Common Mode Filter Damping for Power Converter Resonance
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Solution Overview
Problem
Power converters in industrial applications face challenges in suppressing common mode noise due to unknown load characteristics and long line lengths, leading to resonant circuits that amplify noise components, and existing solutions like additional filter stages or EMC ferrites are inadequate in damping these frequencies.
Innovation Solution
Incorporating a common mode filter device with a frequency-selective passive damping circuit connected to a common mode transformer, which uses a combination of resistors, capacitors, and inductors to provide selective damping, avoiding unwanted differential-mode losses and resonance shifts, and arranging the common mode filter on the line side to target common mode resonant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional filter stages are used to suppress common mode noise, then common mode noise suppression is improved, but device complexity and installation volume increase
Solution Approach 1:
The patent changes the parameter of damping by introducing a frequency-selective passive damping circuit with specific resistance, capacitance, and inductance values. This circuit is designed to provide adequate damping at common mode resonant frequencies (particularly below 1 MHz) without requiring additional filter stages, thus suppressing common mode noise while maintaining simple device architecture
Solution Approach 2:
The patent introduces a damping circuit as an intermediary element connected to the secondary winding of the common mode transformer. This damping circuit acts as a mediator that dissipates resonant energy through controlled resistance, preventing noise amplification without adding complex filter stages to the main power path
2Object-affected harmful factors
If EMC ferrite beads are used for common mode filtering, then common mode noise is reduced, but damping effectiveness is insufficient at frequencies below 1 MHz
Solution Approach 1:
The patent employs a composite damping circuit consisting of multiple passive components (resistors, capacitors, and inductors) connected in specific configurations. This composite structure provides frequency-selective damping that is particularly effective below 1 MHz, overcoming the limitations of single-material solutions like EMC ferrite beads which lack adequate damping capability at these frequencies
Solution Approach 2:
The patent specifically designs the damping circuit with parameter values (resistance R, capacitance C, inductance L) optimized for low-frequency operation below 1 MHz. The frequency-selective nature of the circuit ensures adequate damping at common mode resonant frequencies where ferrite beads are ineffective, while maintaining reliability across the operating range
3Object-affected harmful factors
If additional filter stages are added, then common mode noise suppression is improved, but differential-mode losses increase
Solution Approach 1:
The patent segments the noise suppression function into two independent parts: the common mode transformer handles common mode noise filtering, while the frequency-selective damping circuit connected to the secondary winding provides targeted damping at resonant frequencies. This segmentation allows each component to perform its specific function efficiently without the differential-mode losses associated with additional series filter stages
4Object-affected harmful factors
If additional filter stages are used, then common mode noise suppression is improved, but resonance points are shifted or additional resonance points are created
Solution Approach 1:
The patent converts the harmful resonant oscillations into beneficial heat energy through the frequency-selective damping circuit. By connecting the damping circuit to the secondary winding of the common mode transformer, resonant energy is dissipated through the resistor in the damping circuit, transforming the harmful resonance into useful thermal energy and stabilizing the system's frequency response
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
Effectively dampens common mode resonant circuits at specific frequencies, reducing noise amplification and maintaining low losses across a range of frequencies, thus meeting electromagnetic compatibility standards without increasing costs or installation volume.
Implementation Method 1
a common mode transformer (21), wherein the common mode transformer (21) has at least two first windings (221 . . . 223) arranged equidirectionally on a common core (81, 91) and coupled in series into electrical conductors (17) connected to the converter device (12)
Implementation Method 2
By damping is understood that a noise component is converted at least to some extent into heat, analogously to an ohmic resistor which is effective at the frequency of the noise component
Implementation Method 3
The common mode resonant circuit can have a plurality of different resonant frequencies. Each of these resonant frequencies can be excited by any source of interference in the network composed of power converter and loads
Data Source
AI summary
Various embodiments of the teachings herein include a power converter. The power converter may include: a converter for converting between a first electrical voltage and a second electrical voltage; a common mode filter having a common mode transformer; and a second winding connected to a frequency-selective passive damping circuit arranged on a common core. The common mode transformer has at least two first windings arranged in the same direction on the common core and coupled in series into electrical conductors connected to the converter device.