Nonlinear H-infinity control for hybrid excited synchronous generators

The model of a hybrid excited synchronous generator is analyzed and a nonlinear optimal (H-infinity) control method is proposed for it. This type of generator receives primary excitation at its stator's winding through an AC/DC and DC/AC converter, and auxiliary excitation at a secondary winding that is fed by an AC to DC converter. Through the hybrid excitation scheme more control inputs are applied to the generator, thus achieving better performance for the system's control loop. To implement the proposed control method the dynamic model of the generator undergoes approximate linearization around a temporary operating point which is recomputed at each time-step of the control algorithm. The linearization procedure relies on Taylor series expansion and on the computation of the associated Jacobian matrices. For the approximately linearized model of the hybrid excited synchronous generator a stabilizing H-infinity feedback controller is designed. To compute the controller's feedback gains an algebraic Riccati equation is repetitively solved at each iteration of the control method. The global stability properties of the control scheme are proven through Lyapunov stability analysis.