SLCC Main-Loop Parameter Calculation for Weak-Grid Stability
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Solution Overview
Problem
The existing Line Commutated Converter (LCC) direct-current transmission technology faces challenges such as dependence on commutating voltage, high reactive power consumption, slow circuit breaker switching, commutation failures, and harmonic pollution, particularly in large-scale renewable energy systems.
Innovation Solution
A method and system for calculating main circuit parameters of the Statcom and Line Commutation Converter (SLCC) using Newton-Raphson iteration to determine direct-current voltage, current, active and reactive power, and SVG reactive power output, incorporating equivalent and simplified circuit models to ensure parameter accuracy and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If LCC direct-current transmission technology is used, then long-distance and large-capacity power transmission is achieved, but dependence on commutating voltage makes it difficult to operate stably in weak systems
Solution Approach 1:
The invention segments the control system into two independent branches: voltage source branch and current source branch. This segmentation allows each branch to operate independently with its own control strategy, enabling the system to maintain stability in weak AC systems while achieving large-scale power transmission. The voltage source branch provides voltage support while the current source branch handles power flow control.
Solution Approach 2:
The invention changes the control parameters by introducing dual-branch control with independent voltage and current source characteristics. This parameter change enables the system to adapt to weak AC systems by dynamically adjusting voltage and current parameters, thereby improving operational stability without sacrificing power transmission capacity.
2Power
If LCC direct-current transmission technology is used, then power transmission is achieved, but large amount of reactive power is consumed requiring large reactive power compensation devices
Solution Approach 1:
The current source branch provides self-service reactive power compensation by generating reactive power internally through its current control mechanism. This eliminates the need for external large-capacity reactive power compensation devices, as the system compensates for its own reactive power consumption through the coordinated operation of the dual-branch architecture.
Solution Approach 2:
The invention merges the reactive power compensation function into the main transmission system by integrating it with the current source branch. This combination allows reactive power compensation to occur within the transmission pathway itself, reducing the need for separate compensation devices and improving overall system efficiency.
3Reliability
If reactive power compensation device is configured, then reactive power support is provided, but switching speed of circuit breaker is slow causing excess reactive power and overvoltage during faults
Solution Approach 1:
The invention replaces the mechanical circuit breaker switching system with electronic control in the current source branch. This substitution enables rapid response to faults through electronic switching and control, eliminating the slow mechanical switching of traditional circuit breakers while maintaining reactive power support capability through coordinated control of the dual branches.
4Power
If LCC technology is used, then power transmission is achieved, but commutation failure risk exists which may expand accidents in multi-circuit systems
Solution Approach 1:
The invention applies local quality control by implementing independent control strategies for each branch (voltage source branch and current source branch). This localized control allows each branch to maintain its own commutation stability independently, preventing commutation failures from propagating across multiple circuits and expanding accidents in multi-circuit systems.
5Measurement precision
If SLCC dual-branch control is implemented, then calculation accuracy of main circuit parameters is improved, but calculation complexity increases due to deep coupling between parameters
Solution Approach 1:
The invention segments the calculation system into two independent calculation branches corresponding to the voltage source branch and current source branch. This segmentation decouples the previously deeply coupled parameters, allowing each branch to be calculated independently while maintaining high accuracy. The segmentation reduces calculation complexity by eliminating the need to solve highly coupled nonlinear equations simultaneously.
Data Source
AI summary
A method and system for calculating main-loop parameters of an SLCC, and a readable medium. The method comprises the following steps: according to an equivalent circuit model and a simplified equivalent circuit model, calculating an ideal no-load rated direct-current voltage by means of a Newton-Raphson iteration method (S10); according to the ideal no-load rated direct-current voltage and in combination with an alternating-current system reactive power control target and a direct-current system angle control target, calculating main-loop parameters in the equivalent circuit model and the simplified equivalent circuit model (S20); and determining whether calculation results of the main-loop parameters are within a preset range, and if the calculation results of the main-loop parameters are within the preset range, outputting the calculation results, and if the calculation results of the main-loop parameters are not within the preset range, after the parameters are modified, performing the above steps again until the calculation results of all parameters are within the preset range (S30).