A Charging Infrastructure for Wide-Scale EV Adoption
To ensure that electric vehicles (EVs) have the same freedom to roam as today’s fossil-fuel cars, infrastructure challenges need to be addressed
By: Alessandro Mastellari, Technical Specialist, Avnet Abacus
Concerns about carbon emissions and urban pollution are encouraging the automotive industry to introduce hybrid and fully electric powertrains. Their work is being aided by steadily improving battery and motor technology, but is held back by the ’chicken and egg’ problem of charging the resultant vehicles. Charging has to become faster, the world’s network of petrol stations needs to be upgraded with electric-charging facilities, and standalone charging stations need to be introduced to compensate for EV’s relatively limited range.
Why is this? A back-of-the-envelope calculation suggests that filling your tank with petrol is like connecting your car to a 5MW energy source. By contrast, Tesla announced in March 2019 that its V3 Superchargers will deliver energy at rates of up to 250kW, although it will take a liquid-cooled charging cable to make this possible. Despite EVs using their stored energy more efficiently than fossil-fuel cars, electric charging has a way to go before it can match petrol’s ability to enable useful work in a vehicle. It will take a combination of high voltages, high currents and sophisticated power conversion, filtering and charge-management systems to close the gap. This, in turn, will demand the deployment of some pretty sophisticated connectors, cables, relays, conversion electronics, and passives, to ensure the same kind of fast, safe energy top-up offered by today’s petrol stations.
Charging network growth
So how close are we getting to a ubiquitous charging network that drivers can rely upon to be there whenever they need it, rather than having to plan their journeys between chargers? Starting with the highest profile player, Tesla said during its V3 announcement that it now has more than 12,000 Superchargers across North America, Europe, and Asia, covering more than 99% of the US population now, and expects to achieve similar coverage in Europe by the end of this year. Tesla also said that it has recently passed 90% coverage of China’s population.
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Figure 2: Regional Charging Network Growth
In Europe, the number of EV charging points is increasing rapidly, thanks to public subsidies for buying EVs, new regulations, and the willingness of some fuel companies to install chargers in their petrol stations. According to the latest figures from the European Alternative Fuels Observatory, Europe now has 161,426 public charging points, 136,958 of them for charging at rates of up to 22kW, and the rest at rates greater than 22kW, so-called ’fast charging’. The UK has just over 19,000 of the aggregate total, France nearly 25,000 and Germany around 27,400 (please refer to graph).
Building charging networks also looks like it will be big business, if a report from market analysts Markets and Markets is to be believed. It forecasts that the market for EV charging stations will grow from $3.22bn in 2017 to $30.41bn by 2023, or 41.8% a year, every year, from 2018 to 2023. The report offers a number of justifications for its forecast, including subsidy programmes for purchasing EVs in various countries, and a US government initiative to develop 48 charging networks that will together cover about 25,000 miles of US highways across 35 states. This initiative led 28 states, utilities, charging firms, and electric vehicle companies, including GM, BMW and Nissan, to start working together.
AC or DC charging
These raw numbers appear encouraging for potential EV drivers but mask the fact that there is still a lot of variety in charging methods, the infrastructure available to support them, and therefore their usability to the average user.
Perhaps the biggest issue is whether an EV is charged using Direct Current (DC) or Alternating Current (AC). Batteries have to be charged with DC, and so the real difference between the two charging strategies is where the necessary rectification is done. Grid power is delivered as AC, and so some vehicles take AC onboard, in either single- or three-phase form, and rectify it to the appropriate DC charging voltage. Others expect rectification to happen in the charging stations, so that they can be charged with DC delivered over the cable.
DC charging can usually deliver more power, because charging stations can use larger, more efficient and better-cooled rectification circuitry than would be possible in a vehicle. Along with charging rate, the choice of AC or DC charging is also driven by decisions about who covers the capital cost of rectification: the operators of DC charging networks, or each owner of an AC-charged EV. Some charging standards also allow bidirectional energy flow, so that a distributed network of charging vehicles can act as both energy sinks and sources to stabilise the energy grid – which, in turn, can attain them regulatory support in some regions.
As you would expect in this phase of a rapidly developing technology, there is a tension between vendors trying to control their customer base by installing proprietary chargers and connectors, and the benefits of adhering to standards that expand the charging network for all. As has been seen multiple times in other technology evolutions, the perceived benefits of lock-in are slowly giving way to standardisation efforts, as EV customers begin to demand ubiquitous charging facilities and weigh their availability more highly in their buying decisions. This is leading to a shake-out in the market for EV charging.
Tesla has its proprietary supercharger strategy, while Japanese companies including Nissan and Mitsubishi have backed CHAdeMO (for Charge de Move), which allows bidirectional charging. China, the world’s largest EV market, is establishing GB/T as its charging standard. In Europe, meanwhile, BMW, Mercedes-Benz maker Daimler, Ford and the Volkswagen group, which includes Audi and Porsche, are all backing the Combined Charging System (CCS), an effort to establish a multivendor, multi-technology standard.
CCS is being developed through the Charging Interface Initiative (CharIN), which is busy producing technical specifications and position papers for its vision of the future of charging. Its efforts include defining which protocols should control the charging process, suggesting what sort of signage, dashboard and user information should be provided at charging stations, and taking a view on the requirements for a possible future interoperable wireless-charging standard.
One of the most striking of CharIN’s definitions, at least from a circuit designer’s point of view, is the classification of DC charging levels. Its ’DC20’ specification defines DC voltages of between 200 and 500V, currents of between 1 and 40A at 500V, for a relatively modest charging power of up to 20kW. At the top end of the classification schema, though, HPC350 (or High Power Charging) defines DC voltages of 200 to 920V, charging currents ranging from 5 to 380A at 920V, and a charging power of up to 350kW.
The connector conundrum
With such a large amount of power crossing what is effectively a consumer-managed interface, connector design is critical.
The Type 1 connector, mainly used in Asia, is a single-phase AC charging plug that supports charging powers of up to 7.4kW. Type 2 plugs support three-phase AC charging, at up to 22kW in private settings such as a home garage, and up to 43kW at public charging stations. CCS plugs add two more contacts to a Type 2 plug for fast charging, enabling AC and DC charging powers of up to 170kW. The CHAdeMO connector allows for charging powers up to 50kW, while Tesla uses a modified version of the Type 2 Mennekes plug to enable its proprietary fast-charging approach. Interestingly, given the importance of the Chinese market, Tesla and others are starting to fit a GB/T fast-charging socket alongside their standard sockets.
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Figure 3: Types of Connectors used in EV Applications
As you might expect, a third-party industry has sprung up marketing converters and adaptors to allow drivers to charge their cars from any charging station, although the charging rates achieved over such adapted connections may not be as high as when using the native connector.
The component opportunity
The automotive industry is vast, producing close to 100 million vehicles year, and the transition to EVs offers huge opportunities to reshape it, for example through the emergence of new market entrants in China, a possible shift away from vehicle ownership to mobility as a service, and the potential for integrating vehicles into the power grid.
All this change creates huge scope for component makers to sell their existing parts and to innovate to enable new opportunities. For example, simply making the power devices used for in-vehicle rectification more efficient will have an immediate effect on the utility of an EV by enabling faster AC charging. More effective filtering will be needed to damp down high-power spurious signals. Connector design, as previously discussed, will become a key gating factor on charging rates and hence people’s perceptions of the practical range of an EV.
All these innovations will have to meet rapidly evolving national and international standards, and be expressed in components that are delivered globally, in volume, to strict automotive safety and quality specifications. And as EVs take over from fossil-fuel vehicles, and our transport moves inexorably closer to consumer-electronics market perceptions and timescales, that means that component development and qualification will have to accelerate to match. It’s going to be a hard-fought race to EV market dominance.