Individually Regulated Multiple-Output WPT System With a Single PWM and Single Transformer

Abstract

This paper proposes a new individually regulated multiple-output wireless-power-transfer (WPT) system using single pulsewidth modulation (PWM) and a single multi-output transformer. The proposed system mainly consists of a single primary transmission channel, bandpass filters (BPFs) corresponding to each output, and a digital controller unit. The digital controller generates a single PWM signal comprising an array of distinct frequency components reserved for each output of the multi-output converter. The primary transmission channel includes a high-frequency inverter circuit and a primary transmission coil. When the inverter circuit is driven by the PWM signal, all the underlying frequency components are transmitted through the inverter circuit and the primary transmission coil. Each of these frequency components is separated at the receiver side coil by the resonant BPF connected to each of the outputs. Because the central frequencies of each BPF differ from each other, each filter allows only signals that are within their frequency band. Each output voltage of the multiple-output converter is regulated by modulating the frequency and amplitude of the frequency components corresponding to each output (or the BPF) inside the digital controller. Compared with all the other resonant topologies, the series-series resonance topology is efficient and facilitates applications involving loosely coupled WPT. However, the Q-factor of the series-series resonance topology is relatively low compared with the remaining resonance topologies. The interaction between each of the outputs increases as the Q-factor of the BPF decreases, which results in load regulation failure. The proposed multiple-output WPT system uses an efficient AM-FM hybrid control technique to regulate all the outputs independent of each other. Moreover, in order to analyze and design the proposed converter controller, an accurate and simple multiple-output wireless transformer model is proposed. The transformer model and analysis of the equivalent circuit presented in this paper simplify the conventional design of the power stage and generate a small converter signal. The technical challenges, feasibility, and the advantages of the proposed converter concept are discussed. Finally, the performance of the proposed multiple resonance-based wireless converter system has been validated using a 100-W hardware test of an independently controlled four-output resonant converter system.