Fuzzy control strategy for voltage stability in electric field coupling wireless power transfer systems based on switched capacitors

Abstract

Abstract

This thesisinvestigates output-voltage instability in Electric FieldCoupling Wireless Power Transfer System (CPT) under load disturbance andproposes a switched-capacitor-circuit-based fuzzy logic control strategy. Thestudy follows a complete route from CPT modeling and voltage-characteristicanalysis to SCC actuator design, PLECS/Simulink cross-platform verification andnon-ideal implementation discussion.

The open-loopanalysis shows the necessity of closed-loop regulation. For the dual-LCcompensated CPT system, the ideal voltage gain is mainly determined by thecompensation-parameter ratio under resonant conditions. However, when the loadchanges from 70Ω to 30Ω, the simulated open-loopoutput voltage decreases from 57.79V to 55.77V, corresponding to a voltage dropof about 3.49%. This confirms that the ideal constant-voltage condition cannotguarantee voltage stability under practical load disturbance.

To address thisproblem, a switched capacitor circuit (SCC) is introduced into the secondarycompensation network as an adjustable equivalent-capacitance actuator. Bychanging the SCC switching delay or phase shift, the equivalent compensationcapacitance can be actively detuned. A dual-input single-output fuzzy logiccontroller is then designed, using voltage error E and error variation CE asinputs and the SCC delay-time increment as the output. The controller isimplemented with a 5 x 5 fuzzy rule base, Mamdani inference and centroiddefuzzification.

ThePLECS results demonstrate the effectiveness of the proposed fuzzy controller.Under single-load conditions from 30Ω to 70Ω, the controlled output voltage isregulated within 12.0015-12.0077V, and the maximum steady-state error is onlyabout +0.064%. The settling time remains within 2.37-6.14ms. Under continuousload disturbance, the post-switching voltage deviation is kept below 0.309%,showing strong disturbance rejection around the 12V target.

The controlleralso achieves fixed-load target-voltage tracking. Under a 70Ω load, the averageoutput voltage tracks 15-35V references with steady-state errors within about+/-0.03%. As the target voltage increases, the settling time decreases from10.98ms to 1.73ms, and the overshoot decreases from 46.52% to 8.89%. This trendis consistent with the T_d-based SCC mechanism: lower voltage targetsrequire a larger delay-time correction and stronger active detuning of theequivalent C2, whereas higher targets require weaker detuning and thereforeexhibit faster and less oscillatory transients. These data show that the fuzzycontroller not only restores the disturbed output voltage but also providesmulti-target voltage regulation capability.

To strengthen the no-hardware validation, thefuzzy-controlled CPT-SCC model is reproduced in Simulink/Simscape and comparedwith the PLECS results. The summarized PLECS/Simulink cross-validation keepsthe average-voltage difference at the millivolt level, with a maximumdifference of 6.4mV among the reported single-load, dynamic-load andtarget-tracking cases. The thesis further quantifies the efficiency-stabilitytrade-off caused by active detuning and discusses non-ideal implementationeffects, switching stress, EMI-related spectra and loss/thermal risk. Theseresults indicate that the SCC-based fuzzy control strategy is effective forsingle-receiver CPT voltage regulation, while its extension to multi-receiversystems, dynamic charging and complete multi-objective optimization remainsfuture work.

 Keywords: Electric Field Coupling Wireless PowerTransfer System; Voltage stabilization; Fuzzy control; Switch-capacitor; Loaddisturbance; Cross-platform simulation; Switching stress; EMI; Loss analysis.