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Abstract: Dispersed or decentralized storage and generation of electric energy (noted DSG) finds its source in cogeneration using either clean fuels or renewable resources, such as solar and wind. Typically these small energy sources are grafted to existing networks through weak utilities ties. This paper discusses a particular operating problem that may be faced by the electrical utility wishing to integrate DSGs. The latter are especially at risk of losing their utility ties following some electrical disturbances such as short circuits, line outages, etc. and consequently risk losing synchronism or being separated from the main network. Hence the anticipated penetration of DSGs in distribution networks will be accompanied by an increase in system vulnerability. Here we describe transient stability simulations of distribution networks in which DSGs are integrated, and in particular we investigate their needs in terms of frequency regulation. In our simulations the distribution network is fed simultaneously by the main power system and by one or two DSGs; this allows us to study the interactions between all of the components. All simulation scenarios include a small three-phase turbine-alternator powered on gas (TAG) synchronously connected to the distribution network. The second DSG is either a directly-connected TAG, or photovoltaic cells (PV) interfaced to the distribution network through a three-phase converter and accumulators. Equipped with a continuous frequency measurement capability, real time transient stability assessment of DSG distribution/main network interconnections is now possible. An algorithm, which achieves that goal, has been developed and tested on a power system model subjected to various contingencies. [Copyright &y& Elsevier]

Load behavior can significantly influence power system oscillations and the paper explores this interaction. Based on a generic load model, it is shown that loads provide a feedback, which can be used to influence system damping. The result is achieved through a MIMO (multi inputs/multi outputs) minimal realization algorithm based on a singular value decomposition (SVD). Feedback interpretation of load dynamics underlies this technique.The development of accurate load models on a system wide basis, the assessment of their impact, and the design of reliable and accurate load modulation in large-scale studies are a formidable task. To mitigate this problem several approaches are illustrated to take into account uncertainties on load behavior and modulation. This culminates into a damping control obtained with the Liapunov theory and the generalized Popov criterion. A variable structure linear state feedback controller, in terms of the controls at the vertices of the polyhedral output constraint set, is presented. The concept is illustrated and demonstrated by simulation runs on the 9-bus 3-aeras WSCC test system and a representation of the Hydro-Que´bec network. [Copyright &y& Elsevier]

• A centralized online method for voltage control following a security purpose is proposed for active distribution grids. • Sensitivity of the load and the equivalent impedances of a load bus to control variables is investigated. • The load impedance margin TLIM is used as a target for voltage control in distribution networks. • A multi-step optimization problem in terms of impedance sensitivities is formulated. • The contribution of each DG unit in change the impedances is carried out. With the rapid increase in hosting large penetration levels of Distributed Generation (DG), voltage stability problem has raised a main concern for distribution networks. This study proposes a new centralized voltage control method following a security purpose for active distribution grids. The method is based on a sensitivity analysis to optimally dispatch the control variables. The sensitivity analysis uses a Thevenin-based load impedance margin (TLIM) derived from the nodal measurements to take into the consideration the changes in the system operation, especially those caused by the rapid-response devices of DGs. Sensitivity of load and equivalent impedances to control variables is investigated via the derivation of nodal voltage and current with respect to control variables. Accordingly, the contribution of each control variable in change TLIM and, hence, in voltage control can accurately be obtained. The changes of the impedances of pilot bus, which has the smallest value among all the TLIMs, are formulated in a multi-step optimization problem in terms of impedance sensitivities for the optimal dispatch of controls. The proposed sensitivities and their application in voltage control are successfully validated by a 11-kV distribution grid including 77 bus and hosting 22 DG units. Simulation results show the validity and the accuracy of the proposed sensitivity method in voltage control during different scenarios. [ABSTRACT FROM AUTHOR]

Highlights • The proposed method is more advantageous than conventional ones. • This method reduces wind power losses. • It keeps the temperature variation unperceived. • An important reduction in electrical power fluctuation is achieved. Abstract Energy produced by wind turbines is characterized by its uncertainty which causes high fluctuations. Two types of fluctuations exist: the first one is represented by the slow power variation measured during large period; the second is the fast power variation measured from minute to minute that is known by the ramping rate. In this paper, the second type is studied. The high level of penetration of these fluctuations may affect the power network quality and may cause voltage and frequency instability. Power smoothing that is defined in this paper by ramping rate control is an important issue to avoid these fluctuations and to maintain the power network stability. Conventional methods based on storage system and on delta control of wind turbines are published in literature for this purpose. Unfortunately, storage systems are either small or expensive and delta control reduces yield energy. Another approach consists of adding to the delta control the power consumption control of heating and ventilation air conditioning (HVAC) systems installed in large buildings. This would provide positive and negative electrical power reserve for the compensation of wind power fluctuations. Unfortunately, this technique is still limited by a small margin of control since neither the temperature nor the humidity of the air-conditioned zones should be affected. This paper suggests an improvement of this margin of control by integrating in the regulation process the supply fan with the return fan. A numerical study based on real data shows that the proposed method is more advantageous than using slow response heat storage systems or expensive storage batteries or DC controllers. Moreover, this method reduces wind power losses and keeps the temperature variation unperceived, although an important reduction in electrical power fluctuation is achieved. [ABSTRACT FROM AUTHOR]

Abstract This paper shows that the Demand Response Program is not sufficient to solve the problem of high penetration level of Plug-in Electric Vehicles (PEVs), even when energy management systems are used in homes. In the presence of Time-varying electricity price, PEVs tend to charge during low price periods. The problem starts when the number of PEVs exceeds a certain threshold. A total load of all homes on a transformer may exceed its capacity and create high peak-demand during low-electricity price. To overcome this situation, we propose a novel Soft-Constrained Distributed Strategy. The novelty consists of defining a new distributed information exchange between Power Utility and end-users, new constraints are developed at home level taking into account the transformer and Distribution Network's technical limits, and a new optimization model is proposed to implement the strategy. A case study is conducted using data provided by Hydro-Quebec. Simulations and comparative results show the validity of our approach. The proposed strategy reduces the peak–demand, energy loss, depreciation cost, transformer's Loss Of Life, and voltage deviations. Lastly, our study shows that it is not necessary for the power utility (e.g. Hydro-Quebec) to upgrade all Distribution Transformers on the network and the infrastructure during the increasing penetration of PEVs. [ABSTRACT FROM AUTHOR]

An increasing penetration of renewable power resources (particularly wind farms) is observed in power systems during the last years. There is a frequency control concern with these kinds of power resources because they do not provide the so-called inertial response. Since the doubly fed induction generator (DFIG) equipped with Variable Speed Wind Turbine (VSWT) is the mostly used type of generator in wind farms, this paper proposes a new control approach allowing the DFIG to participate more efficiently in the power system frequency control. The approach consists of three steps: (1) Estimating the active power mismatch Δ P 0 between the active electrical power and the mechanical power which appears at the first moment after the perturbance at the DFIG, (2) based on Δ P 0 determine the electrical power reference P ref of the active power controller, and (3) appropriate removal of Δ P 0 if the power frequency deviation is above a prescribed value and the automatic generation control (AGC) is activated. The obtained simulation results on a simple 2-bus system and on IEEE 14-bus test system show that the proposed approach has several advantages over existing approaches. [ABSTRACT FROM AUTHOR]

Nowadays, integration of new devices like Distributed Generation, small energy storage and smart meter, to distribution networks introduced new challenges that require more sophisticated control strategies. This paper proposes a new technique called Optimal Coordinated Voltage Control (OCVC) to solve a multi-objective optimization problem with the objective to minimize the voltage error at pilot buses, the reactive power deviation and the voltage error at the generators. OCVC uses Pareto optimization to find the optimal values of voltage of the generators and OLTC. It proposes an optimal participation of reactive power of all devices available in the network. OCVC is compared with the classical method of Coordinated Voltage Control and is tested on the IEEE 13 and 34 Node test feeders with unbalanced load. Some disturbances are investigated and the results show the effectiveness of the proposed technique. [ABSTRACT FROM AUTHOR]

This paper presents an efficient algorithm to solve the multi-objective (MO) voltage control problem in distribution networks. The proposed algorithm minimizes the following three objectives: voltage variation on pilot buses, reactive power production ratio deviation, and generator voltage deviation. This work leverages two optimization techniques: fuzzy logic to find the optimum value of the reactive power of the distributed generation (DG) and Pareto optimization to find the optimal value of the pilot bus voltage so that this produces lower losses under the constraints that the voltage remains within established limits. Variable loads and DGs are taken into account in this paper. The algorithm is tested on an IEEE 13-node test feeder and the results show the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

This paper presents a secondary voltage control that applies discrete controllers to regulate the voltage in the Hydro-Québec power network. Firstly, an artificial intelligence methodology is presented for partitioning the Hydro-Québec network into smaller and separated areas. The proposed methodology uses a self-organizing map (SOM) and is based on an original concept in which competitive and learning vector quantization (LVQ) neural networks are used to partition the power system. Secondly, pilot buses are chosen to represent the most controllable buses in each area. Finally, discrete controllers are designed to overcome and avoid propagation of disturbances on the network. The proposed methodology and the results obtained with the Hydro-Québec network are presented in this paper and show the effectiveness and performance of the controllers. [ABSTRACT FROM AUTHOR]

This study proposes a secondary voltage control based on a systematic approach that decomposes a transmission system network into several areas. Network decomposition and pilot buses selection are fundamental in area voltage control. The proposed decomposition approach is hierarchical with two levels of decomposition. The first level is based on the clustering analysis; at this level, the appropriate number of areas is determined. Only several buses (named as control buses) are assigned to each area at this level. The aim of the second level is to assign the remaining buses (named as load buses) to a given area among the already obtained areas in the first level. Buses classification at this level is based on proximity analysis. The control uses reactive power compensation at critical buses, as well as at pilot buses to eliminate voltage violation resulting from disturbances at these buses. For pilot buses selection, a pilot index is proposed. The critical buses are determined based on the sensitivity factors. The IEEE 39‐bus and IEEE 118‐bus are used to illustrate the performance of the proposed approach. [ABSTRACT FROM AUTHOR]

• New and fast method for voltage sensitivity analysis in smart distribution networks. • Construction of ABCD matrix, which the proposed method depends on. • Comparison with well-known methods for voltage sensitivity analysis. • Applicability of the proposed method through transient and dynamic voltage control. Sensitivity Analysis plays a significant role in voltage prediction and control of power networks. However, the classical sensitivity methods require significant computation time. As active distribution networks require real-time implementation for voltage control, reducing the computation time becomes a necessary task for network operators, especially in the context of optimization techniques. This work develops a new analytical and fast voltage sensitivity analysis method via the derivative of the nodal quantities (power, current and voltage) with respect to power injections. The proposed method mainly depends on the construction of the ABCD matrix. The values of the matrix elements remain the same regardless of the bus on which the power is injected. Thus, it has a high potential to be implemented in online applications. To make a complete separation between the sensitivities to active and the sensitivities to reactive power injections, the analytical formulations are expressed in Cartesian coordinates. A radial distribution network including several DG units is used to verify and assess the proposed sensitivity method under different scenarios. [ABSTRACT FROM AUTHOR]

This paper presents coordinated secondary voltage control based on partitioned power network and decentralized controllers designed for each region. The elements of control are installed on pilot buses (critical point for voltage control in each region). The aim is coordination among elements of control in each region or between different regions to regulate voltage of buses and increase the security of the power network. The elements of control are considered as nodes of a graph and reactive power will be transferred through edges of this graph. This gives capability of transfer of reactive power between regions in case of voltage violations in a special region that cannot be regulated by controllers installed on that region. The control uses decentralized controllers to eliminate voltage violations resulting from load variations and disturbance in the power network. The methodology is applied to the IEEE 118-bus network. The results show and verify the performance of coordinated control scheme to regulate the voltage and to avoid propagation of contingency between regions. [ABSTRACT FROM PUBLISHER]

This study presents a secondary voltage control based on an optimisation algorithm to locate the control buses and regulate the voltage. Control buses are the buses where compensators will be installed on these buses to regulate voltage and avoid voltage violations. Firstly, partitioning algorithm using fuzzy C‐means has been implemented on the power network. Partitioning techniques split the power system into regions to avoid the propagation of disturbances between regions by using local controllers. Then, a number of buses are labelled as control buses displaying the critical point for voltage control in each region. The control algorithm is a decentralised controller which tries to eliminate voltage violations in power system resulting from load variations and disturbances. The decentralised controllers are implemented using flexible AC transmission system (FACTS) devices such as static synchronous compensator (STATCOM). The methodology is applied to the IEEE 118‐bus network. The results show the performance and ability of the partitioning algorithm and bus control selection to regulate the voltage and avoid propagation of disturbances between regions. [ABSTRACT FROM AUTHOR]

This paper investigates a secondary voltage control based on a graph partitioning method. The method divides the power system into regions to eventually prevent the propagation of disturbances and to minimize the interaction between these regions. The optimized number of regions is found based on the bus voltage sensitivity to disturbances being applied to loads in each region. Then, a number of representative buses are labelled as pilot buses displaying the critical point for voltage control in each region. The control uses decentralized controllers to eliminate voltage violations resulting from load variations and disturbances in the system. The decentralized controllers are implemented by fuzzy logic which is trained via offline simulations; they inject required reactive power into the regions to correct voltage violations. The methodology is applied to the IEEE 118-bus network. The results show the performance and ability of graph partitioning and fuzzy secondary voltage control to regulate the voltage and to avoid propagation of disturbances between regions. [ABSTRACT FROM PUBLISHER]

• A new and fast sensitivity method for choosing the most effective controls for voltage instability prevention. • Performing the sensitivity analysis on a voltage stability index, namely TVSM. • The loading margin sensitivity is a function of the voltage (magnitudes and angles) sensitivities to preventive controls. • Robustness of the proposed sensitivity method during stable and unstable voltage conditions. • Applicability of the proposed method in voltage stability control. Voltage instability is one of the serious problems in power networks due to the growing demand. Sensitivity analysis has been widely hailed as an effective method for voltage stability prediction and control. However, the common loading margin sensitivity approaches are not appropriate for real-time applications. This is because those approaches are based on continuation power flow or the singularity of the Jacobian matrix to find the maximum loading point. In this study, a new sensitivity method is developed for choosing the most effective control variables for voltage instability prevention in power systems. The sensitivity analysis is performed on a voltage stability index, namely Thevenin-Based Voltage Stability Margin (TVSM), derived from the coupled single-port circuit concept to capture the changes in power system operation. The sensitivity approach is computed via the derivation of nodal voltages (magnitudes and angles) with respect to preventive controls. The proposed sensitivity approach is tested on the IEEE 39 bus network and the IEEE 118 bus network to verify their accuracy. [ABSTRACT FROM AUTHOR]