Coordinated STATCOM and Wind Turbine Control for Unbalanced Voltage Suppression
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Solution Overview
Problem
In dispersed wind farms, unbalanced grid voltage due to weak grid conditions and varying load patterns, such as those caused by high-speed trains, leads to instability and over-modulation issues in cascaded H-bridge STATCOMs, which can result in unbalanced dc capacitor voltages among three-phase clusters, affecting the system's stability and power distribution.
Innovation Solution
A coordinated control strategy is implemented, where PMSGs and STATCOMs work together to suppress unbalanced grid voltage through negative-sequence current injection, with PMSGs sharing the remaining unbalanced voltage if STATCOM capacity is insufficient, using participation factors adjusted based on remaining capacity and voltage unbalance factors to maintain power quality and prevent over-modulation and over-current limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If STATCOM injects negative-sequence current to suppress unbalanced voltage, then voltage unbalance is reduced, but dc capacitor voltage becomes unbalanced among three-phase clusters
Solution Approach 1:
The patent changes the voltage parameter by injecting zero-sequence voltage to redistribute active power among three-phase clusters. This parameter change restores the balance of dc capacitor voltages while maintaining the negative-sequence current injection for unbalanced voltage suppression, thus resolving the contradiction between voltage balance improvement and system stability.
2Productivity
If STATCOM fully utilizes negative-sequence current injection capability, then unbalanced voltage suppression is improved, but over-modulation and over-current limitations occur
Solution Approach 1:
The patent applies partial action by coordinating multiple inverters to share the negative-sequence current injection task. Instead of one inverter working at excessive capacity leading to over-modulation, multiple inverters contribute partially, achieving the same suppression effect while maintaining reliable operation within current limits.
Solution Approach 2:
The patent segments the negative-sequence current injection function across multiple inverters (wind turbine converters and STATCOM). Each inverter handles a portion of the compensation task according to its capacity, avoiding over-modulation and over-current limitations while maintaining effective unbalanced voltage suppression.
3Reliability
If multiple inverters share unbalanced voltage compensation, then system reliability is improved, but coordination complexity increases
Solution Approach 1:
The patent introduces participation factors as control parameters to simplify the coordination of multiple inverters. Each inverter's negative-sequence current injection is adjusted according to its participation factor, which is determined by its capacity and operating conditions. This parameter-based coordination method reduces control complexity while maintaining system reliability.
Data Source
AI summary
The disclosure discloses a system and method for suppressing unbalanced voltage at the Point of Common Coupling (PCC) of dispersed wind farm. According to the disclosure, the wind farm comprising a STATCOM and plurality of wind turbines, dispersed wind farm controller, STATCOM controller, wind turbine controller. The dispersed wind farm controller decides that whether the STATCOM or the wind turbines inject negative-sequence current or not. Adaptive virtual negative-sequence output admittance controller is incorporated into the STATCOM controller and wind turbine controller, which can provide the negative-sequence current reference according to their participation factor. The compensation efforts of STATCOM and wind turbines can be flexibly controlled by changing their participation factor, which is related to the voltage unbalance voltage reference and the remaining capacity. The disclosure has significant advantages in cost and effectiveness to suppress the unbalanced voltage of PCC and improve the wind farm Low voltage fault recovery capability.