Compensation for three-coil wireless power transfer for misalignment and efficiency improvement in wireless charging system / Peyman Darvish

Peyman , Darvish (2021) Compensation for three-coil wireless power transfer for misalignment and efficiency improvement in wireless charging system / Peyman Darvish. Masters thesis, Universiti Malaya.

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Abstract

Wireless power transfer (WPT) using two or more magnetic resonance is commonly known as inductive power transfer ( IPT ). This technology can transfer power over distances without physical contact, offering significant benefits to modern automation systems duo its convenience, environmentally friendly, and efficient power transfer. Two coil WPT system is the most popular design over the past decades. However, recent studies have proven that a three-coil WPT design shows better performance and has higher efficiency compared to the two coil designs. This is especially critical when the source resistance and transmission distance between the primary and receiver coil increases. Li-ion batteries are the most commonly used batteries for Electric Vehicles ( EVs ) applications because of their longer cycle life, higher power density, and improved battery safety. A constant current ( CC ) charging process followed by a constant voltage ( CV ) charging mode is the preferred charging technique for Li-ion batteries. Generally, in the first stage of battery charging which is commonly known as CC mode, the battery voltage rises quickly until it reaches its predetermined voltage level while the current remains the same. In the second stage of the charging process, the battery voltage remains constant, and the magnitude of the current begins to reduce. Once the current drops to almost zero, the charging process will be stopped. This technique of charging has been adopted in Two-coil WPT systems. Moreover, Zero Phase Angle conditions ( ZPA ) for both modes could be achieved to reduce the reactive power, increase efficiency, and prevent the hard switching of the MOSFETs. Three-coil WPT system, similar to two-coil system, is capable of achieving constant output current and constant output voltage with ZPA. However, in the CV mode of the conventional three-coil design, the efficiency of the light load system dramatically decreases as the load becomes smaller. Genreallly, In this work, a new Series-Series- LCLCC (S-S-LCLCC) compensation design for three-coil WPT system with load-independent output voltage, which is capable of realizing ZPA characteristics during the entire process of charging process, is proposed. The new design is capable of significantly improves the energy efficiency stiffness against the load variation, misalignment, increases the flexibility to optimize the system efficiency, reduces the voltage stress and increases the power delivery to load compared to the conventional topology. Moreover, the quality factor analysis for both conventional and the new design has been simulated, and the results show the novel system has the potential to improve the overall performance. The lab-made experimental design of a three-coil S-S-LCLCC WPT system with power rating of 420W and 96 V output voltage shows that the overall trend of efficiency of the proposed design is higher than the conventional S-S-S design as the load decreases and the new system has approximately 10% higher efficiency when the battery equivalent load resistance reaches 222 Ω. Moreover, the new design shows much better performance than the conventional system in the case of misalignment. Simplified models of S-S-LCLCC and S-S-S have also been successfully proposed and tested in this work to ease the simulation and the theoretical analysis.

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