INTEGRATED VOLT/VAR OPTIMIZATION IN DISTRIBUTION SYSTEMS IN PRESENCE OF DISTRIBUTED GENERATION

Abstract

In recent years, smart grid initiatives, such as improvement in energy efficiency, demand reduction, better utilization of equipment, have created growing interest in Volt/VAr Optimization (VVO). The VVO can be effectively utilized to enhance the efficiency of a distribution network by means of coordinating Volt/VAr Control (VVC) devices. This research aims to study the effect of smart-grid technologies on the performance of traditional VVC devices and developing VVO frameworks in the presence of new technologies. With motivation to tackle new challenges, the research work presented in this thesis is divided into three parts, viz., identifying a suitable load model for volt/VAr optimization, VVO framework considering distributed generation in presence of harmonics, and development of VVO strategies for future distribution network. Each one of this is briefly discussed below. In a distribution network, the proper load modeling is necessary in order to accurately schedule the VVC devices. Previously, most of the research has been carried out to evaluate the energy losses of the distribution network by considering the constant power type of loads. A few researchers have considered different types of load models, such as constant power (PQ), constant current (I) and constant impedance (Z). However, there is no research on the effect of load models on the scheduling of VVC devices. The purpose of this research is to show the impact of load models on various operating parameters in the VVC. In this thesis, the impact of different load models on the scheduling of VVC devices is analyzed. Time-series simulations are carried on a modified IEEE-123 node unbalanced radial distribution network, where industrial, commercial, and residential loads are connected at various locations. A comparative study is performed under VVO framework to analyze energy consumption, losses, and peak load demand. It has also been observed that the load models make considerable effects on the settings of VVC devices. Therefore, the first objective of this thesis is to find the best settings of VVC devices with various load models while minimizing apparent energy losses of the network. Loads of a practical distribution network are voltage-dependent. Both real and reactive power components of a load will be affected by the variation in the terminal voltage. Consequently, rather than minimizing the active energy demand of the distribution network, the focus of this thesis to reduce the daily apparent energy demand of the network utilizing VVO. i In this, On-Load Tap Changers (OLTC) and Voltage Regulators (VRs) are used for voltage optimization, whereas Capacitor Banks (CBs) have been utilized as a local reactive power (VAr) generators (in the distribution system) provided operational and system constraints satisfied. This research also focuses on the minimization of daily apparent energy demand of the substation by means of optimal scheduling of OLTC, VRs, and CBs. The Solar Photovoltaic (SPV) systems and wind turbine generators are also assumed to be connected in the distribution system. Moreover, this study is extended to consider the effect of harmonics in the load currents. All the simulations are performed on the modified IEEE 33-bus (single-phase balanced) and IEEE 123-bus (three-phase unbalanced) radial distribution systems. More savings in terms of substation apparent energy are accomplished when DGs are connected into the system. Reductions up to 20% in substation’s apparent energy and 37% in network energy losses have been achieved. In the present scenario, many SPV systems have been installed in the distribution network, most of them are operating at the unity power factor, which do not provide any reactive power support. In the future distribution grid, there will be significant advances in operating strategies of SPV systems with the introduction of smart inverter functions. The new IEEE Std. 1547-2018 incorporates dynamic VVC for smart inverters. These smart inverters can inject or absorb reactive power and maintain the voltages at points of common coupling (PCCs) based on local voltage measurements. With multiple inverter-interfaced SPV systems connected to the grid, it become necessary task to develop local, distributed or hybrid VVC algorithms for maximization of energy saving. This research aims to estimate the substation energy savings by means of centralized and decentralized control of inverters of SPV system along with various VVC devices. The control strategies of each SPV inverter have been accomplished in compliance with IEEE Std. 1547-2018. The time series simulations are carried out on the modified IEEE-123 node test system. The results show that considerable energy savings can be obtained by considering smart inverter functions. The saving can be further increased by incorporating optimal intelligent VVC characteristics. All the proposed case studies are verified using simulation performed on standard test systems. The results and important findings obtained through simulation studies are presented in this thesis.