What are the methods for controlling conducted emissions?

In recent years, we have witnessed a rapid development of the electric vehicle (EV) market, and consequently — the infrastructure for their charging. The number of electric cars is growing quickly — in the UK alone, there are over 32.5 million registered vehicles, with an increasing share being electric or plug-in hybrid vehicles. This creates a huge demand for efficient, safe, and standards-compliant EV chargers.

For many companies, especially startups, entering this market means enormous growth potential. However, developing such equipment entails significant challenges — particularly in the area of electromagnetic compatibility (EMC), specifically conducted emissions.

Why is conducted emission a problem?

Conducted emission is a form of electromagnetic interference that can enter the power supply network through cables — most often via the neutral or grounding conductor. In the case of EV chargers, which usually contain high-efficiency DC/DC converters, the risk of generating such disturbances is very high. The alternating current generated by the charger, if not properly suppressed, can lead to exceeding the limits allowed by EMC standards.

This is not just a technical issue — non-compliance with standards may prevent obtaining necessary certifications (such as CE, FCC, UKCA), and thus block the product’s market launch.

Impact on EMC compliance and the EV market

From our experience, many young companies underestimate the role of electromagnetic compatibility at the early stages of the project. They often come to us only when their device fails EMC tests, and the costs of delays and redesigns start to increase exponentially.

For this reason, conducted emission is one of the topics that must be understood and controlled from the very beginning of the design work. This issue combines elements of electronics, mechanics, software, as well as knowledge about interference currents and return current paths. Effective management of conducted emission not only avoids formal problems but also improves the overall reliability and safety of the device.

Main sources of conducted emission in EV chargers

The role of the DC/DC converter

At the heart of most modern EV chargers is a high-efficiency DC/DC converter whose task is to convert the voltage to the appropriate battery charging voltage. Thanks to pulse processing, such a system achieves high efficiency but simultaneously generates strong disturbances at frequencies of tens of kHz or more. Some of these disturbances penetrate into the neutral or protective conductor (PE), creating uncontrolled conducted emission. Without proper filtering and electromagnetic wave separation, the DC/DC converter can become the main source of interference that returns to the customer’s installation and other devices in the power network.

Return path of the signal and grounding

Conducted emission always follows the shortest return path to the source of interference. In EV chargers, this signal usually returns via the neutral or protective conductor, and in some designs also through enclosure or shielding elements. A key role is played by decoupling capacitors — “Y capacitors” between the primary and secondary sides of the power circuit, and “X capacitors” mounted between the phase and neutral conductors. Their selected values affect the noise attenuation level but simultaneously must not exceed the limits specified by standards (e.g., Y ≤ 4.7 nF) to avoid compromising insulation safety. Understanding the actual return path — along with precise measurement of grounding and conductor impedance — is essential to effectively eliminate conducted emission and ensure stable charger operation.

Good approach to solving EMC problems

Preliminary tests in an EMC laboratory

Before starting modifications of the system, preliminary investigations should be performed in an EMC laboratory. One or two days are reserved there to measure the levels of conducted emissions and determine the disturbance characteristics in a controlled environment.

Simulations and analyses of return paths

Alongside practical tests, simulations of interference return paths are conducted. Based on the DC/DC converter model and filtering circuit, the impedance of individual elements and the distribution of disturbance currents between phase, neutral, and protective conductors are analyzed. This allows predicting which parts of the circuit contribute most to conducted emission. Our results are compared with industry publications (e.g., example simulations described in literature) and verified against real laboratory measurements. Such an iterative method — test → simulation → correction → test — enables achieving very high confidence (even 99%) in the effectiveness of introduced corrections.

Practical methods of reducing conducted emission

Increasing the impedance of the DC/DC converter

An important step was introducing a small additional impedance in the return path between the converter’s ground and earth. Thanks to this, part of the disturbance current at around 1 kHz frequency is “closed” in the circuit instead of leaking into the power network. This correction — although it somewhat lowers the overall system efficiency — allows significantly reducing conducted emission without risking exceeding the permissible attenuation level.

Optimization of capacitor values

Due to the limitation of Y capacitors to a maximum of 4.7 nF and X capacitors to safe values, iterative tests can be conducted to select the most effective capacitances just below the norm limits. This achieves the maximum possible noise attenuation while maintaining full insulation safety and minimal impact on converter operation.

Implementation and testing of solutions

The process of applying corrections

After approving the simulation model and preliminary lab tests, changes must be applied directly to the printed circuit board: components increasing impedance, changed capacitor values, and optimized ground paths. Every modification must be documented and immediately retested under EMC test conditions to verify the effects of the correction.

Final tests and CE/FCC/UKCA certifications

After passing preliminary lab measurements, time must be booked at an EMC facility that will carry out the full set of certification tests. Using the same facility for all tests shortens the homologation time and avoids unnecessary repetitions. After obtaining CE, FCC, and UKCA marks, the client can promptly launch the product on the market.

Summary and recommendations

1. Thorough analysis of emission sources

Identify the main interference generation points (e.g., DC/DC converter and return path) before making changes.

2. Preliminary tests in an EMC laboratory

Regular tests in one trusted facility provide repeatable results and facilitate verification of the effectiveness of every correction.

3. Iterative simulations and measurements

Combine computer analyses with practical lab measurements — this shortens diagnostics time and allows achieving over 99% confidence in solution effectiveness.

4. Optimization of filters (X/Y capacitors)

Select values just below norm limits (e.g., Y ≤ 4.7 nF) to maximize noise attenuation while ensuring insulation safety.

5. Increasing the return path impedance

Introduce a small additional impedance between converter ground and earth to limit disturbance currents entering the network.

6. Final tests in a certified laboratory

Use the same accredited facility at all homologation stages (CE/FCC/UKCA) to avoid inconsistencies and delays.

7. Close cooperation with EMC experts

Build long-term relationships with engineers and laboratories to implement corrections faster and optimize the design.

By applying these principles, any startup or EV charger manufacturer can significantly shorten homologation time, reduce correction costs, and bring a finished product to market faster. Cooperation with experienced EMC engineers and reliable laboratories is the key to success in the dynamic electric vehicle industry.