DC-AC Converter Control for Wind Turbine Grid Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional DC-AC converters in wind turbines fail to consistently supply AC power to the utility grid that meets voltage stability, power factor, active power, and reactive power requirements, especially during changing grid conditions, due to dependency on system impedance and grid faults.
Innovation Solution
A method and controller for the DC-AC converter that measures voltage samples, determines control signals for controllable switches, and adjusts their conduction state within a switching period to produce an AC output voltage with a predetermined grid frequency, using pulse width modulation and filtering to decouple grid impedance from the current controller, ensuring stability and dynamic performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DC-AC converters are used with traditional control schemes, then the system structure is simple, but the voltage stability and power quality requirements of the utility grid cannot be satisfied during changing grid conditions
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the switching frequency of the controllable switches based on grid conditions. The control method modifies the switching parameters (frequency and duty cycle) to maintain voltage stability and power quality during changing grid conditions, transforming the fixed-parameter conventional control into a variable-parameter adaptive control system.
Solution Approach 2:
The patent implements feedback control by continuously monitoring the AC output voltage and using this information to adjust the control signals for the controllable switches. The measured voltage samples are fed back to the controller, which then modifies the switching commands to maintain desired voltage levels and power quality, creating a closed-loop control system that responds to changing grid conditions.
2Speed
If the converter responds quickly to grid changes by reducing the time difference between measurement and adjustment, then the voltage stability improves, but the switching frequency requirements increase
Solution Approach 1:
The patent applies dynamics by making the switching frequency adaptive rather than fixed. The control method dynamically adjusts the switching frequency based on the required response speed and grid conditions. When faster response is needed, the switching frequency increases; when stability is sufficient, the frequency reduces. This dynamic adjustment allows the system to achieve high response speed when necessary while avoiding unnecessarily high switching frequencies during normal operation.
3Adaptability or versatility
If pulse width modulation with filtering is used to decouple grid impedance, then the adaptability to different grid conditions improves, but the device complexity increases
Solution Approach 1:
The patent uses filtering components as intermediaries between the switching circuit and the grid connection. The filter acts as a mediator that decouples the grid impedance from the current controller, allowing the converter to operate adaptively without being directly affected by grid impedance variations. This intermediary filtering stage enables the system to maintain stability and performance across different grid conditions while isolating the control system from external impedance changes.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
It is described a method for controlling a DC-AC converter (119) for converting a DC input voltage to an AC output voltage having a predetermined grid period, comprising: measuring, at a first point in time (509), a voltage sample (140) of a filtered version of the AC output voltage; determining a control signal (143) for a controllable switch (147) of the DC-AC converter (119) based on the measured voltage sample (140); adjusting, at a second point in time (513), a conduction state of the controllable switch (147) based on the control signal (143), wherein a time difference (tc) between the second point in time (513) and the first point in time (509) is less than a switching period (T) for periodically switching the controllable switch (147).