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In this study, the authors introduce a new solution to the alternating current optimal power flow problem based on successive linear approximation of power flow equations. The polar coordination of the power flow equations is used to take advantage of the quasi‐linear P–θ relationship. A mathematical transformation for the crossing term of voltage magnitude is used, which guarantees the accuracy of the linear approximation when the quality of initial points regarding voltage magnitude is relatively low in the first few iterations. As a result, the accuracy of the proposed approximation becomes very high in very few iterations. Linearisation method for the quadratic apparent branch flow limits is provided. Methods to recover the AC feasibility from the obtained optimal power flow solution and correct possible constraint violations are introduced. The proposed method is tested in several IEEE and Polish benchmark systems. The difference in objective functions relative to MATPOWER benchmark results is generally <0.1% when the algorithm terminates. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive optimisation model that combines reactive power (VAR) optimisation and network reconfiguration to minimise power losses and eliminate voltage violations. In this model, the reactive power of distributed generators (DGs), VAR compensators, the position of tap‐changer and the states of branches are formulated as continuous and discrete decision variables. The original non‐convex three‐phase optimisation model was converted to a mixed‐integer second‐order cone programming model using the second‐order cone relaxation, big‐M method and piecewise linearisation. The results of numerical tests showed that the proposed model can achieve significant additional gains in network loss reduction and voltage violation mitigation. This developed method can be used as a basic analysis tool for active distribution networks operation schedule or planning. [ABSTRACT FROM AUTHOR]

An introduction is presented in which the editor discusses various reports within the issue on topics including planning and operating approach for active distribution grids, voltage control for photovoltaic inverters, and optimal scheduling model of microgrid considering battery lifetime.

Substation circuit breakers and other equipment are sized to withstand the maximum anticipated short‐circuit currents. Although the short‐circuit analysis used to design a substation takes into account the expected expansion of the network, over time the maximum short‐circuit current, especially for certain operating conditions, can exceed the circuit breaker ratings. As upgrading the equipment is expensive, the life of the present equipment can be extended if these violation conditions can be identified in real time and operational actions taken to mitigate them. In this study, the authors present a method for on‐line short‐circuit analysis and a method for determining preventive action using transmission line switching. [ABSTRACT FROM AUTHOR]