Grid-Forming Wind Turbine Control for Offshore DRU Systems
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Solution Overview
Problem
Current grid-forming control strategies for diode rectifier unit (DRU)-based offshore wind power transmission systems face challenges in evenly distributing reactive power and controlling frequency among wind turbines without communication, often relying on phase-locked loop (PLL) or GPS signals, which can lead to system instability and increased costs due to additional equipment requirements.
Innovation Solution
A grid-forming wind turbine control method that uses active and reactive power controllers to convert power differences into voltage and frequency references, eliminating the need for PLL or GPS signals by employing lead-lag and integral links, and pulse width modulation (PWM) to control grid-side converters, ensuring even reactive power distribution and frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If phase-locked loop (PLL) is used for frequency control, then frequency control capability is achieved, but system stability deteriorates due to phase locking failure
Solution Approach 1:
The patent extracts and removes the PLL component from the control system, replacing it with a grid-forming control strategy that directly controls frequency and voltage without relying on phase locking to the grid, thereby eliminating the source of instability while maintaining frequency control capability
Solution Approach 2:
The patent introduces an active power controller as an intermediary between the power output and frequency control, using lead-lag and integral links to mediate the control process and achieve stable frequency regulation without direct phase locking
2Reliability
If GPS signals are sent to all wind turbines for frequency control, then frequency control without PLL is achieved, but device complexity increases due to complicated implementation
Solution Approach 1:
The patent enables each wind turbine to autonomously determine its own frequency and phase through local measurements and the grid-forming control strategy, eliminating the need for external GPS signals and complex communication infrastructure while maintaining synchronized operation
Solution Approach 2:
The grid-forming controller performs multiple functions including frequency control, reactive power distribution, and phase synchronization simultaneously, replacing the need for separate GPS receivers and complex communication systems at each turbine
3Ease of operation
If additional equipment is installed to support AC voltage source, then voltage control capability is improved, but cost increases due to weakened economic benefits
Solution Approach 1:
The patent makes the wind turbine's grid-side converter perform multiple functions: it simultaneously provides voltage support, reactive power compensation, and frequency control, eliminating the need for separate STATCOM or other additional voltage support equipment
Solution Approach 2:
The patent merges the voltage control function with the existing grid-side converter of the wind turbine, combining what would traditionally be separate functions into a single integrated system, thereby avoiding additional equipment investment
4Reliability
If reactive power control is implemented without communication, then system reliability is improved, but reactive power distribution uniformity deteriorates
Solution Approach 1:
The patent implements a feedback mechanism where each wind turbine monitors the overall system reactive power demand and adjusts its own output accordingly, using local measurements and control algorithms to achieve uniform distribution without requiring communication between turbines
Data Source
AI summary
A grid-forming wind turbine control method for a diode rectifier unit-based offshore wind power transmission system. A control system for controlling a grid-side converter has a three-layered structure, where a first layer is a combination of an active power controller and a reactive power controller; a second layer is a voltage controller; and a third layer is a current controller. The actual reactive power is represented by a per-unit value of a capacity of a corresponding wind turbine unit. The wind turbine units have the same reactive-power reference value, which is constant and does not change with time. The reactive power controllers of all wind turbine units have the same structure and parameters.