Stochastic frequency constrained unit commitment incorporating virtual inertial response from variable speed wind turbines

Abstract

Increasing the penetration of converter-interfaced renewable energy sources like variable speed wind turbines(VSWTs) leads to drastic challenges in keeping the system frequency stability due to system inertia decrement. In this study, anovel variable virtual inertia control strategy for VSWTs is developed which considers their mechanical restriction. It also makesthe implication of VSWTs virtual inertial response straightforward to be analytically considered in the system frequency dynamicconstraints like rate of change of frequency and frequency nadir. Furthermore, these constraints are formulated andincorporated into a chance frequency constrained unit commitment in order to minimize system operation cost while cooptimizing both inertial response from VSWTs/conventional units and governor-based primary frequency response. Theproposed stochastic methods can curtail the load and wind power to satisfy a predefined level of operation risk which cancoordinate the unit commitment problem with wind turbines. The comparison analysis on a 10 units standard test system and 4case studies illustrates that increasing the penetration level of VSWTs from 17% to 36% can provide important savings up to22.5% while the frequency constraints are also met by VSWTs virtual inertia provision. This helps increasing the penetration ofrenewables from the view point of frequency stability.