This paper investigates the design of a robust H ∞ output feedback controller for a capacitive power transfer (CPT) system. Firstly, a first harmonic model of the CPT system is derived based on first harmonic approximation (FHA). Secondly, by linearizing the first harmonic model at its operation point, a linearized state space model is obtained. Thirdly, variations of coupling capacitances and load in the CPT system are described as polytopic uncertainties in the linearized state space model. Then, we propose a novel robust H ∞ output feedback controller design technique for the linearized state space model with polytopic uncertainties. Finally, both simulation and experiment are carried out to verify the effectiveness of the proposed controller design.INDEX TERMS Robust H ∞ control, dynamic system modelling, capacitive power transfer, class-E inverter.

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This study presents the design of capacitive wireless power transfer systems based on a suboptimal Class-E 2 converter approach. The main reason for selecting the suboptimal Class-E 2 converter is due to its ability of maintaining its high efficiency over a wide bandwidth of operation frequency. However, Class-E 2 converters in general are sensitive to its load's variation. This variation greatly affects the output voltage and increases the switching loss of the system. Motivated by this drawback, the authors develop an auto-frequency tuning mechanism based on a PI approach for the suboptimal Class-E 2 converter to regulate the output voltage and minimise the switching loss. A non-contact communication mechanism is also developed to transmit the secondary side's measurements to the primary side. Finally, simulation and experiment are carried out to verify the effectiveness of the auto-frequency tuning mechanism.

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