DFIG Control Device Using Feedback Linearization for LVRT
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Doubly-fed induction generators struggle to maintain stable control and Low Voltage Ride-Through (LVRT) functionality under unbalanced voltage conditions, such as momentary power failures, due to instability in DC-link voltage control, leading to power generation cessation and increased operational costs.
Innovation Solution
A control device that employs feedback linearization methods to stabilize the DC-link voltage and active power control by decoupling and controlling positive and negative sequency components of the rotor current in a d-axis and q-axis, using new state variables and PI controllers to manage system voltage fluctuations and implement sequence control strategies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional control methods are used for doubly-fed induction generators, then good control characteristics are achieved under balanced three-phase voltage, but control performance deteriorates under unbalanced voltage conditions such as momentary power failures
Solution Approach 1:
The patent segments the control system into separate positive-sequence and negative-sequence control modules. Each module independently controls its respective sequence components of the rotor current, allowing the system to handle balanced and unbalanced voltage conditions separately and effectively. This segmentation enables the controller to maintain stability under unbalanced conditions by treating positive and negative sequence components as distinct control objects.
Solution Approach 2:
The patent changes the control parameters by introducing sequence-component-based current references instead of conventional direct current control. The controller calculates separate d-axis and q-axis current references for both positive and negative sequences, adapting the control parameters to match the actual voltage conditions. This parameter transformation allows the system to respond appropriately to unbalanced voltage by adjusting the current injection strategy in the frequency domain.
2Reliability
If DC-link voltage control is not maintained under unbalanced voltage, then the system cannot supply reactive power, but implementing conventional control fails to maintain DC-link voltage stability under momentary power failures
Solution Approach 1:
The patent implements feedback control by continuously monitoring the actual rotor currents and comparing them with the calculated sequence-component references. The controller uses this feedback to adjust the PWM switching signals in real-time, ensuring that the DC-link voltage remains stable even under momentary power failures. The feedback mechanism enables dynamic adjustment of the rotor current injection to compensate for voltage sags and maintain power generation continuity.
Solution Approach 2:
The patent performs preliminary calculation of the sequence-component current references before the voltage disturbance fully impacts the system. By pre-calculating the required current adjustments based on detected voltage imbalances, the controller is prepared to immediately counteract the disturbance, maintaining DC-link voltage stability and preventing power generation interruption.
3Reliability
If the control device stops operation under system voltage drop, then equipment is protected, but operational factor decreases and power amount reduces due to restart restrictions
Solution Approach 1:
The patent implements dynamic control that adapts the operational state based on real-time voltage conditions. Instead of static stop-start operation, the controller dynamically adjusts the rotor current injection to counteract voltage sags and maintain power generation. The system transitions from a static protective shutdown to a dynamic ride-through mode, allowing continuous operation during transient voltage disturbances while still protecting equipment from sustained damage.
Solution Approach 2:
The patent converts the harmful effect of unbalanced voltage and momentary power failures into a beneficial control opportunity. By detecting voltage imbalances and injecting appropriate negative-sequence currents, the system uses the disturbance itself as a signal to activate compensatory control actions. This transforms what would normally be a shutdown condition into an opportunity for demonstrating LVRT capability and maintaining productivity.
4Adaptability or versatility
If positive and negative sequency components are controlled separately for d-axis and q-axis, then LVRT function is implemented, but control system complexity increases
Solution Approach 1:
The patent achieves multi-functionality by using a single sequence-component control framework that handles both balanced and unbalanced voltage conditions, as well as normal and LVRT operations. The same control structure that calculates positive-sequence components for normal operation also calculates negative-sequence components for LVRT, eliminating the need for separate control systems for different operational modes. This universal approach reduces overall system complexity despite the advanced functionality.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention relates to a control device for a doubly-fed induction generator in which a feedback linearization method is enabled, in more detail, a control device for a doubly-fed induction generator which can implement an LVRT (Low Voltage Ride-Through) function by improving a DC link voltage control performance and an output control performance even under unbalanced voltage, such as a momentary power failure, by controlling a positive sequency component and a negative sequency components, which have non-linear characteristics, to be linearized while controlling the positive sequency component and the negative sequency component of the current of a rotor in a doubly-fed induction generator, respectively, for a d-axis and a q-axis. The present invention provides a control device for a doubly-fed induction generator in which a feedback linearization method is embedded, including a current control device for a doubly-fed induction generator controlled by a power conversion device composed of a system-side converter having an AC-DC conversion function and a generator-side converter having a DC-AC conversion function, is characterized in that the control device divides and measures positive sequency components and negative sequency components from stator voltage and current, rotor voltage and current, and signals of stator magnetic flux and rotor magnetic flux of the doubly-fed induction generator, divides the rotor current into four signals by dividing d-axial current and q-axial current from the positive sequency component and the negative sequency component of the rotor current, and makes a positive sequency component controller and a negative sequency component controller for the rotor current separately control the four signals of the rotor current, using the measured value, in which the positive sequency component controller and the negative sequency controller perform current input-output control, which is linearized by a feedback linearization method, for the d-axial current and the q-axial current.