Dalal Asber

A Decentralized Control of Partitioned Power Networks for Voltage Regulation and Prevention Against Disturbance Propagation

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.

Measuring the efficiency of voltage reduction at Hydro-Québec distribution

The goal of this paper is to describe the methodology used to assess the effectiveness of conservation voltage reduction in the Hydro-Quebec distribution network. The motivation for attempting to control the load is presented as well as different procedures that have lead to conclude to the economic feasibility of the concept. The rational for the deployment plan is presented.

Active-power stabilizers for multimachine power systems: challenges and prospects

The problem of stabilizing a bulk power system by modulating controllable active loads is investigated. With todays advances in power distribution and home automation, fibre optic communications and networking, such a scheme for improving the reliability of bulk power supply is increasingly attractive. After developing a generic model for active load-modulation studies, time domain modal analysis is applied to a three-machine-nine-bus system in order to assess quantitatively its responsiveness with respect to controller location and observed response signals. This structural analysis shows that proportional control is unsatisfactory and may artificially restrict the economic benefits of active-load modulation. By contrast, using the bus voltage and frequency as input signals, combined with suitable dynamic compensators, yields a fully decentralized, two-loop load stabilizer able to add damping to all grid modes in the sample power system. Finally, placement and sizing issues are considered and preliminary observations based on transient stability studies are made.

A Monitoring Technique for Reversed Power Flow Detection With High PV Penetration Level

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.

Large-scale active-load modulation for angle stability improvement

Analyses, operating experience and simulations of a large power system are used to demonstrate that active-load modulation can improve the systems dynamic performance to a large extent, with just a fraction of the base load available for control. At a time when the cost effectiveness of FACTS devices for damping interarea oscillations is constantly being questioned, it is natural to look to active-load modulation as a potential alternative method of insuring grid reliability. In developing the case, it was found that continuously modulating load stabilizers need to be fed with global signals for full efficiency. Although more difficult to design, implementation of a discontinuous control scheme shows good prospects, especially with regard to decentralization and robustness against communication delays.

Coordinated Control Strategy Considering Effect of Neighborhood Compensation for Voltage Improvement in Transmission Systems

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.

Modeling of Distribution Loads for Short and Medium-Term Load Forecasting

Utilities need to anticipate future load to properly plan system expansion and operation. This paper investigates methods to forecast future mid-term distribution system loads. In this horizon, the prevailing weather plays an important role. Other important considerations include the load composition, its residential and commercial mixture, lifestyle dependency, as well as secondary factors such as wind and solar radiation. The objective of this paper is to demonstrate how one can use a general load-modeling framework to systematically extract the essence of specific modeling problems and to obtain practical models. The key requirements for practical load modeling tools are to make maximum use of available load data while limiting the computational burden.

Voltage Flicker Mitigation Employing Smart Loads With High Penetration of Renewable Energy in Distribution Systems

This paper deals with modeling and control of smart loads for demand-response management under increased penetration of renewable power generations (RPGs) at distribution level. The increased penetration of RPGs, particularly wind energy at distribution level, is associated with adverse impact on voltage quality. A permanent magnet synchronous generator based variable speed wind energy conversion system is modeled with a wind speed considering stochastic and periodic effects. The emulated wind power into the distribution system produces stochastic and periodic power variations. For the load demand response management, full-bridge self-commutated switches based converters are employed to control smart loads (SLs). These SLs are controlled for participating in grid bus voltage regulation and flickers mitigation. From various case studies, it is found that SLs are effective in improving the voltage profiles of the test feeder.

Graph partitioning of power network for emergency voltage control

This paper presents an electrical network graph partitioning technique that divides a power network into zones. The idea of partitioning is to prevent the propagation of disturbances between zones and avoid cascading events in response to disturbances. Identifying coherent groups of buses in power electrical networks is crucial to implement efficient control strategies based on partitioning techniques. Furthermore, the coherent buses can be used for model reduction of complex power systems. Graph theory has an excellent capability to simplify large connoted networks such as the case with large power networks. In this paper, graph partitioning algorithm is applied to electrical networks including IEEE 39-bus and IEEE 118-bus. Graphs with and without weights are considered to investigate and compare the results of using graph partition algorithm. Weights in a graph power system can be real, reactive or apparent power transferred between buses. Finally, disturbances are intentionally inserted on the loads to verify the performance of partitioned power network to violation. The results show the performance and ability of graph partitioning when used in conjunction with a large power network.

Application of distance relay for distribution system monitoring

The traditional distribution network is primarily composed of radial feeders, designed for unidirectional power flow. Therefore, many operation regulation, protection and control system, in distribution network, are based on the radial distribution systems assumption. The integration of decentralized renewable sources will create a multidirectional power flow condition in the distribution grid which was originally designed for unidirectional power flow only. Integration of that active element increases the importance of new distribution system monitoring. In addition, based on the distributed generation interconnection of some utilities, over current protection is not sufficient for feeder protection in presence of renewable energies integration. Therefore, it is recommended to install a distance relay as the main protection of feeder. This paper presents using the distance relay not only as a protection device, but also as a monitoring tool at presence of renewable energies.