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ABSTRACT Decentralized Reactive Power Control for Advanced Distribution Automation Systems

CURRENTLY, the power network is undergo plete reconstruction. Motivated by technical, economic ing a command environmental factors, this reconstruction will lead to the new concept of smart grid. In [1], advanced distribution automation (ADA) is described as the “heart of the smart power delivery system.” Generally speaking, ADA is a concept that will make the distribution system fully controllable and flexible. In ADA all controllable equipment and control functions are to be automated to achieve the optimal operation of the system. Incorporating advanced control strategies, new technologies and communication schemes, ADA will result in higher reliability, minimal losses, optimal utilization of distribution system assets, and integration of larger amounts of renewable energy into the existing distribution systems.

In order to achieve the ADA concept, it is essential for many distribution system equipment to become intelligent. These devices will range from power quality management devices and monitoring devices to voltage and Var control equipment. Hence, the ADA concept, in part of it, will evolve as a large distributed intelligence platform in which the distribution system operation functions will be achieved. As a result, there is a need for advanced control techniques to utilize the distributed intelligence in the system in order to carry out the system operation in an optimal manner.

For decades the Var control has been identified as one of the crucial operation functions of the distribution system. Efficient Var control reduces system losses, improves voltage profile, and hence enhances the delivered power quality and overall system reliability.

As a matter of fact, the increasing penetration of distribution generation (DG) in distribution systems in recent years makes it even more crucial to have efficient reactive power operation schemes. In reality, the presence of DG in distribution feeders change its voltage profile greatly and hence interrupt the voltage sensing capabilities of capacitor banks which, basically, depends on ever-decreasing feeder’s voltage profile. On top of that, efficient coordination between feeder’s capacitors and DGs can allow for the integration of more DGs in the system.

Most of the research in Var control area was concerned with the planning of the reactive power. The optimal capacitor sizing and allocation problem has been studied extensively in the literature [2]–[4]. On the other hand, the operation of the reactive power control equipment had received little attention. It has been the usual practice in utilities to operate capacitor banks based on local signals such as time of day or current magnitude with the aim to have the capacitors connected at maximum load and disconnected at minimum load. Currently, there is a need to adopt a more efficient reactive power control schemes in order to achieve the goals of the smart grid by having a more efficient and reliable distribution system. Several solutions have been reported in literature to achieve the optimal reactive power control in the presence of DG. Forming the reactive power control as a centralized optimization problem has been proposed in different works [5]–[8].

In these techniques, a central point monitors the status of the reactive power control equipment, perform a load forecast for a certain horizon, solve a reactive power optimization problem based on the forecasted conditions and finally determine the optimal settings for the reactive power control equipment. The problems with this approach are, first, for large systems, the centralized approach will be too cumbersome. Second, given that this approach is based on load forecasting, there is no guarantee for the accuracy of the solution especially in the presence of renewable-based DG with varying output power. Another emerging approach is solving the problem in a decentralized manner. In [9], a multiagent decentralized reactive power DG dispatch for the support of the system voltage was proposed. The problem with that approach is that it assumes the existence of a moderator point which takes bids from DGs and calculates the optimal overall solution which is, more or less, a centralized way of solving the problem. In another work [10], a decentralized approach for the control of DG reactive power output was proposed to mitigate the voltage rise due to the connection of the DG. This work is not applicable for the control of other reactive power control equipment of the system such as capacitors.

In this paper, we propose a decentralized optimal reactive power control scheme. The proposed scheme controls the switched capacitor banks, and possibly other reactive power control devices, in real time. This approach is based on the existing loading conditions to minimize the system losses while maintaining acceptable voltage profile for the feeder. The proposed scheme is based on the coordination between RTU located at each DG and at each shunt capacitor of the feeder to form a multiagent system.

This paper is structured as follows; Section III details the voltage profile estimation technique based on the readings of the RTU located at the DG buses and the capacitors buses. Following that, the estimation of the change of the voltage profile due to the injection of the reactive power at the capacitor bus is discussed in Section IV. Based on the results of Sections III and IV, the proposed system structure for the reactive power control is presented in Section V. The reactive power control algorithm is presented in Section VI for the case of single capacitors and is generalized in Section VII. Simulation study is provided in Section VIII to validate the proposed technique. The paper’s conclusions are drawn in Section IX.