Investigations on control techniques for optimized operation and stability enhancement of power distribution system with microgrid

Abstract

Energy is critical and it indirectly plays a vital role in the growth of the economy of both developing and developed countries. India is amongst Demand for electrical energy continues to grow steadily. But the generation is not growing proportionately to meet the growing demand. Currently the total installed capacity in India is around 237 GW. But in India 35% of the rural power generation capacity, before 2017, to satisfy the projected demand. Until this new capacity addition is done, existing power generation capability has to address the present and future increase in demand which is much higher than generation capacity. This leads to increased levels of complexities in power management. To overcome this problem, an interconnected grid system should be used on the basis of demand. But the dynamic behaviour of the integrated power system is accompanied by more complexities that gives rise to the problems in planning, operation and control. For proper system planning, flexible operation and control of the system is necessary to enhance the power quality and reliability. This situation has led to an increase in systems which provide the required solutions. Normally the power system is highly non linear in nature which makes it difficult to control. Control of power swing oscillations is an important control problem. Conventionally, linear controllers are used to stabilize the power system. Since the linear 6 controllers are not able to predict the non local behaviour of the system when it is far away from the operating point, the linear controllers may not be adequate to stabilize the system. Recently, the widespread use of power system controllers, such as Power System Stabilizer (PSS) and Flexible AC Transmission Systems (FACTS) controllers, has led to the analysis of their effect on the overall stability of power systems. In this research work, a nonlinear control law to enhance the asymptotic stability of a Single Machine Infinite Bus (SMIB) system using Immersion and Invariance (I&I) control strategy is developed. The control law is designed using MATLAB/ SIMULINK based on modeling equation of a SMIB system with a first order model of the Controllable Series Capacitor (CSC), to achieve enhanced stabilization of power system by damping of electromechanical oscillations in the system. The proposed control law which includes the damping factor quickly damps out the power system oscillations caused by interruptions. Nowadays, due to depletion of fossil fuel resources, the conventional power system has become more and more stressed. The conventional grid has limitations, in terms of efficiency and environmental impact as well as stability to sustain them, which have given rise to renewable energy resource options for researchers. The power industry is responsible for renovating the structure of power generation, and providing a clean, safe and reliable electric energy supply. Hence there is a need to enhance the capacity and flexibility with new emerging trends of generating energy by using nonconventional energy sources like wind, solar, fuel cells, microturbine etc. These types of electric distribution technologies satisfy both supply side and 7 demand side by integration of distributed energy resources to the utility grid. Distribution networks are the final connection between the transmission networks and electricity consumers. A distribution network with Distributed Generation (DG) unit is termed as active distribution network to incorporate flexible and intelligence concept through microgrid. A microgrid consists of a cluster of loads and distributed generators which operate as a single controllable system. The generators or microsources are employed in a microgrid are usually renewable/non-conventional DERs integrated together to generate power at distribution voltage level. To obtain stable and secure operation, the microgrid can be connected to the main utility power system as a single controlled unit to meet local energy needs. Control of power systems is a big task when the system is interconnected. As power systems have evolved through continuing growth in interconnections, use of new technologies and controls, different forms of system stability issues like voltage stability, frequency stability and inter area oscillations have become a greater concern. Due to interconnection, the frequency deviates, and through additional control the frequency support can be improved. In a microgrid, microsources are normally installed close to the customer s premises so that the electrical/heat loads can be efficiently supplied with satisfactory voltage and frequency profile. The main challenge identified in microgrid related research is how intelligently the power loss can be reduced to meet the improvement in voltage profile. In this research, soft computing algorithm is developed to analyze the stability performance of the power system integrated with microgrid. The better stabilization is observed 8 in terms of reduction of power loss and also maintenance of suitable voltage level using proposed hybrid algorithm. Whenever the load variation is more, power loss is also more, an improved algorithm is developed to investigate the stability enhancement of systems using Adaptive Neuro-Fuzzy Inference System (ANFIS) and Particle Swarm Optimization (PSO) techniques. In this research work, using the proposed algorithm, the microgrid is optimally fixed in a suitable location, so that more reduction in power loss and better voltage profile is obtained. All tests and comparisons are illustrated using IEEE 30- bus benchmark systems. Recently electric storage has shown much attention due to their technological improvements and economic benefits. In order to use renewable energy sources to supply the variable demand, integration into the electricity system and the development of a future decentralised energy supply system, reliable and affordable electricity storage technologies are required. Energy storage systems should provide quick and cost effective solution to the problem of balancing electricity generation and consumption. A delayed response to a power requirement and inadequate or excessive power levels are unacceptable to industrial, commercial and private consumers can lead to application failures. In most proposed microgrid operation strategies, electric storage such as batteries is used to store energy when there is extra generation, then at peak times the stored energy is served to the grid through power electronic inverters. 9 Apart from various energy storage technologies Compressed Air Energy Storage (CAES) technology is one of the newer technologies is preferred in the case of absence of water reservoirs facilitates. The focus of this work includes the potential of power system with microgrid consists of compressed energy storage technology, to provide effective air flow control, stabilizing mechanism and demand response. The maintenance of frequency stabilization under the variation of load demands by employing compressed energy storage system is illustrated through simulation results. The research work can also be extended in future by incorporating advanced hybrid intelligent algorithms to initiate load shedding before controlling the power loss. Consequently, this research work can be further enhanced by integration of a number of energy storage systems to balance the power demands.