Design of a wireless power transfer class-E DC-DC converter controlled by an optimal power point tracking algorithm

Summary This thesis work aims to realize a wireless power transfer class-E DC-DC converter controlled by an innovative method. The circuit is composed of a primary and a secondary side which are isolated and works like an inverter and a rectifier stage coupled by two inductor coils (i.e. two coupled coils that work as a transformer with low coupling factor k). The wireless class-E converter is usually designed for a specific load value and a specific k and only in this configuration the optimal solution is guaranteed. Furthermore, this circuit is very sensitive to variations in the load (the simplification of the time-variant electronics that must be fed by the converter) or the coupling factor (changing with distance, misalignment or medium between the coils). The idea is to implement a control algorithm capable of guaranteeing and eventually tracking the Optimal Power Point (OPP) for different power levels in different scenarios that arrive from variations of the load value or the distance between the primary and the secondary circuit. This new method doesn’t use a feedback mechanism based on telemetry to maintain the converter at the optimal working point, but it exploits only a regulator at the secondary side (either a series or parallel). It gives the possibility to have control based only on the primary side electrical waveforms like the input voltage and the input current. This control method requires a voltage or current limiter at the receiver side as additional hardware parts and is based on an OPP identification in the input voltage – input current characteristic when the converter is designed in the correct way. This OPP is a corner point and so a discontinuity point in the derivative. An uncontrolled regulator dissipates too much power and so is useless, using this OPP method the minimum power dissipated is guaranteed (theoretically zero). This process can be applied both to loads requiring constant voltage or constant current driving. In the first chapter, a little introduction to how wireless power transfer systems are normally designed is proposed followed by an introduction to the tracking algorithm method. In the second chapter, the whole theoretical analysis is covered: the design of a general wireless class E converter is analyzed and the mathematical notions are presented. Then the innovative control method is treated and explained in all its parts, pointing out the important considerations about it. Finally, some simulations are used to verify all the previous points. In the third chapter, a real prototype is designed using MATLAB and Python scripts and, after implementing it, some laboratory tests are done to verify the correct behaviour of the converter input voltage – input current characteristic. Finally, in the fourth chapter, a simple control tracking algorithm is described and a possible implementation is proposed. Eventually, the conclusions are drawn.