Primary Side Attributes based Control of DC Link Capacitor-Less Bi-directional Wireless Charger for Electric Vehicles

In recent times wireless charging systems for electric vehicles are gaining popularity mainly due to the convenience it offers to the end user and the electric grid. There are numerous Bi-directional AC-DC inductive charging systems and their controls have evolved in the recent past. These chargers conventionally use a bulky DC link capacitor and grid filters which hampers the power density of the charging system. In this connection, this work establishes a PWM technique to alleviate the dominant grid frequency harmonics and controls the power transfer bi-directionally for an LCC-LCC compensated DC link capacitor-less AC-DC charging system. The control is developed such that the grid-side filtering is necessary only for the resonant frequency harmonics, which reduces the size of grid side filter. The work also estimates the load current by sensing the primary side attributes to have all the control on the primary side to reduce the size of the off-board assembly. This established primary control for the converter system is tested for different values of bi-directional power flows and for variations in load and coupling changes as well. The developed control along with the PWM strategy is also evaluated for the grid current THD, estimation of the load currents, and the grid power factor for a wide range of current references and for their bidirectional flows.