Power Line CDNs
- August 5, 2019
- Posted by: Dominique
- Category: Conducted Immunity Testing
Is my CDN compliant to the latest IEC 61000-4-5 requirement?
The latest amendment of IEC 61000-4-5 (2017) raises issues related to the use of surge CDNs for high current and DC applications. In fact there are two separate issues that need to be considered.
Issue 1: High Current Applications
The IEC 61000-4-5 standard specifies a value of decoupling inductance below 1.5 mH selected so the EUT voltage drop is less than 10%.
For example, a EUT supplied directly with 230 V and 200 A per phase will experience a voltage drop of 40% when supplied through a CDN that uses 1.5 mH decoupling inductors.
Because the waveshape is defined for a specific current range, a single CDN can no longer be used across the whole range from zero to 200A. Four CDNs with fixed inductor values would be required. A 200 A CDN with 0.3 mH does not provide a compliant impulse waveform when used with 32 A EUTs.
Fortunately, the solution is available from EMC PARTNER and HV TECHNOLOGIES, Inc. A new range of CDNs has been designed with range switching to provide the user with multiple current ranges in one device.
Issue 2: DC is not DC
Using an IEC surge CDN for DC applications can present a particular problem. DC is no longer present in the classical form we expect from a battery, for example. Modern systems use Pulse Width Modulation (PWM) to generate the DC voltage. Because this is a signal with steep rise and fall times, there is a possibility for resonance to occur between filter capacitors on the DC supply output and decoupling inductors in the CDN.
This resonance causes overshoot and undershoot of the PWM signal with potential to cause shutdown of the power supply. Two methods are suggested in Amendment 1 / 2017 of IEC 61000-4-5 Ed. 3 for tackling distortion of DC signals caused by CDN interaction.
The first is to reduce decoupling inductance value (can be achieved by using a CDN with higher EUT current rating) or introduction of a diode-resistor network in the circuit. The issues related to decoupling inductors was covered already in section 1. Adding a diode-resistor network between the charging station and decoupling inductors of the CDN is a technique that can be used to eliminate distortion completely.
The series resistor value should be adjustable from 1 Ω to 220 Ω, to determine optimum performance. A DC-DC diode-resistor network from EMC PARTNER packages the required components into an off-the-shelf commercial product. A range of products are available for voltages up to 1,500 Vdc and currents up to 200 A.
Further information on these topics can be found in the white paper “Charging station and EV connected through Coupling/Decoupling Network: a signal analysis”.