Types of electric vehicle charging and common topologies

With the increase in the EVs on the roads, the demand for the electricity that is needed to charge them is also rising at an exponential rate. It is estimated around 230 TWh of energy will be needed in 2030 to charge these vehicles compared to the 11 TWh demand of today. To serve this many cars and the accompanying electricity demand, nearly 30 million chargers will be required. While most of the chargers will be installed at personal homes, more than 1.2 million public chargers will need to be installed to service EVs on the go.

Cumulative Charger demands need for EVs

Home chargers typically use the common, readily available AC power supply. On the other hand, public chargers are designed to provide a fast and reliable charging experience like when refueling a traditional internal combustion engine (ICE) vehicle. This means that public fast chargers need to have enough power delivery capability (up to 600kW) to provide a full charge to EVs in less than 15mins. This is only possible with DC charging.

Types of Charging

AC charging refers to charging using the normal power available in a typical home, which is available in the form of alternating current (AC), hence the name. This kind of charging requires an on-board charger (OBC) in the EV that converts the power from AC into DC, which is required for charging the battery using AC.

Level 1 AC

This is the most basic charger which receives 120-240Vac (13-16A) from the grid and then supplies it to the EV with a charging cable. It is the slowest charger type, but it is also the most portable and can be plugged in almost anywhere. Most models are usually rated up to 1kW.

A level 1 AC charger

Level 2 AC

A level 2 AC charger still uses the readily available 120-240Vac power supply. The main difference is that it is rated for higher current (32-40A). These AC chargers can usually be found permanently wired to homes and to poles in public spaces. They are usually rated up to 11-22 kW.

A level 2 AC charger

DC Charging

To decrease charging times for EVs, the only way to go is DC charging. DC chargers deliver power directly to the EV battery by bypassing the on-board charger in the EV.

Level 2 DC Charging / Level 2+ / DC wallbox

For power levels around 20-25kW, a common solution would be referred to as a “level 2” DC charger, even though there is no official naming convention. These can be found in both residential and commercial locations.

The biggest difference compared to AC charging is that there is an additional built-in power block converter that performs the rectification from AC to DC (e.g., “AFE” - active front end). Then, this DC current is fed into the car via a charging cable to charge the battery. Depending upon the selection of the power devices, it can also provide bi-directional functionality.

A level 2 DC charger

Level 3 DC Fast charging (DCFC)/ rapid / superchargers

Level 3 DC chargers are often called DC fast chargers (DCFCs) or superchargers. The power levels for this type of charger can easily vary from 50kW to up to 1MW. These chargers are made of multiple power blocks of 20, 30, 50, 60kW or even higher to obtain the desired power level. Depending on the capacity, these fast chargers can charge a typical EV battery in less than 20 mins.

A level 3 DC Fast Charger

Charging standards

Just like we have different charger levels to differentiate power levels, there are also different standards for the connectors used.

Types of charger connectors

Common AC-DC Topologies

For AC/DC power conversion, single-phase and three-phase topologies can be used. Single-phase topologies are most common for home charging or when power levels are less than 6.6kW, while three-phase topologies are better suited for higher-power charging blocks (>11kW) :

•  Totem Pole/PFC
•  NPC/ANPC – Neutral Point Contact PFC / Active Neutral Point PFC
•  AFE–Active front end PFC
•  Vienna Rectifier
•  T-type PFC

For knowledge on each topology circuit, recommended parts and reference designs, please visit Wolfspeed’s Application note:  PRD-08367: EV Charging Power Topologies Design Guidebook | Wolfspeed.

Common DC/DC Power Topologies

After converting the AC power into a typical DC bus voltage of 400V-800V, we can now convert this to the necessary voltage for charging the EV batteries. There are various DC/DC topologies addressed below that can help achieve it:

•  DAB -Dual Active Bridge
•  PSFB – Phase shifted Full Bridge
•  LLC Converter
•  CLLC Converter

For knowledge on each topology circuit, recommended parts and reference designs, please visit Wolfspeed’s Application note: PRD-08367: EV Charging Power Topologies Design Guidebook | Wolfspeed.

Summary

In the continually evolving field of electric vehicle charging, there is a strong push for higher power and higher density solutions to reduce charging downtime compared to typical internal combustion engine vehicles, which remains a widespread bottleneck. This has led to increased adoption of innovative multi-level topologies to meet these power demands, requiring batteries to support the grid during peak demand periods when not in operation, as well as requiring topologies to support bidirectional power.

Both requirements further strengthen the need to have more efficient power semiconductor switches. Wolfspeed’s silicon carbide devices are perfectly suited to support these next-generation requirements. Visit Wolfspeed's website to find product offerings, reference designs, and design support tools that you need to start your own EV charger design journey.  

(a) Wolfspeed^® Discrete, (b) Modules & (c) A 60kW LLC Reference design