A Nonlinear Optimal Control Approach Based on the Control-Lyapunov Function for an AC/DC Converter Used in Electric Vehicles

Abstract

AC/DC converters used in electric vehicles generally consist of two stages: an input power factor correction (PFC) boost AC/DC stage that converts input AC voltage to an intermediate DC voltage and reduces input current harmonics injected to the grid, and a DC/DC converter that provides high-frequency galvanic isolation. Since there is a low-frequency ripple (second harmonic of the input ac line frequency) in the output voltage of the PFC AC/DC boost converter, the voltage loop in the conventional control system typically has a very low bandwidth to avoid distorting the input current waveform. This causes the conventional PFC controller to have slow dynamics against load variations. This paper presents a new control approach that regulates the input power of the converter instead of the output voltage by using an optimal nonlinear control approach based on the Control-Lyapunov Function (CFL). In this paper, it is shown that the proposed controller is able to eliminate the low bandwidth voltage control loop in the conventional PFC controller, thus allowing the front-end AC/DC boost PFC converter to operate with faster dynamic response than with the conventional controller approach. Experimental results from a 3 kW AC/DC converter are presented in the paper to validate the proposed control method and its superior performance.