An Explicit Minimum-Loss Control Strategy for Dual VSI DFIG-DC Systems

This article presents a new minimum-loss control strategy for vector-controlled dual-voltage source inverter (VSI) doubly-fed induction generator (DFIG)-dc systems. The optimization is based on a simplified formalism using Lagrange multipliers to determine the optimal stator frequency, stator/rotor magnetizing current split, and the magnetizing flux magnitude as a function of the machine operating conditions, namely speed and torque. Compared with existing minimum-loss control schemes, the proposed approach provides an explicit solution for all three optimal quantities, which makes the implementation and control design easier, thus avoiding the use of an additional proportional–integral (PI) controller to solve the flux implicit optimality condition. The theoretical framework also includes a sensitivity analysis against DFIG parameter variations, to appraise the robustness of the proposed control scheme. The devised approach and related control implementation scheme are validated with the simulation and experimental results.