12-Pulse Converter Harmonic Elimination via Inductance Adjustment
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Solution Overview
Problem
Existing 12-pulse converters generate line-side harmonics that lead to voltage distortions due to unequal overlap angles at the network-side inputs of diode bridges, resulting in residual harmonics like the 5th and 7th, which are not completely eliminated by existing filter circuits.
Innovation Solution
Assigning inductances to each diode bridge and setting their values to ensure equal overlap angles at the network-side inputs, using adjustable air chokes or cables of different lengths to compensate for transformer winding tolerances, thereby eliminating residual harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If additional filter and blocking circuits are connected in parallel to the converter to reduce harmonics, then the proportion of 6-pulse characteristic harmonics is reduced, but the device complexity increases and residual harmonics (5th and 7th) remain due to unequal overlap angles
Solution Approach 1:
The patent changes the electrical parameter (inductance value) of each diode bridge to adjust the overlap angle. By setting different inductance values for different diode bridges, the overlap angles are equalized, which eliminates residual harmonics without requiring additional complex filter circuits. This parameter adjustment approach resolves the contradiction by achieving harmonic reduction through simple parameter optimization rather than adding complex filtering hardware.
2Object-affected harmful factors
If the overlap angle is maximized to reduce 6-pulse characteristic harmonics, then the effectiveness of harmonic reduction improves, but manufacturing tolerances of transformer windings cause unequal overlap angles and residual harmonics
Solution Approach 1:
The patent implements a feedback mechanism where the actual overlap angles of different diode bridges are measured or calculated, and based on this feedback, the inductance values are adjusted to equalize the overlap angles. This feedback loop compensates for manufacturing tolerances in transformer windings, ensuring that even with varying physical characteristics, the electrical performance (equal overlap angles) is achieved, thereby eliminating residual harmonics.
3Object-affected harmful factors
If inductance values are adjusted to equalize overlap angles and eliminate residual harmonics, then the converter becomes nearly perfect with negligible harmonics, but the device complexity increases due to adjustable inductances
Solution Approach 1:
The patent uses parameter changes (adjustable inductance values) to equalize overlap angles and eliminate residual harmonics. While this does increase device complexity compared to fixed inductances, the adjustment mechanism allows for precise control of harmonic content. The complexity is justified by the significant reduction in residual harmonics, achieving nearly perfect converter operation with negligible 5th and 7th harmonics.
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 approach effectively eliminates the 5th and 7th harmonics, creating an almost 'perfect' 12-pulse converter by ensuring equal overlap angles, reducing line-side harmonics to negligible levels.
Implementation Method 1
Each of the diode bridges is assigned an inductance. The values of these inductances are set in such a way that the overlap angles of the current curves at the network-side inputs of the diode bridges are largely the same.
Implementation Method 2
a transformer T having a plurality of windings. The transformer T is connected to a first diode bridge D1 via a first inductance L1.
Data Source
Figure 1
Figure 2a~2b
Figure 3
AI summary
The circuit (10) has a transformer (T) connected to an electrical grid and coupled to two diode bridges (D1, D2) e.g. 6-pulse diode bridges, at which a load rests. The diode bridges are attached to inductors (L1, L2), which are formed as air-core coils, where values of inductors are adjusted such that an overlapping angle of current flow at inputs of the diode bridges is large. A time period is read in an angular degree below the overlapping angle of the current flow. The diode bridges simultaneously guide electric current in the time period, and are separated in a current feed.