Converter Common Mode Filter Secondary Branch
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Solution Overview
Problem
Existing common-mode filters for converters with actively switched line-side converters are inadequate in filtering common-mode interference, particularly at switching frequencies, and often require high capacitance and resonate at frequencies that amplify motor harmonics, making them unsuitable for effective noise reduction.
Innovation Solution
A secondary branch with a series connection of a resistor and a capacitor is arranged on the mains side, allowing for better filtering of common-mode interference by shifting the resonant frequency to a range without harmonics of the fundamental frequency, thereby using lower switching frequencies and reducing the need for high capacitance, and is designed to connect between the grid-side and load-side converters, effectively filtering interference from both sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an output filter with a secondary branch is used to dampen resonant amplitude, then resonant frequency is shifted to lower frequencies, but the solution is only suitable as an output filter and does not filter common-mode disturbances from the grid-side converter
Solution Approach 1:
The patent positions the secondary branch with the RC circuit in the grid-side three-phase line, making it a universal solution that filters common-mode disturbances from both the grid-side converter and the load-side converter. This multi-functional placement allows the filter to address resonant amplitude damping while simultaneously filtering grid-side switching frequency disturbances
2Object-affected harmful factors
If the resonant frequency is chosen to be sufficiently high to prevent amplification of motor harmonics, then harmonic overtones are filtered, but the switching frequency must be correspondingly high requiring higher switching frequencies
Solution Approach 1:
The patent converts the harmful resonant amplification effect into a beneficial damping effect by introducing the RC circuit in the secondary branch. The RC circuit is specifically designed to dampen the resonant amplitude, allowing the resonant frequency to be lowered below the switching frequency while preventing harmonic amplification. This transforms the previously harmful resonance into a useful filtering mechanism
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
This configuration effectively filters common-mode interference from actively switched line-side converters, reducing noise above the resonant frequency and allowing for lower switching frequencies, while avoiding the need for high capacitance and series connections of capacitors, thus improving overall filtering efficiency.
Implementation Method 1
shifting the resonant frequency to a range without harmonics of the fundamental frequency
Implementation Method 2
a series connection of a capacitor and a resistor is arranged in a secondary branch
Implementation Method 3
This dampens the resonant amplitude of the current-compensated inductor and shifts the resonant frequency to lower frequencies
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
Converter comprising a main current branch with a grid-side three-phase line (4), with a DC link (5) and with a load-side three-phase line (6), wherein the grid-side three-phase line (4) is connected to the DC link (5) via a grid-side converter (1), wherein the DC link (5) is connected to the load-side three-phase line (6) via a load-side converter (2), a secondary branch arranged in parallel to the grid-side converter (1) between a first connection point (8) in the grid-side three-phase line (4) and a second connection point (9) in the DC link (5) or the load-side three-phase line (6), wherein the secondary branch has a series connection of a resistor (R) and a capacitor (C1), wherein the main current branch has an inductor (L1) between the first connection point (8) and the second connection point (9).