Just how Fast is EV “Fast Charging”?

  November 15, 2021

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Drivers of electric vehicles are a diverse bunch, but they are united by two questions: How far can my car go? and Where can I charge?...Today, we will be talking about that specific concern—electric vehicle (EV) charging.

According to the China Electric Vehicle Charging Infrastructure Promotion Alliance, the total number of charging stations nationwide was 1.681 million at the end of 2020. By July 2021, this number rose to 2.015 million, an increase of 50.2% YOY. Growth is obviously quite strong.

However, some people have predicted that the number of new-energy vehicles (NEVs) in China is expected to reach 33.5 million by 2026. If the vehicle-to-charge point ratio is estimated at 3:1, then by that time, the cumulative demand for electric vehicle charging points in China is set to exceed 11.16 million! The gap between supply and demand is quite significant indeed.

In addition to the number of EV charge points, the charging speed is also a “point” of concern. For example, charging a car with a capacity of 60 kWh using a 100 kW DC charger would take about 36 minutes to reach a full charge, which would give the driver about 330 kilometers of driving distance. For comparison, refueling a traditional fuel vehicle for the same distance only takes 3-5 minutes. The gap in user experience will inevitably be hard for electric car manufacturers to face, but at the same time, they cannot ignore it.

Therefore, "fast charging" has become a key issue to solve in the building of EV charge points.

Approaching the Threshold of “Fast Charging”

How fast can "fast charging” go? In order to answer this question, we need to take a look at how electric vehicles charge. There are two types of charging: AC charging and DC charging, each with a different technological architecture.

When AC charging mode is adopted, the AC from the grid is connected to the on-board charger (OBC) of the electric vehicle through the AC socket or charge point; the OBC converts AC to DC, and the DC voltage and current charges the battery.

For DC charging, the AC power from the grid is converted to DC power outside the vehicle (usually by a charge point), meaning that the battery can be charged directly without going through the OBC. Since AC-DC conversion is performed outside of the car, it is not overly restrictive in terms of space, cost, weight, or thermal management. This gives DC charging more room for improved charging power, so it has become the important “fast track” for the fast charging of electric vehicles.

Figure 1: Comparison of the two charging architectures (DC and AC) for electric vehicles (Image source: Yole Development)

According to a popular classification method, EV charging can be divided into three levels:

• Level 1: In this level, electricity is mainly from the city supply, which can provide AC voltages of 120VAC/230VAC and charging currents of 12A to 16A. This gives a charging power within the range of 2kW.
  

• Level 2: This level, also AC, relies on a multi-phase 240VAC charge point. Charging current can be increased from between 15A to 80A, and charging power can reach 22kW.
  

• Level 3: Whenever power higher than 22kW is needed for charging, DC charging becomes necessary. In level 3, a high-voltage DC output of 300V to 750V from the DC charge point can directly charge the battery, and the power can reach hundreds of kilowatts—such as in Tesla's V3 Supercharger, which can support up to 250kW peak charging power. It is claimed that the V3 can charge a Model 3 to 250 km in a mere 15 minutes. At present, the most often seen DC charging power ranges between 22 to 150 kW; 200 to 350 kW is the main target for many manufacturers; and DC charging of up to 400 kW is also being attempted.

Obviously, the threshold for "fast charging" will only be reached with Level-3 DC charging.

Different Fast-Charging Standards

However, this “three-level” classification is not very strictly defined. To bring everyone up to pace at building fast charging infrastructure (EV charge points), various industry organizations and leading manufacturers are rushing to push for the necessary standards and regulations.

For example, the IEC 61851 international standard for electric vehicle conductive charging systems, formulated by the International Electrotechnical Commission (IEC), subdivides EV charging into four modes. The first three are AC charging, and the fourth is a DC charging mode capable of providing 600V at a maximum current of 400A, with a maximum charging power reaching 240kW.

In the North American market, the Society of Automotive Engineers (SAE) has launched their SAE J1772 management standard, which defines four charging modes: AC Level 1 and AC Level 2, and DC Level 1 and DC Level 2. Among the four, DC provides a voltage between 200-500V, and DC Level 1 and 2 support up to 40kW and 100kW of charging power, respectively.

CHAdeMO is an association established by several Japanese manufacturers, including Nissan, Mitsubishi, Toyota, Hitachi, Honda, and Panasonic, along with some European participants. The association has formulated the CHAdeMO protocol specifically for DC fast charging. CHAdeMO 2.0, the latest version, supports 400kW/1000V DC charging. Reportedly, CHAdeMO is jointly developing an ultra-high-power charging standard "ChaoJi" with the China Electricity Council (CEC). Their goal is a hefty 900kW!

In the field of DC fast charging, there is also the CCS (Combined Charging System) standard that deserves attention. CCS is jointly promoted by 8 vehicle companies in the United States and Europe. It aims to unify the chaotic incompatibility among charging interfaces. The idea of CCS is to support, all in the same physical interface, both AC charging and DC charging. The CCS system is compatible with the standards of IEC, SAE, and ISO, and supports both single-phase and three-phase AC charging. Currently, it supports 200kW DC charging, and a solution to support 350kW charging is in the works.

An Agile Solution

The evolution of DC fast charging standards obviously poses new challenges to the development of EV charge points, which manifest in two aspects: first, products and solutions need to be able to adapt their architectures to the requirements of each standard and power level; second is scalability and keeping pace with standard "upgrades". In other words, designs need to be agile.

To achieve agility, modularization is one feasible path. Using a modular approach, developers can stack power modules from 15kW to 75kW (or higher) in a charge point system. This would allow the point to easily provide DC charging applications for electric vehicles ranging from 150V to 1000V according to the particular need, while voltages and powers are also optimized.

Figure 2: Multiple power modules are stacked to form a high-power EV DC fast charging system (Image source: ON Semiconductor Corporation)

For example, ON Semiconductor is developing a 25kW DC charging module with bidirectional capability. It supports 400V and 800V battery charging, and is optimized to support higher voltage levels.

Figure 3: Bidirectional 25kW DC charging module developed by ON Semiconductor (Image source: ON Semiconductor Corporation)

In short, with the development of the electric vehicle market gaining speed, the demand for EV DC fast charging has quickly revved up and taken off. When will EV fast charging change from “perk” to “part of every life”? It all begins with the era of electric vehicles.

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