In wireless charging systems, the H-bridge converter's switching frequency is set close to the system's natural resonance for achieving optimized zero voltage switching (ZVS). Variations to the system's natural resonance are commonly tracked by following the changes in the resonant current's polarity, i.e., current zero-crossings. The main implementation challenge is accounting for the time delay between the real monitored current and the final resulting switches’ commutations. This becomes critical at high switching frequencies, particularly when the magnetic coupling and loading vary widely. This paper proposes an auto-resonant detection method that continuously ensures optimized ZVS turn-on with the minimal circulating current over the operable range of magnetic coupling and load. The suggested implementation provides two split variable references for the resonant frequency detection, which adaptatively compensate for the propagation delay based on the resonant current slope. The auto-resonant scheme is benchmarked against the commonly employed method with fixed current detection references. The results highlight the auto-resonant strategy's advantages, namely extended operable range, wider ZVS turn-on region, ease start-up, and improved DC-to-DC efficiency. The auto-resonant features and functionality are verified experimentally with a 200 W low-voltage e-bike wireless charger. Finally, the benefits of the presented method are analytically explored for high-power applications by considering the H-bridge semiconductor losses of a state-of-art 50 kW wireless charging system.

中文翻译：

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用于磁耦合和负载变化较大的 IPT 系统中优化 ZVS 操作的自谐振检测方法


在无线充电系统中，H 桥转换器的开关频率设置为接近系统的自然谐振，以实现优化的零电压开关 (ZVS)。通常通过跟踪谐振电流极性（即电流过零）的变化来跟踪系统自然谐振的变化。主要的实施挑战是考虑实际监控电流和最终产生的开关换向之间的时间延迟。这在高开关频率下变得至关重要，特别是当磁耦合和负载变化很大时。本文提出了一种自谐振检测方法，可在磁耦合和负载的工作范围内持续确保优化的 ZVS 导通和最小环流。建议的实现为谐振频率检测提供两个分离变量参考，其基于谐振电流斜率自适应地补偿传播延迟。自谐振方案以具有固定电流检测参考的常用方法为基准。结果凸显了自谐振策略的优势，即扩展的工作范围、更宽的 ZVS 开启区域、轻松启动以及提高的 DC-DC 效率。自动谐振特性和功能已通过 200 W 低压电动自行车无线充电器进行实验验证。最后，通过考虑最先进的 50 kW 无线充电系统的 H 桥半导体损耗，分析探讨了该方法在高功率应用中的优势。