Design Methodology of Constant Power Speed Range for Surface-Mounted Permanent Magnet Machine in Flywheel Energy Storage System

Conventionally, flywheel machines are designed by selecting the maximum speed as the rated speed and determining the rated power underId= 0 control strategy. Such an approach leads to current overloading during constant power operation at low speed and fails to guarantee a sufficient constant power speed range (CPSR). To overcome these limitations, this paper proposes a CPSR-oriented design methodology for surface-mounted permanent magnet synchronous machines (SPMSMs) consideringId= 0 control. Unlike existing studies that rely on single-speed design or multi-point optimization, the proposed method directly plans the permanent magnet (PM) flux linkage and synchronous inductance based on the operating characteristics of flywheel machines to achieve a specified CPSR. Specifically, a comprehensive analytical model is established to quantitatively reveal the influence of PM flux linkage and inductance on CPSR, from which explicit design constraints are derived. Based on these constraints, the optimal PM flux linkage and inductance are determined by considering the power factor and minimizing the average charge/discharge current over the entire CPSR. Furthermore, an efficient and iterative dimensional design procedure is developed to ensure that the machine geometry accurately realizes the selected electromagnetic parameters. The effectiveness of the proposed design strategy is validated through finite element method analysis and experimental testing of a fabricated prototype.