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• An integrated gas and electricity network with heat electrification is developed. • Correlated uncertainties of renewable generation and demand are modelled. • Overload probability of power lines and gas pipelines is evaluated. This paper presents a probabilistic method for assessing overload probability of power lines and gas pipelines in integrated gas and electricity networks with the consideration of heat electrification. The proposed model fully considers the correlated uncertainties associated with intermittent generation and fluctuating loads using suitable probability distribution functions and copulas. The effectiveness of the proposed method is verified with application in two test systems: the integrated 9-bus electricity and 8-node gas network, and the integrated IEEE 39-bus and Belgian 20-node gas network. Numerical results show that heat electrification increases the overload probability of some power lines due to a major shift of heat loads to the electricity network. When the correlations of wind and photovoltaic generation as well as electric, gas and heat loads are considered, the overload probability of these power lines further increases showing the importance of correlation modelling for an accurate estimation of power flows and line overload probability. When an uneven distribution of heat loads (i.e., clustering of low-carbon technologies) in the electricity network is considered, the overload probability of some power lines further increases. Heat electrification decreases the overload probability of most gas pipelines, although the probability of overloading a few gas pipelines increases as a result of supplying gas to gas-fired power generators to meet the electrified heat demand. [ABSTRACT FROM AUTHOR]

This paper presents a comparative study on various implementation techniques of Unified Power Flow Controller (UPFC) in load flow algorithms. The comparison is done among; decoupled technique, comprehensive technique, load injection technique, π load injection technique, indirect technique, and matrix partitioning technique. The merits and demerits of these techniques are presented. Beside these techniques, the paper presents a developed UPFC model based only on current injection approach. The model is implemented in Newton–Raphson current injection load flow method (NR-CIM). This model addresses the main drawbacks of previous techniques. Test results are presented using IEEE standard systems which demonstrate the effectiveness of the developed model. [ABSTRACT FROM AUTHOR]

This paper presents an innovative management strategy for distributed battery storages that greatly increases the capability of distribution networks to absorb and utilize photovoltaic (PV) generation. Optimal daily energy profiles for each storage unit are calculated using a Fourier series description based on one day ahead energy forecasts. Each battery charge/discharge profile is optimized to minimize a cost function that includes network and battery losses, battery cyclic costs and the network voltage profile. The optimization method combined an interior-point algorithm and pattern search algorithm. Simulations are carried out on a three-phase distribution system over a period of 24 h at 15 min interval with time varying loads. The adopted technique in this paper shows significant control abilities in peak shaving and load leveling. Results also indicate that proposed approach can enhance the performance of the grid by improving the voltage stability and reducing distribution losses thus providing the required security for consumers. Results also illustrate capacity and charging/discharging rates of batteries highly depend on the location of the controlled consumer battery and amount of controlled batteries. [ABSTRACT FROM AUTHOR]

This paper presents an iterative approach for incorporating doubly fed induction generator (DFIG) based variable speed wind farms in steady state studies such as load flow analysis. The proposed approach is based on an accurate steady state equivalent circuit of a DFIG. In the proposed approach, the power flow model of a node with DFIG is determined based on the reference to reactive power control loop of rotor side converter. In addition, the proposed approach takes into consideration various limits associated with the DFIG. Case studies on sample 6-bus system and 418-bus equivalent system of Indian southern grid are presented to validate the proposed approach. [ABSTRACT FROM AUTHOR]

• Proposed method of loss allocation simplifies the complexity associated with the bifurcation of cross-term mathematically, without any assumptions and approximations. • Normalization is not required as it is not suffering from under-over-recovery of losses. • It assigns losses with due consideration to both load demands and geographical locations of the end-users. • Investigates effectiveness at different load models with various types of DG power injections so as to provide efficient allocations as far as network topology is concerned. • Examines responses as regard to variations in load power factors with due respect to practical field of implementation. • Statistical analysis has been carried out on the loss allocation results of the consumers with constant power factors to show efficiency as regard to minimum degree of variation. Owing to huge penetration of distributed generators (DGs) and subsequent flow of reverse currents in power distribution networks, loss allocation (LA) has become very complicated which gets further complicated for different load models and DG power injections. In this context, this paper develops a new circuit theory-based branch oriented LA technique which simplifies the difficulties associated with the decomposition of cross-term of power loss equation mathematically, without any assumptions and approximations. It assigns the exact amount of losses to the network participants with due consideration to their load demands, power factors and geographical locations with/without DGs at various load models without normalisation. The effectiveness of the proposed LA procedure is not only investigated simply at different load models rather with various types of DG penetrations (i.e. Unity power factor DGs, Zero power factor DGs, Leading power factor DGs and Lagging power factor DGs) considering two test distribution systems i.e. 9-bus and 33-bus and the results are compared with that of the other existing techniques: Proportional sharing method, Quadratic method, Exact method and Cross term decomposition method. The performance analysis of the LA method with respect to load power factor variation is the other highlight of the paper. [ABSTRACT FROM AUTHOR]

This paper presents an alternative approach to power system computations, Graph Trace Analysis (GTA), and applies this approach to solving the power flow problem. GTA is derived from the Generic Programming Paradigm of computer science, and uses topology iterators to move through components in a model and perform calculations. The implementation of KVL and KCL in GTA is described. The GTA based power flow algorithm is shown to solve IEEE standard transmission models, IEEE standard distribution models, and integrated transmission and distribution models (hybrid models) constructed from modifying IEEE standard models. Comparisons with widely used, primarily matrix based, power flow algorithms are provided. Two advantages that GTA brings are the separation of system equations from component equations and the ability to distribute calculations across processors. [ABSTRACT FROM AUTHOR]

In the energy transition context, the use of steady-state time series is a promising approach to account for temporal interdependencies and flexibilities in modern distribution power system analysis, planning, and operation processes. This paper proposes a distributed backward–forward sweep power flow algorithm executed in a discrete-event, agent-based simulation framework. The algorithm shows fast convergence, allows for concurrent execution, and scales up to large-scale multi-voltage level grids with arbitrary topology. An agent-based simulation model integrates the developed algorithm to generate detailed grid utilization, asset, and system participant time series. We demonstrate the capabilities of our approach by performing several simulations, leveraging the proposed algorithm, on nine different benchmark grid models. The selected models comprise grids at a single voltage level, medium voltage level, and combined multi-voltage levels. The evaluation of the numerical results validates the approach and demonstrates its capabilities. • New distributed backward-forward sweep algorithm for power flow calculations • Introduction of centralized and decentralized algorithm solution protocols • Application and implementation in an agent-based, discrete-event simulation • Algorithm validation against reference results to demonstrate its functionality • Investigations indicate fast execution times for multi-voltage level grids [ABSTRACT FROM AUTHOR]

In this paper, an attempt has been made to develop a new algorithm for distribution system planning. The proposed algorithm does not require prior knowledge of candidate substation location and can automatically select location of a substation, the optimal feeder configuration and the optimal sizes of branch conductors while satisfying constraints such as current capacity, voltage drop and heuristic rules. Several algorithms are proposed for distribution systems planning. A generalized algorithm is developed for obtaining the optimal feeder path and the optimal location of substation on minimum loss criterion. Heuristic rules are incorporated in the above algorithm. Another algorithm is for branch conductor optimizations. Modified load flow method is also presented in the paper, which can handle composite load models. The load flow algorithm is used for solving radial distribution networks (RDN) and branch conductor optimization algorithm. The load flow algorithm and branch conductor optimization techniques are used as subroutine in the generalized distribution systems planning algorithm. Through numerical example the validity of proposed method is verified. [Copyright &y& Elsevier]

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

Load flow is the most used calculations in power system operation planning. Renewable resources have caused that system operator has to do power flow analysis and/or contingency analysis as fast as possible in order to predict next step in power system control. LU Decomposition of Jacobian matrix remains the most computationally expensive task during Newton–Raphson iterative method. Computational time appears to be critical issue when load flow calculation is performed on large power system load flow models. In this case, Jacobian matrix LU decomposition should not be performed in iterations in which convergence rate is not violated but performed in iterations in which convergence rate drop below specified level. In other words, modified Newton–Raphson Method which eliminates the repeated Jacobian matrix LU decomposition and generic Newton–Raphson method are combined depending on convergence rate. The paper presents application of proposed combined Newton–Raphson method which is based on convergence rate control. Comparison of combined, Shamanskii, generic, and modified Newton–Raphson methods is carried out taking into consideration computational time and number of iterations required to achieve convergence of load flow models of various dimensions. [ABSTRACT FROM AUTHOR]

This paper presents a new current injection-based load flow procedure in which the Y-bus matrix becomes the main building block of the Jacobian. Starting from a conventional complex formulation, an augmented incremental model is developed comprising both complex and real unknowns, corresponding to PQ and voltage-regulated buses respectively. Then, details are provided on the incorporation of voltage regulating devices (PV buses and tap changers) into the proposed hybrid model. Test results are presented showing that, when solution adjustments are considered, the proposed approach is competitive with the conventional power mismatch-based Newton's method, and performs much better than sensitivity-based schemes usually adopted in combination with current injection-based load flow solutions. [ABSTRACT FROM AUTHOR]

• Consensus-based control of distributed generators to minimize frequency deviation. • Consensus-based control of interlinking converters to align AC subgrid frequencies. • Modifications on Backward/Forward Sweep-based three-phase AC-DC power flow analysis. • Accurate, scalable and generic method for networked islanded hybrid microgrids. This paper proposes the incorporation of distributed and decentralized control models of generators and converters into the power flow analysis of islanded hybrid microgrids (IHMG). The absence of a slack bus in an islanded microgrid presents challenges to its frequency and voltage regulation as well as power flow calculation. While droop mechanism as the primary control has been well incorporated into load flow analysis, distributed secondary control has only recently been developed for islanded microgrids. This paper proposes a distributed secondary control for a) generators in an AC subgrid of an IHMG and b) interlinking converters in networked IHMGs. Both the distributed and droop control are incorporated into a three-phase power flow calculation based on a modified Backward Forward Sweep method. The algorithm has been tested on several case studies, and the power flow results have been verified against a time-domain simulation. The proposed method proves to be accurate and useful for the planning and design of three-phase networked IHMGs. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new load flow formulation to solve active and passive electric distribution networks. The fundamental idea discussed here is how to obtain the power flow solution by using the elements of a unique quasi-symmetric matrix called TRX in the iterative process. The method is formulated for single-phase balanced and three-phase unbalanced radially operated networks. It works with real variables as opposed to complex variables used in previous backward/forward sweep algorithms discussed in literature. The proposed TRX matrix constitutes a complete database by including information of network topology structure as well as branch impedances of the distribution feeder. Data arrangement is suitable to be exchanged under standard Common Information Model (CIM) under Distribution Management Systems (DMS) environment allowing an efficient computation of the state of the system for on-line and off-line study applications. The proposed methodology was applied on a group of IEEE test systems and a real distribution system of 49,000 nodes. [Copyright &y& Elsevier]

Abstract: This paper presents an efficient approach for capacitor allocation in radial distribution systems that determine the optimal locations and sizes of capacitors with an objective of reduction of power loss and improving the voltage profile. A loss sensitivity technique is used to select the candidate locations for the capacitor placement. The size of the optimal capacitor at the compensated nodes is determined simultaneously by optimizing the loss saving equation with respect to the capacitor currents. The performance of the proposed method (PM) was investigated on several distribution systems and it was found that significant voltage profile improvement and loss saving can be achieved by optimal allocation of capacitors in the system. However this method is sensitive to the distribution network configuration. In a 28 node feeder the matrix of capacitor sizing becomes close to singular or badly scaled and results may be inaccurate. In 85 node feeder the same matrix becomes singular and no solution obtained. For the 28 node feeder a two stage technique is proposed: a reconfiguration of the feeder in the first stage followed by optimal capacitor allocation as a second stage. For the 85 node feeder a slight movement of the capacitor location was sufficient to reach optimal capacitor allocation. The proposed two stage technique is also applicable to the 85 node feeder for given optimum configuration of the tie switches. Simulations, using genetic algorithm are conducted for the two (28 and 85 nodes) systems allowing detection of loss reduction and voltage improvement due to capacitor placement. [Copyright &y& Elsevier]

Abstract: In this paper an artificial neural network (ANN) based methodology is proposed for (a) solving the basic load flow, (b) solving the load flow considering the reactive power limits of generation (PV) buses, (c) determining a good quality load flow starting point for ill-conditioned systems, and (d) computing static external equivalent circuits. An analysis of the input data required as well as the ANN architecture is presented. A multilayer perceptron trained with the Levenberg–Marquardt second order method is used. The proposed methodology was tested with the IEEE 30- and 57-bus, and an ill-conditioned 11-bus system. Normal operating conditions (base case) and several contingency situations including different load and generation scenarios have been considered. Simulation results show the excellent performance of the ANN for solving problems (a)–(d). [Copyright &y& Elsevier]

Abstract: Continuation methods have been shown as efficient tools for solving ill-conditioned cases, with close to singular Jacobian matrices, such as the maximum loading point of power systems. Some parameterization techniques have been proposed to avoid matrix singularity and successfully solve those cases. This paper presents a new geometric parameterization scheme that allows the complete tracing of the P–V curves without ill-conditioning problems. The proposed technique associates robustness to simplicity and, it is of easy understanding. The Jacobian matrix singularity is avoided by the addition of a line equation, which passes through a point in the plane determined by the total real power losses and loading factor. These two parameters have clear physical meaning. The application of this new technique to the IEEE systems (14, 30, 57, 118 and 300 buses) shows that the best characteristics of the conventional Newton''s method are not only preserved but also improved. [Copyright &y& Elsevier]

Abstract: In this paper, a new generalized current injection model of the modified power system using Newton–Raphson power flow algorithm has been proposed for desired power transfer with Flexible AC Transmission Systems (FACTS) devices. So that the FACTS devices can be incorporated in the proposed algorithm and, therefore, whole system with these devices can be easily converted to power injection models without change of original admittance and the Jacobian matrices. Power flow algorithm has been modeled in such a way that it can easily be extended to multiple and multi-type FACTS devices by adding a new Jacobian corresponding to that new device only. Power flow algorithm with the presence of Thyristor Controlled Series Compensators (TCSC), Unified Power Flow Controller (UPFC), and Generalized Unified Power Flow Controller (GUPFC) has been formulated and solved. To demonstrate the performance of the proposed algorithm for multiple and multi-type FACTS devices, different case studies of IEEE 30-bus system has been considered and the results are tabulated. The proposed algorithm is independent of the size of the system and initial starting conditions of the FACTS devices. [Copyright &y& Elsevier]

The unified power flow controller (UPFC) has the capability of controlling the steady state power flow of a particular branch in a transmission network. This paper proposes a simple method of solving the controlled load flow problem of a power system in the presence of UPFC. First, a new static model of the UPFC is proposed to control the power flow. Some standard load flow programs are then carefully modified to incorporate the effects of the proposed UPFC model without practically changing the basic computational algorithm of the program. During the iteration process, the computed bus voltages are used to modify the control parameters of the UPFC in such a way that the functionally dependent line power flow can be kept at the desired or specified value. The effectiveness of the proposed method is then demonstrated on a power system by solving a number of controlled load flow problems. It has been found that the proposed method is very efficient and reliable. [Copyright &y& Elsevier]

• A simplified model for small-signal analysis in residential microgrids considering the effect of the frequency on the YBUS is proposed. • The effect of the variations of the droop controls and time constants are considered. • Variations on the operative point were considered using a Montecarlo simulation. This paper presents a model for the small signal analysis in island microgrids, that includes the effect of time constants and droop controls as the effect of the frequency in the parameters of the grid. It is demonstrated that high values of the time constant and/or the droop constant could lead to unstable operation. However, the microgrid is robust to changes of cable length, power factor and scenarios of generation. A Newton's algorithm, particularly designed for island operation of microgrids, is also proposed. This algorithm demonstrates to be highly accurate in comparison to the stationary state point obtained by solving (numerically) the dynamic model. [ABSTRACT FROM AUTHOR]

• This paper proposes a holomorphic embedding load flow method for hybrid microgrid. • To deal with hybrid microgrid, converters are modeled for load flow equations. • Comparative analysis shows the efficacy of proposed method over existing methods. • Robustness test has been performed over the proposed method also. Load flow study is a steady state analytical tool for power system network analysis where mostly iterative numerical methods are used to solve the load flow equations. But with the rise in complexity of the power networks due to amalgamation of both AC and DC power system within a network, the convergence time of these iterative load flow algorithms has been increased quite high. To resolve this problem a recursive load flow method has been developed called Holomorphic Embedding Load Flow Method (HELM) which reduces time complexity and also increase the probability of existence of the load flow solution. Here a new holomorphic embedding load flow problem formulation for a hybrid AC-DC microgrid system using line impedance values has been proposed. By using Padẽ approximant, we solve this holomorphic embedding load flow functions which guarantees the solution of load flow problem. Comparative study with well-known load flow methods over different test cases and a practical Indian distribution grid shows the efficiency and applicability of this method over the hybrid power networks. [ABSTRACT FROM AUTHOR]

• We propose a new method to model the effect of series impedance changes on the bus impedance matrix. • We verify the method by showing its relationship with Sherman–Morisson identity and numerical simulations to verify accuracy. • Tests with systems of different sizes show that our method is accurate and faster than others making it more suitable for online applications. This paper derives new expressions for updating Bus Impedance Matrix ( Z bus) elements to account for the modification of the series impedance of a line connected between two existing buses. Such kind of modification is not accounted for in Brown's method and requires building Z bus all over again which is time-consuming, and redundant. Afterwards, we show that a modified form of Sherman–Morisson identity is the generalization of our work. We test our modeling approach with seven systems of different sizes. Results show very minor errors between the predictions of our techniques and Brown's method. Further, speed comparison shows that our method substantially improves calculation speed from a few minutes with Brown and Bus Admittance Matrix ( Y bus) inversion methods to seconds (1.35 s and 2.9 s for 2383 and 3120 bus systems, respectively) making it more suitable for online applications. [ABSTRACT FROM AUTHOR]