Basic study of improving efficiency of wireless power transfer via magnetic resonance coupling based on impedance matching

Reconfigurable Wireless Power Transfer Systems With High Energy Efficiency Over Wide Load Range

“…Different placements of the passive circuits have been suggested. An LCC circuit has been inserted in the transmitter circuit in reference [21], while an LC circuit is placed after the high-frequency rectifier on the receiver circuit in [22] and before the rectifier in [23]. In the 4-coil WPT systems [24], [25], two coupled coils are placed the transmitter and receiver resonators in order to provide two extra mutual inductance terms for impedance matching with the impedance of the input power source.…”

“…Manual adjustments of the coupled coil locations with respect to their coupled resonators can be made to maximize the power transfer. The techniques in [21]- [25] are based on the maximum power transfer theorem that requires impedance matching with the power source. This approach, as explained previously, suffers relatively high power loss in the power source resistance and is therefore suitable only for very low power applications (say <1W).…”

Wireless powering by magnetic resonant coupling: Recent trends in wireless power transfer system and its applications

“…Therefore, a system to maintain the high efficiency without shifting the resonant frequency at coupling distance variation is required. Several approaches, like optimum frequency adjustment [53,56,62], coupling manipulation [57], adaptive matching using multi-loop coils [63,64] and LC circuits [65][66][67][68], adjusting resonant parameters [69], and use of antiparallel resonant loop [70], have been discussed to deliver power at improved efficiency in the resonant coupled system. Some research articles also studied the effect of axial and angular misalignment of the coil which is one of the major issues in WPT implementation for movable devices, such as electric vehicle charging.…”

“…Also, tuning the coupling among resonators or parameter variation is not feasible in all applications. As a result, efficiency maximization using additional matching circuits [66][67][68] becomes popular as it satisfies the ISM band and needs less space. Beh et al [68] proposed an automatic impedance matching using L-matching circuit implemented for improving efficiency of a 2-coil resonant coupled system operating at 13.56MHz.…”

Performance Improvement Using Real-Time Detection of Time-Variant Load Impedance of the Receiver in Wireless Power Transfer System

“…이러한 문제를 해결하 기 위해 대표적으로 자동 주파수 동조 회로를 추가시켜 최대 전력 전송 효율이 가능하도록 한다. 구체적인 방법 으로는 송신시스템에서 주파수 함수를 갖는 입사 전력과 반사 전력을 방향성 결합기로 지속적으로 측정하여 임피 던스 정합 회로를 제어하는 방법 [7], [8] , 송/수신 전송 코일 간의 위치 및 경사 배치에 따라 공진 주파수 분리 현상을 줄이는 방법 [9] , 송신 코일에 흐르는 전류를 감지하여 차 동 증폭기에 의해 전압으로 변환한 후, 위상 보정기를 거 쳐 위상 고정 루프(PLL)를 통한 동일한 주파수 생성 방법 [10] , 가변 용량의 다이오드를 이용한 임피던스 정합 회로 를 통한 방법 [11] 등이 연구가 수행되었다. 본 논문에서는 그림 1과 같은 결합 모델을 가지는 무선 송/수신시스템에서 수신단의 시변 부하 임피던스와 결합 계수에 따른 시스템의 효율 변화를 설명하기 위해서 그 림 1과 같이 반사 임피던스(reflected impedance)의 개념을 도입하였다.…”