Phase-Shifted Transformer Groups for Harmonics Cancellation
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Solution Overview
Problem
Cascaded H-bridge converter systems face challenges in minimizing input harmonics, especially when redundancy is applied at the converter cell level, due to complex winding strategies and asymmetries in transformer design, which limit effective harmonics cancellation and increase total harmonic distortion (THD) values.
Innovation Solution
A converter system with a multi-pulse transformer design where secondary windings are arranged into groups with phase-shifted AC cell input voltages, allowing for higher order harmonics cancellation and reduced THD, even with redundant converter cells disconnected, by using at least two equal phase-shifts per group and minimizing transformer complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multi-pulse transformer with complicated winding strategies (Zig-zag, Poligon) is used to generate well defined phase-shift angles, then phase-shift accuracy is improved, but device complexity increases and manufacturing precision becomes more difficult to maintain
Solution Approach 1:
The transformer secondary windings are divided into multiple groups, where each group contains windings with specific phase-shift characteristics. This segmentation allows the complex phase-shift requirement to be distributed across simpler sub-units, reducing the complexity of individual winding strategies while maintaining overall phase-shift accuracy.
Solution Approach 2:
The invention changes the approach from using complicated winding strategies to using parameter-based phase-shifting through controlled impedance networks and switching mechanisms. This allows phase-shift angles to be adjusted by changing electrical parameters rather than relying on complex physical winding configurations.
2Adaptability or versatility
If different secondary windings have different coupling factors and short-circuit impedances, then phase-shift flexibility is improved, but harmonics cancellation effectiveness deteriorates
Solution Approach 1:
The invention implements homogeneity by ensuring that all secondary windings within each group have identical coupling factors and short-circuit impedances. This uniformity across symmetric units enables effective harmonics cancellation while maintaining phase-shift flexibility through the grouping configuration rather than individual winding variations.
3Reliability
If redundancy at converter cell level is applied to increase reliability, then system reliability is improved, but harmonics cancellation effectiveness deteriorates when defective cells are disconnected
Solution Approach 1:
Converter cells are grouped into modules where multiple cells operate together to provide redundancy. When a cell fails, the modular structure allows the remaining cells in the group to continue operation while maintaining the overall phase-shift configuration, thus preserving harmonics cancellation effectiveness despite individual cell failures.
Solution Approach 2:
The system is designed with pre-configured redundant converter cells that are ready to take over in case of failures. This beforehand preparation ensures that when cells are disconnected due to defects, the system can maintain its operational configuration and harmonics cancellation performance through the pre-established modular structure.
4Object-generated harmful factors
If number of secondary windings is increased to improve harmonics cancellation, then harmonics cancellation is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of using a single complex multi-pulse transformer with many windings, the invention segments the system into multiple transformer modules, each with fewer windings. This segmentation reduces the complexity of each individual transformer while achieving the same overall harmonics cancellation effect through the combined operation of multiple simpler units.
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 effectively maintains low THD levels in the converter system, ensuring reliability and efficiency even when redundant cells are disconnected, and reduces the complexity of the transformer design, enhancing the system's operational stability and reliability, particularly in subsea applications.
Implementation Method 1
a transformer with a plurality of secondary windings, each secondary winding connected with one converter cell and providing the AC cell input voltage of the one converter cell
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A converter system (10) comprises a plurality of converter cells (26), each converter cell (26) being adapted for converting an AC cell input voltage into a cell output voltage and a transformer (18) with a plurality of secondary windings (22), each secondary winding (22) connected with one converter cell (26) and providing the AC cell input voltage of the one converter cell (26); wherein the secondary windings (22) are arranged into at least two groups (G1, G2, G3) and the converter cells (26) connected to one group (G1, G2, G3) are series-connected; wherein the transformer (18) is designed such that the secondary windings (22) of different groups (G1, G2, G3) provide AC cell input voltages that are phase- shifted with respect to each other, such that higher order harmonics generated by the converter cells (26) cancel each other; and wherein the secondary windings (22) of one group (G1, G2, G3) provide AC cell input voltages with at least two different phase-shifts (θ1, θ2, θ3, θ4, θ5, θ6).