Wind Turbine DC-Link Voltage Control Using Predictive Current Injection
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Solution Overview
Problem
Conventional DC-link voltage control methods in wind turbines have limited disturbance rejection capability, leading to unstable DC-link voltage and increased risk of capacitor degradation and harmonic distortion in AC currents, due to their inability to effectively handle changes in generator speed and grid conditions.
Innovation Solution
Implementing a generalized predictive control (GPC) module that uses a physical model of the generator and grid side converters to derive a reference value for the DC current, optimizing control signals to maintain stable DC-link voltage by predicting future states and minimizing a cost function across a prediction horizon.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional PI controller is used for DC-link voltage control, then the control scheme is simple and easy to implement, but the disturbance rejection capability is relatively low
Solution Approach 1:
The patent transforms the control approach by changing from conventional PI control parameters to predictive control parameters. The generalized predictive controller uses a prediction horizon parameter (N) and cost function weights (Q, R) instead of traditional PI gains, enabling better disturbance rejection while maintaining implementation feasibility through parameter optimization
2Reliability
If large integral coefficients are used in the PI controller to speed up transient processes, then the disturbance rejection capability is improved, but overshoot is more likely to appear and system stability is reduced
Solution Approach 1:
The generalized predictive controller performs preliminary action by predicting future DC-link voltage values over a prediction horizon before the disturbance fully affects the system. The controller calculates optimal converter current references in advance based on predicted voltage deviations, preventing overshoot while maintaining stability through proactive control adjustments
3Speed
If finite-control-set model predictive control (FCS-MPC) is used, then the control response is improved, but the switching frequency becomes unfixed causing AC current distortion with harmonics distributed on a wide frequency band
Solution Approach 1:
The patent implements dynamic switching frequency control by adjusting the sampling period and prediction horizon based on operating conditions. The controller dynamically balances between fast response and harmonic reduction by adapting the control cycle, maintaining fixed switching frequency while preserving rapid response capability through optimized prediction horizons
4Speed
If deadbeat predictive control is used, then the control speed is improved, but static control error occurs due to parameter mismatches and fast accurate DC load power estimation is required which is difficult and undesired
Solution Approach 1:
The generalized predictive controller incorporates feedback mechanisms by using actual measured DC-link voltage values to update predictions and adjust control actions. The cost function continuously compares predicted voltage with reference voltage, providing feedback that eliminates static control errors without requiring complex power estimation, as the controller adapts to actual system behavior through iterative optimization
Data Source
AI summary
An a arrangement for controlling a DC-link-voltage of a DC-link connected between a generator side converter portion and a utility grid side converter portion of a wind turbine includes: a generalized predictive control module adapted: to receive as control module input values a current value of the DC-link-voltage and a reference value of the DC-link-voltage and to derive a reference value of a DC current based on the control module input values, the reference value of a DC current defining the DC current to be injected into the DC-link, wherein the arrangement is adapted to control the generator side converter portion and/or the utility grid side converter portion based on the reference value of the DC current.