Study On Contactless Power Transfer Mode Based On Envelope Modulation

In contactless power transfer (CPT) systems, the disadvantages of traditional power transfer mode have limited the application of CPT technology. The main disadvantages include low efficiency, complicated control, low input power factor, low power density, high cost and so on. To overcome these disadvantages, this paper presented a novel power transfer mode based on an envelope modulation method, funded by National Natural Science Foundation of China. Several typical CPT systems are studied for the novel power transfer mode. And corresponding circuit topology and control methods are optimized according to different power supply demands. The main works of the paper include:1. The drawbacks of direct contact power supply mode and the necessity of developing CPT technology are analyzed. The fundamental theory and research status introduction (include theory and industrialization) have been reviewed. And the research aim, contents and significance are given based on drawbacks analysis of the traditional contactless power transfer mode.2. A novel energy transfer mode based on envelope modulation is presented. This mode achieves power conversion and transfer by carrier modulation technology according to load power requirements. The fundamental theory, the basic system structures and the relative key techniques are studied in detail. A full bridge series tuned resonant circuit is taken for example to investigate the feasibility of this envelope modulation mode. The advantages of this envelope modulation mode are presented compared with the traditional power transfer mode.3. The drawbacks of AC-AC type CPT system with traditional power transfer mode are analyzed. The system structure under envelope modulation transfer mode is studied. A novel AC-DC-AC conversion topology is proposed. In an AC-AC type CPT system with this proposed topology, the operating modes of both primary and secondary resonant tanks are analyzed. And the soft-switching condition of this topology and the system dynamic analytical model are obtained consequently. Both simulation and experiment results verifies the proposed topology.4. The drawbacks of DC-AC type CPT system with traditional power transfer mode are analyzed and a system structure under envelope modulation transfer mode is proposed. In the proposed structure, the system circuits and control strategy are simplified, and the systematic efficiency and the power density are promoted. An asymmetric DC-AC topology is taken for consideration to study the envelope modulation mechanism. The system steady-state model is built up with state space method and verified by both simulation and experiment results.5. An AC-DC type CPT system structure based on envelope modulation mode is presented. An energy injection AC-AC type topology is proposed for the structure. Its system characteristics are analyzed. The energy critical equilibrium criterion, envelope prediction method and optimal control strategy are presented in sequence. Simulation and experiment results verify the analysis results.6. A novel circuit topology for current-fed CPT system is proposed to realize wide magnitude envelope modulating on the condition that input voltage and couple parameters are constant. The steady-state equivalent model is built up, based on which, the control characteristics and key parameters design formulas are derived and verified by both experiment and simulation results. The theoretical results are helpful for system design and analysis.The main contributions of this paper are as follows.1. A contactless power transfer mode based on envelope modulation technology is presented. This mode is load power requirement oriented. Power carrier and modulating technology is employed to achieve contactless power transfer. The disadvantages of traditional power transfer mode, such as low power factor, low power density etc., are overcome and the systematic efficiency is increased. With the proposed modulation technology, the application fields of CPT technology are extended.2. A converter topology, which can realize flexible control of transferred power, is proposed according to Buck and Boost principles and the current-fed CPT system characteristics. The envelope magnitude can realize wide range adjustment with the proposed topology. Therefore, the load adaptive ability of the system is extended greatly. The topology can also be applied to general power conversions.3. A novel control strategy of the resonant power is proposed which realizes constant magnitude envelope modulation in an AC-AC high frequency conversion topology by adjusting the injected power of the resonant tank dynamically. The strategy can also be applied to other type envelope modulations.