Inverter Sequence Control Fault Modeling for Short-Circuit Analysis
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Solution Overview
Problem
Traditional fault analysis methods for inverter-interfaced renewable energy sources (IIRESs) are inadequate due to their decoupled sequence control (DSC) systems, which complicate fault modeling and protection systems, especially in transient phases and under asymmetric conditions, leading to inaccurate fault current estimation and protection challenges.
Innovation Solution
A generalized fault analysis model for IIRESs with DSC is developed, incorporating positive and negative sequence components calculation (PNSCC) modes, including dual synchronous reference frame, dual complex-coefficient filter, dual second-order generalized integrator, delayed signal cancellation, and notch filter-based structures, to create a unified fault model that accounts for control delays and fault phases, enabling precise inrush current estimation and accurate short-circuit current calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electromagnetic transient (EMT) simulation models are used to analyze IIRES fault behavior, then general cognition of fault behavior is achieved, but systematic fault analysis theories cannot be built and industrial application is restricted due to high dependency on numerical algorithms
Solution Approach 1:
The patent replaces the numerical algorithm-based EMT simulation system with an analytical mathematical model system. By deriving closed-form expressions for fault current in different phases (detection phase, control transient response phase, and steady-state phase), the invention eliminates dependency on numerical algorithms while maintaining analysis accuracy, thus enabling systematic fault analysis theories and industrial application.
2Ease of operation
If traditional fault analysis methods are applied to IIRESs, then simple analysis procedures are used, but accurate fault current estimation is not achieved due to different fault characteristics of IIRESs
Solution Approach 1:
The patent segments the fault analysis into three distinct phases: fault detection phase, control transient response phase, and steady-state phase. Each phase has its own analytical model and characteristics. This segmentation allows the use of simple analytical procedures for each phase while accurately capturing the different fault characteristics of IIRESs, thus resolving the contradiction between simplicity and accuracy.
3Reliability
If decoupled sequence control (DSC) systems are implemented in IIRESs, then control performance is improved, but fault modeling complexity increases and protection systems become more challenging
Solution Approach 1:
The patent changes the modeling approach by deriving analytical expressions that explicitly account for DSC system parameters (control delays, filter characteristics, controller gains) in different fault phases. By incorporating these parameters into phase-specific analytical models, the invention maintains control performance while reducing fault modeling complexity compared to comprehensive EMT simulations.
Data Source
AI summary
A method for analytically studying fault responses of an inverter-interfaced renewable energy source (IIRES). The IIRES includes a decoupled sequence control (DSC) system, and the DSC system includes a converter, a current controller, a low-voltage ride-through (LVRT) control unit, and positive and negative sequence components calculation (PNSCC) structures. The method includes: determining a detailed fault model of the IIRES; determining a unified model of the PNSCC structures; determining a simplified fault model of the IIRES in a fault detection phase; determining a simplified fault model of the IIRES in a control transient response (CTR) phase; detecting a short-circuit fault; cutting off an outer loop of the DSC system; switching the DSC system to a current control mode through the LVRT unit by the current controller; analyzing the short-circuit fault; and designing an enhanced fault-ride-through control of the IIRESs to suppress an inrush current to protect the IIRES.