Load Dependent Power Control in Series-Series Compensated Electric Vehicle Inductive Power Transfer Systems

In inductive battery charging systems for electric vehicles the power flow to the battery has to be controlled according to the battery state of charge (SOC), the magnetic coupling between primary and secondary side and other operation parameters. It is well known that the output power can be controlled by fixed frequency or variable frequency techniques applied to the high-frequency inverter (HFI). Furthermore an additional DC/DC converter can be used to adjust the input voltage of the HFI. These three techniques are analyzed and compared by theory and laboratory measurement. It results in using an additional DC/DC converter is the best option with the best efficiency at full load. Nevertheless this technique has the highest component count and therefore the highest costs. Another technique is Asymmetric Dutycycle Control (ADC) which reaches the second best efficiency. In contrast to DC/DC converter control there is no need for additional components making this technique a good choice. Furthermore this analysis reveals that Symmetric Dutycycle Control (SDC) and Phase Shift Control (PSC) as well as Variable Frequency Control (VFC) techniques cannot compete in terms of efficiency.