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• A new methodology for the Steady-state security region for the security assessment of distribution systems with the presence of DER. • Consideration of the intermittent characteristic of the DER generations. • The proposed methodology can be used in online or offline environments. • The proposed tool can be used in planning studies of distribution systems. • The proposed methodology can also be used for DER Regulation and Allocation in Distribution Networks: Volt/Var optimization and Congestion Relief. Modern Electric Power Systems are evolving from a centralized generation model toward a complex infrastructure with the presence of Distributed Energy Resources (DER). The transformative changes are especially pronounced at the level of the distribution system. The emergence of new generation technologies as solar, for example, affects the customer profile, expansion planning, and operation procedures of distribution utilities. Therefore, this paper describes a new methodology based on steady-state security regions concept for the security assessment of distribution systems with the presence of DER. The main objective of the proposed methodology is to allow an effective evaluation of the operating conditions of distribution systems with high penetration of DER, focusing on the intermittence of the new generation resources. The proposed methodology has been tested using two distribution systems. The first one is a tutorial 13-bus system, which is a small tutorial feeder, and the second one is a real large-scale model of a distribution network. The results presented indicate the effectiveness of the proposed technique in the distribution system security analysis. The proposed methodology is implemented using the Python language and uses the OpenDSS software as a power flow solver. [ABSTRACT FROM AUTHOR]

• A new unbalanced three-phase governor power flow formulation. • Both synchronous generators and droop-based distributed generators modeling. • Allows the evaluation of the system frequency due to active power unbalance. • The losses are distributed among the generating units in a more realistic way. • From this formulation any bus of the system can be the system reference bus. This paper presents a new unbalanced three-phase governor power flow formulation using the three-phase current injection equations (TCIM) expressed as a function of voltages expressed in rectangular coordinates. The proposed technique considers the representation of the primary frequency regulation for synchronous generators, as well as, voltage and frequency regulation in a droop-based control for distributed generation units (DGs). The static response of the generation governor, droop control equations and an equation to define the network reference angle for a given value are incorporated into the modeling. As the system is unbalanced, an internal additional bus, having balanced voltages, was created for each synchronous generator. As a consequence, two additional equations were included to keep internal voltages balanced. The inclusion of new equations results in an augmented formulation which is then linearized and solved using the Newton–Raphson method, in which the original structure of the Jacobian matrix from the current injections method is preserved. The proposed formulation allows the distribution of the active losses among the generating units as well as the determination of the frequency deviation due to variations, either in the total amount of generation or in the total system load. Any bus (load or generation bus) of the system can be chosen as the system reference bus. The results obtained using the unbalanced three-phase 6-bus test system were validated using the well known RTDS (real time digital simulator). The 25-bus islanded test system was also used in the simulations with the inclusion of synchronous generation (SG) units to demonstrate the effectiveness of the proposed methodology. [ABSTRACT FROM AUTHOR]