Selected-Interharmonic-Injected Pulse Density Modulation for One-to-Many WPT Systems

Multifrequency one-to-many wireless power transfer (O2M-WPT) is advantageous for charging various medium- and small-power loads, offering cost-effectiveness, simplicity, and minimal cross-coupling effects. However, inevitable hard switching caused by the multifrequency modulation method may lead to significant switching losses. To reduce the switching losses, a novel selected-interharmonic-injected pulse density modulation (SI
²
PDM) method for simultaneous O2M-WPT systems is proposed in this article. SI
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PDM actively injects the selected interharmonics into the primary coil for multifrequency modulation. Besides, SI
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PDM artfully regulates the interharmonic by choosing the optimal sequence from the sequences with the same pulse density to achieve independent power allocation. Most importantly, the switching frequency is reduced below the maximum operating frequency, which is beneficial for reducing switching losses and improving efficiency. Comparative experimental results between SI
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PDM and an existing method reveal a remarkable 18.58% to 82.83% reduction in inverter power losses and a substantial 1.23% to 20.27% improvement in dc-to-load efficiency. These results affirm the feasibility and effectiveness of SI
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PDM in achieving independent power allocation and enhancing efficiency in simultaneous O2M-WPT systems.