| The aim of this dissertation is to design, analyze and optimize wireless charging system and its control method in the electric vehicles (EVs) or/and plug-in hybrid electric vehicles (PHEVs) application. Wireless charging is more convenient, safe, reliable and environmentally adaptive compared with conventional plug-in conductive charging. It also provides an effective and alternative solution to extend the driving range for EVs. Inductive power transfer (IPT), the main technology used in EV/PHEV wireless charging, is based on the Faraday’s law of induction. The main part of the IPT system is a loosely coupled transformer, the primary and secondary windings of which are physically separated. By injecting a high frequency alternating current into the primary winding, a time-varying magnetic field is generated in space around. The time-varying magnetic field induces an alternating current in the secondary winding if a close circuit is formed. Thus, the electrical energy is transferred wirelessly to the secondary side to charge the battery. The much lower efficiency and the sensitivity to frequency and parameters variations are the major limitations of wireless charging in EVs/PHEVs application. Therefore, a comprehensive characteristics analysis is essential to design an efficient and robust wireless charging system. The main focuses of this dissertation are proposing several modeling methods, studying the characteristics of wireless charging systems based on the proposed models, finding a tuning method for zero voltage switching (ZVS) operation to improve the efficiency, proposing wireless charging pad design procedure, investigating the effects of parameter variations and proposing an appropriate wireless charging strategy with robust control.At first, conventional equivalent circuit model (CECM), voltage dependent equivalent circuit model (VDECM) and voltage dependent dynamic state-space model (VDDSSM) are proposed to analyze the characteristics of the EVs/PHEVs wireless charging systems. The double-sided LCC compensated wireless charging system and magnetic integrated LCC compensated wireless charging system are also proposed. The characteristics of the series-series (SS) compensated and double-sided LCC compensated wireless charging systems are analyzed and compared based on the VDECM. The feasibility of inter-operation between wireless chargers manufactured by different companies is also studied. Moreover, the characteristics of the magnetic integrated LCC compensated wireless charging system is investigated based on VDDSSM.Our research shows that the resonant frequency of the double-sided LCC compensation topology is independent on coupling and load. The output current is constant, irrelevant to the battery voltage when it is operated at the resonant frequency. The current on the primary main coil is also constant, only related to the input voltage, which is important for multiple secondary sides. Comparing with SS compensation topology, the advantages of the double-sided LCC compensation topology is obvious. It is less sensitive to the variations of self-inductances caused by the change of the relative position of the primary and secondary coils. In order to investigate the inter-operability between different types of compensation topology, the critical self-inductance of primary or secondary main coils, which reveals the power transfer capability and controllability of the inter-operated wireless charging system, are derived based on fundamental harmonic approximation. The magnetic integrated LCC compensated wireless charging system can transfer the same amount of power with smaller additional inductances, compared with one that is not integrated. Four operation modes of the magnetic integrated LCC wireless charging system are discovered and investigated according to VDDSSM.A model-based parameter tuning method is also proposed to realize ZVS operation. In order to get an accurate parameter tuning method, the high order harmonics are considered when the capacitance of the secondary series capacitor is tuned for the double-sided LCC compensated wireless charging system. Moreover, considering the different couplings and different voltage gains, a VDDSSM-based numerical method to tune the secondary series capacitor for ZVS realization is proposed for magnetic integrated LCC compensated wireless charging system. Thus, ZVS can be achieved over the entire operating range. Given these situations, the tuned wireless charging can be called as semi-resonant wireless charging.Then, a wireless charging pad design method based on electromagnetic theory is put forward. Electromagnetic loss is taken as an important factor in the design method. It is obvious from the simulation and measurement results that undesired cross couplings are inevitable for the magnetic integrated wireless charging system. The VDECM of the magnetic integrated wireless charger considering the cross couplings is proposed. Equations reflect the effects of the cross couplings are derived step by step. Besides, the mistuning effects due to the self-inductance variations of main coils are investigated based on this model.Considering the parameter variation and parameter statistical uncertainty, a proper wireless charging strategy is proposed based on μ-synthesis robust control for the EVs/PHEVs wireless charging systems. The influence of the parameter statistical uncertainty on the wireless charging system is investigated by applying Monte-Carlo method. An improved generalized state-space averaging model (GSSAM) for the uncertain wireless charging system was proposed. Meanwhile, the charging control strategy for the EVs/PHEVs wireless charging system was put forward with the μ-synthesis robust control based on the improved GSSAM.Finally, the simulations and experiments are investigated to verify the proposed modeling methods and the conclusions of the model-based characteristics analysis. Both the double-sided LCC compensated and magnetic integrated LCC compensated wireless charging systems are demonstrated to be efficient EVs/PHEVs wireless charging systems. The simulation and experimental results verified that the fundamental characteristics of the wireless charging systems can be analyzed using the VDECM. Moreover, the VDDSSM is more accurate and actual. It can reflect the operation modes of the wireless charging system besides the fundamental characteristics. |
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