Nonlinear optimal control for multilevel inverters

The article proposes a nonlinear optimal (H-infinity) control approach for the model of modular multilevel inverters. The article's results are of interest for power grid applications were to handle high voltage one can use low voltage semiconductors. To solve this control problem, the dynamic model of the inverter undergoes first approximate linearization around a time-varying operating point. The linearization procedure relies on Taylor series expansion and on the computation of the related Jacobian matrices. To compute the feedback gains of the H-infinity controller, an algebraic Riccati equation has to be solved at each time-step of the control method. To prove the global asymptotic stability of the control loop as well as robustness properties, Lyapunov stability analysis is performed.