Optimization of a self-oscillating power converter for resonant switching in a contactless inductive energy transfer system for low voltage onboard supply system in lightweight construction electric vehicles

Abstract

In the future, mobility will be dominated by different forms of e-mobility. The related disadvantages such as the limited range could be compensated by automatic systems for inductive charging. With highly automated and intelligent inductive charging systems, every parking and stopping process can be used to recharge the traction batteries without any interaction of the driver. For e-vehicles smaller than the size class of electric passenger vehicles, as here for instance an electric go-kart, generally low voltage batteries (instead of high voltage batteries) are used. Hence, different standards are required for charging systems for these low voltage batteries, as for example a lower voltage drop on the secondary side and a simple technical implementation. One possible approach is the use of a high-power oscillator on the primary side in combination with a double-sided parallel compensation. A system like this, just due to circuit state, safe operates by principle in terms of open circuit and short circuit stability. If the windings are taken away from one another, the power transfer performance decreases in proportion to the coupling factor down to zero, only because of the circuit state. Therefore, monitoring system is not necessary. In this paper, the optimal design of the parallel compensated charging system for a charging power of 1 kW with a 60 V traction battery is presented, as well as the optimization of the high-power oscillator for high efficiency and the avoidance of EMI-relevant switching interference.