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

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, a novel variable virtual inertia control strategy for VSWTs is developed which considers their mechanical restriction. It also makes the implication of VSWTs virtual inertial response straightforward to be analytically considered in the system frequency dynamic constraints like rate of change of frequency and frequency nadir. Furthermore, these constraints are formulated and incorporated into a chance frequency constrained unit commitment in order to minimize system operation cost while co-optimizing both inertial response from VSWTs/conventional units and governor-based primary frequency response. The proposed stochastic methods can curtail the load and wind power to satisfy a predefined level of operation risk which can coordinate the unit commitment problem with wind turbines. The comparison analysis on a 10 units standard test system and 4 case studies illustrates that increasing the penetration level of VSWTs from 17% to 36% can provide important savings up to 22.5% while the frequency constraints are also met by VSWTs virtual inertia provision. This helps increasing the penetration of renewables from the view point of frequency stability.