This paper proposes a new control technique, which only employs the primary-side controller and load identification approach to adjust the charging voltage/current for both series-series (SS) and series-parallel (SP) compensated wireless power transfer (WPT) systems. The advantage is that dual-side wireless communication for real-time charging current/voltage adjustment is avoided as well as it is suitable for different charging modes, e.g. constant voltage (CV) and constant current (CC) charging defined by the battery charging profile. The load identification approach, which utilizes the reflected impedance theory and quadrature transformation algorithm for calculating the active power, is proposed to estimate the equivalent load resistance. Then, the CV/CC charging for both SS and SP compensation are achieved by PI controlled phase shift H-bridge inverter. The simulation and experimental results validate the feasibility of the proposed method. During the CC charging, the 3.01A and 3.03 A for SS and SP compensation with the error of 1.2% and 1.4% are achieved. During the CV charging, the 25.8 V and 25.7 V for SS and SP compensation with the error of 1.1% and 1.3% are realized. The proposed method improves the performance of both SS and SP compensated WPT systems to be more suitable for the applications that require compact and light weight receiver.

Charging current and efficiency of a wireless power transfer (WPT) system depend on the equivalent load resistance of supercapacitor load, which varies during charging. To achieve constant current (CC) charging and maximized efficiency under variable loads, control method that uses primary-side phase shifted H-bridge inverter and secondary-side semi-active rectifier are proposed. The secondary-side control method not only achieves CC charging, but also ensures no reactive impedance seen into the semi-active rectifier. On the other hand, the maximum efficiency tracking is based on searching the minimum system dc input current for any given output power and realized by the phase shifted H-bridge inverter controlled by the perturbation and observation algorithm. Experiments are performed to validate the feasibility of the proposed control method. During CC charging of 3 A, the maximum efficiency is 81% and the largest efficiency improvement is 15.2% at light load. The proposed method improves the system performance and is suitable for practical applications that require compact receiver and no wireless communication link between the transmitter and the receiver.

In this paper, a novel magnetic coupler of wireless power transfer (WPT) system for the solar wing driving of the spacecraft is designed. Compared with the traditional slip-ring power supply, the proposed magnetic coupler is characterized by non-contact, high efficiency, wear-free, safety and reliability. Particularly, it can be applied to the rotating condition. To realize light-weight and small-volume of the receiver, the magnetic coupler has been optimized from both compensation topology and coil configuration. Firstly, a Series-None (S-0) topology is employed to eliminate the bulky secondary-side compensation capacitor. Secondly, a new nested solenoid coil with strip core (SCSC-type) is proposed to ensure miniaturization, stable power transfer and high efficiency. Finally, the experimental setup is built to verify the performance of the designed magnetic coupler. Experimental results are well-matched to simulations, demonstrating that the weight of the prototype is 1.3 kg and the transfer power is 3 kW at an AC-DC efficiency of 92.7%.

Wireless power transfer (WPT) systems have attracted much attention because of their safety, convenience and environmental friendliness. For wireless supercapacitor charging, the system efficiency and charging current are highly dependent on the load that varies over a wide range. In this paper, a simultaneous maximum system efficiency (MSE) tracking and constant current (CC) charging control scheme for a supercapacitor is proposed. For CC charging, a double-sided LCC (DS-LCC) topology is chosen due to its characteristic of providing a load-independent output current. Furthermore, the impact of the coil internal resistance on the system characteristics (especially the charging current) is investigated, so a semi-active rectifier is introduced on the secondary side to achieve accurate CC charging and improve the system robustness. Based on the variable-step perturbation and observation (VS-P&O) algorithm, the MSE is tracked by searching for the minimum system input DC current using a primary-side Buck converter on the premise that the charging current reaches its target value. The above two control loops are independent, and the mutual communication is unnecessary when they cooperate; thus, the system is simplified. The simulation and experimental results show great consistency with the theoretical analysis. The experimental system maintains the MSE of 86% during charging the supercapacitor from 20V to 50V with 2 A.

The multiphase receiver for more steady output is proposed in this paper. The conventional power supply rail with multipole such as I-type has a main drawback: the induced voltage of the double-D coil of receiver has a sinusoidal fluctuation. The multiphase receivers are proposed to solve the problem. The fluctuation factor, effective value of induced voltage and mutual inductance, cost and loss of different numbers of phase in different connection modes are analyzed and compared. The applicable conditions of different types are given. The structural size of single-phase coil is optimized to achieve larger coupling coefficient. The influence of distance between phases on fluctuation factor and induced voltage are calculated and the design principle of the distance between phases is determined. Design guideline is proposed including the constraints of installation environment and the distribution of different phases. The structural size of single-phase coil and the distance between phases are optimized to improve the coupling coefficient and reduce cost, loss and voltage level of resonator. A four-phase receiver of 10kW DWC system is designed and constructed. In the dynamic 10kW experiment, the fluctuation factor is reduced to 0.146 from 0.3 of two-phase receiver and 1.0 of single-phase receiver.

Ambient temperature is a significant factor that influences the characteristics of lithium-ion batteries, which can produce adverse effects on state of charge (SOC) estimation. In this paper, an integrated SOC algorithm that combines an advanced ampere-hour counting (Adv Ah) method and multistate open-circuit voltage (multi OCV) method, denoted as “Adv Ah + multi OCV”, is proposed. Ah counting is a simple and general method for estimating SOC. However, the available capacity and coulombic efficiency in this method are influenced by the operating states of batteries, such as temperature and current, thereby causing SOC estimation errors. To address this problem, an enhanced Ah counting method that can alter the available capacity and coulombic efficiency according to temperature is proposed during the SOC calculation. Moreover, the battery SOCs between different temperatures can be mutually converted in accordance with the capacity loss. To compensate for the accumulating errors in Ah counting caused by the low precision of current sensors and lack of accurate initial SOC, the OCV method is used for calibration and as a complement. Given the variation of available capacities at different temperatures, rated/non-rated OCV–SOCs are established to estimate the initial SOCs in accordance with the Ah counting SOCs. Two dynamic tests, namely, constant- and alternated-temperature tests, are employed to verify the combined method at different temperatures. The results indicate that our method can provide effective and accurate SOC estimation at different ambient temperatures.