Unit commitment in isolated grid considering dynamic frequency constraint

Abstract

Isolated grid (IG) usually has small inertia constant, and the primary frequency regulation ability of IG is limited. In addition, high penetration level of photovoltaic power plants (PV-PPS)integrated to IG deteriorate system inertial and primary frequency regulation ability. To ensure the stability of frequency, UC model considering dynamic frequency limit (DFL) is proposed in this paper, and PV-PPS are deloaded to participate in frequency regulation. Based on frequency response model with PV-PPS participating in frequency regulation, the expression of required minimum frequency regulation capacity of PV-PPS is deduced, which guides PV-PPS retain sufficient but not excessive capacity. Then, a UC model with DFL and frequency regulation capacity of PV-PPS constraints is proposed. And the problem is decomposed into a master problem for UC with DFL and a subproblem for PV-PPS' frequency regulation capacity assessment. Because the master problem is a complex nonlinear mixed integer optimization problem, in order to avoid complexity solving procedure, unit regulation power is used to present frequency regulation ability and generate optimization cut. The optimization cut and benders cut are used for eliminating frequency limit/regulation capacity violations in iteration method. Finally, an IG test system is used to verify the effectiveness and advantages of the proposed scheme, comparing with other two schemes: conventional UC and UC considering DFL without PV-PPS participating in frequency regulation.