105,224 research outputs found
A Novel AC/DC Power Flow: HVDC-LCC/VSC Inclusion Into the PFPD Bus Admittance Matrix
Get PDFIn this paper, the matrix algorithm PFPD is generalized in order to compute the power flow solution of real and large AC/DC transmission networks. In particular, it is demonstrated that the HVDC-VSC/LCC links can be seen from the AC power systems as PV/PQ constraints, which englobe both the AC and DC characteristics of the HVDC links. The proposed analytical formulation to assess the PV/PQ constraints is valid for any other numerical methods (e.g., Newton-Raphson and derived, Gauss-Seidel, etc.). Furthermore, an iterative procedure for estimating the reactive power absorption of HVDC-LCC links from the power system is proposed. In order to validate the algorithm, solution comparisons with the commercial software DIgSILENT PowerFactoy are presented. This validation procedure shows that the algorithm can analyse large and real HVAC/HVDC networks (e.g., the Italian transmission one with its five HVDC links). Therefore, the conciseness, accuracy and performances of PFPD for studying real and large AC/DC power systems is confirmed
The Ossanna's Theorem for the Analytical Determination of a Two-Bus System PV Curve and Voltage Collapse Point
No full textIn the technical literature, the PV curves of the electrical lines are generally computed by only considering their electrical parameters as lumped. This model approach allows finding PV curve formulations without a large computational burden. Notwithstanding, such approximations bring to large inaccuracies for long transmission lines (especially insulated cables), for distribution ones (high r/x ratios) and for low power factor supply conditions. Starting from the Ossanna's theorem, novel and original PV curve and the voltage collapse point formulations for any electrical line are obtained. Moreover, PV curve analytical formulation considering the generator reactive power limits is formulated. Eventually, numerical results on the real-world case studies illustrate the differences with the proposed formulation with the classical ones found in the technical literature
A Three-Phase Power Flow Algorithm for Transmission Networks: A Hybrid Phase/Sequence Approach
Get PDFIn this paper, the three-phase generalization of a single-phase power flow (named PFPD) developed by the first author is presented. This three-phase formulation is chiefly conceived for HV/EHV transmission network applications, but it preserves a general validity for any power system. An iterative method for the solution achievement is throughout expounded. The algorithm quantitatively aims at investigating the impact of the asymmetrical transmission structures on power systems. This impact is evaluated in terms of voltage and current sequence components. Moreover, discussions on possible improvement actions to enhance the power quality are developed. The algorithm is implemented in Matlab environment and tested by several fictitious networks. Eventually, extensive comparisons in terms of execution time, number of iterations and solution accuracy with the software DIgSILENT PowerFactory are presented
A New Algorithm for Multi-Area Power Flow
Get PDFIn this paper, a new algorithm computing the multi-area power flow problem is presented. This algorithm is suitable for AC synchronous areas operating in steady-state conditions and interconnected by means of AC tie-lines. In particular, a new iterative composition/decomposition matrix procedure is adopted. For each area, the classical PV, PQ, and slack bus constraints are defined, allowing the computation of the power flow of each area independently. This independency of the power flow solution of each area allows exploiting the parallel computation technique. The overall power flow is then computed by putting together all the solutions of each area iteratively, by means of the tie-line (i.e., the lines interconnecting the areas) admittance matrix. The present multi-area method is novel and completely general and once the power flow solution of each area is separately achieved by any power flow solver (e.g., Newton-Raphson and derived, PFPD, or other), it makes suitable use of both a Thevenin's theorem generalization and a novel tie-line admittance matrix. In this direction, the method is not a new power flow algorithm but a new multi-area algorithm, which starts from the solutions of the power flow of each area, each considered with its own slack-bus. Applications of the algorithm to standard test cases are presented. Eventually, to test the validity of the method, numerical comparisons with the commercial software DIgSILENT PowerFactory are performed
Renewable Source Power Quality in Italian Grid by Paduan Three-Phase Power Flow PFPD-3P
No full textIn this paper, the matrix algorithm PFPD-3P is extended to consider the presence of inverter based renewable energy sources in the three-phase power flow solution of real transmission networks. In particular, it is demonstrated that the inverter based renewable energy sources can be seen as PV/PQ constraints from the AC power systems. Since three-phase power flow is fundamental to compute the supply power quality, inverter sequence component behavior is considered. Then, the method is tested on the Italian transmission grid, and the voltage unbalance factors are computed for different scenarios. In the first scenario, the electric energy is produced by the current generation mix. In the second scenario, the active power generated by inverter based renewable energy sources is strongly increased. Nowadays, these electric power sources represent the majority of the new installations, in order to respect energy transition goals. Then, some scenarios investigate different mitigation technologies, in order to reduce unbalance factors of the Italian EHV/HV network
Dynamic Power Flow Modeling Primary and Secondary Frequency Regulations
Get PDFIn power systems, the steady-state operations following any disturbance can be assessed by means of time-domain simulations, which consider the dynamic of the system without simplifying hypotheses. This paper proposes a formulation of the power flow problem with distributed slack bus model able to determine the steady-state impact on frequency and generation set-points of primary and secondary frequency regulation. This is done by deriving the real power balance expressions (including power losses, primary/secondary regulation, and the real frequency deviation) before and after the occurrence of any event or disturbance. This is achieved without resorting to the solution of a time-domain simulation. The performance of the proposed formulation is discussed through the standard WSCC 9-bus system and a 102-bus model of the Sicilian grid. Solutions are compared with those obtained with conventional time-domain simulations
Inclusion of HVDC links in the Paduan three-phase power flow (PFPD-3P)
No full textThe aim of the paper is to generalize the matrix algorithm PFPD-3P in order to evaluate the three-phase power flow of real and large AC/DC transmission networks. It is shown that the HVDC-VSC/LCC links can be seen from the AC network busses as PV/PQ constraints, which represent both the AC and DC behaviour of the HVDC links. In HVDC-LCC link, an iterative procedure is exploited to estimate the reactive power request. Since three-phase power flow is fundamental to compute network power quality, converter sequence component behavior is considered for both VSC and LCC. In order to validate the method, solution comparisons with the commercial software DIgSILENT PowerFactoy are performed. Eventually, the voltage unbalance factors in a 76-busbar case study are computed
Effect of Uniformly Distributed Parameter Line Models on the Evaluation of PV Curves and of the Maximum Loading Condition
No full textPV curves are generally obtained by considering lumped models of transmission lines. This approximated model can yield an inaccurate estimation of the maximum loading condition of the system. This letter shows that accuracy can be improved by considering line models with uniformly distributed parameters. Analytical evaluations of the PV curve and of the voltage collapse point of a two-bus system are obtained by applying the Ossanna's theorem. Then the impact of different line models on large-scale systems is evaluated through a continuation power flow analysis of a real-world model of the Sicilian transmission system including the Sicily-Malta 120 km cable connection
Transmission Grid Power Quality: Unbalance Factor Forecast by a Novel Three-Phase Power Flow
No full textThis paper aims at investigating the impact of the increasing demand for electricity on the power quality of the transmission networks. In particular, investigations on the transmission network structure as a source of voltage unbalance are made by performing numerical simulations. All the simulations are carried out by means of the MCA method, and by means of a novel three-phase power flow algorithm named as PFPD_3P. Moreover, proposals and discussions on possible power quality mitigation strategies on the transmission networks are presented (i.e., synchronous compensators installations and/or network reinforcements)
Power flow solution in asymmetrical multiconductor systems
No full textThe power flow solution of a three-phase network can be more easily computed if the power system is assumed as having a symmetrical structure with balanced loads. In this way, only the single-phase positive sequence circuit can be considered since it is wholly representative of the balanced operation of the electrical system. However, technical literature has investigated general methods to compute power flow solution in asymmetrical/unbalanced situations, since these situations may occur in real networks, especially in the distribution ones. Thus, in this paper the authors provide an iterative algorithm (easily implementable into common PCs) for the study of asymmetrical-structure networks and with unbalanced load scenarios. This calculation approach is different from the classical numerical ones (e.g. Newton-Raphson and derived) and it is characterized by a high solution accuracy and low CPU time, even in ill-conditioned cases. Eventually, real case studies showing the existence of negative, zero sequence currents, and voltages in balanced-load and asymmetrical networks are presented
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