Controller design of flywheel energy storage systems in microgrid

For better design of controllers for flywheel energy storage systems (FES) used in DC microgrid, the control model of induction machines in FES is built firstly in this paper based on the field oriented space vector pulse width modulation (SVPWM). Secondly, according to the dual-mode dual-loop control strategy of FES, which is, the outer loop of speed plus inner loop of current under the speed-regulating mode, and the outer loop of voltage plus inner loop of current under the voltage-regulating mode, the second-order transfer function of the current inner loop is derived using the back EMF decoupling method. Based on this, the current loop PI controller parameters are calculated according to the optimal performance index under the integral of time multiplied by absolute error (ITAE) criterion. Thirdly, by approximating the current inner loop to unit ratio function, the third-order transfer function of the speed outer loop is derived and then simplified to second-order, with the speed loop PI controller parameters calculated. Besides, the nonlinear voltage loop PI controller is designed by experiential estimation and debugging. Finally, a simulation testbed of FES is established in PSCAD. The operation of FES under speed and voltage regulation modes are simulated respectively, and the feasibility of the controller designing method is verified.