Optimization Control of Large-Capacity High-Speed Flywheel Energy Storage Systems

As a core component of the flywheel energy storage system (FESS), the electrical motor drives the flywheel rotor to accelerate during the charging status and to decelerate during the discharging status. Generally, the permanent magnet synchronous motor (PMSM) or the brushless DC motor (BLDCM) is chosen as the electrical motor of the FESS due to its high power factor and low heat production of the rotor. However, both the PMSM and the BLDCM have high standby loss including eddy-current loss and magnetic hysteresis loss, which undermines the system's efficiency. By contrast, the synchronous motor (SynM) has the adjustable rotor flux and is capable of mitigating the standby loss by decreasing its excitation current during the idle time. Therefore, the SynM is more efficient in the application of the FESS. In large-capacity high-speed applications of the FESS, an effective control strategy is required to exploit its power capacity sufficiently. In this paper, the traditional vector control strategy is theoretically proven to be inappropriate, and an optimization control strategy based on flux weakening is proposed to implement the high power and the fast dynamic response. The proposal is verified by simulations.