Feature: Electric Vehicles
Mitigation techniques for EMI in chargers Eff ective EMI control is crucial from the initial design phase. Below are several key design strategies to minimise EMI in smart fast chargers 1. Choosing low EMI components • Component selection: Components with low EMI emissions or enhanced noise immunity, such as low-noise op-amps, shielded inductors or specially designed low-EMI integrated circuits (ICs), can signifi cantly reduce EMI.
• Frequency range considerations: Select components that handle high-frequency transients eff ectively, particularly when high-speed switches are in use.
2. Good PCB layout • Minimise loop areas: Large loops in the PCB's power and signal paths can act as antennas and radiate EMI. Reducing loop sizes and ensuring a continuous ground plane helps reduce EMI.
• Use of ground and power planes: A solid ground and power plane structure improves signal integrity by providing low-resistance and low-inductance paths.
• Trace design: Short, wide traces reduce resistance and inductance, lowering EMI. Additionally, reducing the number of vias helps minimise EMI.
3. Proper routing and laying of cables • Twisted-Pair cables: Eff ective for cancelling out EMI in diff erential signal pairs.
• Shielded cables: Crucial for protecting sensitive signals, particularly in analogue or high-speed digital circuits.
• Separation of power and signal cables: Keeping power and signal lines apart minimises the coupling of noise into sensitive signals. 4. Minimising ground loops • Single-Point grounding: A single-point grounding strategy avoids ground loops by ensuring that all grounds converge at one central location.
• Star grounding scheme: T is layout helps further minimise interference from currents fl owing in ground paths.
• Ground isolation: Isolation techniques like isolating transformers or optocouplers help prevent interference caused by ground loops.
5. Eff ective grounding • Low impedance ground paths: Wide traces or dedicated ground planes ensure low-impedance paths that prevent radiation of unwanted noise.
• Shielding enclosures: Using metallic enclosures or Faraday cages for external shielding can block EMI from external sources and contain emissions from the charger itself. 6. Decoupling and fi ltering • Decoupling capacitors: T ese are critical for suppressing high-frequency noise at power supply lines and on the power pins of components.
• Power supply fi lters: Use of inductors and capacitors can fi lter out noise from power supplies before it propagates through the system.
7. Physical placement of components • Shielding sensitive circuits: Position analogue and high-speed digital components as far apart as possible to prevent interference from noisy switching components.
• Distance from external EMI sources: Ensure sensitive signal paths are kept away from potential sources of interference like power supplies, motors, or high-frequency components.
EMI/RFI fi lters for EV chargers To address EMI in smart fast chargers, EMI/RFI fi lters are essential tools. T ese fi lters are designed to reduce or eliminate high-frequency noise that could interfere with both the charger and its surrounding environment. T e MF 620 series EMI/RFI fi lters,
developed by EMIS, are designed specifi cally for DC fast charging stations. T ese fi lters comply with international standards such as UL 2202 and IEC 61851- 23, making them a reliable solution for mitigating EMI in EV chargers.
Key features of the MF 620 series include: • Multistage DC EMI fi lters designed for a variety of voltage and current levels: – DC Voltages: 500V, 1000V, 1500V. – Current Ratings: 150A, 300A, 450A, 600A, 1000A, 1600A. • Y capacitor options: Selectable between 0nF, 100nF, 200nF, and 2000nF.
• Available in diff erent mounting confi gurations and termination types to accommodate a wide range of installation environments.
• UL certifi cation: Compliant with UL60939- 3, ensuring adherence to safety standards.
• Compact design: Smaller footprint and lighter weight off er fl exible installation options.
• Protective covers and accessories: Included for enhanced safety and installation convenience. By integrating these advanced EMI fi lters,
fast charging stations can signifi cantly reduce EMI emissions, protecting sensitive equipment and ensuring compliance with EMC and safety regulations. T e rapid growth of electric vehicle
adoption is driving the demand for fast, effi cient charging stations. However, the increased power levels and high-frequency switching involved in DC fast chargers bring the challenge of EMI. Careful EMI management is crucial to avoid disruptions in both the charger’s operation and surrounding electronics. Mitigation techniques such as careful
component selection, optimised PCB layout, and the use of EMI fi lters like the EMIS MF 620 series play a vital role in addressing these challenges. By adopting these solutions, EV fast charging stations can reduce EMI, enhance performance, and comply with both safety and EMC standards, ensuring a safe, effi cient and reliable charging experience for all users.
www.electronicsworld.co.uk March 2025 17
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