How to select inductors, transformers, and common mode chokes for AC chargers, DC fast chargers, and vehicle-to-grid systems
Introduction
The global EV market is accelerating. Behind every charging station is a complex power conversion system, and at the heart of that system are magnetic components. Whether it is a 7 kW home AC charger, a 250 kW DC fast charger, or a bidirectional V2G system, magnetic components determine efficiency, power density, reliability, and grid compliance.
Shaanxi SiRui Technology Co., Ltd. supplies magnetic cores and custom magnetic components for EV charging manufacturers worldwide.
1. EV Charger Topology Overview
Level 1 / Level 2 AC Chargers (On-Board)
- Power: 3.3 kW – 22 kW
- Key magnetic parts: PFC boost inductor, isolation DC/DC transformer, common mode chokes
Level 3 DC Fast Chargers (Station-Mounted)
- Power: 50 kW – 350 kW (future: 480 kW+)
- Stage 1: Active Front End / PFC — boost inductors (three-phase), grid-side CMCs
- Stage 2: Isolated DC/DC — high-frequency transformers (LLC or DAB), output filter inductors
V2G (Vehicle-to-Grid) Systems
- Bidirectional charging, grid-forming capability
- Magnetic components must handle symmetric bidirectional current
2. PFC Boost Inductor (Grid Side)
Powder cores (Sendust, High Flux, MPP) dominate PFC inductors because their distributed air gap handles DC bias without saturation, with no fringing flux loss. For three-phase DC fast chargers, the PFC inductors are often the largest and heaviest magnetic components.
3. Isolation Transformer (DC/DC Stage)
LLC Resonant Transformer (Most Popular)
- Zero-voltage switching for high efficiency
- Mid-range: ferrite PQ/ER cores (cost-effective)
- Premium/high-density: nanocrystalline toroidal cores (smaller size, higher Bsat)
Dual Active Bridge (DAB) Transformer
- Used for V2G bidirectional systems and higher-voltage DC fast chargers
- Nanocrystalline toroidal cores increasingly adopted
4. Common Mode Chokes (EMI Filtering)
EV chargers have long AC and DC cables that act as EMI antennas. CMCs on both sides are essential for meeting CISPR 11 / EN 55011 EMI limits and preventing ground leakage current.
Nanocrystalline CMCs are increasingly adopted in DC fast chargers for their small size and high-frequency performance. Ferrite CMCs remain cost-effective for Level 2 home chargers.
5. Output Filter Inductors (DC Side)
Powder cores (Sendust or High Flux) handle high DC bias from battery current with stable inductance. For high-power DC fast chargers, multiple parallel inductors are used (one per power module, typically 15–30 kW each).
6. Thermal & Environmental Considerations
DC fast chargers operate outdoors (-30°C to +55°C ambient) with 10+ year 24/7 lifetime. Magnetic components must maintain stable permeability, minimal temperature rise, and withstand thermal cycling for decades.
7. Custom Components from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply powder cores for PFC and output inductors, nanocrystalline cores for transformers and CMCs, ferrite cores for Level 2 OBCs, and finished CMC chokes for EV charging applications.
Conclusion
As the EV industry pushes toward 350 kW+ fast charging and higher efficiency, magnetic material selection becomes an even bigger differentiator.