A novel high voltage operation featured wireless power transfer system for monitoring equipment charging on 110 kV high voltage transmission line based on magnetic resonant coupling is studied and designed. With consideration of operation environment on transmission line and electrical transmission tower, an overall scheme is proposed through installation position, coupling structure and driving topology design. In order to improve system's suitability in high voltage environment, related optimization methods, including constraining power flow path, improving quality factor and coupling have been adopted. Since the coupling coils are fixed at both ends of insulator string, barrel shaped high permeability material layer is added to constrain the magnetic field distribution. Moreover, cross-impacts between transmission line and the charging system are analyzed. The influence of power frequency magnetic field on charging system is calculated and electric distribution of insulator string with the charging system are simulated. Analysis results indicate that cross-impacts can be negligible. Experimental results verify that the transmission power can meet power supply requirements and the designed charging system can be operated stably under high voltage condition.

Magnetic resonant coupling (MRC) wireless power transfer (WPT) technology provides a novel solution to the tricky power-charging issue of densely connected sensor devices in the age of Internet of Things. Due to the cost and space constraints, the one-to-one MRC WPT is not suitable for charging the large number of sensor devices. The one-to-many MRC WPT requires less cost and space, but all receivers receive the power emitted from the transmitter disregarding the receivers' needs, which will lead to the accelerated aging even damage or malfunction of the receivers. In this paper, we propose a selective omnidirectional MRC WPT with multiple-receiver system. The power transmitted by an omnidirectional transmitter composed of three orthogonal circular coils will be received by any receiver located nearby. As the number of the transmitters reduces, the cost and space declines. Based on the band pass filter principle, the receivers selectively acquire the power at a designated frequency, which improves the energy efficiency and increase equipment service life. Moreover, for the proposed model, its magnetic field distribution of the simulation and physical experiments are carefully designed and performed, and their results are examined and analyzed in detail. They all confirm the capabilities of selective power transferring and the omnidirectional power transfer of the MRC WPT.

LLC resonant converter is a nonlinear system, limiting the use of typical linear control methods. This paper proposed a new nonlinear control strategy, using load feedback linearization for an LLC resonant converter. Compared with the conventional PI controllers, the proposed feedback linearized control strategy can achieve better performance with elimination of the nonlinear characteristics. The LLC resonant converter's dynamic model is built based on fundamental harmonic approximation using extended describing function. By assuming the dynamics of resonant network is much faster than the output voltage and controller, the LLC resonant converter's model is simplified from seven-order state equations to two-order ones. Then, the feedback linearized control strategy is presented. A double loop PI controller is designed to regulate the modulation voltage. The switching frequency can be calculated as a function of the load, input voltage, and modulation voltage. Finally, a 200 W laboratory prototype is built to verify the proposed control scheme. The settling time of the LLC resonant converter is reduced from 38.8 to 20.4 ms under the positive load step using the proposed controller. Experimental results prove the superiority of the proposed feedback linearized controller over the conventional PI controller.

State of charge (SOC) estimation of deep-discharging Li-ion batteries under complicated working conditions at different temperatures is still challenging. The depth of discharge (DOD) of batteries in electric vehicles (EVs) is generally low nowadays, resulting in the insufficient use of battery energy. This paper proposes a SOC estimation method using a novel partial adaptive forgetting factors recursive least square (PAFFRLS), which adjusts the forgetting factors based on the own physical properties of each pa-rameter in equivalent circuit models (ECMs) to accommodate to greatly changing under deep-discharging range and highly dynamic working conditions. The gain matrix in the proposed method is split to update independently according to each parameter, which solves the issue of mutual influence between parameters vary with different rates. In addition, four typical test profiles including DST, UDDS, US06 and EUDC are employed to simulate different working conditions of EVs. Eventually, numerous simulations and experi-ments at different temperatures are employed to verify the validity of the proposed method. The average errors of the SOC estimation under four different kinds of working conditions are all less than 1.3% as well as the peak errors are all less than 5%. The peak errors are all less than 3% while DOD is larger than 90% which illustrates the effectiveness of the proposed method in the case of deep-discharging and provides a better guidance to the design of battery management system (BMS) in EVs.

LLC resonant converter would have light-load voltage regulation problems due to the effect of parasitic capacitances in high frequency range. In this paper, an energy feedback control method is proposed to improve the light-load regulation capacity by using synchronous rectifiers (SRs). The SR bridges are controlled ahead of the primary inverter bridges to deliver the energy from load to source, reducing the output voltage independent of the load. Then the desired voltage can be achieved even in no load conditions by regulating the operation time of the energy feedback mode. The gain, voltage ripple and efficiency performances of the proposed control method are discussed based on the precise analysis and accurate model of the converter. Moreover, the light-load operations of the LLC resonant converter are analyzed deriving the critical load condition. Finally, the proposed control method is verified by the experiments of a 12V/8A LLC resonant converter prototype.

Wireless power transfer (WPT) technology has become a popular solution to battery charging of mobile equipment. However, the variation of the load power will affect the transmission capacity of the system, which might make the electrical load cannot gain the required rated power and function improperly. Based on the analysis of power transmission characteristic and resonance state of WPT system, this paper adopts the simulated annealing (SA) method to track the maximum power point (MPP) of WPT in bifurcation state. The power tracking effectiveness of the proposed SA method is compared with that of the traditional maximum power point tracking method in WPT system based on perturbation and observation. The SA method performances under different parameters are assessed with consideration of the number of iterations needed for convergence and the convergence probability. Experimental validation of the maximum power tracking of WPT based on SA method is presented under different load conditions. Experimental results verify that the proposed SA method realizes the maximum power tracking when the WPT system works in the power bifurcation area, thus making full use of the inverter's VA capacity and approaching a unity power factor.