Magnetic resonance coupled wireless power transfer systems
Wireless power transfer (WPT) technology has many potential applications such as consumer electronics and electric vehicles (EV). High transmission efficiency with long transmission distance and with large lateral misalignment is desired in WPT systems. Magnetic resonance coupled (MRC) WPT systems are suitable for midrange high efficiency wireless power transfer (WPT). In chapter 2, commonly used four-loop and two-loop MRC-WPT system configurations are analyzed and compared in terms of transmission efficiency and transmission distance first based on the simplified circuit model. An example symmetrical system simulation shows that with the same Tx, Rx, source and load, the four-loop system has longer transmission distance but with relatively lower transmission efficiency compare to the two-loop system. Then, A 3-D physical model of 5-turn, 400mm outer diameter spiral shape four-loop WPT system is developed and simulated by using ANSYS® HFSS® software package. Operation distance of 550mm with nearly constant maximum transmission efficiency of 92.3% is achieved. Laterally misaligned MRC-WPT system is investigated in chapter 3. The TEVD, a region on the transmission efficiency versus Rx lateral misalignment amount curve where the transmission efficiency first sharply drops from high efficiency down to zero and then recovers to a low efficiency value, is identified in this work. The identification of TEVD is verified by simulation results obtained from a developed ANSYS® HFSS® 3-D physical model. Simulation results of the ANSYS® HFSS® 3-D physical model with 5-turn, 60cm outer diameter spiral shape MRC-WPT system show that when the Rx is 30cm vertically away from the Tx, TEVD exists when the lateral misalignment value ranges from 50cm to 70cm. An elimination method for TEVD is proposed in chapter 4. The proposed method utilizes angular rotation of the Rx (or Tx) to eliminate the zero-coupling point which causes the TEVD and boosts the coupling coefficient such that the TEVD is eliminated and the high efficiency region is extended. ANSYS® HFSS® 3-D physical model simulation results show that the proposed method eliminates the TEVD and extends the high efficiency region from 50cm lateral misalignment (83.3% of the Rx diameter) to 70cm lateral misalignment (117% of the Rx diameter). Chapter 5 summarizes the thesis conclusions and sheds the light on future work.