Soft Switching of Wireless Power Supply System for Robot DC Motor Based on E-Class Inverter
Mao Ling1, Zuo Xiaolei1, Yin Yifan1, Zhao Jinbin2, Zhang Junwei1
1. College of Electrical Engineering Shanghai University of Electric Power Shanghai 200090 China; 2. Engineering Research Center of Offshore Wind Technology Ministry of Education Shanghai University of Electric Power Shanghai 200090 China
Abstract：With the rapid development of robotics technology, robots are increasingly applied in fields like industrial automation, smart homes, and healthcare. However, as robot application scenarios diversify, traditional wired power supply methods limit robotic arm flexibility due to complex wiring and space constraints, making it hard to meet growing demands. In contrast, through non-contact power transfer, wireless power supply technology addresses traditional cables' drawbacks and has become a key alternative in robotics. Particularly, wireless power transfer (WPT) systems based on E-class inverters with high-frequency and efficient inversion characteristics are ideal for powering robotic joint motors. However, a major challenge for E-class inverters is that during DC motor startup, dynamic load changes often lead to hard-switching during startup, increasing switching losses, reducing efficiency, and potentially damaging switches. This paper proposes a dynamic secondary capacitance matching method to address the persistent hard-switching problem during motor startup and ensure soft switching throughout. First, this paper investigates the variation of load characteristics during the startup to steady-state operation of a DC motor. Experiments reveal that, during the initial startup phase, the current increases rapidly, causing the equivalent impedance of the load to change quickly. As a result, the reflected impedance exceeds the design range of the E-class inverter, entering a hard-switching state, which increases switching losses and reduces system efficiency. Next, the paper models the E-class inverter and analyzes the load variation range under soft-switching conditions. Accordingly, a dynamic matching strategy is proposed to ensure the system maintains soft switching throughout the startup phase, improving system performance and reliability. An experimental prototype with a power rating of 50 W is constructed, with an input voltage of 40 V and an input current of 1.25 A. The output voltage is 24 V, the output current is 1.81 A, and the output power is approximately 43.44 W, resulting in an efficiency of 86.9%. The loss is 6.56 W. In the experiment, when the secondary side is normally compensated, the system operates in a hard-switching state at startup due to the sizeable equivalent load. However, hard switching gradually decreases as the DC motor starts, and after 1.4 ms, the system enters a soft-switching state and remains stable. When the secondary side is zero-compensated at startup, the system remains soft-switching throughout the startup process. When the system switches at 0.52 ms, its response time is approximately 25 μs, and the system quickly stabilizes and maintains soft switching. The startup time required for the zero-compensation strategy of the secondary capacitor is only about one-third of the time for the normal secondary-side compensation startup. The following conclusions can be drawn. (1) During DC motor startup, the current surges and then stabilizes, while the equivalent resistance increases. The reflected impedance decreases. When it exceeds the optimal design value, ZVS is not maintained, leading to hard switching. (2) Removing the secondary compensation capacitor during startup and using full compensation under rated conditions can dynamically adjust the inverter’s load parameters, ensuring soft switching throughout startup.
毛玲, 左孝磊, 尹伊凡, 赵晋斌, 张俊伟. 基于E类逆变器的机器人直流电机无线供电系统软开关[J]. 电工技术学报, 2025, 40(14): 4406-4417.
Mao Ling, Zuo Xiaolei, Yin Yifan, Zhao Jinbin, Zhang Junwei. Soft Switching of Wireless Power Supply System for Robot DC Motor Based on E-Class Inverter. Transactions of China Electrotechnical Society, 2025, 40(14): 4406-4417.
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2025, Vol. 40 
