DFIG Power Control With DC Buffer for Grid-Constrained Output
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Solution Overview
Problem
Variable speed wind turbines face challenges in maintaining grid stability due to increased wind power penetration, leading to fluctuations in grid voltage and frequency, which can result in adverse effects on performance and stability, especially when operated as grid-forming assets with limited active power changes and constrained grid power transfer limits.
Innovation Solution
A method and system for controlling a power generating asset, such as a double-fed generator, by determining a non-deliverable and deliverable component of its total power output, using a controller to generate control signals that divert the non-deliverable component to a DC energy buffer, thereby precluding its delivery to the electrical grid and ensuring stable operation without altering the active power injected into the grid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If wind turbines operate as grid-forming assets with increased power penetration, then grid voltage and frequency stability improve, but power fluctuations cause adverse effects on PLL and current control performance
Solution Approach 1:
The patent segments the total power output into deliverable and non-deliverable components. The deliverable component is injected into the grid to maintain stability, while the non-deliverable component is diverted to a DC energy buffer. This segmentation allows the system to maintain grid-forming capabilities while isolating fluctuations that would otherwise degrade PLL and current control performance.
Solution Approach 2:
The patent introduces a DC energy buffer as an intermediary between the generator and the grid. This buffer acts as a mediator that absorbs the non-deliverable power component, preventing it from causing harmful fluctuations in the grid voltage and frequency that would adversely affect the PLL and current control systems.
2Speed
If turbine control functions increase generator torque for speed regulation, then speed control performance improves, but active power injection into the grid increases beyond grid constraints
Solution Approach 1:
The patent segments the total power output into deliverable and non-deliverable components. The deliverable component is constrained to match grid limits, while the non-deliverable component (including excess torque for speed regulation) is diverted to a DC energy buffer. This allows speed control functions to operate independently without violating grid power transfer constraints.
Solution Approach 2:
The patent extracts the non-deliverable power component from the total power output and directs it to a DC energy buffer. This extraction allows the turbine to maintain speed regulation capabilities through torque control while preventing excess active power from being injected into the grid beyond its transfer limits.
3Productivity
If wind power penetration into the grid increases, then renewable energy utilization improves, but grid voltage magnitude and frequency variations increase
Solution Approach 1:
The patent extracts the non-deliverable power component from the total power output and directs it to a DC energy buffer, preventing it from causing voltage magnitude and frequency variations in the grid. This allows increased wind power penetration to be utilized while maintaining grid stability by removing the destabilizing component.
Solution Approach 2:
The DC energy buffer serves as an intermediary that absorbs the non-deliverable power component, acting as a buffer between the variable renewable power source and the stable grid. This intermediary prevents power fluctuations from directly impacting grid voltage magnitude and frequency, enabling higher renewable energy utilization without compromising stability.
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 approach decouples drivetrain shaft power control from active power injection into the electrical grid, allowing wind turbines to manage loading independently of grid constraints, reducing the risk of shutdown during transient events and maintaining grid stability by utilizing the non-deliverable component for torque and power needs.
Implementation Method 1
The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft
Implementation Method 2
The generator then converts the mechanical energy to electrical energy
Implementation Method 3
delivering the non-deliverable component to or from the DC energy buffer via the line-side converter
Data Source
AI summary
The system and method described herein provide control for a power generating asset having a double-fed generator connected to an electrical grid. Accordingly, a non-deliverable component and a deliverable component of a total power output of a generator of the power generating asset is determined via a controller. A compensation module of the controller then determines a first control signal based, at least in part, on the non-deliverable component. The first control signal is configured to establish a modified rotor current setpoint. Additionally, a buffer module of the controller then determines a buffer control signal for a DC energy buffer based, at least in part, on the non-deliverable component. The DC energy buffer is operably coupled between a line-side converter and a rotor-side converter of a power converter of the power generating asset. In response to the first control signal and the buffer control signal the non-deliverable component is delivered to the DC energy buffer via the line-side converter, thereby precluding the delivery of the non-deliverable component to or from the electrical grid. The deliverable component of the total power output of the generator is delivered to the electrical grid.