Research Projects

Indigenous development of on-board chargers (OBCs) for electric scooters demands focused research on the power factor correction (PFC) rectifier and DC/DC stages. Most of the existing literature deals with the efficiency improvement of PFC and DC/DC stages with little emphasis on the EMI reduction aspect. However, a commercial OBC must adhere to the CISPR 32 EMI specifications to avoid any unwanted interaction between the OBC and digital communication lines of vehicular electronics. A general approach to address this issue is to introduce a bulky EMI filter at the AC input which impacts the power density of the OBC. In this project, two simultaneous approaches will be taken to improve the EMI performance of an OBC by reducing the common mode current flowing through the scooter chassis. The first technique reduces the strength of the noise source, and the second method minimizes the common mode capacitances. For the AC/DC stage, boost PFC and totem-pole PFC are two competent topologies. While boost PFC offers better EMI performance due to relatively weaker noise sources, achievable efficiency with the totem-pole PFC is superior. Therefore, during the project’s first year, a quantitative comparison between boost PFC and totem-pole PFC will be carried out concerning efficiency and conducted EMI emissions considering the gallium nitride (GaN)-based design of both these topologies. Innovation in modulation techniques is envisioned for EMI performance improvement without compromising the converter efficiency. A conducted EMI test setup will be built to experimentally evaluate the EMI performance of both topologies. Input current total harmonic distortion (THD) and efficiency measurements will also be done. For the DC/DC stage, LLC and LCC resonant converters are two competing circuit configurations. While the LLC converter offers better efficiency, the LCC converter is expected to showcase superior EMI performance due to slow transitions of the transformer voltage waveform. So, during the project’s second year, a quantitative comparison between LLC and LCC resonant converters will be performed in terms of efficiency and conducted EMI emissions. Innovation in synchronous rectifier gating schemes is envisioned for EMI performance improvement without compromising the converter efficiency. GaN-based prototypes of both these topologies will be built and tested for efficiency and conducted EMI performance. During the project’s third year, a consolidated prototype of OBC will be developed using the best-performing PFC and DC/DC stages. A finite element analysis (FEA) tool will be leveraged to estimate the common mode capacitances and hardware arrangements will be made to minimize them. A light EMI filter will be designed to meet the CISPR 32 specifications, if necessary. The outcome of this project will be a compact and efficient OBC prototype with low EMI emissions for electric scooters.