Nonlinear resilient controller design for EV fast charging unit with multiple dual active bridge (DAB) converters

High-power fast charging units for electric vehicles (EVs) usually consist of multiple modules which are connected in parallel in order to achieve high power density and ratings. Considering the fact that these units are integrated within the modern smart grid infrastructure, there is always the danger of cyber-attacks and failures in measurement/sensor/communication links. In this paper, an EV fast charging unit consisting of multiple parallel connected dual active bridge (DAB) converters is considered and a novel nonlinear resilient controller (NLRC) is proposed for accurate output power regulation during abnormal scenarios, while inherently limiting each individual DAB converter current. Furthermore, taking into account the multiple parallel connected module structure of the charging unit, equal power distribution among the modules is accomplished. Utilizing the invariant set and ultimate boundedness theory, it is proved that the power (or current) delivered to the EV battery by each converter is always bounded below a maximum value. Based on the dynamics of the NLRC, it is shown that when an abnormal event (setpoint attack, sensor fault) occurs at one or more converters, the output current of the corresponding module is limited, while the remaining unaffected modules regulate their power, in a way that the delivered to the battery power equals to the reference value. Extensive simulation scenarios, including both normal and abnormal situations, were implemented to prove the effectiveness of the proposed NLRC, considering an EV charger that consists of three DAB converter modules.