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The incorporation of distributed generation (DG) units in distribution network voltage control may create operational conflicts with other conventional voltage control devices. Structural changes of networks can also increase the possibility to create control interactions. Control rules-based voltage control methods are not suitable for large scale networks where large number of control choices are available. Similarly, optimization-based voltage control methods are impractical to implement since many control variables have to be used to obtain the optimal solution. Therefore in this paper, a new technique for choosing a global group of the most effective control variables considering the ones with low cost is proposed for voltage regulation in distribution networks. This technique is based on the concept of electrical distances between the voltage control devices and network nodes to derive a correction index (CI). The index represents the level of effectiveness of each control variable with respect to all violated voltages. The index is implemented in two phase algorithms (top–down and bottom-up) to identify the global group of control variables. The proposed technique takes into consideration five aspects: the effectiveness, availability, and cost of the control variables as well as the structural changes of networks and the coordination between control variables to simultaneously eliminate the violation in the voltages. The technique is fast and suitable to be implemented for online voltage control. The proposed method is successfully examined on the modified IEEE 123 distribution system under different scenarios. [ABSTRACT FROM AUTHOR]

Thanks to the unique features, deployment of battery energy storage systems in distribution systems is ever-increased. Therefore, new models are needed to capture the real-life characteristics. Beside active power, the battery energy storage system can exchange reactive power with the grid due to the inverter-based connection. Although some previous works have considered this issue, a detailed linear model suitable for the realistic large scale distribution systems is not addressed adequately. In this context, this paper proposes a mixed integer linear programming model for optimal battery energy storage system operation in distribution networks. The proposed model considers various parts of the battery energy storage system including battery pack, inverter, and transformer in addition to linear modeling of the reactive power and apparent power flow limit. Moreover, a linear power flow model is used to calculate voltage magnitudes and power losses with high accuracy. The proposed model is applied to the IEEE 33-bus test case and the results prove the accuracy and efficiency of the proposed model. The results demonstrate that considering reactive capability of the batteries offers new benefits including voltage profile improvement, decreasing reactive power flow in the network, reducing network losses, and releasing network and substation capacity. • Model BESS considering the parts including battery pack, inverter, and transformer. • Model BESS reactive power contribution based on the 4-quadratnt capability curve. • Mixed Integer Linear Programming model for optimal BESS operation. • Considering voltage magnitudes and network losses with precise linear equations. • Achieving diverse benefits besides conventional load leveling by proper modeling. [ABSTRACT FROM AUTHOR]

Battery Energy Storage Systems can provide various applications in the distribution networks including load leveling, expansion deferral, voltage profile improvement, frequency regulation, fast reserve, and renewable energy time shift. Despite offering various applications, the BESSs are characterized with high investment costs. An optimal investment plan can justify the cots by exploiting multiple simultaneous applications. To this end, this paper proposes a novel planning model for the BESSs in distribution network wherein both load leveling and voltage profile improvement applications are extracted. The load leveling application refers to storing cheap energy at off-peak periods to deliver at peak period with high energy costs. In this way, the load profile tends to be flat and resulting lower energy cost. The voltage profile improvement is achieved by the optimal reactive power control of the inverter located between the BESS and the grid. The idea is that the inverter can allocate rated power capacity to the reactive power exchange at periods with negligible or zero active power conversion. Simulation results demonstrate that the voltage profile can improve in some degrees without increasing planning and/or operation costs. Higher degrees of improvement can be achieved at the expanse of cost increase. Also, the simulations show that the conducted load leveling results to loss reduction, peak shaving, and network expansion deferral subsequently. • Battery energy storage systems are planned under unbalanced loading condition. • Optimal charging-discharging pattern is optimized for three-phase system. • Problem minimizes energy cost, and balance unsymmetrical loading. • Optimal place, capacity, power, and charging-discharging regime of batteries. [ABSTRACT FROM AUTHOR]

• Energy storage system is planned to minimize losses in active distribution grid. • Network is installed with distributed energy resources. • The planning determines optimal sizing and siting of energy storage systems. • Optimal operation pattern for both active-reactive powers is determined. • AC power flow including reactive power is carried out. This paper deals with energy storage system (ESS) in active distribution networks. The purpose is to install ESSs on the grid to minimize network losses. The problem is expressed as an optimization programming to minimize annualized cost of losses and annualized investment cost of ESSs at the same time. The constraints of the programming are given as security constraints of the network and ESS operational constraints. The network is also equipped with distributed energy resource (DER) and its uncertainty is modeled and dealt by means of stochastic programming. Different DERs including diesel, wind, and solar resources are modeled and studied. The proposed nonlinear mixed integer stochastic programming is solved by particle swarm optimization (PSO). AC power flow is adopted to consider both active and reactive powers in the model. The ESSs are modeled including both active and reactive powers. The introduced planning finds optimal location, capacity, and power for ESSs. Furthermore, the charging-discharging regime for active power of ESSs and injection-absorption pattern for reactive power of ESSs are determined. The introduced methodology is successfully simulated on a typical distribution network. The simulation results confirm that the planned strategy properly installs ESSs on the grid and minimizes network losses. The results demonstrate that the ESSs decrease network losses about 22%. Finally, considering reactive power for ESSs results in about 24% cost reduction. [ABSTRACT FROM AUTHOR]

This paper presents a new approach in monitoring of a power distribution system. It uses the bus voltage and injected current to extract the apparent impedance seen from the measuring unit location. Then the apparent impedance variation is used for the monitoring of different electrical quantities of the feeder such as feeder power factor, and the minimum and maximum of active and reactive power flow. This paper also presents the mathematics for defining the monitoring zone on the R-X plane to detect those parameters variations. The proposed method was tested with the unbalanced distribution system feeder loading, distributed and lumped model of solar, and wind power generations. OpenDSS and MATLAB are used to test the effectiveness of the method with the IEEE 8500 node test feeder. The dynamic performance of the proposed method is studied for online monitoring of the reactive power capability requirement of a Canadian utility for a wind farm integrated to the system. The results show that the monitoring method based on the apparent impedance has a good capability to detect different operation conditions. In addition, the simplicity of the proposed method allows easy application of it in smart grid and traditional distribution system. [ABSTRACT FROM PUBLISHER]

The integration of renewable energy resources (RESs) in power systems poses many research challenges. Research shows that the RES output may exceed the consumed power during the day. Consequently, the direction of the power flow on distribution lines can be reversed during some periods. As the voltage regulator is normally designed for unidirectional power flow, this may cause voltage violations on the distribution feeder. Therefore, most utilities try to set a penetration level (PL) limit for safe operation. On the other hand, time varying and unbalanced loading are the main characteristics of distribution systems. Moreover installation of intermittent and nondispatchable photovoltaic (PV) devices increases the control problems of distribution system. This paper presents an impedance-based monitoring method for detection of distribution system current behavior. It will be shown that by utilizing this monitoring technique, not only the small variation of PV PL can be easily detected, but also some fast transients such as the effect of cloud movement on PV system can be monitored. This monitoring technique employs only local measurements of bus voltages and line current to measure the apparent impedance seen at the installation point. The practical application of measured impedance as a monitoring technique shows its effectiveness for distribution system monitoring in presence of various PV PL. [ABSTRACT FROM PUBLISHER]

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]

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]

The purpose of this paper is to demonstrate the impacts of mobile battery and diesel DG in integrated electrical-heating networks for promoting the resilience, self-adequacy, load restoration, power quality as well as reducing the load shedding and operational cost. The case study is IEEE 33-bus electrical system with both the electrical and heating demands. Several buses of the grid are integrated with combined heat and power (CHP). The battery is moved between the buses hourly and the diesel DG is moved seasonally. The transfer time between origin and destination buses is considered in the given model. The electric network feeds three regions (i.e., three different loading patterns) including residential, industrial and agricultural areas where the major activity of the industrial loads is at night due to low energy price and the major activity of the agricultural loads is in the spring and summer. The outage of electricity and natural gas (NG) are two faults that are imposed on the network in order to evaluate the resilience and load restoration. The demand response program (DRP) is included in the model. Both the active and reactive powers are considered for battery, diesel DG and CHP. Several cases are simulated, studied and compared like fixed, mobile and mixed fixed-mobile locations for energy resources. The simulation results show that the proposed model reduces the total annual cost by 16.5% while the other costs such as purchased energy, NG and losses are reduced by 16.5%, 22.9% and 21.5%, respectively. The self-adequacy of network is increased by 2.5 h and the electrical-heating load restorations are increased by 36% and 38%, respectively. • Application of mobile battery for load restoration in electrical-heating system. • Optimal movement of disel DG and battery to minimize operational cost. • Modelling the shiftable/curtailable/critical loads and load shedding strategy. • Incorporating the uncertainty behavior of all loads and renewable resources. [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]

Power systems are complex systems that have great importance to socio-economic development due to the fact that the entire world relies on the electric network power supply for day-to-day life. Therefore, for the stable operation of power systems, several protection and control techniques are necessary. The power system controllers should have the ability to maintain power system stability. Three important quantities that should be effectively controlled to maintain the stability of power systems are frequency, rotor angle, and voltage. The voltage control in power systems maintains the voltage and reactive power within the required limits and the power factor control enhances the efficiency of power distribution systems by improving load power factors. Among various controls, the frequency control is the most time-consuming control mechanism of power systems due to the involvement of mechanical parts. As the control algorithms of frequency stabilization deliver control signals in the timescale of seconds, load frequency control (LFC) systems cannot handle complicated data validation algorithms, making them more vulnerable to disturbances and cyber-attacks. In addition, the LFC system has extended digital layers with open communication networks and is designed to operate with less human intervention. Moreover, the frequency fluctuation due to load change or cyber-attack in one area affects all other interconnected areas, and thus threatens the stability of the entire network. Due to these circumstances, research activities are still carried out in the field of frequency control and cyber-security. In this paper, a comprehensive review of the cyber-security of the LFC mechanism in the power system is presented. The highlights of the paper include the identification of attack points of different configurations of the LFC system, discussion of the attack strategies, formulation of various attack models, and a brief review of the existing detection and defense mechanisms against cyber-attacks on LFC. [ABSTRACT FROM AUTHOR]