Load balancing in the EV charging infrastructure

Concerns about range are still holding back electric vehicle (EV) uptake. One of the key sources of “range anxiety” is the availability and distribution of public charging points.

In its Policy Brief on Public Charging Infrastructure the International Energy Agency (IEA) says as much, arguing: “Experience has shown that perceptions about charging infrastructure availability correlate positively with EV adoption.”

Nonetheless, EV sales are rising. Take the UK as an example market. According to the UK’s Society of Motor Manufacturers and Traders (SMMT), sales of battery EVs in April 2022 were nearly 41% greater than in April 2021, and for the year to April 2022, BEVs have doubled their share of the market vs the year to April 2021.

The IEA’s tracker of alternative energy vehicle uptake shows a similar story internationally, with BEV sales growing rapidly in China, Europe and the U.S.

To an extent, this success is making a rod for the EV industry’s back, creating an imbalance between charging capacity demand and charging point availability. SMMT’s November 2021 analysis found the ratio of EVs to public charging points in the UK fell from 11:1 in 2019 to 16:1 in 2020. This compares to ratios of 3:1 in South Korea, 5:1 in Netherlands, 9:1 in China, 10:1 in France, and 13:1 in Belgium and Japan. Only Germany, at 17:1, lags the UK. The analysis further suggests that in the UK only a single standard public charging point, i.e., one operating at up to 22kW, is being added for every 52 EVs sold. There are also regional differences in charge point density, with urban areas faring much better than rural areas – doing little to assuage concerns about EV range on cross-country journeys.

Accessing charging capacity

Installing more public charging points will make it easier for EV owners to plug in to charging networks, but it won’t necessarily help them charge their vehicles in the way they expect.

Why is this? The first challenge is generating capacity: will the aggregate generating capacity of a country be enough to charge its growing population of EVs? This is hard to predict, given that many countries are adding capacity at the same time as the EV usage is growing.

The second challenge is to manage the concentration of demand for charging capacity. The first such concentration is by location: think how adding EV charging points to the parking lot of an apartment block concentrates demand, potentially absorbing the entire power budget of the cabling infrastructure serving that block. Pushing that demand upstream, to a substation serving a dense urban area with multiple such apartment blocks, and its capacity may need upgrading in turn, along with the infrastructure that feeds it from the wider power grid.

The second kind of concentration is by phase. Think of a street with multiple residential charging points fitted by a variety of contractors without reference to each other. It would be easy enough for many of these charging points to end up sharing one phase of an area’s three-phase supply, and then having to be manually redistributed to other phases under the direction of the local energy distribution company to balance and protect its infrastructure.

The third type of concentration is in time. For example, when EVs go on charge just as domestic demand peaks in the early evening. If your energy supplier is offering advantageous pricing to encourage the uptake of overnight charging, this could also lead to substantial demand peaks as multiple EV users start taking advantage of the low-cost charging slot at once. Indeed, the UK government has just passed legislation that asks EV equipment makers to program their chargers to avoid peak demand periods by default, although this can be overridden by the customer. This helps smooth demand, shifts charging to periods when generation is greener, and nudges consumers to thinking differently about how they consume energy. The act also says that chargers must be able to insert a random delay before they start charging to avoid the kind of sudden demand peaks that may happen at the start of low-cost tariff periods.

Load sharing policies and regulation

Load sharing in EV charging is like the management of any other scarce resource. You either leave it to market forces, or you implement policies that manage access to charging power that serves both policy goals and the consumer. Given the urgent need to decarbonize transport, one such goal would be to accelerate the uptake of EVs by ensuring that users can access a limited charging capacity fairly.

Consider a residential area in early evening as school ends and workers arrive home. The aggregate charging demand of the residents’ EVs could be greater than the capacity of the local infrastructure. How, then, should these vehicles be charged?

The first step is to ensure that each residential charging point caps its EV’s demand so that the home can operate as normal. Otherwise, no one’s getting an evening meal. The next step is to consider how the group of EVs, sharing the same energy delivery infrastructure, will be charged once domestic demand has been protected.

One approach could be described as “winner takes all” – the first EV to connect gets as much power as it needs until fully charged, and any remaining power is distributed to the second, third, fourth…vehicle as capacity allows. This kind of queuing system is well understood but could create perverse incentives: It’s easy to imagine EV drivers racing home to be first to plug in at the end of the day. And it does nothing to incentivize vehicle efficiency, or more careful matching of vehicle choice to real user need.

A second approach distributes the available power equally between all the vehicles on charge. If there are four vehicles on charge, each gets 25% of the power. When a fifth vehicle joins, they each get 20% – and so on.

Variants of these approaches can implement different forms of fairness to nudge user behavior. For example, smart chargers could equalize the charge level of all the vehicles in a group. At first, the vehicle with the lowest charge level gets access to the most charging power. Once all the vehicles have levelled up, each vehicle is then charged at a rate which increases its charge level in step with all the others. One side effect of this approach might be that EVs with very large batteries would be seen as holding back the ability of other users to gain charge. A further refinement would consider both a vehicle’s initial state of charge and its efficiency in terms of km/kWh, so that the charging network first equalizes the range of all the vehicles and then adds range at the same rate to all.

Another approach to load sharing explicitly prioritizes some users. In our thought experiment, this might mean that any resident who relied entirely on an EV for their mobility would get priority access to charging power. In a commercial setting, it might mean creating priority-charging parking bays for visiting customers, and in a fleet management context, prioritizing emergency vehicle charging over that of support vehicles.

Tesla manages access to another scarce resource: its Supercharger network of high-power chargers. Tesla charges customers an idling fee if they leave their fully charged vehicles connected to its chargers. The per-minute fee doubles if all the other Superchargers nearby are already occupied, incentivizing users to free up access to their space quickly.

Addressing the load-sharing challenge

Electrification of vehicles at mass scale is creating challenges and opportunities for multiple industry sectors including power generation companies, national grid operators, local distribution companies, charging equipment suppliers, vehicle makers and, of course, end customers.

All these stakeholders are having to get used to sharing charging power and energy distribution capacity in increasingly dynamic and collaborative ways, using a blend of technical solutions, policymaking, regulation and behavioral change initiatives. The process will involve overcoming complex electrical engineering, electricity distribution, charging equipment infrastructure, regulatory, policy, and consumer behavior issues. It will also demand a rigorous attention to physical and cyber-security issues, especially as bidirectional charging schemes make our EVs part of our critical national infrastructure.

Addressing these issues will demand that EV supply equipment makers form strong partnerships to ensure they understand rapidly changing worldwide technical regulations on charger design, the impact of new policies and incentives on charging practice, cybersecurity challenges and new technology options.

Avnet Silica can be your trusted partner as you navigate these challenges while developing EV charging solutions.

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