Negative Sequence Current Injection for Wind Turbine Grid Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Wind turbines face challenges in maintaining connection to the electric grid during low voltage periods or grid signal instability, as traditional systems struggle to coordinate voltage, current, and power capabilities effectively for both positive and negative sequence grid conditions, leading to system controllability degradation and repeated transients.
Innovation Solution
A method and apparatus that track and orient negative sequence components of the grid signal to inject them back into the grid, modifying disturbances and maintaining connection by controlling voltage and current, thereby reducing transients and enhancing system controllability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional current regulated approaches are used to eliminate negative sequence current, then system simplicity is maintained, but system controllability degrades and protection measures are repeatedly activated
Solution Approach 1:
The patent segments the grid signal into positive sequence and negative sequence components, allowing independent control of each. The controller separately tracks and manages these components, enabling precise control of negative sequence current injection while maintaining overall system stability and avoiding repeated protection activation.
Solution Approach 2:
The patent dynamically changes control parameters by adjusting the negative sequence current injection level based on grid conditions. The controller modifies current magnitude and phase angle in real-time to optimize system controllability during asymmetric grid voltage conditions, preventing repeated crowbar circuit activation.
2Reliability
If the rotor side converter supplies negative sequence voltage and current during grid faults, then low voltage ride through capability is improved, but the converter reaches capacity limits and loses controllability
Solution Approach 1:
The patent introduces negative sequence current injection as an intermediary mechanism to support low voltage ride through. By injecting controlled negative sequence current into the grid, the system provides the necessary support during faults without overloading the rotor side converter, maintaining controllability while achieving LVRT capability.
3Reliability
If protection measures like crowbar circuits are activated frequently, then generator protection is enhanced, but system transients are repeated and controllability is lost
Solution Approach 1:
The patent applies preliminary anti-action by proactively injecting negative sequence current before grid faults occur and during the fault period. This pre-emptive control prevents the need for repeated crowbar circuit activation, maintaining generator protection while avoiding repeated transients and preserving system stability.
4Adaptability or versatility
If non-linear control behaviors are used to address grid disturbances, then system adaptability to asymmetric conditions is improved, but system modeling complexity increases
Solution Approach 1:
The patent implements feedback control by continuously tracking the grid signal's positive and negative sequence components and adjusting the negative sequence current injection accordingly. This feedback mechanism provides adaptability to asymmetric grid conditions while maintaining a relatively simple linear control structure that is easier to model compared to fully non-linear approaches.
Data Source
AI summary
Method and apparatus that provide a response to the negative sequence current demands during a disturbance of the grid system connected to power-generating equipment, such as a wind turbine system, provide for tracking components in the grid signal, orienting at least a portion of the signal, and injecting the oriented portion. Controlled injection of negative sequence current provides for extending small-signal control response, and also provides for modifications of the apparent impedance to the grid interconnect of the power conversion equipment.