Abstract：Brushes and slip rings in rotary steerable systems are the main equipment for power transmission under rotational conditions to charge the batteries in steering control and measurement modules. However, this transmission method is prone to generating electrical sparks, potentially triggering safety risks. In addition, the wear and tear caused by long-term operation may lead to poor contact, resulting in unstable power transmission, which reduces the stability of the power supply in a rotary steerable system. Wireless power transfer (WPT) technology can address the issues of poor power supply safety and stability caused by traditional brushes and slip rings. The capacitive power transfer (CPT) system offers advantages such as low eddy current loss and strong resistance to electromagnetic interference. It is well-suited to withstand harsh conditions in the downhole. The battery charging process typically includes two stages: constant current charging and constant voltage charging. Firstly, the charging is carried out in constant current mode, where the charging voltage rises rapidly as the equivalent load of the battery increases. Once the voltage reaches the rated value, it switches to constant voltage mode until the charging process is complete. This paper proposes a CPT system that automatically switches between constant current and voltage modes. The system achieves a smooth, automatic transition from constant current output to constant voltage output without additional active control while maintaining zero phase angle (ZPA) operation in both output modes. The topology of the CPT system with automatic switching between constant current and constant voltage modes was presented. The electric field coupler adopted a single transmitter and dual receiver structure in the system. Therefore, the coupler’s voltage source equivalent model was established. Then, a decoupled secondary-side single-transmitter dual-receiver coupler model was designed based on physical parameter design to avoid mutual interference between the secondary side inputs. The system's output characteristics were theoretically analyzed. The system's output characteristics gradually transition from constant current output to constant voltage output as the load increases. The system maintains the ZPA state throughout the entire charging process. Electromagnetic simulation of the electric field distribution of the coupler was conducted using the finite element method. The simulation results show that the leakage electric field generated by the coupler during system operation does not interfere with the normal operation of the instruments in the rotary steerable system. Then, a prototype was built. The experimental results indicate that the system can achieve a constant current output of 1.5 A and a constant voltage output of 60 V. The current fluctuation is less than 5% in the constant current output mode, the voltage fluctuation is less than 3% in the constant voltage output mode, and the maximum transmission efficiency is approximately 90% during system operation. These results meet the constant current and constant voltage requirements for battery charging.
吉莉, 张家琦, 张江洪. 一种恒流/恒压输出自切换的电场耦合式无线电能传输系统[J]. 电工技术学报, 2025, 40(24): 7879-7890.
Ji Li, Zhang Jiaqi, Zhang Jianghong. A Capacitive Wireless Power Transfer System with Self-Adaptive Output Switching Between Constant Current and Constant Voltage. Transactions of China Electrotechnical Society, 2025, 40(24): 7879-7890.
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