Enhancement of Inductive Power Transfer (IPT) for Wireless EV Charging

The decarbonisation of road transport through the use of ultra-low emission vehicles (ULEVs), including electric vehicles (EVs), is seen as critical to helping the UK achieve its climate change obligations and to improving air quality, particularly in major cities such as London. However, state-of-the-art batteries for EVs show much lower energy density compared to fossil fuels (240 Wh/kg energy density of Lithium-ion (Li-ion) battery, 2% of petrol's energy density), which significantly compromises the driving range. Without foreseeable breakthroughs (4 times energy density increase by 2035) in battery technology, frequent and convenient battery charging is the only way to enable EVs as the dominant means of decarbonised transportation.

Most current fast and rapid charging process for EVs requires drivers to connect the tethered electrical outlet to the vehicle, leaving drivers prone to hazards. Limited charging opportunities cause a long dwell time of each recharge and range anxiety. In contrast, energy can be transferred between the primary source side (on-ground) to the secondary battery side (on-board) by using time-varying magnetic fields through the air, known as the inductive power transfer (IPT). The absence of physical connection offers unobtrusive and hassle-free charging. The paradigm will shift from infrequent lengthy charging at centralised charging hubs to distributed charging places conducting charging automatically. Therefore, charging events can be seamlessly integrated into regular vehicle operation and becomes part of daily background life thus plug-in forgetfulness will never happen again. The long lead-time and large cost of upgrading infrastructure for centralised charging hubs can be reduced and frequent charging reduces the discharge depth, which extends the lifetime of the battery. Lack of human intervention of IPT can enable future autonomous EV operation and charging other machines such as robots, unmanned aerial or underwater vehicles (UAVs, UUVs).

This research is the first to use nanocrystalline cores based coils for IPT applications and also the first to combine frequency and duty ratio control with a dual-active bridge topology (DA-IPT). New control algorithms, such as MinAPPT and hard-switching mitigation techniques, will be explored, together with the use of SiC MOSFETs in both the inverter and rectifier of DA-IPT to improve the power density and efficiency in misaligned charging conditions. A multi-objective design optimisation process using a combined DA-IPT topology and nanocrystalline core based coils will designed and continuously improved for future development and other relevant power electronics research.
The research aims to achieve 92% efficiency or above, at 30% vertical and lateral misalignment with a power density of 2 kW/kg, 4 kW/dm3 or above. A 7.7 kW (Level 2 EV charging) prototype will be built and experimentally validated with deliverables such as simulation models and design tools. An 11 kW prototype is the next step with potential industrial investment. The success of this research will exploit and validate the theoretical merits from proposed ideas and establish a solid foundation for continuous investigation, including bi-directional power flow for V2G, improvement of mechanical robustness, EMC and objective rejection methods of applicable DA-IPT systems in the future.

The infrastructure for EV charging plays a pivotal role in accommodating a large penetration of EVs as proposed by the Modern Transport Bill (banning non-zero emission new sale cars by 2040). The UK and most other EU countries have set deadlines of non-zero-emission cars such as Netherlands (2025), Sweden (2030), France (2040), the largest car market with a third of global car sales - China (2050), showing the urgency and importance of new charging infrastructure. IPT-based wireless charging has been commonly considered to be a much more convenient, safe, and adaptable solution to charging EVs automatically over a larger amount of geography and time. The technology is valid yet undeveloped for real applications, hence deserving intensive investigation.

Introduction of new technologies will strengthen the UK's global position as a leader in the automotive industry and benefits the UK's economy. For example, the overall economic and social benefit of EVs to the UK's economy may be in the order of £51bn per annum by 2020. It is also anticipated that these technologies will provide a significant boost in employment opportunities, with 25,000 new jobs in the automotive industry 2030 ("On the road to sustainable growth - Boosting electric vehicles in the UK," IMI Report, 2016).

Specifically, impacts will be made in following areas:

Economic: The proposed new wireless system envisions a fresh idea of EV charging to car OEMs and Tier 1 suppliers. The proposed IPT technology for wireless EV charging can achieve hundreds of millions annual revenue in the future, hence stimulate the productivity of the UK EV/PHEV supply chain, and stimulate export and improve the balance of import and export of EV/PHEV products. New supply chain relating to IPT products will strengthen the automotive manufacturing sector in the UK, and stimulates further investments.

Social: The project will create 1 skilled job opportunities (PDRA). This technology reduces particulates in air supply, improves health conditions, reduces healthcare burden, and improves quality of life. The absence of physical connection offers unobtrusive and hassle-free charging. The paradigm will shift from infrequent lengthy charging at centralised charging hubs to distributed charging places conducting charging automatically. Therefore, charging events can be seamlessly integrated into regular vehicle operation and becomes part of daily background life thus plug-in forgetfulness will never happen again. The long lead-time and large cost of upgrading infrastructure for centralised charging hubs can be reduced and frequent charging reduces the discharge depth, which extends the lifetime of the battery

Academic and education: It is expected that significant ongoing research opportunities for the University of Cambridge in continuing to develop research and widen the links with the automotive industries. This will bring direct academic benefits, including further opportunities for PhD research. Projects such as this directly translate over the medium term into the University's teaching curriculum. This will play an important role in educating the next generation of electrical engineers designing vehicles in the UK. The IPT system encompasses many cutting-edge technologies in power electronics and the cross-theme nature of this IPT research involving converter topologies, electromagnetic components, power electronic devices, and control is immediately relevant to academic communities from different areas, especially the power electronics such as the EPSRC Centre for Power Electronics.