Control design of an advanced high-speed FESS for pulsed power applications

Control of an advanced high-speed flywheel energy storage system (FESS) based on a high-speed surface mount permanent magnet synchronous machine (PMSM) is explored in this paper. A PWM inverter/rectifier controls the bi-directional flow of energy for charging and discharging the flywheel. During charging, an inner current loop controller and an outer speed loop controller regulate the system performance. During discharging operation, the outer speed loop controller is made inactive and instead a DC bus voltage regulator along with the current regulators control the FESS discharging mode of operation. Current, speed, and DC bus voltage regulations are realized by proportional plus Integral (PI) controllers. A novel design algorithm is used to generate the entire set of stabilizing PI controllers for the current and speed loops of the FESS. The PI gains for the voltage controller are designed based on the pole-zero cancellation theory, because of the non linear operation of the controller. Next, the operation of a 240 kW, 19-23 krpm FESS with its control system is evaluated by simulation. Finally, experimental results are presented to verify the control system performance.