Incremental Power Flow Research Articles

Fixed Transmission Charges Based on the Degree of Network Utilization

The core objective of transmission tariffs is the recovery of costs related to the transport of electricity. A usual component of a tariff is a fixed charge that covers the costs of the network infrastructure. As many customers use the power grid, the rate of this charge should reflect, as closely as possible, the actual costs of supplying energy to the individual consumers. These costs result from which network elements have been used in delivering the electricity, and to what extent these elements have been used. Therefore, the fixed transmission rates should depend on the degree of network utilization. This article investigates definitions of the degree of network utilization based on the active power flow. To calculate the degree of network utilization, the flow of electricity on a branch must be decomposed into the streams flowing to individual customers. For this decomposition, two methods are examined: a power flow tracing method, based on the proportional sharing principle, and an incremental power flow method, based on the superposition principle. The analyzed methodology is applied to a small test system for conceptual discussions, as well as to the transmission network of the Polish power system, as an example of practical application. The results of this study were then compared with the commonly used “postage stamp” method. Finally, several practical aspects related to the potential implementation of the presented methodology are discussed.

Quantitative Analysis on Relationship between VDCOL Controller Parameters and Voltage Stability Factor in Multi-infeed DC Transmission System

Based on the incremental power flow equation, the influence of VDCOL controller parameters on voltage stability factor VSF was studied by sensitivity analysis method, and the mathematical relationship between the two was obtained for the first time. Based on the analytical relationship, the quantitative relationship between VDCOL control parameters and voltage stability factor VSF was made clear, which lays a mathematical and theoretical foundation for the controller parameters tuning. Taking CIGRE standard DC system parameters as typical parameters, the relation curve between VDCOL control parameters and VSF was obtained. Combined with the relation curve, the influence of VDCOL parameters on the system voltage stability was further expounded, and some useful conclusions were obtained. The simulation analysis shows that the method and conclusions obtained in this paper are correct and effective, and have important theoretical guidance and practical significance on the design and operation of the system.

Planning of different types of distributed generation with seasonal mixed load models

The comparison of different types of distributed generation (DG) may help for appropriate selection of type of DG for distributed generation planning (DGP) in distribution system for various load scenario. The load on each bus of distribution system may be, in practice, the composition of industrial, residential, and commercial types of load which may also vary with seasonal day, and night. Therefore, in this paper the seasonal mixed load models at each bus are assumed and study is carried out with bus voltage and line power capacity limits for different types of DG using incremental power flow and exhaustive search method as deterministic approach. This analysis shows that mixed load model, types of DG, and power factor of DG have significant impact on size and location of DG.Keywords: Distributed generation, distribution system, distributed generation planning

Identification of vulnerable lines in power grids with wind power integration based on a weighted entropy analysis method

Vulnerable overhead electricity lines are a cause of serious risk to power distribution grids as damage can be the cause of large scale blackouts and cascading failures. With the integration of large scale wind power into generating capacity, both the topology structure and the distribution characteristics of power flow in distribution grid have undergone various changes that have increased line vulnerability. A novel approach to identify vulnerable lines based on the weighted entropy analysis method is proposed in this paper. In this approach, an assessment index, named the incremental power flow entropy, is first developed, which is used to describe influences caused by variation of the lines' capability of carrying power flow transfers on the vulnerability of the lines themselves at the same aggregation level. A second assessment index, named structural importance, describes the structural changes of a power grid that are caused by the integration of wind-generated electric power. The two assessment indices then are merged into one index by using the entropy weight analysis method, which can assess the vulnerability of the lines from the two aspects of power flow transmission and structural links. Vulnerability analysis under different situations, such as with and without the integration of the wind farm, and sharp fluctuations in wind speed at the wind farm, were carried out on an IEEE 39-bus system integrated with a 75 MW wind farm. Simulation results verified that the proposed assessment index not only can identify the vulnerable lines in a power grid with wind farm integration but also accurately reflected the vulnerability of the internal lines of the wind farm itself.

Multi-Objective Optimal Power Flow Using Efficient Evolutionary Algorithm

Abstract A novel efficient multi-objective optimization (MOO) technique for solving the optimal power flow (OPF) problem has been proposed in this paper. In this efficient approach uses the concept of incremental power flow model based on sensitivities and some heuristics. The proposed approach is designed to overcome the main drawback of conventional MOO approach, i. e., the excess computational time. In the present paper, three objective functions i. e., generation cost, system losses and voltage stability index are considered. In the proposed efficient MOO approach, the first half of the specified number of Pareto optimal solutions are obtained by optimizing the fuel cost objective while considering other objective (i. e., system loss or voltage stability index) as constraint while the second half is obtained in a vice versa manner. After obtaining the total Pareto optimal solutions, they are sorted in the ascending order of fuel cost objective function value obtained for each solution leads to the Pareto optimal front. The proposed efficient approach is implemented using the differential evolution (DE) algorithm. The proposed efficient MOO approach can effectively handle the complex non-linearities, discrete variables, discontinuities and multiple objectives. The effectiveness of the proposed approach is tested on standard IEEE 30 bus test system. The simulation studies show that the Pareto optimal solutions obtained with proposed efficient MOO approach are diverse and well distributed over the entire Pareto optimal front. The simulation results indicate that the execution speed of proposed efficient MOO approach is approximately 10 times faster than the conventional evolutionary based MOO approaches.

Solution of multi-objective optimal power flow using efficient meta-heuristic algorithm

An efficient meta-heuristic algorithm-based multi-objective optimization (MOO) technique for solving the multi-objective optimal power flow (MO-OPF) problem using incremental power flow model based on sensitivities and some heuristics is proposed in this paper. This paper is aimed to overcome the drawback of traditional MOO approach, i.e., the computational burden. By using the proposed efficient approach, the number of power flows to be performed is reduced substantially, resulting the solution speed up. In this paper, the generation cost minimization and transmission loss minimization are considered as the objective functions. The effectiveness of the proposed approach is examined on IEEE 30 and 300 bus test systems. All the simulation studies indicate that the proposed efficient MOO approach is approximately 10 times faster than the evolutionary-based MOO algorithms. In this paper, some of the case studies are also performed considering the practical voltage-dependent load modeling. The simulation results obtained using the proposed efficient approach are also compared with the evolutionary-based Non-dominated Sorting Genetic Algorithm-2 (NSGA-II) and the classical weighted summation approach.

Efficiency improvements in meta-heuristic algorithms to solve the optimal power flow problem

This paper presents three efficient approaches for solving the Optimal Power Flow (OPF) problem using the meta-heuristic algorithms. Mathematically, OPF is formulated as non-linear equality and inequality constrained optimization problem. The main drawback of meta-heuristic algorithm based OPF is the excessive execution time required due to the large number of load flows/power flows needed in the solution process. The proposed efficient approaches uses the concept of incremental power flow model based on sensitivities, and lower, upper bounds of objective function values. By using these approaches, the number of load flows/power flows to be performed are substantially, resulting in the solution speed up. The original advantages of meta-heuristic algorithms, such as ability to handle complex non-linearities, discontinuities in the objective function, discrete variables handling, and multi-objective optimization, are still available in the proposed efficient approaches. The proposed OPF formulation includes the active and reactive power generation limits, Valve Point Loading (VPL) effects and Prohibited Operating Zones (POZs) of generating units. The effectiveness of proposed approaches are examined on the IEEE 30, 118 and 300 bus test systems, and the simulation results confirm the efficiency and superiority of the proposed approaches over the other meta-heuristic algorithms. The proposed efficient approaches are generic enough to use with any type of meta-heuristic algorithm based OPF.

Scheduled incremental and unscheduled interchange cost components of transmission tariff allocation: a novel approach for maintaining the grid discipline

A novel approach of transmission tariff allocation (TTA) is proposed in this study. TTA comprises scheduled incremental cost (SIC) and unscheduled interchange cost (UIC) components. This approach demonstrates the use of proposed SIC and UIC components of tariff in incremental revenue reconciliation along with the provision of heavy penalty to maintain the grid discipline against extreme unscheduled withdrawal. SIC has been allocated to users of transmission network for their scheduled injections or withdrawals. UIC take care of excessive unscheduled interchange (UI) in load or generation. Incremental power flow in MVA is used to asses and allocation of these components. The scheduled increment (SI) in load or generation is associated with planned load growth rate whereas the UI in load or generation may arise intermittently. All generating units are participating to generate both active and reactive power as per their generation participation factor to match the SI and UI demands. The SIC component may be added to the nominal TTA to user. The UIC component of tariff is an additional burden or penalty imposed on users because of extreme unscheduled withdrawal. The results are obtained for SIC and UIC components of TTA by using 6 bus and IEEE 14 bus systems.

Faster evolutionary algorithm based optimal power flow using incremental variables

This paper proposes an efficient approach for evolutionary algorithm based Optimal Power Flow (OPF). The main drawback of evolutionary based OPF is the excessive execution time due to large number of power flows required in the solution process. The proposed Efficient Evolutionary Algorithm (EEA) uses the concept of incremental power flow model, based on sensitivities. With this, the number of power flows are reduced substantially, resulting in solution speed up. The original advantages of the evolutionary algorithms, like: the ability to handle discontinuities, complex non-linearities in the objective function, discrete variables, and multi-objective optimization, are still available in the proposed approach. The OPF solution is obtained with single objectives (fuel cost, loss, voltage stability index) and multiple objective (fuel cost and voltage stability index). The potential of the proposed approach is tested on IEEE 30, 118 and 300 bus systems, and the results obtained with proposed EEA are compared with other evolutionary algorithms. The proposed approach is generic one and can be used with any evolutionary algorithm based OPF.

Complete adjoint-based incremental power flow equations

This paper derives a new complete set of incremental power flow equations based on adjoint networks and Tellegen's theorem. The adjoint networks model the power system passive network, the loads or PQ buses, the generators or PV buses, and the reference bus. The adjoint solutions are used as coefficients to the new equations. The new equations are exact. The power system can be submitted to changes in network configuration, changes in loads, and changes in the values specified for generation. The equations presented in this paper relate those changes with the corresponding changes in voltages. A five-node system example chosen so as to illustrate some specific details of the adjoint-based power flow solution allows the replication of final and intermediate results by the reader. The performance of the equations for a realist transmission network is also presented.

열적용량과 전압안정도를 고려한 ATC 계산 방법에 관한 연구

본 논문은 가용송전용량(ATC)를 계산하기 위한 두 가지 빠른 계산 기법을 제안한다. 이 방법들은 선로의 열적 용량한계(Thermal ATC)와 전압 안정도한계(Voltage ATC)를 제약조건으로 ATC를 계산한다.<BR> 먼저 선로의 열적용량을 고려한 방법에서는 모선의 전력 변화에 대한 선로의 조류 감도인 PlDF와 n-1 상정사고를 고려한 LODF를 이용하였으며, 전압안정도를 고려한 방법에서는 2모선 등가 시스템을 이용하여 최대 전력을 구하는 방법을 이용하였다. 제안된 방법은 IEEE 30모선 계통에 적용하였으며 그 결과를 다른 방법과 비교하여 제안된 방법의 타당성을 입증하였다.

Effect of Parameter Uncertainties on Dynamic Performance of an Interconnected Power System with AC/DC Links

In the present work, a study on dynamic performance of two-area interconnected power system with parallel AC/DC links is performed. The optimal load frequency controller (LFC) designs based on optimal control theory and unity rank control concept are presented. A comparative study is carried out by considering variations in the parameters associated with power transmission system: (1) synchronizing coefficient of AC tie-line (Tiz) and (2) time constant associated with DC link (T dc ). The uncertainties considered in these parameters are in the range of 25% to 75% of their nominal values. The investigations carried out reveal that the system dynamic performance is highly sensitive to variation in synchronizing coefficient of AC tie-line but it is almost insensitive to variation in time constant of DC link. It is further inferred that the system dynamic performance may be improved considerably by implementing the proposed load frequency controllers. For the present study, DC link is considered to be operating in constant current control mode and incremental power flow through the DC link is modelled based on frequency deviation at rectifier end.

Fast calculation of linear available transfer capability

This paper presents a detailed formulation and implementation of a fast program for available transfer capability (ATC) calculations. The formulation is based on the linear incremental power flow to account for the line flow thermal loading effects. An efficient linear ATC implementation enhances speed in processing a large number of contingencies to determine ATC for each specified transfer. Test and performance results for practical power system models are presented.

An analytical approach for transaction costs allocation in transmission system

This paper proposes an analytical approach for allocating transmission transaction costs among users in transmission services. The proposed method allocates the transaction costs over the participants proportional to the ratio of incremental power flow caused by each participant and the total power flows on a designated transmission line. To determine the individual participant's impact on the transmission power flows, the line utilization factors (LUFs) of each participant are developed from a set of power flow equations. In the developed framework, one can directly evaluate the sensitivity of the flow on a line with respect to power generation at all buses. Although the developed allocation rule is very similar to the existing MW-mile method, especially to the modulus method, it does not require load flow analysis to be performed whenever each wheeling transaction is exercised. The main advantage of the developed method lies in its capability to consider multiple wheeling transactions simultaneously.

Quadratic Loss Formula For Reactive Dispatch

A loss formula based on the incremental power flow being a reduced form of the power flow is derived. The algorithm for its determination which utilizes the Jacobian matrix is given and the properties of the coefficients characterizing the incremental power flow are discussed. The key concept is the determination of a quadratic form such that second derivatives of the incremental power flow and of the load flow variables agree. The concept lends itself to load flow optimization, in particular for reactive dispatch for which an example (118 bus AEP system) is discussed. The results prove the expected high performance.