Autonomous pulse density modulation for parity-time-symmetric WPT system with flexible power regulation

Parity-time symmetric wireless power transfer (PT-WPT) systems exhibit fixed constant-power output, which fails to meet the power regulation requirements for applications such as drone wireless in-flight charging. To address this limitation, this paper proposes an autonomous pulse density modulation (APDM) strategy. Within the strong-coupling region, the constant-power level can be flexibly regulated by adjusting the pulse density without disrupting the 'gain-loss balance' of the PT-symmetric state, thereby adapting to multi-scenario power demands. First, a high-order primary-series (S) and secondary-single-inductor-double-capacitor (SLDC) topology is designed to effectively expand the constant-power region of the system. Then, an APDM strategy with uniform energy injection is proposed, which optimizes pulse sequence distribution to suppress output current fluctuation and enable full-range zero-voltage switching (ZVS). Experimental results demonstrate that the system maintains the robustness of PT symmetry against coupling fluctuations while achieving autonomous and flexible power regulation across the designed pulse density range, with efficiency maintained at 88% and stable ZVS implementation. These results confirm the superiority of the proposed solution in power regulation, significantly expanding the application potential of PT-WPT systems in multi-power-demand scenarios such as drones.