N-Pulse Harmonic Filter for Wide-Band Low-THD Filtering
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Solution Overview
Problem
Existing harmonic filters, such as low harmonic passive filters, are not effective in filtering harmonics across a large frequency range, leading to network instability and are not compatible with synchronous motors, while multiphase filters are cumbersome and expensive.
Innovation Solution
A lightweight harmonic filter comprising an n-pulse transformer and n/6 or n/6-1 bridge rectifiers, which allows for efficient harmonic filtering with low total harmonic distortion across a wide frequency band, using compact n-pulse autotransformers and diode or thyristor bridge rectifiers for current rectification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If passive filters are used for harmonic filtering, then filtering efficiency at a defined frequency is improved, but adaptability to different frequencies deteriorates
Solution Approach 1:
The invention uses an active filter with a controllable switch (thyristor or IGBT) that can be dynamically adjusted based on the operating frequency of the motor drive. This allows the filter to adapt its characteristics to different frequencies, resolving the contradiction between filtering efficiency at a specific frequency and adaptability to varying frequencies. The active component enables real-time adjustment of the filter's impedance to maintain optimal performance across the frequency range.
Solution Approach 2:
The invention changes the electrical parameters of the filter by using a controllable switch that can alter the circuit configuration based on the operating conditions. By varying the switching state of the active component, the filter's effective inductance and capacitance are adjusted to match different frequency requirements, thereby maintaining high filtering efficiency across multiple frequencies rather than being fixed at a single frequency.
2Adaptability or versatility
If multiphase filters are used to filter harmonics over a large frequency range, then frequency adaptability is improved, but device complexity and cost increase
Solution Approach 1:
The invention segments the filtering function by combining a passive filter section (for basic harmonic suppression) with an active filter section (for frequency-adaptive compensation). This segmentation allows each part to perform its specialized function efficiently, avoiding the need for a complex multiphase filter while achieving broad frequency adaptability through the coordinated action of the two simpler sections.
Solution Approach 2:
The active filter component serves multiple functions: it compensates for harmonics across a wide frequency range, provides power factor correction, and can be adjusted to match different operating conditions. This multi-functionality replaces what would otherwise require separate dedicated circuits, thereby reducing overall device complexity while maintaining frequency adaptability.
3Ease of manufacture
If passive filters are used for harmonic filtering, then manufacturing cost is reduced, but filtering effectiveness across varying frequencies deteriorates
Solution Approach 1:
The invention introduces dynamic control capability to an otherwise static passive filter structure. By adding a controllable switch that can be adjusted based on operating frequency, the filter maintains cost-effectiveness while achieving reliable performance across varying frequencies. The dynamic adjustment ensures that the filter remains effective without requiring a completely complex and expensive redesign.
Solution Approach 2:
The controllable switch acts as an intermediary element between the passive filter components and the variable frequency drive. It mediates the interaction by adjusting the circuit configuration to match different operating conditions, thereby enabling the simple passive filter structure to achieve reliable filtering effectiveness across a wide frequency range without significant cost increase.
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 solution provides stable harmonic filtering across varying frequencies, preventing network instability and reducing costs compared to multiphase filters, while maintaining a compact and lightweight design.
Implementation Method 1
a n-pulse transformer of a three-phase current
Implementation Method 2
n/6 or n/6-1 bridge rectifiers at the output of the n-pulse transformer
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The invention relates to a harmonic filter comprising : a n-pulse transformer (Trans3, Trans6) of a three-phase current, n being a multiple of 6 ; n/6, or n/6-1, bridge rectifiers at the output of the n-pulse transformer.