Design, analysis and application of forced oscillating and self-excited oscillating wireless power transfer systems

Abstract

Magnetic coupled wireless power transfer (WPT) systems are becoming more and more popular due to their flexibility, high security, low maintenance and electric isolation. According to the operating frequency, WPT systems can be classified as forced oscillating (FO) WPT systems and self-excited oscillating (SEO) WPT systems. In this thesis, many aspects of these two kinds of WPT systems are researched. Firstly, the traditional FO WPT systems are discussed according to their transmission efficiency. Various schemes to improve the efficiency of such WPT systems are summarized. Also, the schemes to regulate the output power and achieve zero-voltage switching (ZVS) are discussed. With just primary control, a hybrid modulated WPT system with output controllability and efficiency optimization is presented. The pulse frequency modulation (PFM) is adopted to regulate the output power, while the optimal equivalent load resistance is obtained through on-off keying modulation (OOK) so as to improve the system efficiency. Then in Chapter 4, a static wireless charging system using pulse frequency modulation is adopted to achieve both constant-current (CC) charging and constant-voltage (CV) charging. In Chapter 5, the novel SEO wireless charging systems are given. The self-excited oscillating WPT systems mean that the inverter operation is related to the primary current. The operating frequency is not fixed. The relevant transmission efficiency characteristics and the power transfer characteristic are both different from the traditional FO WPT systems. In Chapter 6, an autonomous frequency modulation scheme for WPT systems is proposed. This WPT system is self-excited in that its operating frequency may vary on its own to achieve the splitting frequency. Therefore, the capacity for transferring power is more than with the conventional PFM method. The efficiency of transmission is comparable with that of conventional forced oscillating WPT systems. The output power using autonomous pulse frequency modulation (APFM) can be adjusted by adjusting its duty ratio. The ZVS is achieved to reduce the switching loss. In Chapter 7, WPT for electric vehicles (EVs) and unmanned aerial vehicles (UAVs) uses the SEO WPT technology. A two-stage CC charging phase is utilized in wireless charging for EVs. Feedback control and APFM are adopted to help the system achieve CC charging and CV charging. Also, LCC-S compensation is adopted in the wireless charging system for UAVs to achieve fast charging. In Chapter 8, an automatic coupling coefficient identification method for WPT systems based on SEO is proposed. The secondary-side load is short-circuited. It is theoretically proved that the system will operate on the splitting frequency and this splitting frequency is related to the coupling coefficient. By measuring the operating frequency, the coupling coefficient can be calculated. In Chapter 9, the dynamic wireless charging for electric vehicles with autonomous frequency control is proposed. By adopting WPT system based on SEO, constant output power is achieved when electric vehicles are moving on the road. To verify the proposed WPT systems, theoretical analyses, numerical simulations, and experimental verification are all conducted and presented to provide in-depth discussions and validations for FO and SEO WPT systems.