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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.

Active distribution networks will meet new challenges in voltage and congestion control due to the high penetration levels of distributed generations (DG). Optimal voltage control techniques are mainly based on the relation between the network voltages and control variables (i.e. power injection). Thus, in this paper, a centralized real time scheme using a fast method for computing the sensitivity coefficients is presented to control congestion and voltage problems. The sensitivity coefficients of network voltages as well as the branch line currents are obtained via direct analytical derivation. A 11KV, 75-bus distribution system including several DGs is used to validate the proposed method. Simulation results show that the proposed method is able to maintain the network voltages and line currents within acceptable limits.

As distribution networks continue in integrating Distributed Generation (DG) units, voltage stability problem becomes an important issue. On other hand, future distribution networks have the ability to support the transmission network. Thus, this work presents an online centralized controller for voltage stability improvement and High-Voltage (HV) side support. The method uses multi-step optimization method to obtain the changes in power injection by DG units while satisfy the system security constrains. The control method follows a security purpose and it is formulated based on the sensitivity of the load and the equivalent impedances to power injections from DG units. An 11kV, 77-bus test network with various DG units is used for this work. Simulation results validate the accuracy of the proposed approach in improving the voltage stability of distribution networks and providing ancillary services to HV side.

Sensitivity Analysis has been widely used for voltage control of power grids. Typically, the sensitivity coefficients of network voltages are extracted from the inverse of Jacobian matrix. However, updating these coefficients based on the network operation conditions requires significant consuming time, which may add a new challenge for online voltage control of future power grids with distributed generation (DG), especially in the context of optimization techniques. In this paper, a fast sensitivity method is presented to find the sensitivity coefficients of network voltages via an analytical derivation. The approach is based on network admittance matrix and does not require extensive computing time, which is an advantage to be implemented in online applications. A IIKV, 75-bus distribution network is used to verify the proposed method. A simple voltage control scenario is also presented to demonstrate the potential application of the proposed sensitivity method.

Preventive control selection for voltage stability concerns with determining the preventive controls that have to be activated, and finding a coordination between these preventive controls. This work develops an index, namely correction index CI, that can be used to rank the preventive controls for voltage stability analysis. This ranking helps the operators to select the most effective preventive controls to simultaneously mitigate the impacts of system contingencies on the critical buses. In other words, if such index is used for control selection, the useless (or less effective) controls can be ignored. This index is based on the degree of the effectiveness of the preventive controls to improve the voltage stability margin of power systems. The index can measure the efficiency of each preventive control not only to one bus (i.e. pilot bus), but to multiple critical buses of the system. The cost aspect is also involved in index calculation to distinguish between the cheap and the expensive controls. This means that the correction index helps the operators to select only the cheap and the high-effective controls. The proposed method is tested on the IEEE 39 bus network under a contingency scenario. The results show that the proposed index is accurate and valid for control ranking.

In this work, a novel method for choosing a global set of preventive controls for voltage stability analysis is developed. The method depends on top-down and bottom-up approaches to obtain the set of controls according to voltage stability sensitivity analysis. At first, the sensitivities of the voltage stability margins of network buses to preventive controls are obtained. The average of the sensitivities referred to each preventive control is then calculated, which gives an indicator about how each preventive control can improve the voltage stability margin of power system. The average is done over the sensitivities of different critical buses located at different locations. The two approaches (top-down and bottom-up) are then performed on the averaged sensitivities to choose a set of the most efficient controls. The proposed method is able to simultaneously eliminate the impact of system contingencies on network buses. The proposed method is checked on the IEEE 39 bus network. The results demonstrate the accuracy and the validity of the proposed method for control selection.

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.

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.

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.

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.