HVDC Trigger Angle Control for AC Fault Commutation Failure
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Solution Overview
Problem
Existing HVDC transmission systems face commutation failures during AC system faults due to the slow response and large control errors of conventional extinction angle regulators.
Innovation Solution
A method that involves obtaining three-phase voltage data from the converter bus, calculating zero-sequence and αβ component amplitudes, and using these calculations to determine trigger-angle commands for the extinction-angle controller, thereby adjusting the trigger angle to prevent commutation failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a conventional extinction angle regulator is used, then the control system is simple, but the response speed is slow and control error is large during AC system faults
Solution Approach 1:
The patent segments the voltage signal analysis into three distinct components: zero-sequence component (U0), positive-sequence component (U+), and negative-sequence component (U-). Each component is calculated separately using specific formulas, allowing the controller to respond to different fault conditions independently and rapidly without requiring a complete system redesign
Solution Approach 2:
The patent pre-calculates the extinction angle (γ) using the formula γ = arccos[(XT*×Id*)/(√3×UL′×cosφ)] before faults occur, and pre-determines the trigger angle compensation amounts (Δα0, Δα+, Δα-) for different fault types. This preliminary preparation enables the controller to immediately apply the correct compensation during faults without calculation delays
2Reliability
If the extinction angle is maintained at a threshold value to ensure normal shut-off, then valve shut-off reliability is improved, but commutation failure occurs during AC system faults due to voltage drop and phase jump
Solution Approach 1:
The patent implements a feedback mechanism where the controller continuously monitors the three-phase voltage at the converter bus, calculates the zero-sequence, positive-sequence, and negative-sequence components in real-time, and dynamically adjusts the trigger angle compensation based on the detected fault conditions. This closed-loop feedback ensures the extinction angle remains adequate even during AC system faults
Solution Approach 2:
The patent changes the trigger angle parameter dynamically based on fault detection. When faults are detected through voltage component analysis, the controller applies compensation amounts (Δα0, Δα+, Δα-) to adjust the trigger angle, thereby maintaining the extinction angle above the threshold value and preventing commutation failure while preserving normal operation during healthy conditions
3Reliability
If a faster response controller is implemented to reduce commutation failure, then commutation reliability improves, but the control algorithm complexity increases
Solution Approach 1:
The patent segments the complex fault response into three independent voltage component calculations (zero-sequence, positive-sequence, negative-sequence), each with its own dedicated formula and compensation amount. This segmentation allows the complex control task to be divided into manageable, parallel calculation paths that can be executed rapidly without requiring a monolithic complex algorithm
Solution Approach 2:
The patent introduces sequence component analysis as an intermediary mechanism between voltage detection and trigger angle control. The three-phase voltage is first transformed into zero-, positive-, and negative-sequence components, which then serve as intermediate signals to determine the appropriate trigger angle compensation. This intermediary layer simplifies the overall control logic by providing a structured intermediate representation of fault conditions
Data Source
AI summary
A method, an apparatus and a device for suppressing a first HVDC commutation failure under an AC system fault are provided. The method includes: obtaining a three-phase voltage of a converter bus, and calculating a zero-sequence component amplitude and an αβ component amplitude; calculating a first trigger-angle command for a single-phase fault and a second trigger-angle command for a three-phase fault; selecting a smaller one of the first trigger angle command and the second trigger angle command as a trigger-angle command for an extinction-angle controller; and adjusting a trigger angle of the HVDC transmission system by using the trigger-angle command as an upper limit value for an output of the extinction-angle controller of the HVDC transmission system.