Active Filter Power Converter for Adaptive EMC Noise Reduction
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Solution Overview
Problem
Existing power converters face challenges in meeting EMC standards due to passive filters that are ineffective under changing grid conditions, often requiring large components designed for worst-case scenarios and unable to adapt to additional noise.
Innovation Solution
An active filter circuit with an auxiliary active rectifier and DC/DC converter is integrated, capable of reducing both differential and common mode noise, allowing smaller passive filter components and adaptive noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive filters are used to meet EMC standards, then the power converter can connect to the AC supply grid, but the filter components become large due to worst-case scenario design
Solution Approach 1:
The patent implements an adaptive filter system that dynamically adjusts filter parameters based on real-time grid conditions. The control unit continuously monitors grid impedance and noise characteristics, then adjusts the active filter's output impedance and damping characteristics accordingly. This dynamic adaptation allows the system to achieve EMC compliance with significantly smaller filter components compared to static worst-case designs.
Solution Approach 2:
The system changes filter parameters (impedance, damping factor, cutoff frequency) based on operating conditions. The control unit calculates optimal filter parameters by measuring grid impedance and adjusting the active filter's transfer function. This parameter adaptation enables the use of smaller passive components while maintaining EMC performance across varying grid conditions.
2Reliability
If passive filters are designed for worst-case scenarios, then EMC standards are met under all conditions, but additional noise from external environments cannot be addressed
Solution Approach 1:
The patent employs a feedback control mechanism where the control unit continuously monitors grid conditions including impedance, noise levels, and harmonic content. Based on this feedback, the system dynamically adjusts the active filter's compensation signals and impedance characteristics. This closed-loop control enables the system to adapt to changing grid conditions and external noise sources while maintaining EMC compliance.
Solution Approach 2:
The filter system transitions from static worst-case design to dynamic adaptive filtering. The control unit real-time adjusts filter parameters based on measured grid conditions, enabling the system to respond to external noise sources and impedance variations. This dynamic behavior provides both robustness against worst-case scenarios and adaptability to changing conditions.
3Reliability
If larger passive filter components are used, then EMC standards are reliably met, but switching losses increase
Solution Approach 1:
The active filter provides partial filtering action that complements the passive filter, allowing the passive components to be sized for typical operating conditions rather than worst-case scenarios. The active filter handles the variable and transient noise components, while the passive filter provides baseline filtering. This division of labor reduces passive component size and associated switching losses while maintaining overall EMC compliance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The active filter circuit effectively reduces noise, enabling smaller passive filter components and lower switching losses, while maintaining efficient operation under varying grid conditions.
Implementation Method 1
The DC/DC converter is configured to operate as an active common mode noise filter
Implementation Method 2
The auxiliary rectifier circuit is preferentially a 3-phase AC to DC converter
Implementation Method 3
The active filter circuit comprises a capacitive connection to a ground or neutral potential of the converter
Data Source
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AI summary
A power converter with a DC link with at least one DC link capacitor, an active rectifier circuit connected between AC terminals of the converter and the DC link, an active filter circuit connected between AC terminals of the converter and the DC link, wherein the active filter circuit comprises an auxiliary active rectifier circuit with auxiliary AC terminals and auxiliary DC terminals and an active filter inductor in each line between the converter AC terminals and the auxiliary AC terminals, the active filter circuit comprises a DC/DC-converter having first and second auxiliary DC terminals, the first auxiliary DC terminals being connected to the auxiliary DC terminals, wherein the DC/DC converter is configured to operate as an active common mode noise filter and the active filter circuit comprises a capacitive connection to a ground or neutral potential of the converter.