Abstract
The transfer coils of traditional Magnetic Coupling Resonant Wireless Power Transfer (MCR-WPT) systems are generally arranged coaxially. Coplanar coils can be an alternative scheme that can save more space in some applications, such as mobile phone wireless charging. However, the inductances of coplanar coils are sensitive to foreign objects, which leads to a reduction in transfer efficiency and output power. A MCR-WPT system with coplanar coils and its control strategy are proposed in this paper. First, the characteristic of the mutual inductance and the magnetic field distribution between the coplanar coils are analyzed. A formula to calculate mutual inductance between the coplanar coils is proposed in this part. Secondly, the effect of inductance offset and frequency detuning on transfer efficiency and output power are analyzed. Then, the control strategy to eliminate frequency detuning is proposed. The proposed method implements switched capacitor to take place of constant compensation capacitor. The equivalent capacitance of switched capacitor is adjusted when the frequency detuning occurred. Thus, the inherent frequency of the resonant tank tracks the source frequency all the time. Since the switched capacitor of each side is controlled based on the quantity of their own, the control process is independent and does not require wireless communication. The complexity and the cost of the system are reduced. At the end of the article, the veracity of mutual inductance formula and the effectiveness of the proposed control strategy are verified by experiments. The experimental coils are placed in in an environment full of interference. The inductances of the coils are reduced from 224 μH to about 214 μH. The transfer efficiency and output power of MCR-WPT system with closed-loop control are higher than the one without control. At a distance of 5 cm from edge to edge, the transfer efficiency is 76.37% under the proposed control and 72.21% under no control. The output power is 285.66 W under the proposed control and 271.37 W under no control.
Highlights
Magnetic Coupling Resonance Wireless Power Transfer technology (MCR-WPT) is one of the most popular research topics at present
The equivalent circuit of a MRC-WPT system is depicted in Figure 1, where L1,2, C1,2, and R1,2 are the inductors of coils, compensation capacitors, and Equivalent Series Resistance (ESR) respectively
M is the mutual inductance between the primary coil and the secondary coil. η S is the efficiency from primary side secondary side, whichis calledtransfer transferefficiency efficiencyin in the the efficiency from thethe primary side to to thethe secondary side, which isiscalled called transfer efficiency in efficiency from the primary side to the secondary side, which following sections
Summary
Magnetic Coupling Resonance Wireless Power Transfer technology (MCR-WPT) is one of the most popular research topics at present. The output power is controlled robustly and the transfer efficiency becomes more stable. In [12,13], the adjustable capacitor is only implemented on the primary side to keep the inherent frequency of the primary side equal to the source frequency This method has no effect on the secondary side. A novel dual-side independent switched capacitor control strategy for MCR-WPT systems with coplanar coils is proposed. By applying the control strategy, the frequency detuning of dual-side resonant tanks can be dealt with and the transfer efficiency increases compared to the system without control. This paper is organized as follows: Section 2 analyzes the mutual inductance and magnetic field distribution between coplanar coils, in which the formula of mutual inductance is derived.
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