Developing the charging infrastructure for wide-scale electric vehicle adoption
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
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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.
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