The rapid proliferation of electric vehicles (EVs) has driven unprecedented demand for reliable and efficient charging infrastructure. Current transformers (CTs), critical components in electrical systems, play a pivotal role in ensuring the safety, accuracy, and functionality of EV charging stations. This study delves into the technical requirements, operational principles, and practical applications of CTs in EV charging systems, supported by industry standards and real-world case studies.
Current transformers are designed to convert high primary currents into measurable secondary currents while maintaining isolation between the high-voltage primary circuit and low-voltage measurement/protection systems. Key types include:
Electromagnetic CTs: Widely used for AC current measurement, leveraging magnetic cores to induce secondary currents proportional to primary currents.
Electronic CTs: Utilize Rogowski coils or Hall-effect sensors for high-frequency and wide dynamic range applications, ideal for detecting DC components and harmonics .
Residual Current CTs (RCDs): Specifically designed to detect leakage currents. Type B RCDs, compliant with IEC 62752 and UL 2231, are mandatory for EV charging due to their ability to detect both AC (30 mA) and DC (6 mA) leakage .
CTs enable accurate monitoring of charging currents, essential for billing, energy management, and load balancing. For example:
PCB-mounted CTs (e.g., IVY-CT-PCB-01-10A) with 0.1-class accuracy and 3000V dielectric strength are integrated into charger PCBs for real-time current and power sampling .
Split-core CTs (e.g., KCT series) allow non-invasive installation on existing cables, supporting retrofitting of smart charging stations .
CTs are critical for safeguarding against electrical hazards:
Type B RCDs in EVSE (Electric Vehicle Supply Equipment) detect DC and AC leakage currents, ensuring compliance with GB/T 18487.1-2015 and IEC 62955 standards. For instance, Xiamen ZTC’s Type B CTs achieve 6 mA DC/30 mA AC sensitivity with fast calibration (≤240 ms) .
Differential Protection: CTs in ground fault detection systems (e.g., Littelfuse RCMP20 series) monitor current imbalances, triggering circuit disconnection within milliseconds to prevent electrocution and equipment damage .
Advanced CTs facilitate intelligent charging optimization:
Dynamic Load Balancing: FULSOLEN’s Smart A01 charger uses CTs to distribute power across multiple charging points, preventing grid overloads. This technology enables 22 kW charging with 68 miles of range per hour .
PV Integration: CTs in hybrid solar-charging systems prioritize renewable energy usage, reducing grid dependency and operational costs .
To ensure interoperability and safety, CTs in EV charging must adhere to rigorous standards:
IEC 62752: Mandates Type B RCDs for Mode 3/4 charging stations, requiring detection of DC leakage ≥6 mA and AC leakage ≥30 mA .
UL 2231-2: Specifies safety requirements for EV charging connectors and cables, including CTs’ electromagnetic compatibility (EMC) and thermal stability .
GB/T 18487.1-2015: China’s national standard for EV charging systems, emphasizing CT accuracy (±0.5% for metering) and response time (<100 ms for protection) .
EV chargers, particularly high-power DC units, generate DC components and high-frequency harmonics that 干扰传统 AC CTs. Solutions include:
Wideband CTs: Using nanocrystalline cores (e.g., IVY-CT-PCB-01-10A) to maintain linearity across 0–1 MHz frequency ranges .
Digital Signal Processing (DSP): Algorithms in modern CTs filter noise and compensate for phase errors, improving measurement accuracy in complex waveforms .
High-precision CTs (e.g., 0.01S class) are costly. Innovations addressing this include:
Integrated PCB CTs: Reducing size and assembly costs while maintaining 0.1-class accuracy (e.g., ZTC’s Type B CTs with 110 mW power consumption) .
Modular Design: Littelfuse’s RCMP20 series integrates CTs with thermal management modules, optimizing space and cost in high-current chargers .
Electromagnetic interference from switching power supplies can distort CT outputs. Mitigation strategies:
Shielded Cores: Using ferrite or mu-metal cores to reduce external EMI (e.g., Eleq TQ series with EMC-compliant design) .
Isolated Signal Paths: Digital CTs (e.g., MD0630T41A) with UART/Modbus interfaces minimize analog signal corruption .
Digitalization and IoT Integration:
Smart CTs with embedded IoT sensors (e.g., ZTC’s Type B CTs) enable real-time data monitoring and predictive maintenance via cloud platforms .
Blockchain-based energy trading systems leverage CT data for secure, decentralized power transactions .
Advanced Materials and Design:
Silicon Carbide (SiC) CTs: Emerging for high-temperature environments (e.g., 150°C), enhancing reliability in ultra-fast chargers .
3D-Printed Cores: Customizable geometries improve efficiency and reduce eddy current losses .
Standardization and Global Harmonization:
Tesla Supercharger: Uses 25063A CTs for phase current monitoring in 32A AC chargers, ensuring safe operation across 220V/380V grids .
Xiamen ZTC’s EV Charging Solutions: Type B CTs deployed in 150+ cities across China, achieving 99.9% fault detection accuracy with 6 mA DC sensitivity .
Littelfuse RCMP20 Series: Used in Mode 3 chargers to detect DC faults missed by Type A RCDs, reducing false trips by 40% .
Current transformers are indispensable in EV charging infrastructure, ensuring safety, accuracy, and efficiency. While challenges like DC injection and cost persist, advancements in materials, digital signal processing, and modular design are driving solutions. As the EV market grows (projected 210 million units by 2030), CTs will continue to evolve, supporting smarter, greener charging ecosystems. Industry stakeholders must prioritize compliance with international standards and invest in R&D to unlock the full potential of this critical technology.
