Self-Oscillating Pulsewidth Modulation for Inductive Power Transfer Systems

This paper presents a new self-oscillating tuning loop for inductive power transfer (IPT) systems using a combination of phase shift and pulsewidth modulations (PS-PWMs). Self-oscillating methods are the uncertainty-tolerant solution for power and frequency control of resonant converters. However, constant duty-cycle operation affects their effectiveness with extra dc-link current ripples and losses. In this paper, PS-PWM is achieved by instant phase displacement controlling between the two legs of the inverter, which guarantees zero voltage switching (ZVS) for transients and light-load conditions. The presented solution simultaneously integrates PWM and PS switching methods with a fast dynamic response even under nonlinear conditions, e.g., battery loads, and sudden load changes. In the presented work, an optically controlled phase shifter is proposed, which has a simple structure and smoother phase regulation in comparison with digital potentiometers. Moreover, this paper analyzes the behavior of the proposed method in bifurcation condition and shows the reliability and stable operating area of the system. To show the feasibility of the presented switching technique, a prototype is implemented based on series-series (SS)-compensated topology and investigated for different operating frequencies and loads.