Conventional Load Flow Methods Research Articles

Modified load flow algorithm suitable for modern power systems under variable weather conditions

Conventional load flow algorithms are very commonly used in the system planning. In the conventional load flow methods, system electrical parameters at specific weather conditions will be considered. These methods gives results for given loading condition and have no provision to incorporate weather condition of a specific geographical location. If the load flow has the provision to incorporate the dynamic electrical characteristics of the conductors based on the operating weather condition, the results of the methods are going to be more accurate or in other words the results are close to the real values. In view of the above, in this paper a modified load flow algorithm incorporating the thermal modeling of the conductors with ambient temperature, wind velocity, conductor surface absorptivity, global solar radiation, Wind direction factor etc. is proposed. To verify the effectiveness of the proposed algorithm, the thermal mathematical model of transmission lines available in IEEE Std. 738™ -2006, IEEE Std. 738™ -2012 and CIGRE WG 22.12 are considered. In the proposed algorithm, new variables corresponding to Conductor Temperature are incorporated. The proposed algorithm is tested with the real time weather data of India and demonstrated on IEEE 30 and 118 bus systems.

Performance Study of Load Flow Algorithms in Well and Ill-Conditioned Systems

Existing transmission systems are classified as either ill systems or healthy systems. Most of the load flow algorithms works proficiently under well-conditioned systems. However, some of those algorithms fail to produce the accurate results for ill-conditioned systems. This paper investigates the performance of eight load flow algorithms based on the conventional Newton-Raphson, Fast-decoupled and Second-order Load Flow methods for a wide range of electrical bus system sizes. Tests are carried out for each load flow algorithm on six different standard bus systems, each with five different ill-conditioning levels. The results show that improved load flow model with constant Jacobian has advantages over the conventional load flow approach in both well and ill-conditioned system, especially for large-scale system.

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.

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.

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.

A hybrid Improved Quantum-behaved Particle Swarm Optimization–Simplex method (IQPSOS) to solve power system load flow problems

This study proposes a new approach, based on a hybrid algorithm combining of Improved Quantum-behaved Particle Swarm Optimization (IQPSO) and simplex algorithms. The Quantum-behaved Particle Swarm Optimization (QPSO) algorithm is the main optimizer of algorithm, which can give a good direction to the optimal global region and Nelder Mead Simplex method (NM) which is used as a local search to fine tune the obtained solution from QPSO. The proposed improved hybrid QPSO algorithm is tested on several benchmark functions and performed better than particle swarm optimization (PSO), QPSO and weighted QPSO (WQPSO). To assess the effectiveness and feasibility of the proposed method on real problems, it is used for solving the power system load flow problems and demonstrated by different standard and ill-conditioned test systems including IEEE 14, 30 and 57 buses test systems, and compared with the conventional Newton–Raphson (NR) method, PSO and some versions of QPSO algorithms. Furthermore, the proposed hybrid algorithm is proposed for solving load flow problems with considering the reactive limits at generation buses. Simulation results prove the robustness and better convergence of IQPSOS under normal and critical conditions, when conventional load flow methods fail.

Power Flow Analysis of RDS by Artificial Network Technique

This paper shows an application of Artificial Network Technique for the analysis of load flow and determines the power system static states that is, bus voltages magnitudes and voltage angles of a balanced radial distribution system, without executing the power flow algorithm, for any given load. As the performance of the conventional load flow methods such as Fast decoupled load flow, Newton-Raphson load flow is found to be very poor under critical conditions such as high R/X ratio, heavily loading condition etc. The proposed method makes use of a multi-layer feed forward ANN with error back propagation learning algorithm. The effectiveness of the proposed ANN-BPN based approach is tested by sample IEEE 33-bus, indicating its viability for RDS load flow assessment and results are presented.

Load flow analysis using decoupled fuzzy load flow under critical conditions

The conventional load flow methods like Newton-Raphson load flow (NRLF), Fast Decoupled load flow (FDLF) provide poor performance under critical conditions such as high R/X ratio, heavily loading condition etc. Exploiting the decoupling properties of power system, reliable fuzzy load flow is developed to overcome the limitations of the popular methods. Both power mismatch and summation of power mismatches are taken as two inputs for fuzzy logic controller. Considering magnitude of power mismatch and sign of power mismatch, new 25 fuzzy rules are created from two sets of inputs. The proposed Decoupled Fuzzy Load Flow (FDLF) is applied to IEEE 14 bus, IEEE 30 bus, IEEE 57 bus and IEEE 118 bus under stressed situations. The test results prove that the proposed algorithm provides better performance than the conventional methods under critical conditions.

Static security based available transfer capability (ATC) computation for real-time power markets

In power system deregulation, the Independent System Operator (ISO) has the responsibility to control the power transactions and avoid overloading of the transmission lines beyond their thermal limits. To achieve this, the ISO has to update in real-time periodically Available Transfer Capability (ATC) index for enabling market participants to reserve the transmission service. In this paper Static Security based ATC has been computed for real-time applications using three artificial intelligent methods viz.: i) Back Propagation Algorithm (BPA); ii) Radial Basis Function (RBF) Neural network; and iii) Adaptive Neuro Fuzzy Inference System (ANFIS). These three different intelligent methods are tested on IEEE 24-bus Reliability Test System (RTS) and 75-bus practical System for the base case and critical line outage cases for different transactions. The results are compared with the conventional full AC Load Flow method for different transactions.

STATIC SECURITY-BASED AVAILABLE TRANSFER CAPABILITY USING ADAPTIVE NEURO FUZZY INFERENCE SYSTEM

In power system deregulation, power transactions between a seller and a buyer can be scheduled only when sufficient available transfer capability (ATC) is available. The information about the ATC is to be continuously updated in real time and made available to the market participants through Internet-based system, open access same-time information system (OASIS). The static security-based ATC is to be computed for the base case system as well as for the critical line outages of the system. The critical line outages are based on static security analysis. Hence the computation of static security-based ATC using conventional method(s) is a tedious and time consuming process. In this paper static security-based ATC has been computed for real-time applications using three artificial intelligent methods viz., (i) back propagation algorithm (BPA), (ii) radial basis function (RBF) neural network and (iii) adaptive Neuro fuzzy inference system (ANFIS). These three different intelligent methods are tested on IEEE 24-bus reliability test system (RTS) and 75-bus practical system. The results are compared with the conventional full ac load flow method for different transactions.

Chaotic particle swarm optimization based robust load flow

A reliable load flow algorithm based on chaotic particle swarm optimization (CPSO) technique has been developed. To obtain optimum solution efficiently and accurately, an innovative formula for adaptive inertia weight factor (AIWF) has been introduced. Novel formulae for constriction factors have been designed for the load flow problems which are also adaptive. In addition to that, chaotic local search (CLS) is used with PSO to get rid of the local optima. To the best of our knowledge, it is the first report of applying CPSO to solve load flow problems. The efficiency and effectiveness of the proposed algorithm has been tested on different standard and ill-conditioned test systems. The proposed method shows its robustness under critical conditions when conventional load flow methods fail.

Esquemas alternativos para o passo de parametrização do método da continuação baseados em parâmetros físicos

O método de fluxo de carga convencional é considerado inadequado para se obter o ponto de máximo carregamento (PMC) de sistemas de potência, devido à singularidade da matriz Jacobiana neste ponto. Os métodos da continuação são ferramentas eficientes para a solução deste tipo de problema, visto que técnicas de parametrização podem ser utilizadas para evitar a singularidade da matriz Jacobiana. Neste trabalho, novas opções para a etapa de parametrização do método da continuação são apresentadas. Mostra-se que variáveis com claro significado físico podem ser utilizadas na etapa de parametrização. As seguintes variáveis foram testadas: perda total de potência ativa e reativa, potência ativa e reativa na barra de referência, potência reativa das barras de geração, e as perdas de potência ativa e reativa nas linhas de transmissão (LT). Além de facilitar a implementação computacional do método de continuação, as técnicas de parametrização apresentadas simplificam a definição matemática e o entendimento do método por parte de engenheiros de potência, visto que os métodos de continuação existentes na literatura sempre utilizam técnicas de parametrização complexas, e de interpretação puramente geométrica. Resultados obtidos com a nova metodologia para os sistemas testes do IEEE (14, 30, 57 e 118 barras) mostram que as características de convergência do método de fluxo de carga convencional são melhoradas na região do PMC. Além disso, durante o traçado das curvas PV, as diversas técnicas de parametrização podem ser comutadas entre si possibilitando o cálculo de todos os pontos da curva com um número reduzido de iterações. Diversos testes são realizados para proporcionar a comparação do desempenho dos esquemas de parametrização propostos.

Load flow solution of radial distribution feeders: a new contribution

This paper presents a new development for solving the load flow problem for radial distribution feeders, without having to solve the well-known conventional load flow equations. The algorithm details are discussed. Two test radial distribution feeders are solved using the proposed development to illustrate the technique. The tables of solution variables such as voltage, injected powers at each node of the feeder and line losses are presented along with comments and conclusions. The performance of the proposed development is also evaluated for a number of feeders that were studied and solved using earlier methods. Also the method is compared with the original method from Baran and Wu (IEEE Trans. Power Delivery 4(1) (1989) 735–743) as well as the standard conventional load flow methods.

Sensitivity analysis of radial distribution network – adjoint network method

This paper deals with the application of the Tellegen theorem for the sensitivity analysis of a radial distribution system using the Tellegen theorem. A modified Tellegen theorem expression was derived and was used to develop the adjoint network of the distribution network. A first order sensitivity expression was developed, in terms of bus voltage magnitudes of actual and adjoint networks and, load real and reactive power values. Sensitivity was calculated for the load changes either real or reactive or both at one or many buses. The authors attempted this algorithm on a 400 V, 12 bus radial distribution system with a main feeder. The results are compared with conventional load flow methods and error was observed to be less than 1%.

Comparative analysis of the convergence characteristics of second-order loadflow methods

The second-order loadflow technique defined in rectangular coordinates has become attractive because of the large amount of computation required in the evaluation of polar trigonometric functions in conventional loadflow methods. Seven versions of the second-order loadflow technique are developed and their convergence characteristics and computing times determined with tests carried out on the IEEE 14 and 30 bus networks. It is suggested that the version based on the CRIC approach warrants further developments into optimal power flows and automatic contingency selection algorithms for real-time control.