A load margin calculation method considering optimized reactive power support

• An improved linear mixed-integer optimal reactive power flow model is presented. • Formulations of predictor and corrector steps involving reactive power adjustments are derived. • A load margin calculation model incorporating optimal reactive power flow and continuation power flow is established. With the development of modern low-carbon power systems, emerging ubiquitous reactive power supply gets more attention in improving power transmission capability. However, reactive power optimization for traditional and emerging forms of reactive power sources is ignored in conventional methods to calculate load margin (LM), which could cause conservative results or even decision-making misplay. Accordingly, this study proposes an improved LM calculation model incorporating optimal reactive power flow (ORPF) and continuation power flow (CPF) models, abbreviated as ORCPF. An approximate linear mixed-integer ORPF is established and integrated into Newton iterations and predictor–corrector steps. The ORPF model involves the Jacobian Matrix as the linearization of power balance relations and generates an approximate optimal solution in which the errors are corrected by following Newton iterations. A constraint interval adjustment scheme is presented to guarantee the errors under control. Meanwhile, the proposed step size control and rollback framework ensure robust iteration and accurate calculation for CPF. Employment of the LU decomposition method allows the CPF predictor coupling with the sensitivity calculation of voltage to reactive power changes (VQ Sensitivity), decreasing the computational burden in identifying the limit-induced bifurcation (LIB). The included case studies based on four test systems demonstrate the effectiveness of the proposed approaches.