Dynamic Load Flow Research Articles

Numerical investigation on thermal-hydraulic performance of cryogenic LNG in sinusoidal channel with airfoil fins under marine dynamic load

For floating liquefied natural gas (FLNG), printed circuit heat exchanger (PCHE) is an optimal choice owing to its compactness and large temperature difference heat transfer in a short time. In this study, a novel sinusoidal channel configuration was established which is with airfoil fins, and its thermal-hydraulic performance was numerically studied. Meanwhile, the effects of marine dynamic load and inlet mass flow rate (IMFR) on the novel configuration were studied. The cold fluid was supercritical liquefied natural gas (S-LNG) at 113.15 K and 32 MPa, while the hot fluid was ethylene glycol at 293.15 K and 0.1 MPa. The pressures are given as relative pressures. The results show that the novel configuration has better comprehensive performance. The local turbulent kinetic energy of the novel configuration is improved by about 19.78%. The temperature and velocity uniformity are improved. Marine dynamic load deteriorates the comprehensive performance of the novel configuration.

Navigating Power Paths: Assessing Line Losses in the IEEE 14-Bus System amidst Electric Vehicle and Renewable Energy Integration

Purpose: This study thoroughly investigates the impacts of Electric Vehicles (EVs) and Renewable Energy Sources (RES) on line losses within the IEEE 14-Bus System, with a particular emphasis on addressing challenges and optimizing power system planning. The primary purpose of this study is to assess and understand the intricate relationships between EVs, RES, and line losses within the IEEE 14-Bus System. The research aims to provide insights that contribute to the development of tailored strategies in power system planning, addressing challenges posed by EV adoption and RES integration. By exploring the impact on grid efficiency, sustainability, and reliability, the study aims to guide future power system planners in optimizing the integration of EVs and RES.
 Materials and Methods: The study utilizes load flow analysis, specifically the Newton-Raphson method, to model and simulate scenarios reflecting EV charging and discharging dynamics alongside intermittent RES integration within the IEEE 14-Bus System. A 24-hour dynamic load flow analysis is conducted to capture the diverse and dynamic impacts under varying load conditions. This comprehensive approach allows for a detailed assessment of line losses in the presence of EVs and RES.
 Findings: The study reveals nuanced impacts, indicating higher EV adoption and increased RES integration result in notable escalations in line losses. This highlights challenges associated with grid efficiency, emphasizing the need for tailored strategies in power system planning.
 Implications to Theory, Practice and Policy: The study advances theoretical understanding of dynamic interactions between EVs, RES, and power systems. In practice, it underscores the importance of adaptive control mechanisms and optimized strategies for accommodating EVs and RES while minimizing line losses. On a policy level, the findings suggest the need for regulatory frameworks incentivizing sustainable energy practices and technological research to mitigate challenges posed by EV adoption and RES integration.

Scheduling the charging and discharging events of electric vehicles for quasi dynamic load flow calculations of a low-voltage distribution grid with regard to stochastic behavior and grid requirements

In this study, a novel bidirectional Vehicle-to-Grid (V2G) scheduling application is presented to predict Electric Vehicle (EV) charging/discharging based on the user’s stochastic behavior and wishes, as well as the grid operator’s demand. The proposed application takes into account factors such as the initial battery State of Charge (SOC), user’s arrival time, user’s desired minimum and maximum SOC, EV unplugged time, peak-hour period, and the option of applying the grid operator control over EV charging start time. The effectiveness of the proposed application is then evaluated using various case studies in a single residential feeder of the low-voltage (LV) distribution network example in DIgSILENT PowerFactory. The simulation results indicate that appropriate management of EV charging/discharging through V2G technology can mitigate their negative effects on the LV distribution network, resulting in improved load profiles, voltage profiles, distribution lines loading, and power losses.

Cascading Failure Analysis of Cyber–Physical Power Systems Considering Routing Strategy

In this brief, we develop a novel model to study the cascading failure in cyber-physical power systems. We use a discrete packet traffic model that follows a specific routing strategy to describe the dynamic data transmission in the information network. Moreover, the dynamic load flow model that takes into account the power-frequency characteristics of loads and generators is applied to describe the dynamic flow process of the power network. Our proposed model allows to consider the impacts of data packet transmission failures and voltage-related failures in the cascading process. Furthermore, we analyze the effects of routing strategy and information network topology on the severity of cascading failure. Simulation results verify the applicability of the proposed model and reveal the way in which routing strategy affects the cascading failure of cyber-coupled systems. In addition, we show that when the main hub in the information network is used as a dispatching center, a spreadout degree distribution of the information network reduces the severity of cascading failure in the cyber-coupled system.

Evaluating Congestion Management of Power System considering the Demand Response Program and Distributed Generation

With increasing the energy demand, the optimal and safe operation of power systems is the main challenge for engineers. Thus, a technique for the optimal implementation of demand response programs (DRPs), installation of distributed generation (DG) with power transmission distribution factors, and DC dynamic load flow is presented in this paper. In fact, finding the optimal time execution of DRPs and the bus for installing wind units with its probabilistic effects is considered. In this model, the congestion is decreased and the available transfer capability (ATC) rates are significantly improved. According to various types of price-based DRPs, the customers motivate to change their utilization models by shifting the price of electricity at different times. Finally, the proposed model is evaluated on the well-known IEEE 39-bus New England power system. The numerical results show the efficiency of the proposed method because, after its application, the available transmissibility values in the critical buses have significantly increased. At the same time, system peak loads, total system costs, and losses are reduced, and the voltage profile also shows a significant improvement. Totally, numerical results demonstrate that using the recommended algorithm, system loss and cost decrease by 9 percent and $4472.

Optimal operations of transformers in railway systems with different transformer operation modes and different headway intervals

This paper presents an approach to the optimal operations of transformers in railway systems. Railway systems are supplied from bulk supply substations that consist of two transformers that are connected in the main-tie-main configuration. There are three operation modes for these transformers, namely non-parallel mode, parallel mode, and single transformer mode. Due to the fact that the traction loads are inherently dynamic, the optimal operation mode for the transformers requires a thorough simulation by including the train dynamics and train schedules. This paper aims to identify the optimal operation mode of the transformers under different headway intervals. In this study, the railway traction power system of the Mass Rapid Transit 2 (MRT2) in Malaysia is modeled and simulated in ETAP-Etrax Software with the dynamic load flow analysis to achieve an accurate estimation of transformer losses under the three transformer operation modes and different headway intervals. The results show that the parallel mode has lower transformer loss than that of non-parallel mode for all the headway intervals. It is also found that the single transformer mode has the lowest transformer losses for headway intervals of 5 min 48 s and above. Although the percentage of transformer loss reduction and the headway interval margin for optimal operation of single transformer mode may differ, this approach can also be applied to other DC railway systems.

Optimal Power Flow in Uncertain Power System

Due to the increasing demand of electricity in ever-growing electricity market, it is necessary to observe the nature of load and map the effects of load uncertainties on the operation of power system. These uncertainties have also led to voltage instability which is sooner or later considered to be a fundamental cause of blackouts. The distributed generation sources can also be regarded as the source of uncertainties at the load ends of power systems. Along with the load uncertainties, wind turbine generation (WTG) and solar plants have also been used as a source of uncertainties in this paper. The load uncertainties have been incorporated in the system by designing a dynamic load flow program. Corresponding to all uncertain inputs critical case has been identified by the singularity property of load flow jacobian. For the optimal load flow a multi-objective optimization problem aiming to constrained objective function to enhance voltage stability, improve stability index value, reduce system losses and increase reactive reserve margins at generator buses has been formulated. Black hole algorithm has been used to achieve the optimal values of control variables and hence optimal load flow. The aforementioned problem has been tested on standard IEEE-14 bus system.

Probabilistic Load Flow Algorithm of Distribution Networks with Distributed Generators and Electric Vehicles Integration

Probabilistic Load Flow (PLF) calculations are important tools for analysis of the steady-state operation of electrical energy networks, especially for electrical energy distribution networks with large-scale distributed generators (DGs) and electric vehicle (EV) integration. Traditional PLF has used the Cumulant Method (CM) and Latin Hypercube Sampling (LHS) method. However, traditional CM requires that each input variable be independent of one another, and the Cholesky decomposition adopted by the traditional LHS has limitations in that it is only applicable for positive definite matrices. To solve these problems, taking into account the Q-MCS theory of LHS, this paper proposes a CM PLF algorithm based on improved LHS (ILHS-CM). The cumulants of the input variables are obtained based on sampling results. The probability distribution of the output variables is obtained according to the Gram-Charlier series expansion. Moreover, DGs, such as wind turbines, photovoltaic (PV) arrays, and EVs integrated into the electrical energy distribution networks are comprehensively considered, including correlation analysis and dynamic load flow analysis for EV-coordinated charging. Four scenarios are analyzed based on the IEEE-30 node network, including with/without DGs and EVs, error analysis and performance evaluation of the proposed algorithm, correlation analysis of DGs and EVs, and dynamic load flow analysis with EV integration. The results presented in this paper demonstrate the effectiveness, accuracy, and practicability of the proposed algorithm.

A Novel Dynamic Index of Voltage Instability Expectation with Power System Contingency

This paper proposes a novel dynamic voltage instability expectation index which takes into account dynamic voltage stability characteristics, the long-term phenomena and probability state of power system contingency. This index is a meter to measure the general robust power system under critical cases which are identified by contingency analysis. The critical contingencies are precisely analyzed by steady-state power load flow in perturbations to figure out violation cases, the weakness of the power system. The probability states of each of violation cases are calculated through availability and unavailability values of devices. The degree of voltage instability is estimated newly by the smallest determinant of dynamic load flow Jacobian matrix in evolution time of power system simulation. The variables of dynamic devices such as under load tap changer of the transformer, excitation limiters of generator unit, affected on a long-term characteristic of the power system, are considered in dynamic load flow Jacobian matrix. Combining the voltage instability rate and the probability state, a novel index, namely voltage instability expectation in dynamic index, is proposed. This index reflects the mutual correlation between the voltage instability rate and probable contingency cases which result in either voltage violation, overload flow, or voltage instability. The new index is demonstrated in IEE 9-bus test system and actual Vietnam power system. It should be a new measure to make a decision of transmission system expansion planning.

Chance-Constrained Real-Time Dispatch with Renewable Uncertainty Based on Dynamic Load Flow

In this paper, a comprehensive real-time dispatch model considering renewable uncertainty based on dynamic load flow (DLF) is proposed. Through DLF, the primary and secondary frequency regulation amount caused by the variation of renewable energy as well as the line flow when primary and secondary regulation are deployed can be obtained easily. Not only the frequency constraints, but also the regular constraints like generator production limits and line flow limits are respected under both primary and secondary frequency regulation. To solve the dispatch problem with renewable uncertainty, chance-constrained programming based on cumulants and Cornish-fisher expansions (CCP-CMCF) is adopted to get the probability of holding the chance constraints and then the real-time dispatch model can be transformed into a quadratic programming. The simulation results show that the dispatch model proposed in this paper can deal with both primary and secondary regulation well and has a fast computation speed.

Probabilistic dynamic load flow with correlated wind sources

Correlation among different wind sources brings great challenge to probabilistic load flow (PLF) calculation, especially when different wind sources are not normal jointed. In addition, the fluctuation of wind energy output will aggravate the variation of the system unbalanced power, which makes it inappropriate to allocate all unbalanced power to a slack bus. In order to overcome the drawbacks of the existing methods, a probabilistic dynamic load flow (PDLF) model based on the joint‐moments method (JMM) is proposed. Different from the existing approaches, JMM can deal with different correlations among wind sources, which do not limit to normal jointed ones. Furthermore, this model can take the influence of the static power–frequency characteristic (SPFC) of generators and load into consideration, through which the probability distribution of the system frequency can also be obtained. The proposed algorithm was proved to be effective and accurate by applying it to the IEEE 30‐bus system and the IEEE 300‐bus system. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Dynamic optimal power flow of combined heat and power system with Valve-point effect using Krill Herd algorithm

Combined heat and power (CHP) plant generates electrical power as well as heat energy in a single process yielding more than 80% overall efficiency and reduces emission level significantly. The production of power and heat in CHP unit is mutually dependent on each other and is constrained by the feasible operating region. This paper presents a maiden formulation as well as a method for solution of the dynamic optimal load flow problem in power system involving CHP. A bio-inspired Krill Herd Algorithm has been utilized for minimization of cost of production, while maintaining voltage level at all buses and satisfying all other constraints. Herding behavior of Krill individuals is the basis on which this algorithm works. The distance of each Krill individual from food and the highest density of swarm are considered as the fitness function. Two test systems, one with 6 generators and the other with 19 generators have been considered to verify the effectiveness of this algorithm. Both the systems include a number of CHP units and have been adapted from IEEE standard Test Systems. The test results are encouraging.

Evaluation of Measures to Operate Urban Low Voltage Grids Considering Future PV Expansion

Abstract: The Swiss federal government set forth its energy policy, titled ”Energiestrategie 2050,” in which photovoltaics (PV) production would reach 20% of the total yearly electrical energy production by the year 2050. Such a drastic expansion rate of PV and the resulting excess energy thereof, however, can lead to technical challenges for the infrastructure of the power system. In this paper, the impact of the future PV penetration on a real urban low voltage (LV) area is presented. To this end, two PV scenarios are devised and implemented, and quasi dynamic load flow simulations are conducted for every fifteen minutes interval of a whole year. To generate the input data, a load profile generator is developed based on smart meter measurement data. It is concluded that the examined urban area appears to be prepared for a certain amount of further PV integration as there were no violations detected for the medium PV production scenario (43% of the total consumption in the area). However, for the maximum PV penetration scenario to be implemented, violations such as over voltage and transformer overloading are detected. To resolve these issues, different mitigation measures such as battery energy storage system, active power curtailment and short-term overloading of the transformer are implemented and examined with the aid of appropriate mathematical models. As a result, at least 20% of the PV energy needs to be stored, curtailed or used by demand side management, in order to run the low voltage grid as it is. In a further work, an intelligent combination of different measures could be examined to fully utilize the excess energy.

Improvement of Regression Simulation in Fluvial Sediment Loads

In the mid-Atlantic region of the United States, sediment loads from stream runoff generally change more rapidly in the rising limb than in the falling limb of a storm hydrograph. As a result, sediment load reaches its peak prior to flow peak, an observation known as clockwise hysteresis. This dynamic load–flow relationship is poorly reproduced by the existing multivariate linear regression models. This paper explores regressors that attempt to incorporate observed features in a statistical model and thus improve load estimates. These included inverse discharge and flow-change regressors. The load estimates using three regression models for eight rivers are compared, and recommended regression equations are proposed.

Structure-preserved power-frequency slow dynamics simulation of interconnected ac/dc power systems with AGC consideration

A structure-preserved power-frequency slow dynamics simulation model is suggested for interconnected ac/dc power systems with automatic generation control (AGC) consideration, which will be applied to study relevant emergency control in future so that the bulk system viability crisis caused by load-frequency slow dynamics can be released. In the model, the network structure of interconnected power systems is entirely preserved, and the multi-area dynamic load flow (DLF) is developed for simulation. The generator speed governor and rotor dynamics, load-frequency characteristics, simplified models for high voltage direct current (HVDC) transmission and flexible ac transmission systems (FACTS) device thyristor controlled series capacitor (TCSC) suitable for long-term dynamics are considered with their AGC interfaces kept for future emergency-AGC study. However, at this stage, the sub-problem of reactive power and voltage is neglected for modelling simplicity and dc load flow is thus used for network solution. The concept of area centre of inertia (ACOI) is used based on the assumption of uniform frequency in each control area similar to that of the conventional single-area DLF calculation. The application of ACOI concept is attractive because the signal can be obtained from wide-area measurement systems (WAMSs) in real time and used to enhance long-term frequency stability through advanced control in future. The computer test results from 2-area 4-machine and IEEE 30-bus power systems demonstrated the validity and effectiveness of the suggested model and corresponding algorithm.

Lead time selection and the behaviour of work flow in job shops

Few studies in job shop scheduling consider dynamic shop load and work flow issues. However, these issues are of importance to management responsible for shop floor control. This research investigates relevant internal performance measures and their relationship to external measures. As well, a new dispatching mechanism that seeks to even out the distribution of jobs in queue is investigated. Results show that a shop load balance index, which takes both shop load levels and load variability into account, has a very strong relationship to the lead times required to maintain a desired level of delivery performance. It appears that good performance based on internal measures is consistent with good performance based on external measures.

Fast Simulation of Power System Mid-Term Dynamics

Mid-term analysis of large scale power systems requires efficient simulation techniques that involve model reduction of their basic components. This paper outlines a quasi-stationary dynamic load flow algorithm that permits a straightforward computation of the new equilibrium point after each operational or topological variation. Results from its application to a realistic model of an established test power system used by CIGRE. task forces TF 38.02.08 and TF 38.02.11 are presented and discussed.

Dynamic load flow including generator voltage variation

A long-term dynamic load flow that takes generator voltage fluctuations into consideration is presented. P Q decoupling and modified susceplance matrices are applied in the formulation of the method. A model for generator reactive power and voltage dynamics is derived and incorporated in the load flow equations. The proposed dynamic load flow can improve the accuracy of power system long-term dynamic simulation, without a loss in computation speed.

Dynamic Load Flow Technique for Power System Simulators

This paper presents a dynamic load flow technique for power system simulators. The approach presented can be applied to a system when there is a net accelerating or decelerating power in the system. It possesses all the attractive features and basic structure of the normal fast decoupled method, and it does not depend on the selected reference bus. The modifications to the standard fast decoupled power flow algorithm are derived, and power system simulator implementation considerations are discussed. The algorithm has been tested on standard IEEE test cases and on a metropolitan utility 559 bus model. A numerical example of the above algorithm on the 559 test case is presented which demonstrates convergence characteristics and computation requirements of the proposed algorithm. These results are compared with those of normal fast decoupled load flow.

A Dynamic Power System Model With Graded Precision for Fast Extraction of Pertinent Load Flow Information

In many situations of power system restoration or emergency control load flow, often dynamic load flow, results are needed at a time scale which makes regular load flow computations impractical. In this paper a low order dynamic model is introduced which retains fully detailed and precise representation of the critical components (such as strong backbone lines like EHV or weak tie lines) where the interest is focused and reduces the detail of representation of other parts of the system gradually with their distance from the spotlighted sections where details are needed. The result is a low order and hence very fast computation with not only detailed but also quite precise results for those parts of the system which are critical. This approach is very flexible, it can be used to compute tie line load and frequency swings on an interconnection of areas or static loads on the tie lines of such a system affecting third parties in a power trading situation. It can be used to compute precisely and fast the EHV system loads or any combinations of such elements. The operator is quite free to choose what should be represented in precise detail.