EMI Filter Solutions for Power Electronics

Challenges Posed by Conducted Emission

Power electronic systems are integral to modern drive, power supply, and industrial applications. However, the rapid switching processes of power semiconductor devices generate conducted electromagnetic emissions. These disturbances propagate along the supply lines and can significantly impair the functionality of connected equipment. In sensitive applications, such as automotive or medical technology, this interference may lead to malfunctions or even pose safety risks. To ensure compliance with regulatory EMC limits and to enhance system immunity, effective filtering solutions are essential.

Fundamental Operation of Active EMI Filters

Active EMI filters represent an innovative solution for suppressing conducted emissions. Unlike passive filters, which rely on inductors and capacitors, active filters utilize a combination of sensors, power amplifiers, and control circuits. They detect the interfering signal components in real time and generate a counterphase signal that actively cancels out the disturbances. This active control mechanism is particularly effective in reducing low-frequency emissions and asymmetric common-mode noise – challenges that are difficult to address with purely passive methods.

Advantages of Active EMI Filters Over Passive Filter Solutions

Active EMI filters offer several key benefits compared to purely passive filters:

• Compact Design: Since active filters do not require bulky inductors, they enable a space-saving integration into existing and
  new systems.
• Improved Low-Frequency Attenuation: Passive filters often struggle at low frequencies. Active filters can specifically target
  and compensate noise in this range, leading to enhanced EMC performance.
• Reduced Losses: Passive filters can incur increased resistive losses, whereas active filters operate more efficiently, reducing
  additional power losses.
• Dynamic Adaptability: Active filters are capable of responding flexibly to varying interference spectra, making them especially
  advantageous in dynamic operating environments.

A particularly powerful solution is offered by hybrid EMI filters, which combine both passive and active technologies. These systems merge the broadband attenuation capabilities of passive filters with the adaptive noise suppression of active systems, achieving high levels of interference reduction across a wide frequency range. As a result, hybrid filters are increasingly applied in modern power electronic systems. Active and hybrid EMI filters thus provide a promising approach to optimizing electromagnetic compatibility in power electronics and play a crucial role in meeting stringent EMC standards.

For a 1~ PFC application, we have developed both a passive and a hybrid EMI input filter to analyze the advantages and disadvantages of each approach. Converting the passive CM component into an active CM filter circuit allows us to overcome the physical limitations of conventional passive filter components. The active filter circuit demonstrates its greatest potential, particularly in the low-frequency range up to approximately 2 MHz. Due to the higher cutoff frequency, the passive CM chokes can be replaced with more compact alternatives featuring a smaller volume. This results in a 60 % reduction in component height compared to conventional solutions. Overall, the hybrid filter achieves a 25 % weight reduction and a 40 % volume reduction while maintaining the same cost.

For more details, please refer to our product datasheet available for download.

Our expertise in passive EMI filter solutions spans the entire development cycle – from analysis to final validation in state-of-the-art test environments. In the initial phase, we carry out a comprehensive assessment of the interference voltage occurring in the power electronic system, identifying the specific challenges and frequency-relevant areas. Based on this analysis, we calculate the necessary insertion loss, taking into account the valid limit values of the applicable standards.

Subsequently, we develop a customized filter design, with a focus on selecting and fine-tuning the individual components to achieve optimal filtering performance. After assembling the filter solution, we perform the characterization under standardized conditions (CISPR 17). Finally, we validate the overall system performance, including the filter solution, in our own EMC test labs. The measurements enable a well-founded evaluation of the reduction in interference levels and ensure standard-conforming functionality. With this structured and standards-compliant approach, we offer our costumers reliable passive EMI filter solutions that are optimally aligned with the challenges of modern power electronic systems.

Challenges in Predicting Conducted Disturbances

Power electronic systems often operate at high switching frequencies with complex current paths, which can lead to unpredictable conducted emissions. Especially during the early development phases – when the physical system is not yet available for comprehensive measurements – forecasting these interference sources is a significant challenge. The complexity of parasitic couplings and the interactions among components requires detailed models to digitally replicate interference effects and provide realistic predictions.

Our Approach to EMI Simulation

Our methodology begins with the systematic collection of circuit data, whether through detailed schematics or existing layout information. Next, the system is replicated in a circuit simulation where the parasitic characteristics, stemming from the physical layout and connection techniques of the components, are carefully taken into account. Both available layout information and specific requirements regarding component selection are incorporated into the simulation. The simulation then yields predictions of the interference voltages that can be measured using a standard Line Impedance Stabilization Network (LISN). This simulated interference voltage profile serves as the basis for the subsequent filter design – be it an active, hybrid, or passive EMC filter solution.

Advantages of EMI Simulation in the Development Process

EMI simulation offers significant benefits over rough estimations or extensive measurement campaigns. During the concept phase, potential sources of interference can be identified and effectively addressed, leading to considerable reductions in development time and cost. By providing a digital representation of system behavior, simulation allows filter solutions to be optimally adapted to specific requirements, ensuring standard-compliant EMC conformity. Compared to manual measurement procedures, simulation enables an early analysis of interference mechanisms – an essential advantage in developing complex power electronic systems.