Offshore Wind Turbine Grid-Forming Control for Stable AC Voltage
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Solution Overview
Problem
Offshore wind turbines using diode rectifiers (DR) lack controllability, which hinders their ability to provide stable voltage support, necessitating a grid-forming control method to ensure stable alternating current (AC) voltage and frequency.
Innovation Solution
A grid-forming control method for offshore wind turbines that utilizes active and reactive power to control voltage amplitude and frequency at the grid connection point, employing dq decomposition, phase reference calculation, and pulse width modulation to stabilize the AC system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of stationary object
If a diode rectifier (DR) is used in the offshore converter station, then the volume and weight of key equipment are reduced, but the ability to provide stable voltage support is lost
Solution Approach 1:
The patent introduces a grid-forming control system as an intermediary layer between the diode rectifier and the AC grid. This control system includes voltage and frequency control modules that actively regulate the output of the DR, enabling it to provide stable voltage support despite the inherent uncontrollability of the diode rectifier itself. The control system acts as a mediator that transforms the passive DR into an active grid-supporting device.
Solution Approach 2:
The patent dynamically adjusts operating parameters (voltage amplitude, frequency, phase angle) of the offshore wind turbine system through closed-loop control. By continuously monitoring and adjusting these parameters, the system maintains stable voltage support capability while using the lightweight diode rectifier configuration. The control system modifies parameters in real-time to compensate for the lack of inherent controllability in DR.
2Device complexity
If a diode rectifier (DR) is used in the offshore converter station, then the device complexity is reduced, but the controllability of the system deteriorates
Solution Approach 1:
The patent implements a feedback control system that continuously monitors the output voltage and frequency of the diode rectifier and adjusts the system response accordingly. The grid-forming control uses feedback from voltage and frequency measurements to dynamically adjust the operating point, enabling controllability while maintaining the simple diode rectifier hardware architecture. The feedback loop compensates for the lack of inherent controllability in DR.
Solution Approach 2:
The patent replaces the need for complex mechanical/power electronic control mechanisms (like those in MMC) with a control-theoretic approach. Instead of using controllable power electronic switches, the system uses mathematical models and control algorithms (grid-forming control equations) to achieve controllability. This substitutes complex hardware control mechanisms with software-based control logic.
3Stability of the object's composition
If grid-forming control is implemented to enable voltage control using active power, then the voltage stability is improved, but the control system complexity increases
Solution Approach 1:
The patent designs a universal grid-forming control system that can perform multiple functions (voltage control, frequency control, synchronization) through a unified control framework. The same control structure handles both voltage amplitude regulation via active power and frequency regulation via reactive power, eliminating the need for separate control systems for each function. This multi-functionality reduces the overall complexity compared to having dedicated control systems for each parameter.
Solution Approach 2:
The patent merges the voltage control and frequency control functions into a single integrated grid-forming control system. Instead of having separate control loops for voltage and frequency, the system combines them into a unified control architecture that simultaneously manages both parameters. This integration reduces the number of independent control systems needed and simplifies the overall control structure.
Data Source
AI summary
Disclosed is grid-forming control method for an offshore wind turbine, including the following steps: obtaining a grid voltage and current at a grid connection point of a wind turbine, actual values of active power and reactive power of the wind turbine, and references of the active power, the reactive power and an voltage amplitude; calculating a phase reference of a grid-side converter of the wind turbine; calculating a reference of a modulating voltage at the grid-side converter of the wind turbine in a dq rotating coordinate system; and calculating a reference of a modulating voltage at the grid-side converter in an abc static coordinate system according to the phase reference of the grid-side converter of the wind turbine and the reference of the modulating voltage in the dq rotating coordinate system. The present disclosure can control the voltage amplitude of the grid connection point by the active power of the wind turbine, and can control the voltage frequency at the grid connection point by the reactive power of the wind turbine. Furthermore, the wind turbine controlled by the present disclosure can be kept in reliable synchronous running under conditions of startup, power fluctuation, alternating current (AC) fault and the like.