Wind farms, particularly those using Doubly-Fed Induction Generators (DFIGs), are not only power producers but also major sources of power quality issues. The need and logic for configuring mitigation equipment here are significantly different from traditional commercial and industrial applications.
I. Major Power Quality Issues in Wind Farms
Reactive Power Issues (Core target for SVG mitigation):
Turbines themselves require reactive power: The converters and transformers within DFIG turbines absorb reactive power to establish magnetic fields during operation.
Collection line consumption: The long collection lines (gathering lines) are inductive and consume a significant amount of reactive power.
Grid dispatch requirements: According to national grid standards (e.g., China's "Technical Regulations for Connecting Wind Farms to the Power System"), wind farms must possess dynamic reactive power compensation capability. They must be able to automatically adjust the power factor at the Point of Common Coupling (PCC) based on dispatch commands (typically required to be between 0.98 leading and 0.98 lagging) to support grid voltage. This is a mandatory requirement.
Harmonic Issues (Core target for APF mitigation):
Main harmonic source: The converters (AC-DC-AC) within the wind turbines are the primary harmonic sources, generating specific order harmonics like 5th, 7th, 11th, 13th, etc.
Harmonic resonance risk: The cable capacitance of the wind farm's collection system and the grid inductance can form parallel or series resonance at certain specific frequencies, amplifying specific harmonic orders and leading to serious incidents.
Voltage Fluctuations and Flicker:
The intermittent and stochastic nature of wind energy causes fluctuations in turbine output power, leading to voltage fluctuations and flicker at the PCC.
II. The Role and Configuration Strategy of SVG and APF in Wind Farms
The primary principle for configuring mitigation equipment in wind farms is: First, meet the grid's mandatory reactive power requirements, then mitigate harmonics to protect internal assets.
(I) Configuration of Static Var Generator (SVG)
1. Role Positioning: Primary Dynamic Reactive Power Support The core function of the SVG in a wind farm is to replace traditional capacitor/reactor banks (TSC/TCR) to provide fast, smooth, and continuous reactive power adjustment, meeting grid dispatch requirements and stabilizing the PCC voltage.
2. Installation Location: Wind Farm Point of Common Coupling (PCC)
The SVG must be centrally installed on the low-voltage side (35kV or 10kV side) of the station's main step-up transformer.
Mitigation at this location allows for direct adjustment of the PCC power factor, response to grid dispatch commands, and provides reactive power support for the entire wind farm.
3. Capacity Calculation (Critical Step): The SVG capacity must satisfy the maximum value of the following three aspects:
a. Meet Grid Dispatch Requirements: According to grid connection standards, the SVG capacity should be 25% ~ 50% of the wind farm's rated capacity. This is the primary basis for configuration.
Example: A 100MW wind farm typically requires an SVG with a capacity of ±25 Mvar to ±50 Mvar.
b. Compensate for Internal Reactive Power Deficit: Calculate the total reactive power consumption of all turbines, pad-mounted transformers, and collection lines, including a certain margin.
c. Voltage Support during System Faults: Consider that during grid short-circuit faults, the SVG needs to provide sufficient reactive power to support voltage and ensure the turbines do not trip offline (fault ride-through).
Conclusion: SVG capacity is usually dictated by grid codes, taking the maximum value and including some redundancy.
(II) Configuration of Active Power Filter (APF)
1. Role Positioning: Harmonic Mitigation and Resonance Suppression The core function of the APF is to filter characteristic harmonics generated by the turbines, preventing harmonic current from being injected into the grid beyond limits. More importantly, it suppresses potential harmonic resonance, protecting internal assets like transformers and capacitors.
2. Installation Location: Combined Distributed and Centralized Approach
Option A (Recommended): Distributed Installation at Collection Line Ends
Location: Install medium-capacity APFs at the end of each collection circuit (i.e., at the switchgear where multiple turbine lines converge).
Advantages:
More Thorough Mitigation: Compensation near the harmonic source prevents harmonics from flowing and superimposing in the collection lines, reducing line losses.
More Effective Resonance Suppression: Directly alters the impedance characteristics of the harmonic source, fundamentally disrupting resonance conditions.
Higher Reliability: Failure of a single APF does not affect other circuits.
Option B: Centralized Installation at the PCC
Location: Installed alongside the SVG on the low-voltage side of the main step-up transformer.
Disadvantages: Less effective mitigation than the distributed approach, and may not effectively suppress resonance within the collection lines.
Applicability: Suitable for farms where harmonic issues are not severe, or the main goal is to meet national harmonic standards (e.g., GB/T 14549) at the PCC.
3. Capacity Calculation:
Measurement Method: Perform power quality measurements on collection lines or the PCC to obtain harmonic current data.
Estimation Method: APF capacity I_APF ≥ ∑ (Single Turbine Rated Current × Current THDi × Simultaneity Factor)
The THDi of a single turbine converter is typically around 3% ~ 5% (after including LCL filters), but note that harmonic resonance can cause amplification.
Simultaneity Factor: Considering that not all turbines operate at full load simultaneously and harmonic phases differ, a factor of 0.6 ~ 0.8 can be used.
Recommendation: Always conduct field measurements and consult professional agencies, as harmonic resonance issues are highly complex.
III. Configuration Scheme and Typical Architecture
A standard power quality mitigation architecture for a wind farm is conceptually structured as follows:
Wind Turbine Generators (WTGs): Multiple groups of turbines (the harmonic sources and reactive loads) connect via long collection lines.
Collection System (35kV/10kV): Distributed APFs are ideally installed at the end of each collection circuit for targeted harmonic and resonance control.
Main Step-Up Transformer: Steps up the voltage for grid connection.
Point of Common Coupling (PCC): The interconnection point with the main grid.
Centralized Mitigation Layer: Located at the PCC on the LV side of the main transformer. This layer houses:
A large Centralized SVG for bulk dynamic reactive power support and voltage stability, responding to grid commands.
(Optional) A Centralized APF for auxiliary harmonic filtering.
Passive capacitor/reactor banks for base reactive power compensation.
Recommended Scheme:
SVG: Centrally installed on the 35kV bus, capacity sized at 25%~50% of the farm's total capacity.
APF: Prioritize a distributed mitigation scheme, installing units at the end of each collection circuit.
Coordinated Control: The SVG and APF should be integrated into the wind farm's SCADA or Energy Management System (EMS) to receive grid dispatch commands and enable automated operation.
IV. Special Product Selection Requirements
The harsh wind farm environment demands high equipment specifications:
Protection Rating: Outdoor installation requires at least IP54 and corrosion resistance class C4/C5 to withstand wind, sand, salt spray, humidity, and extreme temperatures.
Voltage Level: Must directly match the wind farm's voltage level (e.g., 10kV, 35kV).
Response Speed: Must be extremely fast (<5ms) to respond to wind power ramps and grid faults.
Reliability & Maintainability: High MTBF (Mean Time Between Failures) and modular design for quick replacement are essential.
Certification: Requires certification from power industry product tests, Low Voltage Ride-Through (LVRT) tests, etc.
Summary
Configuring SVG and APF for a wind farm is not a simple selection calculation but a systems engineering task:
SVG is mandatory. Its capacity is determined by national mandatory standards, primarily to meet grid reactive power dispatch and voltage support requirements.
APF is highly recommended. Its configuration scheme (centralized or distributed) and capacity must be based on field measurements and system analysis, primarily to suppress harmonics and prevent resonance, protecting internal assets.
Return on Investment (ROI): This investment is not just a "ticket" to meet grid connection requirements but is essential for ensuring the long-term safe, stable, and efficient operation of the wind farm, avoiding hefty penalties and equipment damage.
During the project's early stages, detailed power quality modeling and simulation must be performed, and professional agencies should be commissioned for measurement and evaluation to develop the most economical, efficient, and reliable mitigation plan.
español
English
français
Deutsch
العربية
中文
compatible con la red ipv6
