Cascaded H-Bridge Converter Harmonic Reduction
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Solution Overview
Problem
Medium Voltage (MV) drives produce multiple harmonics in the line current due to phase shift transformers, which cannot cancel all harmonic currents and introduce additional harmonics, limiting the harmonic cancellation pattern to 6xn pulse.
Innovation Solution
A power conversion system with a phase shifting transformer and multiple secondary winding groups, where phase angle sets are selected to shift secondary winding phases by a specific phase shift δ, forming a 6xn pulse harmonics cancellation pattern, increasing the overall pulse number of harmonic cancellation to higher values such as 18-pulse, 36-pulse, and beyond.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If phase shift transformers are used in MV drives, then power conversion is enabled, but harmonics are produced in the line current that cannot be fully cancelled
Solution Approach 1:
The transformer secondary windings are divided into multiple groups (first group, second group, third group, etc.) with each group having a different number of windings (n1, n2, n3, etc.). This segmentation allows each group to contribute differently to harmonic cancellation, enabling a more comprehensive cancellation pattern that goes beyond the traditional 6xn limitation.
Solution Approach 2:
The invention changes the parameter of winding counts in secondary groups from uniform to non-uniform distribution. By setting different winding counts (n1, n2, n3, etc.) across groups and combining them with specific phase shifts, the system achieves higher order harmonic cancellation (18-pulse, 36-pulse, etc.) while maintaining power conversion functionality.
2Device complexity
If traditional phase shift transformers with uniform secondary windings are used, then the system structure is simple, but the harmonic cancellation is limited to 6xn pulse pattern
Solution Approach 1:
The secondary windings are segmented into multiple groups with different winding counts rather than using a uniform structure. This segmentation enables each group to target specific harmonic orders, achieving superior harmonic cancellation (18-pulse, 36-pulse, etc.) at the cost of increased structural complexity.
Solution Approach 2:
The invention introduces asymmetry in the winding configuration by using different winding counts (n1, n2, n3, etc.) across secondary groups. This asymmetric design breaks the symmetry of traditional uniform winding structures, enabling higher order harmonic cancellation patterns while accepting increased device complexity.
3Object-generated harmful factors
If multiple secondary winding groups with different winding counts are used, then harmonic cancellation is improved to 18-pulse, 36-pulse and beyond, but the transformer structure becomes more complex
Solution Approach 1:
The transformer secondary is segmented into multiple independent groups, each with optimized winding counts (n1, n2, n3, etc.). This segmentation strategy achieves high-order harmonic cancellation by allowing each group to contribute differently to the overall cancellation pattern, accepting increased structural complexity as a trade-off.
Solution Approach 2:
The multi-group winding structure serves multiple functions simultaneously: power transformation, harmonic cancellation at multiple orders (18-pulse, 36-pulse, etc.), and phase shifting. This multi-functionality justifies the increased structural complexity by achieving comprehensive harmonic mitigation in a single transformer design.
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 system effectively reduces harmonics in the line current, improving the harmonic spectrum and increasing the pulse number of harmonic cancellation, resulting in a more efficient power conversion with reduced ripples and improved harmonic cancellation patterns.
Implementation Method 1
a phase shifting transformer including 3-phase primary windings, a core, and a plurality of m secondary winding groups. Each of the secondary winding groups includes n secondary windings in electromagnetic communication with a corresponding primary winding
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
For power conversion, a power conversion system includes a plurality of power converters and a phase shifting transformer. The phase shifting transformer includes 3-phase primary windings, a core and a plurality of m secondary winding groups. Each of the secondary winding groups includes n secondary windings in electromagnetic communication with a corresponding primary winding and feeding the plurality of power converters. Phase angle sets of the secondary winding groups are all different with a non-zero secondary winding phase shift between any two secondary winding groups.