Filter-Based Active Damping of DAB Converter to Lower Battery Degradation in EV Fast Charging Application

Dual Active Bridge (DAB) converter is well suited for off-board fast Electric Vehicle Charging Stations (EVCS) and in DC microgrid-connected EVCS applications. However, proper modification in DAB converter topology is crucial for fast charging, as the charging current is very high, and any oscillations would shorten the EV battery life. As per literature, DAB converter topology integrated with a series inductor at the output for EV battery charging reduces the output current ripple by 40%. However, as per our observation, potentially unstable dynamics are introduced in the system with the inclusion of an LC filter. This affects the controller stability; hence, these dynamics must be damped using active or passive damping. Passive damping is less efficient due to the considerable losses it produces, partly induced by low-frequency noise and partly from switching-frequency noise. Also, placing the damping at the selective resonant frequency is very complex. In comparison, active damping offers selective placement and loss reduction. This paper presents the DAB converter mathematical modeling using the generalized average model (GAM) and the average output current linearization model (AOCLM). The paper presents stability analysis and proposes a novel and robust approach to control the dynamics in the current and voltage control loops during EV charging, thereby reducing battery degradation. The charge flow to the battery is controlled using Constant Current Constant Voltage (CCCV) algorithm. The proposed scheme also eliminates the need for extra sensors by selectively attenuating the oscillations at the frequency of interest. The performance of the proposed model for EV fast charging application is verified using MATLAB/Simulink and experimentally validated in a real-time simulator OPAL-RT hardware platform.