| Summary: | In the past decade, IPT (Inductive Power Transfer) systems have gained successful applications in many different fields owing to its unique contactless/wireless power transferring characteristics. Such a feature allows IPT to be used in operating environments where direct electrical contacts are inconvenient or impossible. However, one of the major technical challenges which limit their further development is the lack of efficient, accurate and fast power flow control methods. This dissertation focuses on developing a new controller which can overcome the limitations of existing controllers for the IPT systems. Techniques such as the magnitude and frequency control of the primary track current, linear voltage regulation, shorting-control, and dynamic tuning/detuning of the secondary pickup, have been proposed and successfully employed in the past for controlling the pickup output voltage. However, each of these power flow control methods has distinguishing advantages and drawbacks. For the magnitude and frequency control on the primary side, the primary power supply can only drive a single power pickup, thus its applicability is limited. Linear voltage regulating or shorting-control on the secondary side is good for multiple pickups, but they suffer from significant conduction losses when operating under light loading conditions. And the existing dynamic tuning/detuning can only achieve single-side regulation using traditional PI control. In this thesis, a novel DTDCA (Directional Tuning/Detuning Control Algorithm) power flow control method has been proposed to regulate the output voltage of the pickup. The DTDCA is designed such that it can correctly track and stabilize the pickup output voltage to a desired value by dynamically changing the tuning condition of the secondary pickup to achieve full-range tuning control. An LCL power pickup has been studied as an alternative tuning configuration in additional to the conventional LC power pickup. Control of the LCL power pickup is achieved by changing the dc excitation current of a saturable inductor which functions as a variable tuning inductor in the resonant tank. The dc excitation current of the saturable inductor is controlled by a linear-mode MOSFET using DTDCA. Effects of variations of different circuit parameters such as the operating frequency, magnetic coupling between the primary and secondary coils, tuning capacitance, and load, on the pickup output voltage have been studied. And the control range for the saturable inductor is determined based on their worst-case integrated effect. It has been found that two main factors, namely the sampling frequency and tuning step-size of the controller, have to be carefully designed to achieve good control result. A large tuning step-size often causes output voltage chattering, and a small tuning step-size can result in sluggish response. An algorithm named Simple Step-Size Adjustment (SSSA) has therefore been developed and integrated into DTDCA to solve the problems associated with the fixed tuning step-size. The proper sampling frequency has been selected according to the approximated settling time of the LCL pickup. The SSSA-DTDCA controlled LCL power pickup has shown to be able to effectively regulate the output voltage. However, it has steady state and dynamic errors. A Fuzzy Logic Based (FLB) tuning step-size control has therefore been proposed to improve the DTDCA control by dynamically changing the tuning step-size according to the error and rate of error of the output voltage. And significant improvements have been achieved in: 1) removing steady state errors; 2) reducing dynamic errors in tuning attempts; and 3) achieving faster control speed compared to SSSA-DTDCA. The proposed FLB-DTDCA is then applied to a simple parallel LC power pickup. Control of the LC pickup is achieved by changing the duty cycle of a switch-mode variable tuning capacitor. Effects of circuit parameter variations on the pickup output voltage have been investigated for determining the control range of the variable tuning capacitor. A control signal conversion method has been proposed to convert the raw controller output into duty cycle controlled switching signals for the variable tuning capacitor to obtain the desired equivalent capacitance while achieving ZVS. Both simulation and practical results have shown that the proposed SSSA-DTDCA and FLB-DTDCA can achieve full-range tuning control of LC and LCL power pickups. The control methods proposed and results obtained are very useful for the development of smart power pickups in the future.
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