Long-term voltage stability assessment using Quasi-Steady State Simulation in Matlab

Abstract

A Quasi Steady State Simulator (QSSS) for long term voltage stability assessment has been developed, tested and verified in Matlab. Theory and modelling assumptions behind QSSS are explained, including many elements present in long term voltage stability scenarios. The software was developed to perform large contingencies for N-bus systems with classical representation of generators and motors in stability studies, including simple control models of Automatic Voltage Regulators (AVR), Overexcitation Limiters (OEL) and Load Tap Changer (LTC). The simulator was finally compared to full time domain simulations in small power systems, showing good accuracy and low computational efforts. It was found that QSSS is able to follow the long term evolution of voltages when the system is still short term stable after each discrete change.