Load Flow Method Research Articles

Impact of distributed generators in the power loss and voltage profile of three phase unbalanced distribution network

Abstract In this paper, using particle swarm optimization (PSO) based method is developed to determine the optimal allocation of distributed generators (DGS) on a multi phased unbalanced distribution network. PSO algorithm has been programmed in MATLAB using open source software called OpenDSS in a co-simulation environment to solve the unbalanced three-phase optimal power flow (TOPF) and to find the optimal location and sizing of different types of distributed generators. Using the IEEE 123 node distribution feeder as a test bed, results from the proposed method is compared to those from the repeated load flow (RLF) method. For a realistic study, mixes of all type of DGs are considered. Results indicate that integrating optimally sized DGs at the optimal locations not only reduces the total power loss in the distributed system but improves the voltage profile as well.

Mega Watt Security Assessment of Power Systems

This paper deals with the security aspects of power system by evaluating the severity of transmission line outage. MW security assessment is made by determining the power flow in the line using load flow for each contingency. The severity of contingency is measured using a scalar index called performance index (PI). DC load flow and Fast Decoupled load flow are used as approximate and exact load flow methods for MW security assessment respectively. Contingency analysis is carried out and ranked lists in the decreasing order of severity based on PI values are prepared for standard test systems. The severity of line is evaluated and compared using these load flow methods. A new method is proposed to avoid Masking problems in MW security assessment. Security analysis is made on standard test systems such as 5, 6, IEEE 14 and IEEE 30 bus systems under present study.

Load Flow Analysis Using Improved Newton-Raphson Method

This paper describes a simple, reliable and swift load-flow solution method with a wide range of practical application. It is attractive for accurate or approximate off-and on-line calculations for routine and contingency purposes. It is applicable for networks of any size and can be executed effectively on computers. The method is a development on conventional load flow principle and its precise algorithm form has been determined to bring improvement to the conventional techniques. This paper presents a comparative study of the new constant Jacobian matrix load flow method built based on several conventional NR load flow methods. Assumptions are made so as to make the matrix constant, thus eliminating the need of calculating the matrix in every iteration. The proposed method exhibits better computation speed.

Mega Watt Security Assessment of Power Systems

This paper deals with the security aspects of power system by evaluating the severity of transmission line outage. MW security assessment is made by determining the power flow in the line using load flow for each contingency. The severity of contingency is measured using a scalar index called performance index (PI). DC load flow and Fast Decoupled load flow are used as approximate and exact load flow methods for MW security assessment respectively. Contingency analysis is carried out and ranked lists in the decreasing order of severity based on PI values are prepared for standard test systems. The severity of line is evaluated and compared using these load flow methods. A new method is proposed to avoid Masking problems in MW security assessment. Security analysis is made on standard test systems such as 5, 6, IEEE 14 and IEEE 30 bus systems under present study.

Classification and assessment of power system static security using decision tree and random forest classifiers

SummaryThe power system static security classification and assessment is essential in order to identify the post‐contingency problems and take corrective measures and to protect the system from blackout. In this paper, application of two data mining classifiers have been proposed for the security classification and assessment of a multiclass security problem. To design the security problem, contingency analysis is carried out under N‐1 line outage, and static severity index (SSI) is computed, which is a function of the line overload and the voltage deviation using Newton–Raphson load flow method, considering the variable load and generating conditions. Corresponding to the computed values of SSI, the voltage, phase angle, Mega Volt Ampere line flow and so on, a 1 × 7 pattern vector is generated. The generated pattern vectors are used to design a multiclass security problem. The designed security pattern vectors are given as inputs to the decision tree (DT) and random forest (RF) model in order to classify the security status of the power system. The proposed classifiers are investigated on an IEEE 30‐bus test system. The classification accuracy of the DT and the RF are compared with state‐of‐the‐art classifier models, namely, multilayer perceptron (MLP), radial basis function (RBF), and support vector machine (SVM).The simulation results clearly indicate that the proposed DT and RF classifiers are more efficient, reliable, and out performs MLP, RBF, and SVM classifiers for the assessment of the security status of the power system. Hence, DT and RF classifiers are found to be suitable for online implementation. Copyright © 2015 John Wiley & Sons, Ltd.

Fast and accurate second order load flow method based on fixed Jacobian matrix

This paper presents the second order load flow method (SOLFM) based on the constant Jacobian matrix, with flat initial guesses (1.0∠0°) in polar coordinates. The proposed SOLFM does not need to calculate the Jacobian and Hessian matrix separately; keeping the PV type buses. Accordingly, the solution sped up the proposed SOLFM to a level that is much faster than the classical Newton Raphson Load Flow Method (NRLFM). Moreover, the polar coordinate system can simplify the proposed method's load flow equation. The convergence characteristic of the proposed SOLFM is superior to the NRLFM due to the usage of the Hessian matrix. The validation of proposed SOLFM is proven by testing the Malaysian 664 bus system with respect to NRLFM and the Fast Decoupled Load Flow Method (FDLFM) in the context of computation time and convergence characteristic.

Load Flow Analysis Using Second-Order Load Flow Methods and its Variations

The load flow or power flow computer program is the basic tool for investigating the steady-state conditions of power system. This paper introduces improved algorithms based on the basic Second-order Load Flow method for a wide range of electrical bus system sizes. It is attractive for accurate or approximate off- and on-line calculations for routine and contingency purposes. Tests of 4 different variations based on the basic Second-order Load Flow method are run on 6 different standard bus systems and the results are discussed in this paper.

Heuristic probabilistic power flow algorithm for microgrids operation and planning

One of the basic components of future distribution networks is renewable energy resources (RER). The uncertainty in power production of renewable resources such as wind and solar as well as load is another characteristic of such networks. Conventional power flow methods may not be suitable for active distribution networks such as microgrids. In this study, a heuristic load flow method considering the effects of intermittent behaviour of RERs and load is modelled in probabilistic load flow (PLF) algorithm. The method is suitable for both radial and weakly meshed distribution networks with RER for operation and planning of microgrids. Imperialist competitive algorithm (ICA) as heuristic-based optimisation algorithm is applied to solve the PLF. Based on PLF technique, calculated parameters of the system such as bus voltages and feeders’ current are extracted as random variables. A modified version of IEEE 33-bus test system with RER is used to evaluate efficiency and capability of the algorithm. Results are compared with Monte Carlo simulation method. The probability density function and cumulative distribution function (CDF) of some network variable are compared. Based on the results, the presented approach can solve the PLF problem regardless of the type of distribution network.

Solving probabilistic load flow in smart distribution grids using heuristic methods

Uncertainties in smart distribution grids operation are important and challenging issues. The integration of the renewable energy resources (RERs) into the conventional distribution networks changes the radial structure of the network while its inherent characteristics such as high R/X ration of feeders remained unchanged. Conventional power flow methods may be not be suitable or efficient for smart distribution networks. This paper proposes a heuristic optimization based Probabilistic Load Flow (PLF) method to overcome new problems of future distribution networks. The proposed algorithm is suitable for any smart distribution networks with RERs. Imperialist Competitive Algorithm is used to formulate and solve the PLF considering RERs. Comparative studies with small and large sample numbers of RERs and load data are done to evaluate the effect of the samples number on the performance and simulation time. The results are compared with Monte Carlo Simulation (MCS) method. Some network parameters such as buses voltage, feeders power, and network loss in modified 33-bus network are given as Probability Density Function and compared by MCS. Based on the results the proposed algorithm can solve the PLF, regardless of the type of distribution network.

Graph theory-based radial load flow analysis to solve the dynamic network reconfiguration problem

Summary Radial load flow (RLF) methods are frequently used in solving distribution system problems. The conventional Jacobian-based load flow methods (e.g., Newton–Raphson) may fail to converge in solving distribution system due to high resistance to reactance ratio of distribution lines. RLF methods are based on sweep-based mechanism and require that the line data must be arranged in accordance with network topology. This problem needs special attention particularly in case of solving dynamic power system problems, where topology of the network changes with tie switches position (network reconfiguration problem). This paper has presented an intelligent graph theory-based RLF analysis to solve “dynamic” problems. The proposed algorithm will help in arranging line data for any combination of tie switch positions, to check the radiality of the system and to ensure that all nodes are connected with the source node. The effectiveness of the proposed method is also validated by solving 16-bus and 33-bus network reconfiguration problem using graph theory-based RLF method. Copyright © 2015 John Wiley & Sons, Ltd.

Investigation of schemes for incorporating generator Q limits in the fast decoupled load flow method

Fast Decoupled Load Flow (FDLF) is a very popular and widely used power flow analysis method because of its simplicity and efficiency. Even though the basic FDLF algorithm is well investigated, the same is not true in the case of additional schemes/modifications required to obtain adjusted load flow solutions using the FDLF method. Handling generator Q limits is one such important feature needed in any practical load flow method. This paper presents a comprehensive investigation of two classes of schemes intended to handle this aspect i.e. the bus type switching scheme and the sensitivity scheme. We propose two new sensitivity based schemes and assess their performance in comparison with the existing schemes. In addition, a new scheme to avoid the possibility of anomalous solutions encountered while using the conventional schemes is also proposed and evaluated. Results from extensive simulation studies are provided to highlight the strengths and weaknesses of these existing and proposed schemes, especially from the point of view of reliability.

Research on Fast Decoupled Load Flow Method of Power System

The power flow calculation is study the steady-state operation of the power system as basic electrical calculations. It is given the power system network topology, device parameters and determines system health boundary conditions, draw a detailed operating status of the power system through numerical simulation methods, such as voltage amplitude and phase angle on the bus system the power distribution and the power loss. Flow calculation is the power system operation, planning and safety, reliability analysis, is fundamental to the system voltage regulation, network reconfiguration and reactive power optimization must call the function, so the trend has very important significance to calculate the power system.

Evaluation of Optimal Access Location and Capacity of DG for Insertion in distribution System with Condensed Power Losses showing improved Critical Bus Voltage Stipulation

This paper intent to enhance the revenue of optimally planned distributed generation (DG) insertion in distribution system in terms of condensed active and reactive power losses, improved critical bus voltage and system voltage profile which may undeniably ensures aided load expansion and system stability. The novelty of this paper is a multi-objective approach based on two port transmission parameters for optimally determining the size and access point for DG insertion in distribution system. To validate the proposed method the results obtained are compared with already published Analytical Method and the well known Exhaustive Load Flow method. The Comparative study presented has shown that the proposed method leads existing methods in terms of its ease, reduced computational time and handling less number of variables. Despite of that cross verification of results with multi-objective approach assures the optimality of estimated parameters with improved efficiency. To exhibit the utility of the method, it is implemented on standard IEEE 16 bus, 33 bus and 69 bus test radial distribution systems. The simulation is carried out in MATLAB environment for execution of the proposed algorithm.

A three-phase algorithm for state estimation in power distribution feeders based on the powers summation load flow method

State estimation approaches for use in transmission systems are common in the literature, however, there are few algorithms intended for distribution systems. This occurs, mainly, due to the small amount of measurement data available in real time and topological complexity of these systems. In this context, this paper proposes a new three-phase state estimation algorithm for radial distribution feeders, which is based on adjustment of loads from a dynamic utilization and imbalance factors, in order to model pseudo-measurements of powers, and take into account the imbalance of loads, frequently presents in feeders. The method performs the estimation by section, starting from the substation toward the loads, where estimated quantities in a section are used as pseudo-measurements to estimate the subsequent section. This procedure provides a computational optimization for real-time methodology presented here. Tests were performed in distribution feeders from a Brazilian power company and the results show satisfactory performance of developed state estimator in respect to adjustment of estimated values compared with corresponding real-time measured quantities.

A novel slack bus-free load flow method for dc microgrids and distribution systems with dc-bus signaling control methods

SUMMARY A significant section of the future electrical power systems, that is, smart grids, will be dc microgrids and distribution systems. Obviously, the voltage control is one of the important issues of these dc power systems. DC-bus signaling (DBS) control methods, as distributed, autonomous, simple, highly reliable, inexpensive, modular and practical control methods, are one of the most important categories of the voltage control methods in dc microgrids and distribution systems. In the dc power systems with DBS control methods, the determination of the generated power shares of the distributed power sources, as vital entries for the conventional load flow methods, before the execution of a load flow method, is not possible. Also, in these dc power systems, none of the power sources can be considered as a constant voltage source, that is, the slack source. Consequently, the conventional load flow methods are not applicable to dc microgrids and distribution systems with DBS control methods. In this paper, a novel, practical, robust, fast, precise load flow method is presented to overcome the mentioned serious complexities in the dc power systems. The proposed load flow method necessitates the least input data. It determines the generated power shares of all the sources during its execution. Besides, the load flow method necessitates no constant voltage source or slack source. Furthermore, the proposed load flow method benefits from low computational time and the storage requirements and the removal of the ill-conditioned problem. The algorithm validation and the numerical results derived in this paper confirm the accuracy and the remarkable performance of the load flow method. Copyright © 2015 John Wiley & Sons, Ltd.

Genetic Algorithm Based Network Reconfiguration in Distribution Systems with Multiple DGs for Time Varying Loads

Abstract This paper describes the implementation of an algorithm which predicts optimum reconfiguration plan for power distribution system with multiple PV generators. Since network reconfiguration is a multi objective and multi constrained problem, genetic algorithm is used for optimization. Forward backward load flow method with time varying load condition is considered. The objective function of the genetic algorithm incorporates all the objectives and constraints required for the reconfiguration plan. The algorithm developed predicts the switching pattern for reconfiguration which gives minimum loss and minimum voltage deviation. It also reduces the number of switching operations along with satisfying the defined limit constraints.

Multi-linear Monte Carlo simulation method for probabilistic load flow of distribution systems with wind and photovoltaic generation systems

In this paper, a probabilistic method is proposed to analyze the steady-state operating conditions of an active electrical distribution system with Wind (WD) and Photovoltaic (PV) generation plants. This method takes into account the uncertainties of power load demands and power production from renewable generation systems and combines Monte Carlo simulation techniques and multi-linearized power flow equations. The power flow equations include models of wind turbine and PV generation units and multi-linearization is accomplished by applying a criterion based on the total active power of the system. The method properly extends a probabilistic method proposed in the relevant literature for traditional passive electrical distribution systems to the field of an active electrical distribution system with WD and PV generation units. Numerical applications are presented and discussed with reference to a 17-bus test distribution system characterized by WD and PV systems connected at different busbars. The results obtained with the proposed algorithm are compared with the results obtained using a Monte Carlo simulation algorithm that included non-linear power flow equations.

Containing Wind Farm Power System Probabilistic Optimal Power Flow Calculation Using the Method of Combined Cumulants and Gram-Charlier Expansion

This paper uses the optimal probabilistic load flow method for power containing wind farm analysis. Based on Computation of optimal load flow using the Interior point method ,considering the stochasticlal power output of wind generator and the random outage of synchronous generator and the stochastic of load power, calculating the probability distribution of branch power flow and node voltage. This paper uses RTS-24 as the example to analysis the method ,and comparison the results with that of the Monte-Carlo method, to analysis the change of power system after the grid connected of wind turbine.

Comparison of various UPFC models for power flow control

This paper presents a comparative study on various implementation techniques of Unified Power Flow Controller (UPFC) in load flow algorithms. The comparison is done among; decoupled technique, comprehensive technique, load injection technique, π load injection technique, indirect technique, and matrix partitioning technique. The merits and demerits of these techniques are presented. Beside these techniques, the paper presents a developed UPFC model based only on current injection approach. The model is implemented in Newton–Raphson current injection load flow method (NR-CIM). This model addresses the main drawbacks of previous techniques. Test results are presented using IEEE standard systems which demonstrate the effectiveness of the developed model.

Power flow control for transmission networks with implicit modeling of static synchronous series compensator

Abstract This paper presents an implicit modeling of Static Synchronous Series Compensator (SSSC) in Newton–Raphson load flow method. The algorithm of load flow is based on the revised current injection formulation. The developed model of SSSC is depended on the current injection approach. In this model, the voltage source representation of SSSC is transformed to current source, and then this current is injected at the sending and auxiliary buses. These injected currents at the terminals of SSSC are a function of the required line flow and voltage of buses. These currents can be included easily to the original mismatches at the terminal buses of SSSC. The developed model can be used to control active and reactive line flow together or individually. The implicit modeling of SSSC device decreases the complexity of load flow code, the modification of Jacobian matrix is avoided, the change only will be in the mismatches vector. Finally, this modeling solves the problem that happens when the SSSC is only connected between two areas. Numerical examples on the WSCC 9-bus, IEEE 30-bus system, and IEEE 118-bus system are used to illustrate the feasibility of the developed SSSC model and performance of the Newton–Raphson current injection load flow algorithm.