Zig-Zag Transformer Harmonic Cancellation in Wind Power Systems
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Solution Overview
Problem
Harmonic currents generated by wind turbines pose a challenge in meeting agency requirements for power quality in utility grids, and existing solutions for aggregating wind turbine outputs to achieve acceptable power quality are either inefficient or costly.
Innovation Solution
The use of zig-zag transformers to phase-shift and cancel harmonics produced by individual wind turbine subsystems, reducing or eliminating harmonic currents through a specific winding configuration that allows each cluster of subsystems to operate at different phase shifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If wind turbines are connected directly to the utility grid, then power generation is simple and cost-effective, but harmonic currents pollute the power grid and fail to meet agency requirements
Solution Approach 1:
The patent introduces an intermediary device (such as a filter or transformer) between the wind turbine generator and the utility grid. This intermediary component captures and mitigates the harmonic currents generated by the wind turbine before they can pollute the power grid, while still allowing direct power transmission. This resolves the contradiction by maintaining the simplicity of direct connection while eliminating the harmful harmonic effects through the intermediary device.
2Reliability
If multiple wind turbines are aggregated to create high pulse number electrical output, then power quality at the point of common coupling improves, but individual turbine power quality falls short and requires additional filtering equipment
Solution Approach 1:
The patent merges the filtering functions of multiple individual wind turbines into a centralized filtering system at the point of common coupling. Instead of each turbine having its own complex filtering equipment, the aggregation of turbines allows for a shared filter that processes the combined electrical output. This reduces the overall device complexity while maintaining or improving power quality at the point of common coupling through the collective effect of multiple turbines.
3Reliability
If phase multiplication transformers are used at each wind turbine to convert modified square wave to 6 pulse output, then aggregated output achieves 24 pulse approximation of sine wave, but system cost and complexity increase significantly
Solution Approach 1:
The patent extracts the phase multiplication function from individual turbine transformers and implements it through a different configuration at the aggregation point. Instead of using complex phase multiplication transformers at each turbine, the invention uses a simpler transformer arrangement that achieves the same 24-pulse sine wave approximation when multiple turbines are aggregated. This extracts the essential function while eliminating the need for expensive and complex individual turbine transformers.
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 zig-zag transformer effectively reduces or eliminates harmonics, enhancing power quality at the point of common coupling while being cost-efficient and reliable, thus improving overall system performance and compliance with utility standards.
Implementation Method 1
The use of zig-zag transformers to phase-shift and cancel harmonics produced by individual wind turbine subsystems
Implementation Method 2
The transformer is provided with two primary windings and the generator is connected to one of the two primary windings via a changeover switch
Data Source
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AI summary
An electrical power system 46, 105, 200 connectable to a power grid includes a plurality of electrical power subsystems 27, 102, 202, each of the plurality of electrical power subsystems including a power converter 37, 122, 212 electrically coupled to a generator having a generator rotor and a generator stator. The electrical power system further includes an intermediate power path 60, 170, 216 extending from each of the plurality of electrical power subsystems for providing power from each of the plurality of electrical power subsystems to the power grid. The electrical power system further includes a zig-zag transformer electrically coupling each of the plurality of intermediate power paths to the power grid, the zig-zag 300 transformer including a primary winding 302 and a plurality of secondary windings 304, each of the plurality of secondary windings connected to one of the plurality of intermediate power paths 60, 172, 216, and wherein at least one of the plurality of secondary windings 304 is a zig-zag winding.