Contactless energy transmission systems with improved coil positioning flexibility for high power applications

In this paper a contactless inductive energy transmission system is presented, which allows a transmitted power up to 1 kW at an overall efficiency of more than 90% and a very high positioning tolerance of both coils to each other. Examples of applications with positioning flexibility are energy supplies for consumers on bad balanced shafts, battery charging systems for wafer processing equipment or medical devices and consumer electronics. The allowable positioning tolerance is strictly related to the type of magnetic coupling which depends on physical parameters such as coil diameter, ferrite material or load conditions and it is mostly afflicted with unwanted effects such as voltage rises or phase shifts. Another important issue especially at consumer electronics is the condition of keeping the limit values for the external magnetic leakage field. This paper shows new possibilities to improve and describe the system characteristics in terms of positioning flexibility and EMC by optimising the compensation technique and the coil parameters. Therefore influences of physical and geometrical coil parameters on the electrical behaviour are analysed. For describing the 3D finite elements analyses (FEA) and analytical methods are used. The paper discusses the pros and cons of different compensation methods and special aspects of the coil optimisation process. As a result, a proposal for an optimised coil geometry is presented and measurement results of an experimental setup which confirm the theoretical analyses are discussed.