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High degrees of coupling freedom in wireless power transfer (WPT) has emerged as a prominent research topic. The challenge lies in achieving a compact structural design for such systems. This article introduces a planar transmitter configuration composed of three decoupled and separately controlled converters to enable three-dimensional (3-D) WPT to an arbitrarily positioned receiver above the transmitter. By theoretical analysis based on the coupled mode equations, it is found that there is a direct relationship between the dc input voltages and currents of the inverters for achieving the maximum efficiency. The spatial magnetic field is shaped by controlling the input voltages based on the measured currents to achieve the best magnetic field coupling for maximum efficiency tracking, regardless of the positioning and alignment of the power pickup. A practical system is built with a 10 × 10 cm transmitter (with three decoupled coils) and 3.5 × 3.5 cm (single coil) receiver, and it is demonstrated that the system can achieve a power transfer efficiency about 80% within 3 cm above the transmitter under all 3-D coupling conditions.

In this brief, a wireless power transfer (WPT) system is proposed with the ability of parameter estimation for charging inspection robots without the need for an additional communication channel. A novel magnetic coupling and circuit tuning structure is proposed to achieve parameter estimation and closed-loop control using a sensing coil on the primary side. The design process is according to the industrial need of the application, i.e., substation inspection robots. One key procedure is the magnetic coupling design, utilizing the DD and Q coils to eliminate the undesired cross-coupling between them. Two practical series (S) and inductor-capacitor-capacitor (LCC) compensating topologies are adopted to tune with coils for improving energy transferability. Especially, the coupling parameters are identified by reconfiguring the LCC-LCC and SS topologies and detecting the two induced DC voltages of the primary detection circuit, providing the basis for the closed-loop control. Then the induced DC voltage of the primary detection circuit is used as a control feedback for realizing constant current (CC) charging, thereby obviating the need for complex pairing procedures and elimination of additional communication channels. A 480W experimental laboratory setup is constructed, and the feasibility of the proposed method has been validated through laboratory testing.