주파수 가변형 자기 공진용 고출력 무선전력전송 시스템 설계

Abstract

In this dissertation, a frequency-tuneable magnetic resonance coil systems and a design method of RF transmitting and receiving systems for WPT to vary the desired resonant frequencies freely are proposed. It is not easy to accurately design a resonant coil a certain frequency in the magnetic resonance technology. Several methods were introduced in the past to vary the resonant frequency, such as by adding fixed capacitors and changing the turns of the resonant coils. However, most of these methods have resulted in defects because of the lack of efficiency, thermal problems, and difficulty in fabrication. In order to vary the resonant frequency, trimmer capacitors are added between the edges of the resonant coils. For designing a frequency-tuneable magnetic resonance coils for WPT, circuit analysis and 3D simulations are carried out prior to fabrication.Spiral resonant coils are chosen owing to their appropriate thickness, and two resonant coils of same size and shape are placed for increasing the mutual inductance. By adding trimmer capacitors (varying from 150 pF to 300 pF) at the edges of resonant coils, the resonant frequency is variable from 3.08 MHz to 4.44 MHz. S21 value are approximately from -3.0 to -2.4 dB as the transmitting and receiving sides of the magnetic coil are separated by 160 mm. In order to fabricate magnetic resonance WPT system, an RF transmitting and receiving circuit should be designed in addition to the coil system. The RF transmitting system consists of an RF signal generator and an RF power AMP. The frequency range of fabricated RF power AMP is from 2.0 MHz to 7.0 MHz, with a 30 dB gain. The I/O characteristic impedance is 50 ohms. The RF receiving system is designed to convert the RF signal received at the Rx load coil into a DC signal, which is used to light the LED stand. Bridge diodes implemented in the Rx system are selected with fast trr (reverse recovery time) for operating in several MHz. The diode and capacitor are chosen through SPICE simulation, and the performance is verified by actual fabrication of the model and measurement. For verifying the frequency-tuneable magnetic resonance coil systems, RF transmitting and receiving systems are connected to light the LED stand. As the frequency of the function generator (F/G) changes, the brightness of LED stand also changes. When the frequency of the F/G is 3.9 MHz, the LED stand is turned off because the resonant frequency of the coil system is 4.5MHz (150 pF capacitors are added). After changing the resonant frequency of the coil system to 3.9 MHz by using trimmer capacitors (capacitance value is almost 200 pF), the LED stand becomes bright at 3.9 MHz. The thermal problem is monitored by using an infrared camera, and the maximum temperature of the resonant coil is 34.2 degrees when the power is on.