What is Digi SILENT Power Factory | HVDC Connected Offshore Wind Farm Fault Analysis?
Digi SILENT Power Factory | HVDC Connected Offshore Wind Farm Fault Analysis is a MATLAB-based technical project and simulation model. Transmitting bulk renewable energy from deep-water offshore wind farms to the mainland grid requires High Voltage Direct Current (HVDC) transmission systems utilizing Voltage Source Converters (VSC) or Modular Multilevel Converters (MMC). Because subsea HVDC cables eliminate the severe capacitive charging current limitations of high-voltage AC cables, they enable efficient long-distance power transfer while decoupling the offshore AC network from the onshore grid. However, grid faults—such as onshore symmetrical short circuits, offshore collection bus failures, or subsea DC line faults—trap energy on the DC link, creating steep overvoltages and risking converter tripping. DIgSILENT PowerFactory provides specialized numerical engines to evaluate these phenomena using Root Mean Square (RMS) transient stability and Electromagnetic Transient (EMT) simulations. This project covers network modeling, converter control design, IEC 60909 short-circuit calculations, dynamic fault simulation, and Fault Ride-Through (FRT) verification for an HVDC-connected offshore wind farm in DIgSILENT PowerFactory.
Project Methodology
The modeling, fault analysis, and transient stability simulation of an HVDC-connected offshore wind farm in DIgSILENT PowerFactory follows a structured power systems engineering workflow:
- Network Topology & Single-Line Diagram (SLD) Setup: Construct the complete electrical model in DIgSILENT PowerFactory:
- An offshore wind farm aggregate comprising Type-4 full-converter wind turbine generators (WTGs).
- Medium-voltage (66 kV) subsea inter-array cable networks and offshore platform step-up transformers (66/220 kV).
- An onshore Point of Common Coupling (PCC) connected to a high-voltage AC grid equivalent with realistic Short-Circuit Ratio (SCR) values.
- Converter Station Modeling & Control Strategy:
- Offshore Wind Farm Side Converter (WFSC): Configure the MMC station in grid-forming mode (AC voltage and frequency control) to establish the offshore AC voltage magnitude and 50/60 Hz frequency reference.
- Onshore Grid Side Converter (GSC): Configure the onshore MMC in grid-following mode with outer DC voltage regulation (Vdc) and decoupled reactive power (Q) or AC voltage control.
- DC Transmission Link & Dynamic Braking Chopper: Model symmetrical monopole or bipolar ±320 kV subsea DC cables using distributed parameter line models. Integrate a dynamic DC Chopper (braking resistor) on the DC bus to dissipate surplus wind power and prevent DC overvoltage during onshore grid voltage sags.
- Steady-State Load Flow Analysis: Execute balanced and unbalanced AC/DC power flow using the Newton-Raphson method in PowerFactory to verify steady-state bus voltages, line thermal capacities, and reactive power compensation.
- Short-Circuit Fault Calculations (IEC 60909): Perform symmetrical (three-phase) and asymmetrical (single-phase-to-ground, phase-to-phase) fault calculations to determine peak fault currents, breaking capacities, and protective switchgear ratings across both offshore and onshore substations.
- Time-Domain Transient Stability (RMS & EMT Simulation): Run dynamic simulations using DIgSILENT Simulation Language (DSL) control blocks across critical contingency scenarios:
- Three-phase bolted short circuits on the onshore AC grid to evaluate Fault Ride-Through (FRT) active power reduction and fast reactive current injection.
- Offshore 66 kV collection feeder faults to test converter current-limiting control and islanded grid restoration.
- Subsea DC cable pole-to-ground faults to evaluate DC protection clearance and transient overvoltage suppression.
- Waveform Analysis & Grid Code Compliance: Extract and plot time-domain curves of DC bus voltages, offshore AC frequency, onshore active/reactive power delivery, and PCC voltage recovery, confirming full compliance with international transmission system grid code standards.
Verified MATLAB Simulation Code Demonstration
Syntax-highlighted executable code demonstration for Digi SILENT Power Factory | HVDC Connected Offshore Wind Farm Fault Analysis:
% State-Space Control & Stability Analysis
clc; clear; close all;
% System Matrices
A = [0 1; -4 -5];
B = [0; 1];
C = [1 0];
D = 0;
sys_ss = ss(A, B, C, D);
Co = ctrb(A, B);
% Pole Placement Control
desired_poles = [-3 + 4i, -3 - 4i];
K = acker(A, B, desired_poles);
sys_cl = ss(A - B*K, B, C, D);
fprintf('State Feedback Controller Formulated Successfully!\n');