Optimal open loop control for a fast transition from normal to active-short-circuit operation

A novel approach for a fast transition to the safe state i.e. active-short-circuit (ASC) based on optimal control prevents the dc-link voltage and the phase currents from exceeding critical limits. Before switching to the ASC, the novel approach controls the permanent-magnet synchronous machine (PSM) to the steady-state short-circuit operational point by assuming the inverter and PSM are still functioning. To design an optimal control pattern, two optimization problem formulations are useful. By finding the dc-link optimal voltage pattern, a critical dc-link voltage overshoot can be minimized. A simplified time-optimal dq-voltage pattern can be used if the dc-link voltage does not have to be taken into account. Simulation results as well as experimental results demonstrate the new approach both in base-speed and field-weakening-area; and compare it to conventional methods like Hard-ASC and Soft-ASC.