PMSM and inverter sizing compromise applied to flywheel for railway application

In this paper the authors study the first step of power inverter and permanent magnets synchronous machine (PMSM) sizing, considering the application to a flywheel energy storage system. Knowing the operating characteristics of the drive defined by the application, our approach is based on determining the evolution of both machine torque and power converter current as functions of the rotational speed. It is shown that those curves strongly depend on the relative speed range of constant power and constant torque operations. The authors explain how to choose Ω_t1 (the rotational speed corresponding to the beginning of the constant power working) in order to obtain a good compromise between the inverter power and the PMSM torque. Finally the authors detail the influence of a real cyclic working on the design of the flywheel system.