Electrical filters ensure the safe, efficient energy flow between chargers and electric vehicles (EVs). This article discusses how filters stabilize electrical currents, mitigate interference, and reduce thermal runaway risks. It also highlights the role of filters in ac and dc charging, comparing key similarities and differences.
Optimizing and safeguarding EV charging
External EV chargers maintain voltage stability with the help of passive and active inductor-capacitor (LC) electrical filters. Passive filters divert and attenuate electrical disturbances, including voltage harmonics and transient signals, through impedance paths at specific frequencies. Active filters dynamically adjust inductance and capacitance levels to counteract voltage fluctuations and mitigate thermal runaway risks. Active and passive filters prevent electromagnetic interference (EMI) and radio frequency interference (RFI).
Electrical filters play a crucial role in preventing damage to chargers and EVs. Unchecked voltage fluctuations, for example, can lead to overcharging or undercharging of EV batteries. Overcharging causes battery overheating, increasing the risk of thermal runaway, degradation of battery cells, and compromised structural integrity. These factors shorten battery life and can trigger fires and even explosions.
Conversely, undercharging results in incomplete chemical reactions within battery cells, leading to sulfation and reduced overall capacity. This decreases the battery’s ability to hold a charge over time, directly impacting EV range and performance.
Similarly, uncontrolled EMI/RFI can lead to fluctuations in power delivery, causing incomplete or erratic EV battery charging cycles. Unchecked EMI/RFI may also induce excess heat and mechanical stress, impairing the performance of onboard chargers (OBC) and battery management systems (BMS). Notably, onboard chargers also incorporate electrical filters to mitigate EMI and prevent voltage fluctuations.
Filtering mechanisms in ac/dc EV chargers
EV ac chargers are equipped with several essential filtering mechanisms. EMI/RFI filters, for example, protect sensitive vehicle electronics from ac supply noise while ensuring adherence to electromagnetic compatibility (EMC) regulations. Harmonic filters counteract distortion from non-linear loads, stabilizing voltage and preventing thermal runaway.
Additionally, ac chargers incorporate power factor correction (PFC) techniques to optimize energy delivery and surge protectors to prevent power spikes.
Figure 1. Multiple EVs connect and draw power at EV charging stations. (Image: EV Engineering)
Dc chargers facilitate rapid and direct energy delivery to EVs. Similar to their ac charger counterparts, dc EMI/RFI filters dampen emissions and prevent high-frequency electronic switching noises associated with rapid charging. Unchecked, these noises can impair charger performance and compromise the integrity of EV electronic systems. In addition to filters, dc chargers include voltage regulators and advanced thermal management systems.
Many public and commercial EV chargers offer ac and dc charging options. These dual charging units integrate the filtering requirements of both systems, employing a combination of EMI/RFI, harmonic, and thermal management filters to support various charging modes and levels.
Comparing ac and dc charging
EV charging is categorized into three primary levels:
- Level 1 (120 VAC) primarily for residential use
- Level 2 (208/240 VAC) for residential and public settings
- Level 3 (400 to 900 VDC) for commercial and public fast charging. While ac and dc charging filters share some functions, they have distinct roles based on specific currents.
Key similarities and differences include:
- Design complexity: Ac chargers typically require more advanced filtering solutions due to variances and phase differences. Conversely, dc chargers prioritize output quality and thermal management to support direct energy storage and rapid charging efficiently.
- Harmonic distortion management: Though not as prevalent in dc systems, harmonic filters are crucial in ac chargers to mitigate distortions from non-linear loads.
- Voltage stability: Dc chargers employ voltage regulation filters for consistent energy flow. Ac chargers, dealing with fluctuating currents, necessitate more sophisticated solutions for voltage regulation and filtering.
- Thermal control: Thermal management is integral in dc chargers, especially rapid and ultra-fast units. AC chargers incorporate less intensive thermal control measures due to lower standard energy transfer rates.
- EMI/RFI: Critical in both ac and dc systems, EMI/RFI filters prevent electromagnetic interference and ensure regulatory compliance.
- Safety: Surge protection is essential in ac and d chargers, defending against voltage spikes and, alongside filters, stabilizing the power supply. Ac and dc chargers strictly adhere to electrical standards and regulations, ensuring safe and reliable energy flow to EVs.
The importance of industry standards
Most EV chargers on the market comply with standards from organizations such as the Federal Communications Commission (FCC), International Electrotechnical Commission (IEC), and Comité International Spécial des Perturbations Radioélectriques (CISPR).
For example, FCC Part 15 Part B discusses EMC management, implicitly mandating filtering for electromagnetic interference mitigation. Similarly, IEC standards 61851-21-2 and 61851-23 specify EMC requirements for EV chargers and their communication protocols, emphasizing the need for effective filtering to meet these standards.
CISPR standards — including CISPR 11/EN 55011 and CISPR 22/EN 55022 — govern electronic emissions and require electrical filtering for compliance. These regulations ensure EV chargers do not disrupt other devices or the electromagnetic environment. Focusing on communication and connectors, ISO 15118 and SAE J1772 further highlight filtering’s crucial role in maintaining EMC and electrical safety.
Summary
Electrical filters facilitate the safe, efficient energy flow between chargers and EVs. Specifically, both passive and active filters stabilize electrical currents, mitigate interference, and reduce thermal runaway risks. Although ac and dc charging filters share some functions, they have distinct roles based on specific currents. Dual chargers, commonly used in public and commercial settings, merge these filtering requirements to support different charging modes and levels with combined EMI/RFI, harmonic, and thermal management filters.
References
- EMC Considerations for Electric Vehicle Charging, AstrodyneTDI
- How to Select and Apply Capacitors to Ensure Efficient, Reliable, and Sustainable EV Chargers, DigiKey
- 7 Questions: Ac vs. dc Charging, BPPulse
- FCC Part 15B Guide: What is FCC Part 15B?, CT Compliance Testing
- Electric Vehicle On-board Charger, Battery Design
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