Governments around the world are pushing both private and commercial vehicle owners toward environmentally cleaner alternatives, such as electric vehicles (EV). However, one of the biggest hindrances to making this change is vehicle range concerns. The majority of low- to mid-range EVs can complete several journeys before recharging is required. But, if you’re planning a longer trip, EV charging en route still requires more time than refueling a combustion engine vehicle.
The industry is working hard to improve charging times by developing fast DC charging solutions that are comparable with refueling a combustion engine vehicle. Unlike the EV’s onboard charger (OBC) that uses household AC, fast DC chargers circumvent the OBC to deliver energy directly to the EV’s battery charging circuitry. And, unlike their AC counterparts, such chargers can charge an EV to 80 percent range in as little as 10 minutes.
Fast DC Chargers for EVs
Current fast DC chargers deliver between 35kW and 50kW, operating at up to 800V. The highest power delivery chargers are typically installed at highway service stations. Whether your EV can sink such power depends on its design and batteries. Most of today’s EVs are limited to charging levels below 300kW.
There are plenty of engineering challenges for such a high power and voltage application. These range from safety and reliability, to serviceability, efficiency, size, and cost—both operating and acquisition. To date, the design approach has relied upon silicon IGBTs and MOSFETs. However, thanks to the introduction of wide bandgap semiconductors, such as silicon carbide from suppliers such as Wolfspeed, SiC MOSFETs are rapidly becoming the preferred choice of power switch.
The Move to SiC MOSFETs for EV Chargers
The core of a fast DC charger can be broken down into two key blocks (Figure 1):
- The AC/DC stage, converting incoming AC to a DC link voltage
- A DC/DC converter that supplies DC to the EV’s batteries.
In addition, there are also payment mechanisms, a human-machine interface, and connectivity elements. The power delivery section of such chargers is constructed of several modules, with each module typically contributing somewhere between 15kW and 50kW to the total power.
Figure 1: Simplified block diagram of the power converters for an EV fast DC charger. (Source: Wolfspeed)
Highest possible efficiency and power density are key design targets, enabling engineers to deliver smaller and lighter modules with fewer heat dissipation challenges.