Dual-Loop Control Method for CPT System Under Coupling Misalignments and Load Variations

Apart from the load variation, the coupling misalignment of a capacitive power transfer (CPT) system can change the resonant frequency, which results in the variation of the output voltage/current. This article proposes a dual-loop control CPT system aiming at reducing the effect of the coupling misalignment and load variation. Based on the modeling of the LC–LC compensated CPT system, the constant-current (CC) and constant-voltage (CV) frequencies are derived. Then the frequency splitting and frequency bifurcation are illustrated. The frequency tuning is realized by tracking the input and output voltage rather than the input voltage and current. This method is helpful for tracking CV frequency accurately, and it can avoid the system operating at other resonant frequencies caused by frequency bifurcations. Based on the proposed control method, a 250-W experimental prototype with a 20-mm transmission distance is built. The CPT system can always operate in the load-independent CC/CV mode and the output voltage/current can be controlled to the target value with 2% error, when the load resistance and coupling misalignment vary from 5 to $50~\Omega $ , 0- to 100-mm $x$ -misalignment, and 0- to 20-mm $z$ -misalignment.