Exact feedback linearization of general four-level buck DC-DC converters
Four-level buck DC-DC converters (FLB), as strongly coupled, multi-input multi-output and under-actuated 4th-order nonlinear systems, require relatively complex control to meet desired demand. Traditional control methods such as proportional-integral (PI) with linear decoupling either have slow dynamic response and incomplete decoupling, which means a conflict in performance among the output voltage and several flying-capacitor (FC) voltages, or need to degrade the circuit, losing the generality. Considering all state variables of general FLB and thus building the 4th-order affine average model, this paper proposes a full-state exact feedback linearization (EFL) nonlinear control method based on differential geometry. Besides, the stability of internal dynamics caused by under-actuated characteristics is concisely analyzed when different output functions are selected. Simulation results show that proposed method has better transient and steady-state performance than PI with linear decoupling when there is a step change in input voltage or load.