An introduction to EV charging infrastructure design

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The rate at which electric vehicles (EV) can be charged is becoming a key differentiator in this rapidly developing market, for a very straightforward reason: charging an EV’s battery is currently a lot slower than refilling a tank with petrol to go the same distance.

Take a generic EV with a battery capacity of 60kWh. Charging this battery from zero to 100%, using a cable plugged in to a standard UK 240V, 13A socket, will take about 20 hours. This isn’t practical for a daily driver, much less for a long-distance traveller.

In practice, most EV owners rely on dedicated chargers, often wired in at home to higher-current ring mains. UK energy supplier E-On, for example, will wire a 7.4kW wall-mounted charger, with either a tethered charging cable or a universal socket for a charging cable, into a 32A ring main. With this charger, our generic 60kWh EV can be charged in more like eight and a half hours.
 

A hierarchy of charging

The rapid growth of the EV market has led to a proliferation of connection and charging strategies, charger designs and charging networks.

Slow chargers are typically rated at 3kW, and are mostly used in homes, ideally through a dedicated wall-box. They’re not really suitable for public use because they charge too slowly.

Fast chargers are found in public places, such as car parks and shopping centres, and may charge at rates of 7kW or 22kW. A 22kW charger could charge our generic 60kWh EV from zero to a full charge in around two and half to three hours.

Rapid chargers often charge using DC, handling the rectification of the AC supply within the charger rather than relying on the EV’s onboard rectifier. Rapid DC chargers commonly provide up to 50kW of power, while rapid AC units are commonly rated up to 43kW. At a 50kW charging rate, our generic EV battery would be recharged in just over an hour.

Figure 1: The Lotus Evija will charge at rates up to 800kW (Source: Lotus)

Tesla goes one better with its current Superchargers, which charge at 120kW through a proprietary connector. Tesla has also announced its V3 250kW supercharger, which it claims add 180 miles of range to a Tesla Model 3 with the long-range battery option in just 15 minutes.

At the top end of the EV scale, Lotus has just announced its Evija EV ‘hypercar’. The battery in this vehicle has been designed to accept charge at up to 800kW, a greater rate than commercially available chargers can yet provide. Once 800KW chargers are available, Lotus says the Evija’s battery could be fully recharged in nine minutes. Using more widely available 350kW chargers, the Evija will take 18 minutes to charge to 100%.

They are only going to build 130 Evijas, so most of us needn’t worry about finding 800kW chargers any time soon, but, as with Formula 1 technology development, this Lotus hypercar is a pathfinder for future mainstream adoption.
 

Getting connected

Along with a hierarchy of charging options, all of which affect an EV’s ‘miles per hour’ there is also a variety of charging connector options, each of which is (mainly) incompatible with the others.

Figure 2: Connector options for EVs

The single-phase AC Type 1 connector, common in Asia, supports charging at up to 7.4kW. Type 2 plugs support three-phase AC charging, at up to 22kW in private settings, 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 at up to 170kW. The CHAdeMO connector allows for charging powers up to 50kW. Tesla uses a modified version of the Type 2 Mennekes plug for its proprietary fast-charging approach. In China, the GB/T fast-charging connector is becoming popular.

These are deployed as follows, at least in the UK. Slow charging is carried out at 3kW using either a standard 3pin plug, a Type or Type 2 connector, or even the ‘commando’ connectors used on caravans. Fast charging, at between 7 and 22kW AC, is done using Type 1 and 2 connectors. Rapid charging is done at 50kW DC using the CHAdeMo or CCS connectors, at 43kW AC using the Type 2 connector, and at 120kW DC using the Tesla Type 2 connector variant. Many vehicles have more than one socket, to enable access to both slow and fast charging stations.
 

Charging networks

The uptake of EVs has led to the rapid development of competing charging networks.

Open Charge Map, a global public registry of charging locations, lists 151,060 charging stations at 74,380 locations, including above the Arctic Circle at the airport on Svalbard Island, and at Tokanui on the southern tip of New Zealand’s southern island.

Some companies are installing charging points as a standalone offering, while others are doing so to diversify their businesses. It makes sense that oil companies BP and Shell would install chargers to keep up with their evolving customer base, but in Germany utility company Telekom, the former state telecoms company, is entering the market by piggybacking a charging network on its communications infrastructure.

The company has installed public charging stations in Bonn and Darmstadt, each offering two vehicles charging at 11kW over a type 2 plug. In Bonn, Telekom has gone a step further with its first 150kW charging station, which will add 100km to an EV’s range in ten minutes. The company plans to introduce 500 rapid chargers in the next three years.

Eurotunnel is also leveraging its infrastructure to support EV driving by installing chargers at both its terminals, with charging for Teslas as well as for any other EV or hybrid that has a CHAdeMO or Type 2 interface.

Car makers are getting in on the act, too. For example, IONITY is a joint venture between BMW, Daimler, Ford, and Volkswagen with its Audi and Porsche brands to build a high-power (350kW) charging network along Europe’s major highways. Its network already reaches from Sweden to northern Spain, with more chargers due to be installed soon.

Energy company E.ON is cooperating with Danish mobility service provider CLEVER to build a similar north-south, ultra-fast charging network in Europe.

The plan is to install several hundred 150kW charging locations, at distances of 120 to 180km apart along the major motorways. An upgrade to 350kW should follow as technology allows.

E.ON already operates 1,200 public charging points and 39 fast chargers in Denmark. CLEVER has been developing a fast-charging network in Denmark, Sweden and Northern Germany since 2009. The joint initiative is co-financed by the Connecting Europe facility of the European Union.

Of course, not all networks charge all EVs in the same way or are equally accessible to all.

Zap-Map, an online platform for all things related to EVs and the supporting charging infrastructure, collates statistics on the growth of the UK’s charging infrastructure. According to the site, as of 26 July 2019, the UK has 9,167 public charging points, with a total of 14,571 devices and 24,768 connectors across those sites. The site has added details of 522 new devices and 857 new connectors in the past 30 days.

Zap-Map stats also show that there are 1605 public rapid charging points in the UK, hosting 2,338 devices and a total of 5,412 rapid connectors. 232 new rapid connectors have been added to Zap-Map’s database in the past 30 days.

EV charging has prompted the development of multiple charging networks, each founded on a slightly different business model. Here are a few examples.

Polar, operated by BP Chargemaster, is the UK’s public charging network It offers both subscription and pay-as-you-go services, accessed either by an RFID card or via a smartphone app.

Pod Point operates the Pod Point network of mainly fast and rapid chargers, many of which are free to use although some have a pay-as-you-go charge.

Charge Your Car is the largest pay-as-you-go network in the UK. It operates, but doesn’t own, a network of charge points across the UK, providing back-office services to the charging units’ owners. Its customers include regional providers, such as Source West, and ChargePlace Scotland, which is backed by the Scottish government.

Zap-Map itself has set up Zap-Home and Zap-Work, peer-to-peer charging networks through which home or business owners can offer registered users access to their chargers under conditions which they set themselves. Payments, if there are any, happen over PayPal.
 

Charger design

The dynamism of the EV marketplace is demanding the development of a wide variety of charging options, usually predicated upon where they will be used.

Home charging solutions can be as simple as using a standard EVSE (Electric Vehicle Supply Equipment) charging cable to plug into a mains socket, or as complex as installing a wall-mounted charger. The design challenge here is to develop a safe, easy to install, charger suitable for production in relatively large volumes.

Workplaces are beginning to install EV charging, to help make EVs viable for staff with long commutes, as well as for visiting customers. The design challenge here is to produce a flexible charging system that can be easily installed in multiple units on a site, perhaps with centralised management, and sophisticated access controls to enable, for example, guest usage.

Chargers for use in public venues must be robust, support fast and, ideally rapid charging rates, and adapt automatically to serve multiple different vehicle types and battery conditions. They often support multiple connections per charger (two is popular). They also need to enable access by customers from multiple public charging services that have developed reciprocal access arrangements to extend their geographical coverage. The design challenge here is to deliver large amounts of charging power in a way that is safe, robust and easy to use.
 

Connectivity options

Even what appear to be the simplest components need careful thought in the context of EV charging.

For example, ITT Cannon offers the ECIER EV charging outlet. It is an IEC (Type 2) EVSE rear-mount outlet that provides low contact resistance and a minimum of 10,000 mating cycles. It is available for single- and three-phase charging systems and has a current rating up to 63A. The outlet uses a canted coil spring to minimise mechanical stress, mis-alignment and power loss. Customisation options include a compression limiter, dust cap, spring cap, drain spout and locking devices.

For chargers with tethered cables, Aptiv produces connectors and pigtail cables with an emphasis on durability, weather sealing, CE, CQC, and UL markings, and compliance with multiple automotive standards including SAE J1772/IEC62196 Type I, IEC62196 Type II, and GB/T 20234.

TE Connectivity also makes charger cables for multiple regions and countries, for use in harsh environments. They are designed to mate more than 10,000 times, thanks to ultrasound welding for sealing and robustness. Safety features include ground monitoring, to detect residual currents, mis-wiring detection, over- and under-voltage management, over-current management to protect against shorts, and overheating detection to monitor the temperature in the charging unit as well as the infrastructure plug.

TE Connectivity is researching the implications of the continuous high current flows, of up to 500A, involved in charging a vehicle at 350kW. The aim of charging at this rate is to make it possible to increase a vehicle’s range by 300km in ten minutes, but this sixteen-fold increase in charging rate brings with it a 256-fold increase in heat dissipation.

Designers are responding by considering using much thicker (and therefore heavier and more costly) cables, or increasing the working voltage of battery packs to 800V. Designers will also have to adjust the assumptions they use to specify components, to take into account the sustained high currents created by high-power charging as compared to the intermittent high current draws of driving.

Figure 3: The high-current path from charger to EV battery pack (Source: TE Connectivity)

This, in turn, will drive the choice of components and connectivity options within the charger’s internal circuitry. TE Connectivity argues that designers need to take a systemic approach to thermal management in the high-voltage, high-current environment of EV chargers. Failing to properly manage the thermal dissipation of any component in the path from the charging infrastructure to the battery pack (see Figure 3) will undermine the efficacy of the whole system.

Amphenol has developed two related connector ranges that address this issue. The ePower connectors are designed for use in hybrid, EV, and utility truck electrical systems, operating at 800V DC to 1000V DC with a 200A to 500A rating. The connectors use patented RADSOK technology to reduce interconnect resistance to enable higher currents with lower temperature rises. The connectors are also designed to save space, so that one 400A ePower connector can replace three conventional connectors.

The related ePower-Lite range is a plastic power connector for use in hybrid EVs, again using the RADSOK technology to reduce connection resistance. The compact, plastic shell is light, and the connector can be installed and repaired in the field.

These are just some examples of the way in which the enabling technology for EVs is evolving. It’s clear that although a lot has already been done, there’s plenty of work left to do to boost the ‘miles per hour’ of EVs. Visit our automotive page to explore our range of solutions for EV charging systems, or if you would like to speak to one of our technical specialists about your design, click the Ask an Expert button to get in touch in your local language.

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