Harmonic Approximation for Dynamic Wireless Charging of Electric Vehicles

Wireless power transfer (WPT) has been established as a feasible solution for a safe and efficient battery charge in the Electric Vehicle (EV). In this context, dynamic wireless power transfer (DWPT) is presented as an alternative to reduce battery size, improve logistic processes (as the vehicle charges in movement) and it can also help with the integration of renewable energy sources. Most research work on dynamic charging uses the First Harmonic Approximation (FHA) method for circuital analysis. This method ignores harmonic content, resulting in imprecise results during the design process, which lead to unreliable implementations. In this paper, the authors analyse the precision of the Total Harmonic Approximation (THA) method as a more precise formulation in the particular context of dynamic charging. A mathematical analysis is also developed to derive the Total Harmonic Distortion (THD) in the resonant circuit, which is a relevant parameter in time-varying conditions as the application under study is. This formulation of THD is taken into account in the design process of the LCC-Series compensation, which is widely used in DWPT systems nowadays. Indeed, from this mathematical model, design guidelines are proposed to reduce the THD while maintaining high efficiency value. In this framework, phase shifting technique is applied in addition to this guideline as a simple but effective solution to reduce harmonics. Adjusting precisely the phase shift angle, the THD can be reduced avoiding the oversize of the components. A series of experiments are performed in the laboratory to validate the mathematical models and the feasibility of the proposal.