Whitepaper
Charging station and EV connected through Coupling/Decoupling Network: A Signal Analysis
This EMC Partner white paper analyzes the signal distortions that arise when a standard IEC 61000-4-5 Coupling/Decoupling Network (CDN) is interposed between a DC charging station and an electric vehicle (EUT) during surge and burst immunity testing. DC charging stations typically use PWM-modulated trapezoidal current pulses, and when the CDN's decoupling inductors interact with the capacitances in the charging circuit, both voltage and current at the EUT terminals become distorted — most critically, negative voltage and current spikes appear that can cause errors or interrupt the charging process. The paper uses circuit simulation to quantify these effects and to evaluate the two remedies introduced in Amendment 1 of IEC 61000-4-5 Edition 3: using a CDN rated for a higher current (reducing decoupling inductance), which only partially mitigates the negative distortions, and inserting a diode-resistor network between the power source and the CDN. Simulation results across three cases show that a parallel resistance of 100 ohms across the diode completely eliminates negative voltage and current distortions at the EUT terminals. The paper concludes that distortion severity scales with the PWM voltage slew rate, the decoupling inductance value, and the EUT input capacitance, and recommends using the lowest parallel resistance value that fully eliminates negative disturbances to avoid potential overvoltage.