Wind Turbine Power Converter Flicker Mitigation via Reactive Current
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Solution Overview
Problem
Wind turbines connected to a power grid experience undesirable low-frequency voltage variations, known as flicker, due to changes in torque command as rotor blades pass the tower, which can violate grid requirements.
Innovation Solution
A method and system that use a controller to modify the nominal reactive current and torque commands based on operational parameters and periodic torque command modifiers, correlating with voltage variations to attenuate low-frequency voltage fluctuations between 1 Hz and 30 Hz.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the torque command is modified as each rotor blade passes the tower, then the wind turbine operation is optimized, but low-frequency voltage variations (flicker) are induced on the power grid
Solution Approach 1:
The controller proactively applies a compensating reactive current command modifier before the torque command modifier can fully induce voltage variations. By detecting the periodic torque command modifier and calculating the appropriate reactive current adjustment in advance, the system counteracts the harmful voltage flicker effects before they fully manifest on the power grid.
Solution Approach 2:
The system continuously monitors operational parameters and the periodic torque command modifier, then uses this feedback to dynamically adjust the reactive current command. The controller correlates the torque command modifier with voltage variations and modifies the reactive current command in real-time to attenuate the induced flicker while maintaining optimal turbine operation.
2Object-affected harmful factors
If the reactive current command is modified to attenuate voltage variations, then flicker is reduced, but the complexity of the control system increases
Solution Approach 1:
The existing power converter controller is enhanced to perform multiple functions: it continues to manage the primary torque control while simultaneously calculating and applying the reactive current command modifier for flicker compensation. This multi-functionality approach avoids adding separate dedicated hardware systems, thereby limiting the increase in overall system complexity while achieving effective flicker reduction.
Solution Approach 2:
The system modifies existing control parameters (reactive current command) rather than introducing entirely new control mechanisms. By adjusting the reactive current parameter in response to the periodic torque command modifier, the system achieves flicker attenuation using established control variable adjustments, which is simpler than designing and implementing a completely new control architecture.
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
Effectively mitigates low-frequency voltage variations in the power grid by simultaneously adjusting the reactive current and torque commands, ensuring compliance with grid requirements.
Implementation Method 1
The rotor blades capture kinetic energy of wind using known airfoil principles. For example, rotor blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between the sides. Consequently, a lift force, which is directed from a pressure side towards a suction side, acts on the blade.
Implementation Method 2
Rotational energy is converted into electrical energy through electromagnetic fields coupling the rotor and the stator, which is supplied to a power grid via a grid breaker.
Data Source
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AI summary
A method for compensating for flicker induced by a wind turbine power system connected to a power grid includes operating a power converter of the wind turbine power system based on a nominal reactive current command and a nominal torque command. In response to receiving a periodic torque command modifier, the method includes determining a reactive current command modifier for the power converter based on one or more operational parameters of the wind turbine power system and/or the power grid and the torque command modifier. The method also includes simultaneously modifying the nominal reactive current command as a function of the reactive current command modifier and the nominal torque command as a function of the torque command modifier. Accordingly, modifying the nominal torque command causes low-frequency voltage variations in the power grid and simultaneously modifying the reactive current command attenuates the low-frequency voltage variations.