Comparing Materials for Onboard Chargers: Silicon Carbide vs. IGBT

Onboard chargers (OBC) play a crucial role in electric vehicles (EVs) by converting AC power from the grid into DC power suitable for battery charging. As the EV market continues to expand, the design and complexity of OBC systems have also evolved. This article explores the key considerations in choosing materials for OBCs, focusing on the comparison between Silicon Carbide (SiC) and Insulated Gate Bipolar Transistors (IGBT).

Overview of OBC Systems

With the tightening of global CO2 emission standards, the demand for higher charging capacities in EVs has surged, making OBCs increasingly essential. An OBC typically consists of key components like an electromagnetic interference (EMI) filter, a power factor correction (PFC) stage, and an isolated DC-DC converter.

1. EMI Filter: Mitigates external noise and prevents the OBC from emitting noise back into the power grid.
2. PFC Stage: Converts AC to DC while minimizing phase distortion in the input voltage and current, ensuring a power factor above 0.9.
3. Isolated DC-DC Converter: Matches the output voltage and current to the battery’s charging requirements while providing electrical isolation between the input and output.

PFC Topologies and Material Choices

The choice of PFC topology in an OBC depends on the specific application requirements, including input AC phase and power levels. Common topologies include traditional boost PFC, bridgeless boost PFC, and totem-pole PFC.

1. Traditional Boost PFC: Simple to implement and low in EMI noise but less efficient. It typically employs Superjunction (SJ) MOSFETs, IGBT, and SiC diodes.

2. Bridgeless Boost PFC: Suitable for single-phase OBCs, offering reduced bridge losses but limited by lower power correction performance.

3. Totem-Pole PFC: Delivers the highest efficiency, especially in continuous conduction mode (CCM) and triangular conduction mode (TCM). It's often used in bidirectional power flow applications and can incorporate SiC MOSFETs and IGBT.

Applications for SiC and IGBT

As the power requirements for EV charging systems vary, designers can choose between SiC and IGBT semiconductors to optimize system efficiency and cost.

1. Silicon Carbide (SiC) MOSFETs: Ideal for high power levels and high-frequency applications, particularly in luxury or performance EVs requiring efficient OBCs. SiC MOSFETs are preferred in 800V battery systems for PFC, DC-DC conversion, and bidirectional rectification due to their superior efficiency and power density.

2. IGBT: Suitable for most 400V PFC topologies and DC-DC stages, though it tends to have higher losses at power levels above 11kW. IGBT is often the go-to choice for cost-sensitive applications in mid-range EVs and low-frequency applications where cost-efficiency is prioritized over maximum efficiency.

3. Superjunction (SJ) MOSFETs: Typically used in lower power applications (below 7.2kW), with performance enhancements possible through Vienna rectifier designs for 11kW and 22kW power levels.

Comparing SiC and IGBT

SiC MOSFETs offer better efficiency at high voltages and frequencies, making them suitable for compact, high-performance EV charging systems. On the other hand, IGBTs provide a cost-effective solution for lower voltage systems where cost savings are more critical than achieving maximum efficiency.

Conclusion

OBCs are pivotal in EV charging, and selecting the right materials and topologies is essential for optimizing performance and efficiency. SiC MOSFETs are the go-to for high-voltage, high-efficiency applications, while IGBTs offer a budget-friendly alternative for lower voltage systems. By understanding the trade-offs between these components, designers can make informed choices that enhance the overall performance of their EV charging solutions.

Novatech offers comprehensive end-to-end solutions, from design to finished product, along with genuine electronic components, ensuring your OBC designs are both reliable and efficient