Branch Flow Research Articles

Multi-objective optimization based optimal sizing & placement of multiple distributed generators for distribution network performance improvement

Integration of Distributed Generations (DGs) into radial distribution network (RDN) is an emerging need to explore the benefits of renewable energy sources (RES). Increasing penetration of RES based DGs in RDN without proper planning leads to several operational problems such as excessive energy losses, poor voltage quality and load balancing. Hence, in this work, multi-objective optimization (MOO) problem is formulated by carefully chosen three conflicting objectives such as power loss minimization, enhancement of load balancing index (LBI) and aggregate voltage deviation index (AVDI). Teaching-Learning-Based-Optimization (TLBO) is used to optimize MOO problem considering placement of DGs at multiple locations in RDN satisfying the constraints on bus voltage magnitude, branch flows and DG size. Comprehensive simulation studies have been carried out to obtain optimal performance for 69-nodes RDN with the increasing penetration of DGs at multiple locations. It is shown that determination of optimal sizing of DGs at multiple locations in RDN with MOO results in lesser power losses, improved voltage profiles and better load balancing as compared to placement of single DG in RDN. Performance measures such as spacing and spread indicators are used for characterizing Pareto solutions for MOO problem. Such set of non-dominated solutions obtained from Pareto front during multi-objective TLBO gives proper guidelines to the utility operator about sizing and placement of DGs based on the assigned priorities to the objectives.

Waiting Cost Based Long-Run Network Investment Decision-Making Under Uncertainty

Traditional system investment decision is costly and hard to reverse. This is aggravated by uncertainties from flexible load and renewables (FLR), which impact the accuracy of network investment decisions and could trigger a high asset risk. Thus, system operators have the incentive to postpone network reinforcement, and `wait and see' whether the request of investment can be reduced or delayed with new information. This paper proposes a novel method to evaluate network investment horizon deferral based on the trade-off between waiting profit and waiting cost under FLR uncertainties. Although deferring investment leads to waiting cost, it is worthy to wait if the cost is smaller than the waiting profits. To capture the impact of FLR uncertainties on system investment, nodal uncertainties are converted into branch flow uncertainties based on a combined cumulant and Gram-Charlier expansion method. The waiting cost is quantified by the options' cost based on real options method and waiting profit is from asset present value reduction due to the deferral. Thus, by paying waiting cost, current investment cost can be reserved until uncertainties are reduced to an acceptable level. The waiting time is evaluated by Sharp ratio and expected return, determined by the waiting cost and uncertainty level. The results show that paying waiting cost is an economical way to reduce the impact of uncertainty and avoid hastily investment.

Design of Simulated Magnetic Gun

STM32F103 single-chip microcomputer is used as the control unit of the simulated electromagnetic squint. The single-chip microcomputer is used to control the function of launching shell and steering gear angle, and the steering gear is used to control the launching angle and direction of the electromagnetic squint. In the design of electromagnetic gun, coaxial coil gun is used as the main part, and two batteries are used as the energy supply device. Then the electromagnetic relay connected with the single-chip microcontroller controls the cycle charging. Firstly, 12V DC power is input into the circuit by the DC stabilized voltage power supply. After the current enters into the circuit, it is divided into two branches. One branch flows through the boosting circuit of electromagnetic relay to charge the thyristor capacitor. With the switch off, the instantaneous discharge of the capacitor generates an inverter magnetic field in the coil, which pushes the metal projectile out at a high speed. What the electromagnetic relay does is to boost the voltage. What the thyristor capacitor needs is high voltage current charging. Another branch supplies 5V DC power to the steering gear through the step-down electromagnetic relay to support the rotation of the steering gear. The system obtains the target position through openmv, and STM32 uses PWM wave to control the rotation angle and direction of the steering gear.

Evidence for a 5d F-theorem

Renormalization group flows are studied between 5d SCFTs engineered by (p, q) 5-brane webs with large numbers of external 5-branes. A general expression for the free energy on S5 in terms of single-valued trilogarithm functions is derived from their supergravity duals, which are characterized by the 5-brane charges and additional geometric parameters. The additional geometric parameters are fixed by regularity conditions, and we show that the solutions to the regularity conditions extremize a trial free energy. These results are used to survey a large sample of mathcal{O} (105) renormalization group flows between different 5d SCFTs, including Higgs branch flows and flows that preserve the SU(2) R- symmetry. In all cases the free energy changes monotonically towards the infrared, in line with a 5d F -theorem.

Fixed-Point Sampling Strategy for Estimation on Current Measurement Errors in IPMSM Drives

Due to the unbalanced three-phase currents and the torque ripples and speed fluctuations to the drive caused by the current sampling errors of three-phase current sensors and corresponding signal processing circuits, the estimation on current sampling errors is of great importance to eliminate these adverse effects. The observer-based methods, however, present two defects: first, they could increase the computational burden to the drives, thus limiting their practical applications; second, their high dependence on the system speed or position feedback information might degrade the estimation accuracy. To solve these problems, this article proposed a fixed-point sampling method of lower branch flows and three phase-currents, which adopts the relations between the measured currents, rather than any complex algorithm, to estimate the current sampling errors. To coordinate with the proposed strategy, a fixed-point sampling scheme was accordingly rolled out. Compared with the observer-based methods, as a fixed-point one, much applicable to actual digital controllers, it could reduce the computational burden of the drive. Meanwhile, its effectiveness was verified by experimental results on a 1.5-kW IPMSM prototype, which showed accurate estimated current sampling errors and the effectively eliminated torque ripples and speed fluctuations.

Dynamics of flow in a branching channel

Flow in a branched channel is studied experimentally using the PIV technique. The presented study is concentrated on clarifying the dynamical behaviour in individual branches. The 11 branches issuing from the main channel perpendicularly, all channels are of rectangular cross-section. First, the time-mean flow-field is shown, then the flow dynamics is investigated using the OPD method. Flow patterns and frequencies are evaluated in three selected branches. The separated flow in branches exhibits highly dynamical behaviour, which differs substantially in the branches close to the inflow, in the main channel middle and close to its end. The typical topologies and frequencies of the detected quasi-periodical structures in the channel braches are shown in the study. Mostly, the flow-fields are populated by trains of vortices with alternating orientation and saddle-like structures. The flow-field close to the channel walls affects heat transfer process between the wall and fluid.

Moyamoya Syndrome in Post-Transplant Children with Type 1 Neurofibromatosis and Congenital Nephrotic Syndrome

Background: Neurofibromatosis (NF) is a genetic disorder of the nervous system that affects the development and growth of neuronal tissues. It is characterized by the development of malignant and benign tumors of the peripheral nerves and meningiomas, and the clinical manifestations can vary, including cerebral vascular compromise that precipitates symptoms characteristic of Moyamoya syndrome. The behavior of a posttransplant child with type 1 NF who presents with characteristics of Moyamoya syndrome and is a carrier of a WT1 genetic mutation is unknown, which is why the report was made. Case Report: A child with type I NF with a history of cryptorchidism, hypospadias, bilateral sensorineural hearing loss, and chronic renal failure was arising from a congenital nephrotic syndrome due to a WT1 gene mutation at 3 years of age began renal replacement therapy initially with chronic ambulatory peritoneal dialysis and hemodialysis for refractory peritonitis. He underwent two episodes of transient ischemic attack (TIA) characterized by right hemiparesis during hemodialysis therapy and during six months post-kidney transplantation present a similar episode. Studies for other causes were negative, and imaging studies show characteristics of NF-related vasculitis, cortical lesions, and focal lesions in the left frontal subcortical white matter with annular enhancement and subcortical edema in the parasagittal region of the left parietal lobe, as well as a decrease in flow in the cortical branches of the middle cerebral artery were described. After four weeks, the clinical manifestations of hemiparesis completely disappeared without leaving any sequels continuing with the regular immunosuppression of the everolimus, mycophenolate and low dose steroids. Conclusion: These findings are suggestive of small and mediumsized vessel vasculitis compatible with Moyamoya syndrome in child post-transplantation associated with arteriopathy by NF.

ON TWO MODELS RELATED TO THE FLOODING AND DEPOSITION OF THE DON DELTA

The results of modeling changes in the water surface level in the eastern part of the Taganrog Bay and the main Don branches in its delta area are presented. A numerical study of the process of saltwater inflow from the Taganrog Bay to the Don delta has been carried out. The hydrodynamics in the Taganrog Bay, as well as the saltwater transport process, are specified using the corresponding two-layer models. A system of Don arms is presented in the form of a graph, the edges of which correspond to open channels, and the vertices correspond to branching points and end nodes. The flow in the main Don branches is described by the Saint-Venant equation. It is assumed that there is no distributed lateral inflow, and the channel cross-section has a parabolic profile. Saltwater inflow into the arms is described by a one-dimensional transport equation. Boundary conditions are specified for each sleeve. At the branching nodes, conditions are set for the equality of the water levels, as well as the equality of the inflowing and outflowing discharges. The description of the algorithm of the process of flooding/drainage of the Don delta area is given. Considering the values of the depths at the nodes of the flat grid, the cells located in water or on land are determined. A logical array characterizing the type of cells (“water”, “land”) sets the configuration of the entire computational domain. Comparison of the calculation results with the observed values of salinity and water level is carried out.

Расчет параметров режима электрической сети с учетом изменяющегося реактивного сопротивления фазосдвигающего трансформатора

The aim of the work is to study the effect the variation of the phase-shifting transformer (PST) reactance has on the accuracy of calculating its control angle and the electrical network operating parameters obtained as a result of this control. The operating parameters, in particular, active power flows in the electrical circuit branches, are controlled by changing the PST angle; however, in view of the PST design features, this control entails a change of its reactance. Depending on the design features of different PST models and the control angle value, the PST reactance may be constant or vary in a significant range. In connection with a growing use of PSTs in industrially developed countries and with the fact that the first samples of this equipment have emerged in the CIS countries, including Russia, an increased attention is paid to this topic in a number of domestic and foreign publications. In particular, matters concerned with the stability of electric operation modes are considered in view of the fact that the PST reactance depends on its control angle, and the effect this dependence has on the operating parameters is estimated. The necessity of taking into account the varying PST reactance in calculating its control angle for controlling active power flows is considered for different cases. Forced redistribution of active power flows in the closed loops of an electrical network by means of a PST can be used to reduce active power losses and to maintain the required loading of the power lines for various reasons, for example, for commercial purposes or in the case of transit power flows between different countries. In view of the complexity of calculations, constant values of the PST reactance are usually assumed, but this approach is valid not for all types of PST designs. In the majority of PSTs, their reactance varies with increasing the control angle. Therefore, calculations carried out without taking this feature into account may yield a fortiori incorrect correspondence between the control angle and the transformer reactance value. In turn, an error will be introduced in the accuracy of the PST control angle calculations, as well as in the calculations of the operating parameters that should be obtained from the control action.

Collaborative Distributed AC Optimal Power Flow: A Dual Decomposition Based Algorithm

This paper proposes a novel dual decomposition based algorithm that solves the AC optimal power flow (ACOPF) problem in the radial distribution systems and microgrids in acollaborative and distributed manner. The proposed algorithm adopts the second-order cone program relaxed branch flow ACOPF model. In the proposed algorithm, bus-level agents collaboratively solve the global ACOPF problem by iteratively sharing partial variables with its 1-hop neighbors as well as carrying out local scalar computations that are derived using augmented Lagrangian and primal-dual subgradient methods. In addition to the algorithm innovation, this paper proposes two distributed computing platforms, i.e. high performance computing based and hardware-in-the-loop platforms, to validate and evaluate the proposed distributed algorithm. The computationand communication performances of the proposed algorithm are quantified and analyzed over typical IEEE test distribution systems. Experimental results indicate that 1) the proposed collaborative distributed ACOPF solver can be executed on a fully distributed computing structure and yield accurate ACOPF solution; and 2) the proposed distributed algorithm has a low communication overhead.

A Day-Ahead Chance Constrained Volt/Var Control Scheme With Renewable Energy Sources by Novel Scenario Generation Method in Active Distribution Networks

With the integration of huge renewable energy sources (RESs) into active distribution networks, how to address the uncertainty outputs of RESs for the day-ahead volt/var control (VVC) is a significant challenge. This paper presents a chance constrained mixed integer second order cone model to handle the nodal power uncertainties and nonlinear branch flow equations. A direct and fast scenario generation method is proposed by employing the group division method and the seven-step probability distribution model of RESs outputs. An efficient and accurate solution method which only uses few larger probability level scenarios instead of all reserved scenarios is also proposed. Numerical simulations on the IEEE 69 standard system show the superiority of the proposed algorithm over traditional Monte Carlo sampling (MCS)-based methods.

Branch flow distribution approach and its application in the calculation of fractional flow reserve in stenotic coronary artery.

To calculate fractional flow reserve (FFR) based on computed tomography angiography (i.e., FFRCT) by considering the branch flow distribution in the coronary arteries. FFR is the gold standard to diagnose myocardial ischemia caused by coronary stenosis. An accurate and noninvasive method for obtaining total coronary blood flow is needed for the calculation of FFRCT. A mathematical model for estimating the coronary blood flow rate and two approaches for setting the patient-specific flow boundary condition were proposed. Coronary branch flow distribution methods based on a volume-flow approach and a diameter-flow approach were employed for the numerical simulation of FFRCT. The values of simulated FFRCT for 16 patients were compared with their clinically measured FFR. The ratio of total coronary blood flow to cardiac output and the myocardial blood flow under the condition of hyperemia were 16.97% and 4.07 mL/min/g, respectively. The errors of FFRCT compared with clinical data under the volume-flow approach and diameter-flow approach were 10.47% and 11.76%, respectively, the diagnostic accuracies of FFRCT were 65% and 85%, and the consistencies were 95% and 90%. The mathematical model for estimating the coronary blood flow rate and the coronary branch flow distribution method can be applied to calculate the value of clinical noninvasive FFRCT.

Steady State Two-Phase Flow Analysis of Natural Circulation in Hybrid Boiler

In this present works, a generalized approach for the two-phase flow analysis of a natural circulation in hybrid boiler. The model uses the combination of node and loop equations and the Newton Raphson technique for the solution of the set of equations. Loop equations have been developed for each evaporator tube with the unique driving force and pressure drop of the concerned loop. Node equations are mainly developed for common risers and downcomers. A unique connectivity matrix has been used to correlate each branch flow with loop and node equations. The model is validated by a unique indirect method by comparing the actual water level and calculated water level. Experiments have been performed with uniform diameter of tubes in 53 channels circulating loop to find the volume of steam. The model shows good agreement with experimental investigations with a maximum of 3.57% absolute error. The model can be used for the design, analysis, and optimization of the natural circulation network.

Optimal Operation for Integrated Electricity–Heat System with Improved Heat Pump and Storage Model to Enhance Local Energy Utilization

As the need for clean energy increases, massive distributed energy resources are deployed, strengthening the interdependence of multi-carrier energy systems. This has raised concerns on the electricity-heat system’s co-operation for lower operation costs, higher energy efficiency, and higher flexibility. This paper discusses the co-operation of integrated electricity–heat system. In the proposed model, network constraints in both systems are considered to guarantee system operations’ security: the branch flow model is utilized to describe the electricity network, while a convexified model considering variable mass flow and temperature dynamics is adopted to describe the heat network. Additionally, novel models for heat pumps and the stratified water tank are proposed to represent the physical system more accurately. Finally, to preserve the information privacy of separate systems, a distributed algorithm is proposed based on the alternating direction method of multipliers (ADMM). Numerical studies show that the co-operation could provide a more economical and reliable solution than the decoupled operation of the heat network and electricity network. Moreover, the ADMM-based algorithm could derive solutions very close to the optimum provided by centralized optimization.

Analisa Head Loss Akibat Percabangan Pada Sambungan Reducing T Dengan Variasi Diameter Penampang

Head loss is a phenomenon of flow losses in the piping system. Head loss is very detrimental in fluid flow, because it can reduce the efficiency of fluid flow. This study aims to determine how much the value of head losses (hT) is that occurs in the reducing T pipe connection with diameter variations on the pipe branch 0.0254m (1 inch), 0.019m (3/4 inch), 0.0127m (1/2 inch). This research was carried out experimentally by measuring the branching flow of the flowing fluid by recording the time and volume of water that had entered the measuring tank, then reading the preasure on the manometer. The results showed that the increase in flow rate (Q) was directly proportional to the head loss (hT). Flow greatly affects the size of the Reynolds number of the three connections, the lowest total head loss occurred in the 1-inch reducing T pipe connection with a value between 0.1715 m- 0.2814 m and the highest total head loss occurred in the reducing T inch pipe connection with a value between 0.4110 m- 0.5867 m.Keyword: Reynold Numbe, debit, head Loss

Probabilistic Load Flow Calculation Considering Correlation Based on Bayesian Network

This study proposes a Bayesian network model for nonlinear dependence of wind speed, solar irradiation, and load. The probabilistic load flow calculation based on a Bayesian network model can effectively obtain the probability characteristics of probabilistic load flow solutions (such as the probability density function of the bus voltage and branch flow) considering the correlation of random variables. First, the wind speed, solar irradiation, and load time series are converted to random variables by the kernel density estimation method, and the probability values of random variables are obtained. Applying the probability value of a random variable as the input data of the Bayesian network, the correlation model is established through structure learning based on the Monte Carlo Markov chain method and parameter learning based on the maximum-likelihood estimation method. Sampling from the Bayesian network, discrete probability values are obtained, and they are transformed to continuous probability values by interpolation. Then, the correlation samples of random variables are obtained by cumulative probability distribution inverse transformation of continuous probability values. Compared to the C-vine copula method and Latin hypercube sampling with modified alternating projections, the proposed Bayesian network model can better present the nonlinear dependence among wind speed, solar irradiation, and load. Finally, the proposed method is verified by probabilistic load flow calculation of the IEEE 69-bus distribution system.

A Note on Branch Flow Models With Line Shunts

When the shunt elements in the $\Pi$ circuit line model are assumed zero, it has been proved that branch flow models are equivalent to bus injection models and that the second-order cone relaxation of optimal power flow problems on a radial network is exact under certain conditions. In this note we propose a branch flow model that includes nonzero line shunts and prove that the equivalence and the exactness of relaxation continue to hold under essentially the same conditions as for zero shunt elements.

Power flow control in parallel transmission lines based on UPFC

The power flow controlled in the electric power network is one of the main factors that affected the modern power systems development. The unified power flow controller (UPFC) is a FACTS powerful device that can control both active and reactive power flow of parallel transmission lines branches. In this paper, modelling and simulation of active and reactive power flow control in parallel transmission lines using UPFC with adaptive neuro-fuzzy logic is proposed. The mathematical model of UPFC in power flow is also proposed. The results show the ability of UPFC to control the flow of powers components "active and reactive power" in the controlled line and thus the overall power regulated between lines.

Tight Semidefinite Relaxation for Interval Power Flow Model Based on Multi-Dimensional Holomorphic Embedding Method

In order to quantify the impact of uncertainties on power systems resulted from renewable energy, a novel interval power flow method based on multi-dimensional holomorphic embedding method (MDHEM) and tight semidefinite relaxation technique are proposed. First, the MDHEM is used to address the spatial correlation of renewable energy basis, and the analytical expressions of bus voltages and active branch flows are derived. Second, the general interval power flow (IPF) model can be cast as a box constrained polynomial optimization problem. Third, a tight semidefinite relaxation is designed to solve this special optimization problem. Simulation results on several large-scale test systems show the effectiveness and computational tractability of the proposed model.

Blood flow simulations in the pulmonary bifurcation in relation to adult patients with repaired tetralogy of Fallot

Understanding the haemodynamic environment of the pulmonary bifurcation is important in adults with repaired conotruncal congenital heart disease. In these patients, dysfunction of the pulmonary valve and narrowing of the branch pulmonary arteries are common and can have serious clinical consequences. The aim of this study was to numerically investigate the underlying blood flow characteristics in the pulmonary trunk under a range of simplified conditions. For that, an in-depth analysis was conducted in idealised two-dimensional geometries that facilitate parametric investigation of healthy and abnormal conditions. Subtle variations in morphology influenced the haemodynamic environment and wall shear stress distribution. The pressure in the left pulmonary artery was generally higher than that in the right and main arteries, but was markedly reduced in the presence of a local stenosis. Different downstream pressure conditions altered the branch flow ratio, from 50:50% to more realistic 60:40% ratios in the right and left pulmonary artery, respectively. Despite some simplifications, this study highlights some previously undocumented aspects of the flow in bifurcating geometries, by clarifying the role of the stagnation point location on wall shear stress and differential branch pressures. In addition, measurements of the mean pressure ratios in the pulmonary bifurcation are discussed in the context of a new haemodynamic index which could potentially contribute to the assessment of left pulmonary artery stenosis in tetralogy of Fallot patients. Further studies are required to confirm the results in patient-specific models with personalised physiological flow conditions.