## 6 Challenges and Future Trends in LEV Charging  
### Wireless Charging  
While conductive modes of charging--both on-board and off-board--remain popular for LEV charging due to their relative simplicity of implementation, there remain certain issues with respect to its usage. Physical connectors may suffer wear and tear due to regular usage and environmental factors. This may result in safety issues for the vehicle and the user. To address these issues, researchers are gradually exploring techniques such as wireless power transfer. Figure 22 shows the schematic block diagram for wireless charging, showing components such as transmitting and receiving coils, and compensators. Figure 21: Qualitative comparison of (**a**) On-Board and (**b**) Off-Board DC-DC converters. On a scale of 1 to 5, 1 = lowest and 5 = highest. Figure 22: Schematic block diagram of wireless charging. Ever since the breakthrough in wireless power transfer by authors of [74]--who demonstrated a system which could transfer 60 W over a 2 m distance--several advancements have taken place in wireless power transfer, with improvement in transfer efficiency and transfer distance [75; 76; 77; 78; 79]. Works such as [80; 81] have explored concepts and trends relating to the adoption of wireless charging in electric vehicles. In [80], different wireless charger topologies--based on two winding model--are compared, and various compensation techniques validated for enhancement of power transfer capability. Furthermore, safety guidelines and scope for integration with renewable energy sources are also touched upon in this study. The authors of [81]--in their study of trends in EV charging infrastructure--also explore concepts and trends in wireless power transfer-based chargers: near field (inductive and capacitive) and far-field (electromagnetic). A state-of-the art on these chargers is presented, and it is inferred that inductive power transfer-based chargers demonstrate superior characteristics--power density, and efficiency--over capacitive power transfer-based chargers. However, capacitive power transfer is superior in terms of misalignment tolerance. Lastly, far field power transfer and wireless dynamic charging--charging of vehicles during movement--are highlighted as means to reduce range anxiety among users. In recent years, many wireless charger topologies have been reported by researchers in [4; 82]. In their reported integrated solar PV-based LEV charger, authors of [4] also discuss the provision for wireless charging of e-bikes. This charger is based on the inductive charging principle, where the transmitting coil is located under the charging tile, and the receiver coil is integrated into the e-bike kickstand. The use of capacitors in transmitter and receiver circuits help enhance the power transfer capability by compensating for reactive power and enforcing a resonant frequency. The misalignment issue is also addressed in this work by using auto-resonant frequency control, which uses an inner control loop to set the system to its natural resonant frequency. To enhance the capability of wireless charging, researchers have recently made a development wherein an intermediate coil or split primary coil is employed within the system [83; 84; 85]. Authors of [84] have presented a three-coil structure-based wireless charger for the e-bike. The given scheme does not employ a communication link to achieve constant current and constant voltage control. Instead, it employs a primary-side load identification technique to control the transition between constant current and constant voltage mode. This transition is further achieved by engaging two primary-side switches. This further eliminates the sensing requirement on the secondary side. Likewise, authors of [83] have presented a two/three coil hybrid topology, which uses two and three coils to achieve constant current and constant voltage, respectively, to charge e-bikes. Furthermore, this scheme can be used to charge multiple e-bikes at once.