A Control Lyapunov Function-based controller for a two-stage AC/DC converter

A two-stage AC/DC converters, generally, consist of an input Power Factor Correction (PFC) in order to improve the quality of the current drawn from the grid, and a DC/DC converter in order to provide galvanic isolation. Since there is a low frequency ripple (2nd Harmonic of the input ac line frequency) in the output voltage of the PFC AC/DC Boost converter due to the power ripple, the voltage loop in the conventional control system should have a very low band-width in order to avoid distortions in the input current waveform. This leads to a very sluggish transient response for the PFC against load variations. This paper presents a new control approach, based on the Control-Lyapunov Function (CLF), which is able to significantly improve the transient response of the PFC stage. Since the dynamics of the PFC stage is highly nonlinear, the optimal controller is derived by solving the Hamilton-Jacobi- Bellman equation. Experimental results from a 3KW AC/DC converter validate the performance of the proposed control method compared to the conventional control technique.