Patrick Bolliger of HV TECHNOLOGIES, Inc. explains why DC-based power supply technologies used in electric vehicle charging stations have created unexpected challenges in the EMC test
Why is there concern over new “DC” technologies for Electric Vehicle charging stations?
An annually increasing number of vehicles emit ever-increasing amounts of CO2. One possible solution to this global problem is to reduce the number of vehicles burning fossil fuels. Electric vehicles could be part of this solution. E-mobility combined with emerging smart grid technologies make better use of existing and future energy generation technologies.
Owning an electric car means being able to charge it too. At home, slow chargers using the normal AC main supply are okay, but in town or out shopping faster chargers for public use tend to charge using DC power.
Any charging station connected to the public power supply has to be tested for EMC and safety. Conformity assessment follows mainly national regulations. But there are issues that prompted the International Electrotechnical Commission (IEC) and the United Nations to issue standards with a global reach. High current fast chargers deliver a chopped DC with fast rise and fall times. Depending on how the rise and fall time, interaction with EMC test equipment, particularly surge Coupling Decoupling Networks (CDNs) can cause malfunction.
What measures can be taken to prevent malfunction in power supply when applying the surge test via CDN?
There are two methods suggested in Amendment 1 / 2017 of IEC 61000-4-5 Ed. 3 for tackling distortion of DC charging signals caused by CDN interaction. These are; reduction of decoupling inductance value (in other words using a CDN with higher EUT current rating) or introduction of a diode-resistor network in the circuit.
Employing a CDN with higher EUT current rating (lowering decoupling inductors from the standard 1.5 mH to 0.3 mH) reduces negative distortion but does not eliminate it completely. So this technique is partially useful and can be applied in some circumstances.
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.
How is HV Technologies helping engineers address these potential challenges?
Engineers need to be aware of the potential impact on both test equipment and EUTs. Reducing the value of decoupling inductors in a CDN is not something test engineers want to get involved in doing. Fortunately, commercial CDNs are available with higher current ratings and switchable current ranges. A higher rated CDN has lower decoupling inductor values, which solves the problem in an elegant manner. Being able to run a 32A or 63A EUT and having the ability to switch in a higher current range is a distinct advantage. CDNs are available from EMC PARTNER up to 1,500Vdc and 200A with full range switching capability and ANSI coupling included.
Further information on this topic can be found in the white paper “Charging station and EV connected through Coupling/Decoupling Network: a signal analysis” available for free at https://incompliancemag.com/CDNforEV
EMC Sales Manager
HV Technologies, Inc.
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