Designing with Silicon Carbide (SiC) in Electric Vehicle DC Fast Chargers
Electric Vehicle (EV) DC Fast chargers bypass the on-board charger installed on the electric vehicle and provide a fast DC charge to the battery directly. DC Fast chargers consist of an AC-DC stage and a DC-DC stage as shown below:

Minimizing charging time while optimizing system efficiency is a major focus for DC Fast chargers. Component selection, voltage range and load requirements, operating costs, temperature, ruggedness and environmental protection, and reliability must be considered when designing these systems.
SiC-based components can provide better performance than traditional Si and IGBT components due to their improved operating temperature, better conduction losses, lower leakage currents, higher surge capacity and max voltage ratings, and overall better power density. To take full advantage of these benefits, however, the power conversion topologies must be optimized.
This article will look at several power conversion topologies to consider for fast-charger systems and some tools/resources that are available, as well as a summarized table with several key comparisons.
Whether in a home or public area, in a highway corridor, or for charging a fleet of vehicles, power demanded from the AC grid can range from 2.2 kW all the way to 1 MW. These systems are typically built as 20- to 50-kW AC-to-DC and DC-to-DC power blocks that can be scaled to meet higher or lower demand based on the charging location and vehicle type. A graphical view of the power levels and how systems are typically stacked is below:

The next step in the design is to analyze the practicalities in DC Fast charging applications. Firstly, these chargers are installed at public areas where a wide battery voltage and a wide load profile is expected. As an example, most EV’s on the road today have batteries in the 350-450V range while newer models are being introduced with 800V batteries. Additionally, each of these EV batteries have different charging profiles which means that EV chargers need to be designed for a wide load profile with high full load capability. Additionally, customer behavior is also important to analyze because unlike home chargers, the vehicle is almost always driven to a charging location which translates to a warm battery and a quick ramp to peak charging power. You can see this on the top left graph along with the ramp down at 80% of battery capacity as recommended by several battery manufacturers.
From a commercial operator perspective, operating costs are critical for investment. As an example, for a single 360kW charging station, 2% better efficiency for a station operating for 12 hrs/day with a 25c/kwH assumption gives a ~$22/day saving per station. The dynamic nature of the EV market also drives the need for high flexibility for new models and smaller installation footprints
Below we can summarize the system objectives for a fast charger system:
- Wide battery voltage range (350V-800V)
- Wide load profile (single/multiple vehicles) and battery buffers (for high performance vehicles)
- Optimized for charging at full load
- Bi-directionality for return-to-grid applications
- Flexible, can adapt to new industry trends/standards
- Small installation footprint
- Reduced operating costs, allow for profitability
- Rugged, wide operating temperature
Let’s explore some power topologies while keeping in mind the above requirements and design goals.
AC-DC Conversion
Topology 1 – (AC-DC): 3-Phase 2-Level Bidirectional Active Front End AC/DC Converter
The first AC/DC option is a simple six-switch, two-level active front end (AFE) configuration incorporating six Wolfspeed 1200V SiC MOSFETs (shown in Figure 1) that provides 25kW. Overall, many improvements can be observed when comparing the SiC components with IGBT devices (also shown in Figure 1).

Metric | IGBT | SiC |
---|---|---|
Fsw | 20kHz | 45kHz |
Power Density | 3.5kW/L | 4.5kW/L |
Efficiency | 97.2% | 98.2% |
Cost | IGBT | SiC |
---|---|---|
Switch | 32% | 62% |
Choke | 40% | 19% |
Driver | 9% | 9% |
Thermal | 19% | 10% |
Figure 1: Three-phase, two-level bidirectional AFE (top) and IGBT vs. SiC comparison (bottom)
Table 1 describes the benefits and challenges associated with this configuration.
Benefits | Challenges |
---|---|
SiC enables smaller choke with 2.5x Fsw | Can’t reduce frequency further to balance core loss |
Low component count and low cost | High DC+/- swing adds MOSFET stress and loss |
Mature control scheme | Hard-switched topology introduces EMI concerns |
Overall simplicity | Large inherent footprint driven by size of choke |
Table 1. 3-Phase 2-Level AFE Benefits vs. Challenges
Employing six SiC MOSFETs, such as the 32-mΩ C3M0032120K by Wolfspeed, can reach a high efficiency (and reduce cost while increasing power density). Another non-discrete option is a single CCB021M12FM3 Wolfpack module providing 25kW. Using an additional module in parallel will double the power rating to 50 kW.
Design resources:
Reference design CRD22AD12N demonstrates a system with either one-phase or three-phase (grid supply) input with a non-isolated output of 650–800 VDC at 22 kW, operating at a peak efficiency of more than 98.5%.
Reference design CRD25AD12N-FMC with an AC/DC configuration consists of an active rectifier operating with three-phase input and 800-VDC output. This arrangement makes use of the CCB021M12FM3 WolfPACK™ module and can provide up to 25 kW of power with peak efficiency greater than 97%, while also providing scalability up to higher power levels by interleaving multiple 25kW AFEs.
Topology 2 – (AC-DC): T-Type Bidirectional AC/DC Converter
The T-type AC/DC converter utilizing 1,200-V SiC MOSFETs allows for lower switching losses when compared with the six-switch approach, although conduction losses dominate at full load in fast-charging applications.
Figure 4 shows a bidirectional configuration utilizing six 1,200-V 32-mΩ SiC MOSFETs used on the outer parts and another six 650-V 45-mΩ SiC MOSFETs used in the mid-section (which provides a better RDS(on) versus temperature conduction and good full-load capability). Using SiC in the mid position is also beneficial for fast-charging applications since the flat RDS(on) vs. Tj curve of silicon carbide which allows more efficient conduction at full load across operating temperatures.

Table 4 lists additional benefits and challenges associated with this implementation.
Benefits | Challenges |
---|---|
Lower switching loss vs. six-switch | High part count |
Lower dv/dt for EMI | High component cost |
Middle 650V SiC better RDSon vs. Temp | Complex control |
Small magnetics (compared to six-switch) | Conduction loss dominates at full load in fast charger app |
Low DC+/- swing, low MOSFET stress |