FEAT
ATURE
POWER
WIDELY-ACCESSIBL E WIRELESS CHARGING CAN INCREASE EV ADOPT ION By Patrik Kalbermatten, distribution promotion product management magnetic, Sensor & Actuator
at KEMET Corp A
s modern cars become more connected and functionally reliant on complex electronic architecture, the vehicle manufacturing industry could finally be preparing t o bid farewell to the internal combustion engine (ICE). A growing number of drivers are already eyeing up the possible benefits of purchasing an electric vehicle (EV), but the mainstream adoption of EVs will not only require t ime but a lso engineering innovations to eliminate t he practical concerns of potential consumers. As part of efforts to change consumer attitudes, p assive component manufacturers such as KEMET are working towards the development of improved solutions for EV systems, such as wireless charging.
T he advantages of EVs are numerous, such as lower operational costs, excellent safet y feat ures and zero direct carbon emissions. However, perhaps because vehicles are such a long-term, high-value purchase, the majorit y of drivers still feel unsure about investing in a fully electric vehicle. Two of the main reasons for this hesitance are centered around vehicle price and concerns about t he range of EVs on a full charge. This so-called ‘range anxiety’ can be slightly irrational, as a 2011 st udy showed that although the average driver only travels around 40 miles (64 kilometers) per day , regardless of whet her they lived in urban, suburban or rural areas, over 50 per cent of the survey’s respondents indicated t hat they would require a range of 200 miles or above in order for them t o consider switching to an EV.
CHARGING P G POINTS: A WAITING GAME
Underst andably, no driver wants to face the prospect of making a longer than usual road trip with an electric car that will not be able to make it to the destination and back on a full batt ery. As public charging infrast ructure is st ill in its infancy, most EV owners rely on an overnight charge from a basic 1kW Level 1 charger that plugs into a standard wall outlet . However, wit h a range capacit y of over 100 miles, an EV battery could take around 20 hours to obtain a full charge, and for a 250-mile range bat tery, up t o 43 hours of charging may be required. It is t hus clear that home charging will not be entirely sufficient for EVs as range continues to be increased.
Increasingly found in urban parking spaces, faster Level 2 chargers bring down the total EV charge time considerably, but
EV charge time considerably, but for many consumers with ICE vehicles this will not be fast enough to compete with the convenience of quick refueling at a gas station. T
refueling at a gas station. The highest-powered chargers currently available, Level 3 DC Fast Chargers (DCFC), begin to bridge this competitive gap, but currently they are rarely found at public charging points, and they are also not always compatible with all makes and models of EVs.
26 MAY 2020 | ELECTRONICS
I IMPROVING ACCESSIBILIT Y WITH WIRELESS CHARGING
MPROVING A
For t he majority of consumers to find EVs practical enough to drive with confidence, a mixture of different charging options must be made widely available, including wireless charging. Similar in principle to wireless
charging for mobile phones, resonant magnetic induction is used to transfer power from a charging pad on the ground to a receiver positioned on the underside of an EV. Current ly , wireless charging can be transferred at rates r anging from 3.3kW to 20kW.
A Wireless Electric Vehicle Charging System (WEVCS) infrast ructure can be implemented in urban areas, with transmit ters embedded in public parking spots. This would enable EVs to recharge incrementally every t ime t hey park, without requiring any int ervent ion from the driver. Additionally , a dy namic WEVCS (D-WEVCS) could be built on areas of public roads such as highways, with a series of embedded charging transmitters that would recharge EVs while they are in motion. Dynamic charging could be most useful for buses and taxis, with charging points placed along dedicated bus lanes, at bus stops or at pickup/ drop-off points.
In both a static and dy namic WEVCS, the transmitt er t akes AC power at 50-60Hz, and after rectification and power factor correction (PFC), the inverter produces an AC out put of 80-160kHz to the power transmit ter coil. The power generated from the transmit ter is t hen coupled int o the receiver coil on the underside of t he vehicle, which generates a stable DC power supply to charge the batt ery , controlled by an electronic battery management system (BMS).
FINEI F NE- -TU -TUNING WEVCS EFFICIENCY
In any system, reliability and energy efficiency are t wo of the most important elements for designers t o achieve, and the WEVCS is no except ion to this rule. The wireless charging infrastructure will be constantly exposed to moisture, extreme temperatures and physical force. The components in both the t ransmit ters and t he receivers will need to be rugged enough to withstand t hese challenges, and t hus KEMET offers environmentally-hardened chokes and filt ers designed expressly for EV charging applications, with new materials developed for smaller components to minimize the size and weight of the receiving equipment mount ed on t he EV.
Wide bandgap (WBG) power semiconductors are essential in both the t ransmitt er’s inverter and the receiver’s AC/DC converter to enable safer, more efficient power conversion at t he wireless power transfer frequency. A better class of ceramic capacitor with superior capacit ance
stability over t emperature and volt age is r equired for these semiconductors to manage very high ripple current s. KEMET’s KC-Link multi-lay er ceramic capacit ors (MLCCs) offer a robust proprietary C0G/NPO base metal electrode (BME) dielectric sy stem that result s in very low equivalent series resistance (ESR) with high thermal stability . Moreover, the effective series inductance (ESL) can be minimized as t he capacitors are mechanically robust enough t o be constructed without a leadframe, also supporting miniaturization efforts furt her. In order to maximize the power transfer efficiency, the induct ive coupling of t he
t ransmitt er and receiver coils can be optimized to reduce the need for precision alignment in order for charging to t ake place, as obstacles may prevent t he driver from position the vehicle perfectly over t he charging pad. Alt ernatively, research has shown t he development of autonomous self-aligning receiver coils can enable consistent charging of up to 5kW at over 90 per cent efficiency.
To aid this optimization, the application of shielding materials t o the power transmit ter and on-board receiver can help to provide a stronger directional magnetic field, thereby further increasing power transfer efficiency. KEMET has developed high-permeability sintered ferrite tiles that effect ively minimize magnetic flux losses and are AEC-Q200 qualified for automotive applicat ions.
With growing demand for EVs, particularly t hose featuring increased range, there is an urgent need for faster, more convenient charging options in public areas. An easily- accessible wireless charging sy stem is an appealing concept to be added to t he EV charging mix, and a dy namic wireless charging sy stem is also possible t o charge vehicles as t hey travel. Making charging widespread, easy and accessible through wireless “top-ups” may help to eliminat e range anxiety for consumers and finally make EVs truly competitive against their ICE counterparts.
KEMET
www.kemet.com / ELECTRONICS
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