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The main objective of this paper is to review and compare two methodologies to solve the power flow problem considering active power generation droop control. The first methodology is based on a DC power flow model, and the second one is based on a conventional full Newton power flow formulation. The study of two test systems is used to validate the proposed analysis; the first one is the 11-bus system with two distinct areas, and the second one is the 39-bus New England power system. The results presented validate and indicate the effectiveness of the DC power flow approach in order to estimate the steady-state system frequency deviations. [ABSTRACT FROM AUTHOR]

The use of Direct Current (DC) transmission links in power systems is increasing continuously. Thus, it is important to develop new techniques to model the inclusion of these devices in network analysis, in order to allow studies of the operation and expansion planning of large-scale electric power systems. In this context, the main objective of this paper is to present a new methodology for a simultaneous AC-DC power flow for a multi-terminal High Voltage Direct Current (HVDC) system with a generic representation of the DC network. The proposed methodology is based on a full Newton formulation for solving the AC-DC power flow problem. Equations representing the converters and steady-state control strategies are included in a power flow problem formulation, resulting in an expanded Jacobian matrix of the Newton method. Some results are presented based on HVDC test systems to confirm the effectiveness of the proposed approach. [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]