Optimal allocation and operation of distributed generation and energy storage in distribution systems

Research Doctorate - Doctor of Philosophy (PhD)Distribution systems start from the distribution substation and deliver the power to the end users. Traditionally, the planning and operation of distribution systems have received less attention than transmission system which leads to the overdesign and inefficiency of distribution systems. Fast developing energy technology together with the environmental concerns has greatly increased the complexity of power grid and distribution systems, where the desire to increase the efficiency of energy distribution and consumption is increased. Additionally, with the requirement of high quality and reliable power supply to consumers, smart grid has been identified as the next generation of electric power systems around the globe. In the context of smart grid, the modern distribution system is changing from passive to active by distributed generation, communication technology, and automation control devices. We can see the significantly increasing penetration of new power engineering technologies, such as renewable energy distributed generation, energy storage, and other factors. There is a need to fully exploit the potential advantages of these new elements in smart distribution systems. The distribution system along with smart devices, as the solution to the need for grid development, provides utilities with many benefits, including improved operational efficiency, flexibility and power quality. However, despite those benefits, the planning of smart distribution system is a problem of vital importance since it concerns how the system is designed to achieve higher efficiency and reliability. The planning methods of the existing distribution system are either inappropriate for practical use in dealing with the emerging elements or impossible to achieve the global optimal solution. As a result, in-depth research is needed to solve these emerging and difficult problems in planning and operation. Most of the existing researches focus on one type of elements in the distribution system without taking other components and their implications on the overall system performance into consideration. In addition, they seldom consider the effects of electricity market or quantify the economic value brought by the reliability of the updated distribution systems. Therefore, in order to improve the economic efficiency and sustainability of smart grids, this research develops advanced planning methods for better integration and operation of new emerging elements, especially the distributed generation and energy storage in modern distribution system. First, a novel method for optimal allocation of renewable distributed generator (DG) is proposed. The optimal allocation of DG can not only reduce power loss through the feeder, but also improve the voltage stability, which is beneficial to both the economy and security of distribution systems. Multi-objective function is applied to quantify the impact brought by the increasing penetration of renewable DGs. To be more practical and accurate, the 3-phase untransposed distribution lines and unbalanced load are considered and modelled in the proposed planning method. Meanwhile, a MPC-based wind farm operation strategy is proposed to enhance the output power quality of DG, so as to meet the grid requirement. After that, with the increasing penetration of electric vehicles, an important aspect of modern traffic system, the ancillary facilities should be properly planned. A novel planning approach based on life cycle cost (LCC) is developed for battery charging/swap stations in distribution systems. Battery swap stations and charging station are compared and optimally integrated into distribution system to meet the requirements of the increasing charging power and minimize the overall investment. At last, the battery energy storage system (BESS), which has potential to facilitate high penetration of renewable energy, is investigated. A novel operation strategy for charging/discharging batteries in distribution system and optimizing the allocation of the energy storage system (ESS) is proposed for the Distribution Company (DISCO). With the increasing penetration of renewable energy in distribution system, the net demand curve will significantly deviate from the forecast curve, resulting in high risk to the DISCO when making its energy purchasing plan. The proposed strategy, aiming at tracking the total forecast demand curve, can mitigate the risk and encourage the demand side bidding. Based on the proposed operation strategy for the BESS, the optimal allocation method is designed to determine the location and the size of BESS, in order to maximize the total profit for the DISCO. Furthermore, BESS can be mobilized to make the operation of distribution system more flexible and reliable. Hence, mobile BESS (MBESS) is modeled in this work as well. The corresponding sizing approach is developed for the sake of reliability improvement. A number of test systems have been used to demonstrate the effectiveness of the proposed advanced planning approaches. Comparative studies on the existing approaches reported in the literature where they are applicable, have also been conducted. The effectiveness and feasibility of the proposed approaches have been verified by simulation results