| The internal diagnosis MEMS has rapidly developed in recent years, which becomes an important field in medical research and application. Currently, most internal microelectromechanical systems are powered by button cells. However, there are some problems existing in this power supply mode, such as the limited battery life and insecurity. The wireless power transmission(WPT) technology can provide an effective energy supply for the internal MEMS with a series of advantages, such as long-lasting, security,stable and ect.Currently, the power generator which is set up by our research group for a WPT system is composed of the signal source and power meter, However, these instruments are bulky, heavy and expensive, not easy to move, and furthermore this power generator does not have the instantaneity function to track system resonance frequency, Therefore, when the mismatch occurs, the power transfer efficiency will greatly reduce, which finally influences the stability of the power transmission. So for the problems above, based on thoroughly analysis on the research results of WPT at home and abroad, this thesis conducts a research to miniaturize the WPT power generator, aiming to set up a portable, low cost, stable transmission circuit for wireless power transmission system. The detailed work accomplished in this thesis are as follows.Firstly, the basic principle and structure of the wireless power transmission system are introduced. Through the analysis of several loop compensation models, and combining with the actual working status of a wireless power transmission system, the optimum compensation model of the wireless power transmission system is obtained here. The three dimensional structure of the wireless power transmission model is analyzed, The mathematical model and efficiency expressions of the power transmission of the system are each obtained here.Secondly, the open loop power generator of a WPT system is designed. The design of the input power supply module, inverter control circuit, main inverter circuit, coupling transformer and secondary receiving circuit are successively introduced. The physical circuit of the power generator is built, and the performance parameters of the power generator has been studied through experiment. It proves that the circuit can satisfy power need of the capsule endoscopy.Thirdly, the mismatch phenomenon of the WPT system is studied which is mainly caused by the environmental and coil parameters change, and the formation mechanism of the mismatch is analyzed. Then, work out the system energy efficiency expressions under every detuning case are worked out, and the experimental verification is carried out. The conclusion is obtained that the frequency detuning of primary coil plays an important part on the efficiency of transmission system, And then the view is put forward that to design a tracking circuit for the primary coil, making sure that the system is working with relatively higher transmission efficiency.Fourthly, the frequency tracking circuit is studied. Based on the analysis of the existing frequency tracking schemes, the frequency tracking method basing on Microprogrammed Control Unit(MCU) is put forward. The design of the track circuit is successively introduced including sampling, waveshaping, phase detection and MCU control strategies etc. The results of the frequency tracking circuit are studied by the experimental circuit. The experimental results show that the frequency tracking circuit of this thesis can well solve the unstable power transmission phenomenon caused by mismatch. |
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