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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]

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]

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]

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]

• 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]

• 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]