Current Controller Design in Discrete-Time Domain for Pmsm/G in Flywheel Energy Storage Systems

Wide speed range operation of the Permanent-Magnet Synchronous Motor/Generator (PMSM/G) in a Flywheel Energy Storage System (FESS) leads to lower sampling-to-fundamental frequency ratio than other PMSM applications. Oscillatory or unstable response can occur if the current controller design does not properly incorporate the discrete nature of PWM modulation method. A current controller directly designed in discrete-time domain is presented in this paper based on an accurate discrete model expressed with complex-vector, and some modifications and approximations are made to extend its application to salient machines. The digital delays are taken into consideration in the accurate discrete model and the coupling problem between d-q axis current loops is well solved. At last, the designed controller is validated by simulations and experiments on a PMSM/G test bench.