Flexible DC Power Flow Model for Control Strategy Switching
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Solution Overview
Problem
Existing power flow calculation methods for flexible DC transmission systems lack a unified model, are complex, and can be affected by unreasonable initial data, leading to potential system instability and calculation errors.
Innovation Solution
A power flow calculation method for flexible DC transmission systems that constructs a unified power flow model with a unified structure, allowing for easy switching between control strategies, and uses inner-outer double-loop iteration to improve convergence and handle changes in main converter stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a master-slave control strategy is used in flexible DC transmission, then the control structure is simple and communication demand is high, but the operational reliability of the system is low
Solution Approach 1:
The patent implements multi-functionality by enabling converter stations to dynamically switch between master and slave roles based on system conditions. The unified power flow model allows any converter station to assume the master function when needed, making the system more reliable while maintaining simple control structures through standardized control blocks that can be activated differently depending on the operating mode.
Solution Approach 2:
The patent applies dynamics by introducing dynamic role assignment where converter stations can transition between master and slave roles during operation. The system dynamically selects which converter station serves as the master based on real-time conditions such as voltage levels and power flow requirements, allowing the control structure to adapt to changing system states and maintain reliability.
2Measurement precision
If power flow calculation methods focus on analyzing different single operating modes separately, then each mode can be analyzed in detail, but the power flow calculation process becomes complicated when converter station operating modes are switched
Solution Approach 1:
The patent merges multiple single-mode power flow calculation methods into a unified power flow model that can handle all operating modes simultaneously. By combining the mathematical formulations for different control strategies (master-slave, voltage deviation, droop control) into a single framework with unified Jacobian matrix structures, the system achieves precise multi-mode analysis without the complexity of separate calculation procedures.
Solution Approach 2:
The unified power flow model provides universality by using the same calculation framework for all operating modes. The model can represent any converter station configuration and control strategy through standardized equations, allowing the power flow calculation to automatically adapt to mode changes without requiring different calculation methods for each scenario.
3Measurement precision
If the Newton-Raphson method is used for iterative calculation of flexible DC transmission system power flow, then calculation accuracy can be achieved, but unreasonable initial data can cause voltage or power to cross limits and affect the final result
Solution Approach 1:
The patent applies preliminary action by implementing preliminary checks and constraints before the Newton-Raphson iterative process begins. The system validates initial data and sets appropriate initial values that are guaranteed to be within feasible operating limits. This preliminary preparation prevents the iteration from diverging or producing unrealistic results, ensuring both accuracy and reliability from the start of the calculation.
Solution Approach 2:
The patent implements feedback mechanisms during the iterative calculation process where each iteration checks whether voltage and power values remain within acceptable limits. If values approach or exceed limits, the system provides feedback to adjust the iteration parameters or switch control modes, preventing unrealistic results while maintaining the accuracy benefits of the Newton-Raphson method.
Data Source
AI summary
A power flow calculation and AC/DC hybrid power flow calculation method for a flexible DC transmission system, the method including: according to the flexible DC transmission system under different control strategies, constructing a unified power flow model with a unified structure; determining a current main converter station, a current control strategy and an initial value and a limit value thereof, and forming the power balance equations under the current control strategy according to the unified power flow model; updating the current DC node voltage according to the voltage variation obtained by solving the power balance equations, and, if the updated DC node voltage exceeds the limit value, switching the control strategy; and if the updated DC node voltage does not exceed the limit value and the iteration constraints are not satisfied, alternating the main converter station according to the priority until iteration is completed.