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Optimal efficiency controller for synchronous reluctance flywheel drive

This paper presents an approach to achieve optimal efficiency over a range of power and rotational speed for a synchronous reluctance motor/alternator drive, to be used in a flywheel energy storage system. Synchronous reluctance machines have distinct advantages over permanent magnet machines in flywheel applications with respect to cost and reliability. A stator-flux-oriented torque control scheme is used to control the motor/alternator. For a given speed and torque, power losses in the machine are a function of only the stator flux magnitude. The optimal flux value can then be found using a one-dimensional optimization algorithm, such as the method of sequential quadratic interpolations. Optimal flux values for the machine are determined using an experimental setup that accurately determines losses in the motor/drive system. This work is part of a broader project at the University of California at Berkeley to develop flywheel energy storage systems. In particular, high-speed synchronous reluctance machines have been designed and built for flywheel applications. Experimental results obtained from the test setup show the validity of the controller and the optimization algorithm.