DFIG Rotor Speed Control Using Fast Terminal Sliding Mode
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional control schemes for doubly fed induction generators (DFIG) in wind turbines suffer from speed fluctuations and mechanical instability, particularly under transient operations, which are not adequately addressed by existing PI and sliding mode control methods.
Innovation Solution
The implementation of a nonsingular fast terminal sliding mode control (NSFTSMC) scheme in the rotor side vector control of DFIG, utilizing a back-to-back voltage source converter with a rotor side converter and a grid side converter, stabilizes the rotor speed by applying a control input based on the wind profile, enhancing mechanical stability and reducing speed fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional PI control scheme is used for DFIG speed control, then the control system is simple to implement, but the rotor speed exhibits fluctuations and mechanical instability during transient operations
Solution Approach 1:
The patent transforms the control approach by changing from conventional PI control parameters to nonsingular fast terminal sliding mode control parameters. The control law uses nonlinear functions of speed error (|e|^α and |e|^β terms) to achieve faster convergence and eliminate the speed fluctuations that occur with linear PI control, while maintaining implementability through a structured control framework.
Solution Approach 2:
The patent introduces dynamic adaptation by using variable control gains that depend on the sliding surface value s and speed error e. The control law adjusts its aggressiveness dynamically through terms like |s|^(1/2)sign(s) and |e|^αsign(e), allowing the system to respond more aggressively to transient disturbances while maintaining stability, unlike fixed-gain PI controllers.
2Stability of the object's composition
If sliding mode control is used to improve speed stability, then rotor speed stability improves, but the system exhibits chattering and increased complexity
Solution Approach 1:
The patent modifies the traditional sliding mode control by changing the convergence characteristics through nonsingular fast terminal sliding mode. The control law uses fractional power terms (|s|^(1/2) and |e|^α, |e|^β) that enable finite-time convergence without the high-frequency chattering typical of conventional sliding mode control, reducing complexity while maintaining stability improvements.
Solution Approach 2:
The patent introduces an intermediate sliding surface formulation that mediates between the raw speed error and the control output. The nonsingular fast terminal sliding surface s = e + λ∫|e|^αsign(e)dt acts as an intermediary that smooths the control action while ensuring finite-time convergence, eliminating the need for complex discontinuous switching functions that cause chattering.
3Stability of the object's composition
If conventional control schemes are used, then the system response is stable, but the convergence speed is slow during transient operations
Solution Approach 1:
The patent applies preliminary action by anticipating the need for faster convergence through the nonsingular fast terminal sliding mode structure. The control law pre-empts slow response by using terms like |s|^(1/2)sign(s) and |e|^βsign(e) that actively drive the system toward the sliding surface and equilibrium point in finite time, rather than relying on gradual asymptotic convergence typical of conventional controllers.
Solution Approach 2:
The patent changes the temporal characteristics of the control response by using nonlinear error terms with different exponents (α and β). These parameter changes enable the system to achieve both fast initial response (through aggressive error correction) and stable final convergence (through diminishing control action as error approaches zero), overcoming the slow convergence of conventional linear controllers.
Data Source
AI summary
A doubly fed induction generator (DFIG) speed control system is provided. The system includes a wind turbine and a wound rotor induction generator connected to the wind turbine through a drive train system and to a power grid. The system further includes a back-to-back voltage source converter (VSC) with a rotor side converter (RSC) and a grid side converter (GSC). The RSC is connected to the wound rotor induction generator and the GSC is connected to the power grid. A wind profile sensor measures a wind profile and a VSC controller provides control to the RSC and the GSC. The VSC controller applies a nonsingular fast terminal sliding mode control (NSFTSMC) scheme at the RSC at least partially based on the received wind profile to stabilize a rotor speed of the wound rotor induction generator.