Abstract
A negative impedance converter (NIC) has been combined with a wireless power transfer (WPT) system to maximize the system efficiency based on non-foster theory. The NIC is composed of transistor, voltage divider, capacitor, and inductor for impedance matching, and resonant circuit operating at 6.78 MHz. The desired negative impedance can be controlled by tunable impedance in the NIC. In this paper, the loss of the transmitting coil is reduced to 0.1 Ω, yielding a quality factor of 7,050, which is 19.1 times higher than that of the conventional coil. The WPT system with the NIC provides high power transfer efficiency (PTE) at various transmission distances. The experimental results are improved from 64% to 96% and from 5% to 55% at the transmission distances of 50 and 200 mm, respectively. Furthermore, the PTE is enhanced from 38% to 87% and from 2% to 38% at the diagonal misalignment distance of 0 and 150 mm, respectively, at a transmission distance of 100 mm. The proposed technology for increasing the receiving power in the receiving coil with a higher PTE can be utilized for numerous applications in the industrial, scientific, and medical band, with a restricted radio frequency power on the transmitter side.
Highlights
In order to obtain the input impedance at the small-signal equivalent circuit at the resonant frequency, the voltages and currents can be determined using Kirchoff’s law: V2 = V1 − I1re
Research on the wireless power transfer (WPT) system has flourished since the Massachusetts Institute of Technology team successfully demonstrated the WPT system using the magnetic resonance coupling (MRC) method in 2007
Kim et al.: Highly Efficient WPT System With negative impedance converter (NIC) for Q-factor Improvement on the transmitter side, it does not consider because this study focus on effectiveness for the WPT system with the NIC
Summary
In order to obtain the input impedance at the small-signal equivalent circuit at the resonant frequency, the voltages and currents can be determined using Kirchoff’s law: V2 = V1 − I1re The effectiveness of the NIC in the WPT system is demonstrated in this paper when the available input power is fixed at 10 dBm. In order to obtain maximum performance of the NIC, the BJT is selected (2N2222AUB model) due to its relatively high cut-off frequency and current gain as well as well-known model [29].
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