Comparison of different control strategies for series-series compensated inductive power transmission systems

For automotive battery charging, the series-series compensated inductive power transmission shows a lot of advantages compared to other compensation techniques. As shown in many recent [1], [2] and older publications, the main advantages are the independency of the secondary current from the load at resonant frequency and the zero phase shift between primary current and voltage. As shown in [3], very high efficiencies from grid to battery of nearly 94-95% can be reached by driving the IPT-system at constant frequency and by adapting the input and the output DC-link voltages. To achieve this control method, extra DC/DC-converters need to be added inside the power transmission path. To avoid the thereby associated higher hardware and also software effort, alternative control strategies needing fewer components are of major interest. In this paper, different control strategies and modulation schemes with and without additional DC/DC-converters are presented, theoretically evaluated with a special emphasis on partial load transmission efficiency and a selection is measured in a real system. The various control strategies were compared on one single coil geometry. The aim is to find a control method which minimizes the total system costs and maximizes the system efficiency at the same time.