Compact Capacitive Compensation for Adjustable Load-Independent Output and Zero-Phase-Angle Input for High Efficiency IPT Systems

For inductive power transfer (IPT) systems, it is desirable to have an adjustable load-independent constant voltage (CV) output or constant current (CC) output with zero-phase-angle (ZPA) between the input voltage and current. In this article, a compact capacitive compensation scheme using a minimal number of compensation capacitors is proposed to realize series/series-parallel (S/SP) compensation for adjustable CV output and series/parallel-series (S/PS) compensation for adjustable CC output, achieving reduced system weight, volume, and cost. The output voltage of the S/SP compensation or the output current of the S/PS compensation is independent of the load and the IPT transformer parameters, making the system design straightforward. In addition, the optimal transformer's turns ratio that maximizes the system efficiency and minimizes the overall compensation capacitance for a given input-to-output transfer function is derived. Experimental prototypes of different IPT transformers are built to illustrate the input-to-output transfer characteristics. Compared with traditional design, the proposed S/SP converter achieves 3% increase in efficiency and 37.6% reduction in compensation capacitance, whereas the proposed S/PS converter achieves a 0.5% increase in efficiency and 52.8% reduction in the compensation capacitance.