Series Grid Side Converter for DFIG Voltage Sag Ride-Through
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Solution Overview
Problem
Conventional doubly fed induction generator (DFIG) wind turbines face challenges in surviving severe voltage sags, leading to high currents, torque spikes, and potential damage due to their semiconductor power conversion architecture, which fails to maintain control during grid faults and low voltage events.
Innovation Solution
An improved DFIG architecture incorporating a power switching network with a series grid side converter connected to the stator windings and a parallel grid side converter, which buffers the system to maintain connection to the grid and control stator flux during voltage disturbances, reducing transient currents and torque levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DFIG wind turbines use semiconductor AC/DC/AC conversion chain to condition power, then frequency and amplitude compatibility with grid is achieved, but during extreme PCC voltage sags very high currents are induced in rotor circuit which can damage rotor side converter and cause undue fatigue on gearbox
Solution Approach 1:
A crowbar circuit is introduced as an intermediary protective device between the rotor circuit and the power grid. During voltage sags, the crowbar circuit activates to provide a controlled path for high currents, preventing damaging current magnification in the rotor circuit while maintaining system stability. This intermediary mechanism protects the rotor side converter and gearbox from damage during grid faults.
2Productivity
If conventional DFIG wind turbines maintain connection to grid during voltage sags, then fault clearing current can be delivered, but high per unit currents and shaft torque pulsations occur which place stringent demands on the system
Solution Approach 1:
The crowbar circuit is pre-configured to activate automatically during voltage sags to counteract the harmful effects before they can damage the system. By preemptively engaging the protective mechanism, the system can maintain grid connection and deliver fault clearing current while the crowbar prevents excessive torque pulsations and current magnification that would otherwise exceed the shaft and converter strength limits.
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
This solution enables continued control of electromagnetic torque and current during grid faults, reducing the impact of voltage sags and ensuring continuous power delivery, thus enhancing the wind turbine's ability to withstand low voltage events and comply with ride-through standards.
Implementation Method 1
A power switching network connected to the input scales magnetic flux in the stator windings in response to voltage disturbances at the collector
Data Source
AI summary
A wind turbine 36 has a back-to-back AC/DC/AC power electronic converter chain in which the grid side converter 48 is connected in series with DFIG stator windings 64. The machine side converter 56 is fed from the rotor windings 54 of the DFIG 44. Series connection of the grid side converter 48 enables voltage sag ride-through capability via control of the stator flux.In the event of a grid voltage sag, the series converter allows for a controlled response in the stator flux and electromagnetic shaft torque, protects the machine side converter and enables continued power delivery to the grid.