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In this revision, it is possible to find different examples of publicly available MatLab Graphical User Interfaces (GUI’s) developed to help researchers and students that have to deal with the challenging problem phase equilibrium data correlation (e.g. LLE, LVE). These examples are: GMcal_TieLinesLL: http://hdl.handle.net/10045/51725 GMcal_TieLinesVL: http://hdl.handle.net/10045/122857 Boundaries_LL_NRTL: http://hdl.handle.net/10045/121471 ParamIni_LL_NRTL: http://hdl.handle.net/10045/130017

The high temperature superconducting (HTS) cable can be used as a low-voltage tie line between substations for its characteristic of high currentdensity. In this way, the remaining capacity on the low-voltage side of the transformer can be fully utilized. Moreover, The HTS cable can run in parallel with the original tie line, forming an electromagnetic ring network, to ensure the power supply of important loads. However, the short circuit current of the distribution network is large, and the electromagnetic ring network operation results in the quench of HTS cable when the short circuit fault is outside the HTS cable. It is important to ensure the safety of HTS cable under various short circuit faults. To ensure the safe operation of HTS cable in Shenzhen Power Grid, this paper built a distribution network model with HTS cable in Matlab/Simulink. The fault current and thermal process in different fault situation were analyzed. The design of fault current limiter (FCL) which is composed of the resistive superconducting fault current limiter (R-SFCL) and a shunt reactor was completed. The model of R-SFCL using R - Q method is build, and the effectiveness of the R-SFCL design is verified.

Sectionalizing switches (SSs) and tie lines play essential roles in reducing the duration of customer interruptions in electricity distribution networks. The effectiveness of such assets is strongly influenced by their placement in the grid. Operation of SSs and tie lines is also inherently interdependent. Due to the structural complexities regarding the mathematical modeling of such dependencies, optimization of the planning and operation of switches and tie lines has typically required either leveraging heuristic and metaheuristic approaches or oversimplifying the network topology. To tackle such issues, this paper presents a computationally-efficient model for reliability-oriented concurrent switch and tie line placement in distribution networks with complex topologies. The proposed model can be applied to grids with several tie lines and laterals per feeder, and yields the optimal location of tie lines, type of tie switches, namely manual or remote-controlled, and the location and type of SSs. Being cast as a mixed integer linear programming (MILP) problem, the model can be efficiently solved with guaranteed convergence to global optimality using off-the-shelf optimization software. The efficiency and scalability of the proposed model are demonstrated through implementation on five networks and the outcomes are thoroughly discussed.

With increasing demand for load, the generation of electrical power should also be increased and the interconnection of the network must be carried out in order to ensure the quality of the power generated and to feed the load. Load Frequency control (LFC) of three unrivalled interconnected thermal, hydro and solar thermal power plants has been designed with PI, PID and Fuzzy Logic controllers. AGC is used to stabilize disturbances in the power system with the use of different controllers. Classical conventional and Smart controllers are used as additional controllers independently to improve the performance of the Load Frequency Control (LFC) system by suppressing the oscillation of three uneven area systems, including Solar Thermal, Hydro and Nuclear Thermal, Systems in Area 1, 2 and 3 respectively. The simulation result shows that Fuzzy controller gives excellent dynamic time-setting responses and effectively mitigates oscillations against both step load and random disturbances, PID controllers are simple and cost-effective. The system using three generation sources is used and simulated in MATLAB2015.

This paper demonstrates a Power Hardware-in-the-Loop (PHIL) implementation of a decentralized optimal power flow (D-OPF) algorithm embedded into the operations of two microgrids connected by a tie line. To integrate the static behavior of the optimization model, a two layer control architecture is introduced. Underneath the dispatch commands from the D-OPF, a primary control scheme provides instantaneous reaction to the load dynamics. This setup is tested in the PHIL environment of the CoSES Lab in TU Munich. In the experiment, the two microgrids cooperatively optimize their operation through an ADMM based unbalanced D-OPF. The operations is then benchmarked against the exclusive use of primary control, without D-OPF. The decentralized approach outperforms, but also shows minor inefficiencies of integrating optimization methods into the real-time operation of the system.

A tie-line security region provides all possible tie-line power injections with which constraints in a regional network will not be violated. With the high penetration of renewables, a sharp increase or decrease of renewable power requires a good depiction of the tie-line security region considering time coupling. However, the tie-line power security region with time coupling is a high-dimension polytope, which leads to a considerable computational burden. This paper presents a fast algorithm to approximate the original high-dimension tie-line security region considering time coupling. A few lower-dimension polytopes associated with combinations of different periods are calculated for the approximation. An evaluation method with clear physical explanations is established to measure the accuracy of the approximation. The method converts the evaluation to two linear programming problems based on the mathematical relationship between optimal points and polytope vertices. Under a Monte Carlo framework, the statistical analysis is employed to measure the accuracy using five presented indices. The performance of the proposed methods is verified by the case studies on the IEEE 118-bus test system and a 661-bus utility system.

This article deals with the Automatic Generation Control (AGC) mechanism for an interconnected, deregulated hybrid power system. The physical generation constraints such as boiler dynamics, governor dead band (GDB) and generation rate constraints (GRC) are included for a more realistic approach. The integration of distributed generation (DG) systems is also considered to match with present scenario. The intermittency nature of the DGs ruins the system's inertia and dynamic behaviour. A novel cascaded fractional order controller configuration 2-DOF (FOPIλDN)-PDN is proposed for the AGC mechanism and a new quasi opposition based volleyball premier league (QVPL) algorithm is employed to optimize the controller gains. On the other hand, the inertia emulation strategy (IES) based modified HVDC tie-line is used parallel to the AC tie-line to retrace the power system's inertia. The impact of the proposed controller and IES based modified HVDC tie-line has been analysed by subjecting to several case studies. The effectiveness of the QVPL based proposed controller has also been tested by comparing it with the previously published works on the same platform.

The inverter’s end of ultra high voltage DC (UHVDC) system under hierarchical connection mode (HCM) is connected to 500 and 1000 kV AC buses through high end converter and low end converter transformers, respectively. The two AC buses are interconnected via coupling transformer and the tie line. This complex structure of interconnection at inverter’s end can make the understanding unclear about each AC system’s strength of UHVDC-HCM. Therefore, this paper covers the system’s strength evaluation by developing the “Hierarchical mode effective short circuit ratio” (HMESCR) index. The HMESCR incorporates the impact of neighborhood AC networks, impedance of coupling transformer, the tie line and strength of the objective AC network. Based on the proposed index, an equivalent model for UHVDC-HCM system is developed. An equivalent model is verified under the steady state conditions such as maximum available power and the transient conditions such as commutation failure immunity index under AC faults. In addition, three different cases are considered in order to get the in-depth and comparative performance analysis of an equivalent model with UHVDC-HCM system. MATLAB and PSCAD/EMTDC are used as analysis tools for illustrating the steady state and transient state conditions. The analysis indicates that the presented equivalent model has similar behavior as UHVDC-HCM system under both steady state and transient state conditions, which verifies the accuracy of proposed index in assessing the strength of both AC systems of UHVDC-HCM.

Interconnection of two autonomous swarm grids (DC clusters) which are designed for energy access can increase power supply availability for power hungry appliances such as water pumps. Here, a surplus or a deficit power in one cluster is balanced by a second cluster through power exchange. Usually, the clusters are connected by a tie line if bus voltages in both clusters are equal and constant. If the bus voltages are different and constant, a single converter is used to interconnect the clusters and to control the power flow between them. In both interconnections, power flow is triggered by bus voltage variations from their constant values. However, if the bus voltages are different and are not constant, the coordination of the power exchange between the clusters is a challenge. In this paper, two buck-boost converters are proposed to interconnect the clusters that have different and unregulated bus voltages. To control the power exchange while reducing transmission line loss, a decentralized control approach which is composed of a voltage droop control method and a mid-point voltage control method is proposed. Simulations of two interconnected clusters carried out in MATLAB/Simulink software show how the proposed control method can efficiently coordinate the power exchange.

Overhead transmission line faults are mostly single‐phase grounding faults, and to ensure the power supply reliability of photovoltaic power plants in the cases of tie line transient faults, a feasible solution is to employ the single‐phase reclosing. However, for the single‐phase reclosing of the tie line, photovoltaic power source may face the over‐voltage problem during the non‐full phase operation, which will seriously affect the success rate of the single‐phase reclosing. This paper, according to different non‐full phase operation control strategies of photovoltaic power source, establishes the corresponding sequence network analysis models, and proposes the theoretical calculation method of non‐full phase operation voltage, which takes account of different neutral point grounding modes of step‐up transformer and different load levels. Meanwhile, the closing impulse problem of the single‐phase reclosing is discussed. The correctness of the theoretical method is verified by digital simulation results. On this basis, the applicable scope and application suggestions of the single‐phase reclosing are given. The research conclusions can provide important guidance and reference for the application of single‐phase reclosing technology in tie line of renewable energy power plant.

Unlike traditional microgrids, Provisional Microgrid (PMG) utilizes only renewable generation and small energy storage units; thus, it does not have an inherent self‐islanding capability and instead, relies on importing power from any coupled microgrid (CMG) for islanding purposes. Therefore, assuring adequate power sharing between interconnected provisional and coupled MGs is crucial for assuring self‐islanding capability and reliable operation. The optimal power that can be transferred between the coupled MG and the PMG is mainly restricted by the size of the interconnecting tie‐line; hence, determining the tie‐line optimal size becomes a crucial task that must be tackled. Furthermore, the amount of power transferred is significantly influenced by the flexibility level of each microgrid. Since battery storage systems (BSS) is the main source of flexibility in PMGs, it becomes also vital to obtain the optimal size of the BSS for planning islanded PMG system. This paper presents an optimization model to jointly determine the optimal size of the BSS in each MG and the tie‐line size to assure optimal power sharing and minimum system cost (tie‐line investment cost, BSS investment cost, and interconnected system’s operation cost). Numerical results demonstrate the effectiveness of the proposed model.

Multi-area economic dispatch (MAED) deals with the optimal dispatch of multiple areas. MAED with tie line constraints, transmission losses, multiple fuel option and valve point effects is considered as a large scale non-linear optimization problem. An accurate optimization method to solve this problem is of great interest. However the conventional particle swarm optimization (PSO) has been applied to solve many optimization problems with success, it suffers from some drawbacks. Therefore, chaotic PSO (CPSO) has been used to treat these drawbacks. Choosing the parameters of CPSO has a great effect on its performance. So, a hybrid CPSO and genetic algorithm (HCPSOGA) method is employed in this paper to solve this problem. The hybrid method is derived by combining CPSO and GA where GA is used to optimize the parameters of CPSO. To show the effectiveness of the hybrid method, two test systems are used. The results show the superiority of the hybrid method over some published methods based on same test systems.

In this study, a maiden application of cascade proportional–integral–derivative with filter (PIDF) and one plus fractional-order derivative (1+FOD), i.e. PIDF(1+FOD) controller is proposed for the load frequency control mechanism. The main purpose of the cascade and fractional order controller is to increase the degree of freedom and reject the disturbances faster. A novel attempt has also been made to model a static synchronous series compensator (SSSC) with AC tie-line and HVDC tie-line. Here SSSC and HVDC tie-line are used to regulate and increase the power transfer capabilities between interconnected areas. Furthermore stored energy in the HVDC tie-line is utilised to improve the system dynamics by inertia emulation control strategy. An evolutionary salp swarm algorithm-based optimisation technique is adopted to optimise control parameters. The performance of the proposed controller is tested on a two-area hydro-thermal interconnected power system in deregulated environment. First, the effectiveness AC–DC-SSSC tie line is shown over AC-SSSC and alone AC tie-line with proposed PIDF(1+FOD) controller followed by the supremacy of proposed PIDF(1+FOD) over classical controllers. Finally, sensitivity is analysed by variation in system parameters, which shows the robustness of the proposed controller.

The short-circuit current characteristics fed by the renewable energy source are quite different from those of the synchronous generator, which may lead to the phase selection error or failure of the traditional fault phase selection component, and then affect the operating reliability of the distance protection and the automatic reclosing. This study analyses the existing issues in the application of traditional phase selection components to the tie-line of renewable energy power, according to the fault characteristics of different renewable energy sources such as photovoltaic power source, direct-drive wind turbine and doubly-fed wind turbine. Furthermore, the sequence voltage expressions in the case of different types of faults, which takes account of the influence of the renewable energy type and the transition resistance, are theoretically derived. Hereby, a novel phase selection method by using sequence-voltage phase comparison and phase-voltage amplitude comparison is proposed. This method is applicable to the tie line of different types of renewable energy power station, and possesses the superiorities of high reliability and strong tolerance towards large fault transition resistance. Digital simulation results verify the favourable performance of the proposed method.

The identification of a tie-line power transmission region is crucial for the secure operation of interconnected power grids. The characterization of a tie-line power transmission region with regional operational constraints is inherently a multi-parametric programming problem, which greatly suffers from a heavy computational burden. In this paper, we propose a fast boundary search approach to efficiently characterize the tie-line power transmission region in AC/DC hybrid grids. The multi-parametric programming method is improved in the following three aspects: (1) the search direction is fixed along the boundary of a region, which avoids the search inside a region; (2) the abundant search of subregions that share a boundary facet is avoided; and (3) a fast guess of the Karush-Kuhn-Tucker (KKT) condition is presented, which reduces the number of optimization calculations. Furthermore, an expansion strategy is presented to enlarge the tie-line power transmission region via quantifying the impact of system parameters on the transmission region. Simulations based on the IEEE 118-bus test system and a 661-bus utility system show that (1) the proposed method can be over 30 times faster than existing methods and (2) the proposed method successfully expands the tie-line power transmission region by identifying the key parameters.

An identification algorithm is proposed for generator outages in external systems given tie-line flow measurements and pre-outage linear sensitivity factors. The problem is challenging due to limited information available to operators in interconnected systems. To overcome the underdetermined nature of the problem (the number of tie-line measurements is smaller than the number of generators), a clustering method based on pivoted QR decomposition is implemented so that the outage location can be identified to the area of origination. Two test systems, the 68-bus New England system and the 500-bus synthetic system, were used for validation. The results demonstrate that with limited knowledge of the external system, the algorithm is able to identify the correct generator cluster in all cases. Another advantage of the proposed algorithm is its high efficiency, which enables detection within sub-milliseconds. In addition, an estimation of the cluster injection change is also provided by the algorithm.

The present article addresses robust control of both frequency and tie line power of a two area six unit diverse energy source based non linear power network. In large interconnected network, deviation in frequency and tie line power occurs due to uncertainty in load variation. In order to keep both frequency and tie line power flow to their nominal values, Automatic Generation Control (AGC) is required. AGC aims proper balance between power generation and electrical demand. In AGC concern the present article proposes a robust type-II fuzzy PID controller to diminish all local error signals (change in frequency ‘Δf’ and change in tie line power flow ‘ΔPtie’) of each control area. Controller tries to keep network frequency and interline power flow within nominal values. To justify supremacy of proposed type-II fuzzy controller a comparative study with fuzzy type-I and conventional PID controllers has been carried out for this analysis. To obtain precious gain parameters of above implemented controllers, a novel hybridized Gray Wolf Optimization and Sine Cosine algorithm (hyGWO-SCA) has been proposed for the study. In fact of this to show supremacy of proposed hyGWO-SCA technique, its performances are compared with host GWO and SCA technique. To verify the robust nature of type-II fuzzy PID controller the work goes through different sensitive analysis. Overall critical assessment of this study concludes, proposed hyGWO-SCA tuned type-II fuzzy controller exhibits superior performance in regard of AGC analysis. Finally the work is extended to four area eight unit interconnected system. Keywords: Automatic Generation Control (AGC), Integral of Time multiplied with Absolute Error (ITAE), Sine cosine algorithm (SCA), Gray wolf optimizer (GWO), Type-II fuzzy controller, Generation rate constraint (GRC)

In this paper, a high-voltage direct current (HVDC) tie-line has been accurately modeled and proposed for multi-area interconnected power system to enhance load frequency control and automatic generation control (AGC). HVDC tie-line has been modeled based on a simple first-order transfer function for AGC system. Time constant of this transfer function indicates the required time by HVDC to set DC current because of load perturbation in multi-area interconnected power systems. It is worth mentioning that the inexact and very simple model of HVDC-line cannot yield a reliable and correct response. Hence, an accurate and interpretable model is proposed for HVDC-link to control the AGC system. To verify the accuracy of the proposed model, it has been analytically compared with the conventional HVDC model. The integrated multi-area power system has also implemented the inertia emulation controller technique which enables AGC system to tackle the accumulated energy in HVDC-line’s capacitance.

The peak–valley difference of power grid will be enlarged significantly with the increasing number of integrated energy systems (IESs) connecting to power grids, which may cause a high operation cost and voltage violations. This study proposes an IES configuration method considering the peak–valley difference of the tie line between IES and power grid. An optimal configuration model of IES is established, which takes the sum of the annual operating cost of the power grid and annual cost of IES as objectives, while the tie line transmission power between IES and power grid are considered as constraints. The elite energy reserve genetic algorithm and branch and bound method are used to solve the proposed model, while the optimal power flow is used to calculate the grid operation cost under a given transmission power of the tie line. The simulation results of an improved IEEE30 node system verify the validity of the proposed method.

The quasi-ternary TiB2-CrB2-WB2 system has been studied up to 2300 °C by means of hot-pressing, SPS and pressureless dilatometry. Liquid phase is generated by two binary eutectics at the TiB2-WB2 edge at 2230 ± 30 °C (e1) and at the CrB2-WB2 edge at 1965 °C (e2). A large homogeneity range of a (Ti,W,Cr)B2 solid solution has been noticed. A new ternary γ-phase emerges from a critical tie line between (W,Cr,Ti)2B4 and α-(Ti,W,Cr)B2 solid solution at 1950 °C, spreads slightly into both the WB2 and CrB2 direction and decomposes by the peritectic reaction P: γ ⇆ α-(Ti,Cr,W)B2 + (W,Cr,Ti)2B4 + Liquid at 2170 ± 30 °C. γ reacts with the CrB2-WB2-rich liquid according to the transition equilibrium T: δ-(Ti,Cr,W)B2 + (W,Cr,Ti)2B4 ⇆ γ + Liquid at 2050 °C. The γ-phase is characterized by broad 00 l x-ray reflections which implies a layerwise accumulation and differentiation of Cr and W atoms in the basal plane of the AlB2-type structure.

A study on the type-2 liquid-liquid equilibrium (LLE) behavior of the {water + valeric or caproic acids + acetate esters (n-propyl, isopropyl, n-amyl, and n-hexyl acetates)} ternary systems was performed at T = 298.2 K and p = 101.3 kPa. Solubility and tie line data were experimentally determined using cloud point and HPLC methods, respectively. The results were validated through acid-base and Karl-Fisher titrator methods. The quality of the experimental tie lines was checked using the Hand equation. For these systems, the thermodynamic models of NRTL and UNIQUAC were successfully applied to fit the experimental tie lines and the values of the binary interaction parameters were obtained. Evaluation of the solvents capacity was performed using the calculation of distribution coefficients and separation factors. The influence of chemical structure of the chosen esters on the immiscibility region was found to be almost small. As a result, all the chosen acetate esters have relatively high separation factors ...

With the increase in wind power penetration, wind power ramping events have increasingly influenced tie line power control in the power grid. Large power changes during ramping events make it difficult to accurately track the scheduling plans of tie lines and can even lead to overrun. Determining how to evaluate the control performance of automatic generation control (AGC) for wind power ramping has become an urgent problem. In this context, this paper studies the control performance of AGC for wind power ramping based on deep reinforcement learning. First, a tie line power control model of a power system with an AGC module is established. Then, measured data, which include thermal power, wind power, hydropower output and tie line power data, and a deep reinforcement learning method are combined for AGC parameter estimation based on the deep Q-network (DQN) algorithm. Next, the AGC parameter in different scenarios are fit by using measured phasor measurement unit (PMU) data, and on the basis of the fitted model, AGC performance evaluation is performed for wind power ramping events. Finally, the simulation results verify the feasibility and effectiveness of analysing the relationship between wind power ramping and AGC performance based on the AGC parameter fitting model.

This article discusses a Whale Optimization (WO) controller for design analysis, stability management, application, and performance analysis of a deregulated two-area multi-source energy system. Within the power grid, the Automatic Generation Control (AGC) maintains the power balance and strengthens the sudden frequency disturbance of the grid. Various researchers are targeted many kinds of fast-acting energy-storing devices to dampen space frequency oscillations and diversion of the tie line because of unexpected load variation. To regulate the power flow between multi-areas, load frequency control (LFC) is used by keeping frequency constant. But, to design a controller for minimizing the issues of LFC remains a challenge within the deregulated atmosphere. The main objective of the proposed methodology is to design a controller for minimizing the issues in LFC within the deregulated atmosphere. A two-area deregulated hydrothermal power system is employed to analyze many LFC problems in the deregulated power grid. During this modeling, the Thyristor-Controlled Phase Shifters (TCPS) and Capacitive Energy Storage unit (CES) are placed in the tie line and its control space. To mitigate the various issues of LFC in a two-area deregulated hydrothermal power system, the CES–TCPS combination is placed between the two control areas and the transient performance of constant is evaluated. The WO controller will increase the system power size to focus on the better performance of low-frequency management tasks. In addition, the effectiveness of the WO algorithm in tuning the proportional integral controller is also compared in a different contract (unilateral, bilateral and contract violation cases) scenarios of the proposed deregulated power system. Finally, the simulation is carried out in MATLAB/Simulink platform and the results obtained for the WO controller is compared with the normal and fuzzy PI controllers.

An optimal planning model of the sectional switch and tie line for the distribution network is proposed considering the trade-off between the system reliability and economy. Firstly, the fault incidence matrixes are established for the distribution network, and the explicit analytical expression of the system reliability index is realized by the algebraic operation of the fault incidence matrixes and fault parameter vectors. Then, the 0-1 integer quadratically constrained optimization model is established for the sectional switch configuration considering the capacity constraint of the tie line. Finally, the sectional switches and tie lines are optimized jointly to ensure the economic investment and maximize the system reliability. The distribution network in Taiwan Power Company (TPC) is used to verify the applicability of the proposed optimization method. Compared with the intelligent optimization algorithm, the mathematical programming method in this paper can always find the global optimal switch configuration quickly. In addition, the influence of the tie line capacity constraints on the sectional switch configuration is also considered, which can provide practical reference for the power network planners in the optimization design of the distribution network.

The inertia constant is a key parameter of synchronous grids that are robust to disturbances. This paper presents an inertia estimation method for a multi-area interconnected electric power system. The method utilizes the electromechanical oscillation response measured with a phasor measurement unit. On the basis of the classical swing equation, the mathematical relationships between inertia and electromechanical oscillation parameters (i.e., oscillation frequency and damping ratio of a mode) are determined. The equivalent inertia of the system can be estimated by extracting the frequency and damping ratio of a mode from the observed active power on the tie line in the electromechanical oscillation response. Moreover, the system damping coefficient can be estimated without additional calculation and measurement. The inertia estimation errors caused by the poor extraction of oscillation parameters are reduced by utilizing the advanced parameter identification technology called adaptive local iterative filtering decomposition to identify the frequency and damping ratio of a mode. The accuracy and robustness of the proposed method are verified by using two simulation examples and an actual system.

Inter-regional power trading plays a crucial role in optimal resource utilization. However, intra-regional operation constraints are currently not well considered in practical implementation, which may lead to internal congestions and economic loss. In this paper, a non-iterative tie-line scheduling framework taking account of both intra- and inter-regional network constraints is proposed. Based on projection theory, admissible set of tie-line injections (ASTI) is defined as the allowable range of tie-line power injections that can be met by a regional system. Then, the ASTI is implemented in tie-line scheduling to ensure the feasibility of the tie-line schedule result for each region. Requirements for practical algorithms that calculate the ASTI in power system applications are analyzed, and a novel vertex-oriented projection algorithm is proposed to efficiently calculate the ASTI. Case studies based on several IEEE and Polish test systems verify the validity and efficiency of the proposed projection algorithm. Simulations based on a four-region system demonstrate the effectiveness of the proposed tie-line scheduling framework.

With the aggravation and evolution of global warming, natural disasters such as hurricanes occur more frequently, posing a great challenge to large-scale power systems. Therefore, the pre-position and reconfiguration of the microgrid defense resources by means of Mobile Energy Storage Vehicles (MEVs) and tie lines in damaged scenarios have attracted more and more attention. This paper proposes a novel two-stage optimization model with the consideration of MEVs and tie lines to minimize the shed loads and the outage duration of loads according to their proportional priorities. In the first stage, tie lines addition and MEVs pre-position are decided prior to a natural disaster; in the second stage, the switches of tie lines and original lines are operated and MEVs are allocated from staging locations to allocation nodes according to the specific damaged scenarios after the natural disaster strikes. The proposed load restoration method exploits the benefits of MEVs and ties lines by microgrid formation to pick up more critical loads. The progressive hedging algorithm is employed to solve the proposed scenario-based two-stage stochastic optimization problem. Finally, the effectiveness and superiority of the proposed model and applied algorithm are validated on an IEEE 33-bus test case.

Small signal stability is the investigation of small disturbances impacts in the operating point of power systems on system stability. Therefor the effect of low frequency (inter and local area oscillation) on system stability is very important topic of research especially when large power is transferred between two areas through a weak tie line. This will be accomplished by evaluating the eigenvalues, eigenvectors and participation factor of the linearized different equation of the system. This work will be achieved using Kundur's network system which consists of two area connected by a tie line of 220km length. Several configurations will be studied such as basic (Static) and dynamic control of HVDC link are an important part of this study that taken into a consideration to evaluate the small signal stability, where HVDC link was connected in parallel with one circuit ac tie line. In addition, an Intelligent method which is Genetic Algorithm (GA) is used for tuning the PSS in order to find the optimum values of the gain (K) that give the best system stability.

This paper deals with the importance of load frequency control (LFC) for single and interconnected power system. It is important to keep the frequency of the system and the inter area tie power stable. The goal of LFC is to maintain the frequency, the desired power output and to control the change in tie line power between control areas in an interconnected power system. Two different techniques have been implemented in this paper which are model predictive controller MPC and conventional proportional plus integral controller PI for LFC of single area power system as well as two area system. To investigate the powerful and robustness of model predictive control (MPC) technique for LFC problems in electric power system, time simulations is performed. The obtained results indicate that the MPC provide better damping to the single area system as well as two-area system in case of load disturbance compared with conventional PI controller. The studied single-area and two-area systems are modelled and simulated using Simulink/Matlab software.

This paper investigates the problem of how to effectively smooth the short-term tie-line power fluctuations for grid-connected industrial microgrids (IMGs) from demand side. A wide-area closed-loop control architecture is proposed by directly and continuously modulating load power consumption, e.g., the aluminum electrolysis load. To optimally design the load smoothing controllers, an output regulation approach combined with LQ optimal control is developed. In particular, dominant frequencies of wind power fluctuations are analyzed and incorporated into the exogenous system that models time-varying disturbances. Simulations are conducted for a real industrial microgrid in the Inner Mongolia, China, to validate the practical feasibility and effectiveness of the proposed smoothing control strategy. It is demonstrated that the demand side control based on output regulation is able to achieve not only zero steady error in rejecting the time-varying wind power disturbance but also guarantee the satisfactory dynamic performance of modulated loads for the grid-connected IMG.

The present study is focused on determination of the liquid-liquid equilibrium (LLE) data for (water + phosphoric acid + 2-pentanol or 4-methyl-2-pentanol) ternary systems at T = (298.2, 308.2, and 318.2) K and p = 0.1 Mpa. Despite of the structural similarity of the chosen sec-alcohols, their polarity and hydrophobicity are different. Thus, the influence of the chemical structure as well as temperatures on the liquid phase behaviour was investigated. Solubility and tie line data were measured using different titration methods such as cloud point, acidimetric, and the Karl Fisher titration techniques. The refractive index measurements were also carried out on the aqueous phase. The experimental tie line data were correlated using the thermodynamic models of NRTL and UNIQUAC. The binary interaction parameters were optimized by the MATLAB fminsearch function. Both the ternary systems exhibit type-1 phase behavior. The quality of the tie-lines was checked using the Othmer-Tobias equation. Distribution coefficients and separation factors were calculated over the biphasic regions.

Electrical power networks usually consist of multi-area systems, which are connected by tie lines. Dynamic economic/environmental dispatch of multi-area approaches are used to schedule such networks. The goal of multi-area scheduling is determining the optimal operation of generation units and the tie line power flow in a certain period by minimizing environmental constraints. Such operation problem is limited by technical constraints of thermal generation units, tie line constraints, and transmission losses. A major limitation of multi-area economic/environmental dispatch problem is the capacity of tie lines. The worst scenario of weather condition is generally employed to set this capacity. This value is called static line rating (SLR). However, the SLR is less than the real-time capacity of overhead line. The capacity of overhead line can be determined by estimation of weather condition data for better utilization of overhead lines. This value is called dynamic line rating (DLR). In this paper, a decentralized methodology is proposed for optimal scheduling generation units taking into consideration environmental constraint, dynamic line rating, wind power generations; compressed air energy storage and power pool market. The e-constraint approach is applied to solve proposed dynamic economic/environmental dispatch of multi-area model. In addition, a fuzzy satisfying technique is used to select the best compromise solution. An interconnected, multi-area power system with cross-border trading in the presence of wind power uncertainty and the storage unit is considered for evaluating the proposed method. The proposed decentralized approach is based on the integrated simplicial decomposition method (SDM), the nonlinear block Gauss-Seidel (GS) method and the augmented Lagrangian method (ALM) (SDM-GS-ALM) decomposition algorithm, because we need to schedule a multi-area network without central operation intervention.

Gas injection process is a very important technology in enhanced oil recovery. Minimum miscible pressure is one of the key parameters in gas injection processes. Various experimental methods such as slim tube are used to measure MMP. These methods are costly and time consuming. Recently computational methods are used in order to achieve a cost-effective and reliable technique to evaluate MMP. In this work, a new methodology has been proposed for determination of MMP using the minimum tie line length method. A real mixing cell model was developed to estimate the MMP, MME and key tie lines. This method is simple, robust, and faster than conventional one-dimensional simulation of slim tube. The new mixing cells method can accurately determine the whole key tie lines to a shift, regardless of the number of injection gas and reservoir fluid components. Unlike other methods of mixing cells, this method automatically corrects dispersion by additional contacts to achieve the low variation domain of tie line slope. Also, the determination and implementation of the minimum miscibility enrichment are investigated. Keywords: Minimum miscible pressure, Minimum miscibility enrichment, Multiple mixing cells method, Enhanced oil recovery, Minimum tie line length method

As an important part of a multi-energy system, the energy hub (EH) accommodates a wide range of input sources and diversified load types. Optimising the equipment type and capacity of the EH is the basis for ensuring the safe and economic operation of the EH. In this context, the basic concepts and models of the EH are first outlined. Then, to reduce the user's electricity cost and user comfort as the optimisation goal, the tie line power constraint and the purchase and sale power state constraints are considered comprehensively.

Phase change materials along the GeTe-Sb isoelectronic tie line are proved to be promising host material for optimization, based on which the well-known golden composition is developed. Here, Sc doped Ge2Sb1Te2 has been proposed for phase change memory (PCM) application, showing higher thermal stability and faster operation speed than those of the golden composition. The fast speed of 40 ns, high 10-year data retention of 160 °C, and good endurance of 6×105 cycles have made Sc0.2Ge2Sb1Te2 a promising candidate for PCM application. The impact of Sc on the microstructure is believed to be essential for those improvements in PCM.

Liquid-liquid equilibrium (LLE) data for poly (ethylene glycol) (PEG) of different molecular weights (600, 1500, 3000, 6000) + sodium formate (NaCHO2), potassium formate (KCHO2) + water at different temperatures (298.15 and 308.15 K) and for PEG (1500) + sodium formate + water at different pH values (8.05, 9.06, 10.92), were determined experimentally. The tie lines and plait point are reported at different PEG molecular weight, pH, temperature and type of cation. Furthermore, the effect of those parameters on binodal curve, tie-line length (TLL) and slope of tie line (STL) are discussed in detail by comparing the results to that of literature data. The effective excluded volume (EEV) values obtained from the LLE data were used to study the effect of the parameters on the binodal curves. The phase composition and the tie-lines’ ends were obtained by measuring the density ( ρ ) and refractive index ( n D ). Furthermore, the binodal curves and the tie-line compositions were well-fitted by using some semi empirical equations.

There is a large amount of controllable loads in the microgrid. They can be described as virtual energy storage to participate in microgrid tie-line power fluctuation mitigation. Firstly, in order to meet the grid-connected requirement, the wavelet packet decomposition algorithm is used to smooth the tie-line power fluctuation. Furthermore, in order to prevent overcharge and overdischarge of battery or virtual energy storage, the power allocation between two types of energy storage is implemented equally based on the concept of energy. In addition, the fuzzy control strategy is applied to revise virtual energy storage power based on its SOC (i.e. state-of-charge), so that virtual energy storage can operate within a reasonable work range. Finally, an example is given to verify the effectiveness of the control strategy.

For a large interconnected power system, the connections between subsystems are getting closer. The influence of the external area (EA) must be considered when the reliability of the internal area (IA) is analyzed. The equivalent method is widely used in the reliability analysis of interconnected power systems to improve the efficiency of evaluation. This paper proposes a high-accuracy tie-line probabilistic feasible region equivalent model, which replaces the traditional network flow method with the multi-objective optimal power flow. Based on the “not loss of load sharing agreement”, the feasible region states of the equivalent tie line are combined to further simplify the reliability assessment. Simulation results of IEEE 9-bus and IEEE-118 bus systems demonstrate the efficiency and accuracy of the proposed equivalent model and its effectiveness in reliability assessment.

In order to realize the coordination and integration optimization of the power system itself, this paper constructed the mathematical model of the hybrid power system and solved the multi-objective optimization problem of the heating system through the optimized particle swarm optimization algorithm. Based on the back-to-back VSC-HVDC grid-connected composite system, this paper studied the integrated control strategy of the device to achieve the simultaneous parallel and tie line currents. At the same time, this paper simplified and improved the proposed disassembly criteria for grid-connected composite devices and integrated them into the grid-connected composite device. In addition, on this basis, the integrated control of the three functions of de-listing, juxtaposition and tie line power adjustment of the same device was further studied. Simulation studies show that the proposed algorithm has certain effects and can provide theoretical reference for subsequent related research.

The power fluctuation characteristics of tieline are analyzed in this paper. Based on two area system DC load flow model derivation is carried out. In the time domain, there is a weighted linear relationship between power fluctuation of tie-line and different power fluctuation source's power injection; in the frequency domain, the self-PSD of tie-line power fluctuation can be expressed as the weighted linear sum of the self-PSD and cross-PSD of different power fluctuation source's power injection. Under certain conditions, the self-PSD of tie-line power fluctuation can be expressed via some simplified formula. The relationship deduced before is verified further in simulation of practical grid example.

This article briefs about an evaluation of dynamic impact of capacitive energy storage (CES) in load frequency control (LFC) in a renewable energy based three area power system. The proposed power system model consists of Thermal and solar thermal power plant in area 1, Thermal and wind plant in area 2, Thermal and Photovoltaic plant in area 3. The areas are interconnected through AC/DC tie line. In this study nonlinearities such as governor dead band and generation rate constraints are considered for thermal generating unit. Tilted-integral-derivative with filter (TIDF) controller is taken as a secondary controller. The system dynamic responses such a frequency deviation, tie power deviation and settling time of the proposed system are compared with and without CES with different types of controller. The simulated results showed that with the coordinated action of CES with proposed secondary controller the system dynamic performances have improved.

This document presents the execution of distributed generation (DG) resources in case of load frequency control (LFC) for three-area multi-source power systems. The DG system by way of a well-coordinated control can significantly progress the stability of the system frequency. Tilted integral derivative (TID) controller is projected here for controlling the objective function. Dynamics values are compared between the differential evolution particle swarm optimization (DEPSO) and teaching-learning-based optimization (TLBO) techniques using TID controller using MATLAB/SIMULINK through numerous simulations. TLBO based three-area system outperforms the DEPSO base system. The system dynamics are enhanced by using DC link to this existing alternating current tie line.

Nowadays, the resilience enhancement is one of the most important concerns in electric power networks. The division of the main microgrid into several sub-microgrids, i.e., microgrid formation (MF), is a resilient strategy for distribution systems against natural disasters and cyber-physical attacks. Such effective solution not only increases the resilience and load restoration but also reduces the costs. The extensive penetration of renewable resources in microgrids increases the issues about safe operation under faults. This chapter presents a resilient microgrid formation in the presence of solar, wind, and diesel Distributed generation (DG) for load restoration maximization. In order to carry out the microgrid formation, several candidate breakers and tie-line switches are considered, and their optimal on-off conditions are determined. Both the active and reactive powers are included in the model. The model is expressed as mixed-integer linear programming (MILP) and is simulated under three various cases including case 1, without formation strategy; case 2, formation strategy with line breaker switch; and case 3, formation strategy with both line and tie breaker switches. The numerical results are carried out based on IEEE 33-bus and 69-bus standard distribution networks. The results emphasize on the effectiveness of the developed formation strategy with both the breaker and tie line switches for load restoration and resilience enhancement. 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG. Scopus 2-s2.0-85107857635

In order to cope with the rapid development of renewable energy in the Northwest Power Grid, it is an urgent need to predict the renewable energy consumption capacity and transaction needs of the provinces, and promote the timely consumption of renewable energy within and between provinces. Therefore, this paper proposes a real-time transaction prediction method based on the generalized tie-line. Based on the definition of generalized tie lines, a multi-objective optimization model is established. The optimization objectives include positive and negative reserve of the provincial power grid and generalized positive and negative reserve of the main and sub-control areas. The method analyzes the power transmission and reception capacity and power transmission and reception needs of the main and sub-control areas in the next few hours, calculates the power purchase and sales capacity among the provinces, and automatically generates intra-provincial replacement and inter-provincial transaction plan based on the transaction rule library to enhance the intelligence level of renewable energy consumption in the Northwest Power Grid.

In order to improve the utilization efficiency of wind energy and reduce the wind energy curtailment as much as possible, this paper proposes an active power control strategy based on peaking and tie line constraints, which divides peaking and tie line absorptive capacity into dynamic zones. Through flexible switching of control modes in different zones, the utilization of peaking and tie line capacity can be maximized. Considering the situation that there is the non-energy dissipation of power grid due to peak load regulation or blocked cross-section, this paper proposes an echelon active power control strategy, taken into account the utilization of hours and the completion of trading power, thus, ensuring the fairness of the generating capacity of each station. The practical operation on a power grid system of northern part China demonstrates the feasibility of the proposed method.