The Research On WPT System Of On-board Equipment Based On Power Wave

Wireless Power Transfer(WPT) technology is a new technology using electro-magnetic filed to transfer electric energy, with which load can wirelessly receive power from the power supply. WPT technology is an integrated technology that includes of the electro-magnetic field, the radio frequency technology, the power electronic technology and the control engineering of multi-discipline and multi-theory. At present, WPT technology is one of the most popular research topics in the field of electrical engineering, and is also one of the hot topics in basic science, applied research and development, and it has a broad prospect in application and development. The WPT technology can solve many problems, such as wiring in disorder, electric plug and pull, short circuit in vehicle equipment, and it has the advantages of safety, convenient and reliable. So in the field of vehicle equipment,the WPT technology has attracted everyone’s great attention and had practical application.WPT systems of on-board equipment have their own characteristics. For example, it uses of the on-board power supply, so the input voltage is low, usually 12 V or 24V; it needs to meet the power demands of different devices; the distance and position between coils are easily changed because of the bumps of the vehicle, so it cause the performance of the transmission to decrease. Due to the loose coils’ coupling coefficient between the primary side and secondary side, these two sides usually keep a same resonant frequency to improve the transmission efficiency or the load power. Traditional WPT system modeling approaches features multiple electric parameters and multiple components, hence the modeling of WPT system generates a series of multi-parameters high-order differential equations or high-order matrix equations. Any slight change in system parameters may cause noticeable changes in WPT system output. The WPT system is a high order nonlinear system, with many parameters to be determined, which may cause a poor transmission performance, or volatility of transmission efficiency and load power.To counter the problems above, the paper proposed the two-port network and power wave theory to model the WPT system, analyze of WPT systems’ power wave of the incident & reflection, and set up the power flow model. The modeling and analysis approaches above can be applied to the WPT systems of on-board equipment. It can solve the WPT system’s actual application problem in on-board equipment, such as low transmission efficiency or low load power. The major contributions are provided as follows.(1) To solve the problems of WPT system such as the traditional modeling approaches which are complex and difficult to solve, the paper analyzed the power flow’s incidence and reflection in key ports using the two-port network and power wave theory, and the model of power flow was established. The transmission efficiency and load power were analyzed and optimized according to the impedance matching and power flow model. Compared with the traditional modeling approaches, the two-port network and power wave theory approaches simplified the modeling and analysis of the WPT system. Power flow models revealed the process of power transfer, decay and loss when the WPT system transferred wirelessly. The results of the research and experiments show that the approaches are not only suitable for the WPT system of on-board equipment, but also can be applied to the modeling and analysis of general WPT system.(2) Because the source impedance is equal to 50Ω in high frequency & low power WPT systems of on-board equipment, the WPT systems were modeled and analyzed following the maximum power transfer theorem. In this paper, the minimum loss mode was used to optimize the system parameters, and the loss caused by the complete matching mode was avoided. A comparative study of the two modes is carried out. The two modes can achieve the ideal transmission performance, but each mode has its own applicable scope.(3) If the equivalent two-port network with multi-resonator WPT system meets complete impedance matching, WPT system can reach high load power of mid-distance transfer. The paper proposed the technique to adjust the distance between input coil & primary side resonant coil, and the distance between secondary side resonant coil & output coil, meantime slightly adjust resonance frequency, when two-port network with multi-resonator WPT system meets complete impedance matched, WPT system can reach high load power.(4) Because of the low source impedance in low frequency & high power WPT systems of on-board equipment, the maximum transmission efficiency theorem should be followed. In this paper, the power wave theory and the impedance matching of key nodes were used to analyze and model the power flow and build the power flow model. The power flow model showed the transmission efficiency reached maximum when the load and two-port network’s output impedance meet the no reflection impedance matching, and the impedance of two-port network’s input port determined the active power input of two-port network and finally decides the load power. The TSST topology was proposed to solve the problems of low transmission efficiency, low load power and load power adjustment. In the end, the relationship of coupling coefficient between input coil, relay coil and output coil coupling coefficient and load were analyzed.