Retrofitting a 22 kW Bidirectional DC-DC Converter from IGBT to SiC: +3.8% Efficiency and 50°C Lower Junction Temperature
How Edrift Electric redesigned the power stage of an existing 22 kW bidirectional DC-DC converter — replacing IGBT switches with SiC MOSFETs — delivering measurable efficiency gains.
01. Client Overview
Strategic Partnership & Objectives
A Bangalore-based EV charging infrastructure company was deploying bidirectional DC-DC converters as the core power conversion stage in their V2G-capable charging stations. Their existing design was performing at 92.3% peak efficiency, creating energy loss and thermal issues.
02. Engineering Challenge
Overcoming Technical Limitations
The client's bidirectional DC-DC converter was built around a Dual Active Bridge (DAB) topology using 1200V IGBT modules. The design was failing on efficiency, thermal management cost, and switching frequency limitations.
Critical Bottlenecks Identified:
03. Technical Constraints
Hard Design Constraints
Electrical & Mechanical
04. Design Approach
Multi-Stage Topology Optimization
Edrift's engineering scope was focused entirely on the power stage — devices, gate drivers, magnetics, and thermal path, while maintaining the DAB topology and control firmware.
SiC Device Sizing
Four SiC devices placed in parallel on each switch position (16 total) to achieve current rating while maintaining junction temperatures within 90°C in passive cooling.
Gate Driver Redesign
Fundamental shift from ±15V (IGBT) to +18V/-4V (SiC). Dead-time reduced 6× from 3.2μs to 480ns, improving phase-shift control resolution.
Transformer Re-Optimization
Redesigned with EE55 N87 ferrite core (34% smaller). Interleaved winding structure reduced AC copper loss by 42%. Leakage inductance precisely controlled at 18μH.
Thermal Redesign
SiC dissipated 62% less heat. Custom aluminium cold-plate replaced fan-cooled heatsink, achieving target temperatures via natural convection.
05. Semiconductor Selection
Power Switch Matrix
The IGBT → SiC selection required analysis at 1200V, where SiC delivers very large performance advantages.
| Parameter | 1200V IGBT | 1200V SiC (A) | 1200V SiC (B) |
|---|---|---|---|
| Rdson / Vce(sat) | 2.0V sat | 40 mΩ | 16 mΩ |
| Switching loss | 3.8 mJ | 0.6 mJ | 0.38 mJ |
| Body diode Qrr | 12 μC | 0 | 0 |
| Max Tj | 150°C | 175°C | 175°C |
Selection Rationale:
- Wolfspeed C3M0016120K enabled lowest conduction loss (4 mΩ effective).
- 10× lower switching loss than IGBT.
- Zero body diode reverse recovery critical for DAB operation.
- Kelvin source package enabled lower gate drive inductance.
Final Device BOM:
06. Efficiency Performance
Measured System Efficiency
Efficiency comparison across power levels for the charge direction.
| Load % | Baseline | Edrift Design |
|---|---|---|
| 5 kW | 88.6% | 93.1% |
| 10 kW | 91.4% | 95.2% |
| 22 kW | 92.3% | 96.1% |
Impact Summary
07. Thermal Analysis
Heat Management & Junction Temperatures
Heat generation reduced by 68% at full load, enabling fan removal.
Custom aluminium cold-plate matched to existing PCB pattern. Natural convection from enclosure surface.
| Device | Baseline | Design | Delta |
|---|---|---|---|
| Primary MOSFETs | 127°C | 77°C | −50°C |
| Secondary MOSFETs | 119°C | 72°C | −47°C |
| Transformer winding | 98°C | 74°C | −24°C |
Thermal Success Criteria Met
Fans eliminated, saving 45W auxiliary power and removing highest failure rate component.
08. Power Density & Form Factor
Volumetric Comparison
Weight reduction and reliability improvement through component integration and cooling elimination.
Volume Recovery Vectors
- 1Reduced core volume: 34% smaller
- 2Eliminated fans and associated auxiliary power stage
- 3Lower gate drive dissipation
- 4Integrated resonant inductance
Mechanical Outcome:
3-year saving per unit: ₹64,420. Saving across 40 stations: ₹25.8 L.
09. Testing & Validation
Rigorous Automotive-Grade Verification
Electrical, thermal, and firmware compatibility testing confirmed successful retrofit.
10. Deployment Outcome
Field Results & Scaling
40 stations upgraded with SiC power stages, showing 0 failures over 8 months.
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