A Novel Algorithm for Designing the PID Controllers of High-speed Flywheels for Traction Applications

High speed flywheel energy storage system (FESS) is one of the most energy dense storage technologies proposed for traction applications. In this paper, performance of a high speed and high power FESS using a permanent magnet synchronous machine (PMSM) is evaluated during both charging (motoring) and discharging (generating) modes of operations. A PWM inverter (rectifier) interfaces between the DC bus and the PMSM. During charging an inner current loop controller and outer speed loop controller regulate the whole system performance and during discharging operation the outer speed loop controller is inactive and instead a DC bus voltage regulator controls the FESS. Current, speed, and DC bus voltage regulations are realized by PI/PID controllers. These types of controllers have been used in motor drives industries for several decades. However, traditional methods based on simplifications, approximations, try and error are used to tune the gains of the controllers. The PI controllers achieved in this way do not guarantee optimal performance of the system. In this paper, the transfer functions of the current loop and speed loop are derived. Then, a novel design algorithm [1] is used to generate the entire set of stabilizing PI/PID controllers for the current and speed loops of the FESS. The algorithm is presented step by step for both current and speed controllers and a 70 kW, 36000 RPM FESS is simulated in PSIM to verify the consistency of the algorithm.