OPTIMAL PLACEMENT OF DISTRIBUTED GENERATION IN DISTRIBUTION NETWORKS

Abstract

Objective of power system operation is to meet the demand at all the locations within power network economically and reliably. The traditional electric power generation systems utilize the conventional energy resources, such as fossil fuels, hydro, nuclear etc. for electricity generation. The operation of such traditional generation systems is based on centralized control utility generators. These generators deliver power to the widely dispersed users through an extensive transmission and distribution network. In the present environment, the justification for the large central-station plants is weakening, due to depleting conventional resources, increased transmission and distribution costs, deregulation trends, heightened environmental concerns, and technological advancements. Distributed Generations (DGs), a term commonly used for small-scale generations, offer solution to many of these new challenges. DGs are also referred to as ‘Embedded Generations’ or ‘Disperse Generations’. CIGRE define DG as the generating plant with a maximum capacity of less than 100MW, which is usually connected to the distribution networks and that are neither centrally planned nor dispatched. There are many definitions of DG in the literature as it depends upon the many technologies and many applications in different environment. Presently, numbers of DG technologies are available in the market and few are still in the research and development stage. Some currently available technologies are reciprocating engines, micro turbines, combustion gas turbines, fuel cells, photovoltaic, and wind turbines. During the last few years, the penetration of DG in the power distribution systems has been increasing rapidly in many parts of the world. As the penetration of distributed generation is increasing in the distribution network, it is no more passive in nature and its characteristics is becoming similar to an active transmission network. Therefore, it is in the best interest of all the players involved to allocate them in an optimal way such that it could increase reliability, reduce system losses and hence improve the voltage profile while serving the primary goal of power injection. It is evident that any loss reduction is beneficial to distribution utilities, which is generally the entity responsibility to keep the losses at low level. Loss reduction is therefore most important factor to be considered in planning and operation of DG. In this work, different types of DGs based on their capability of injecting real and/or reactive power have been proposed to be placed in a planned manner into the distribution systems. The developed methodologies will be helpful to the developing countries like India, for integrating DG into the electrical systems for improvement in the system performance and for mitigation of the power deficiency. The availability of quality supply of electricity is very crucial for the sustained growth of a country. Presently, India is in power deficient state, the average power deficiency is nearly 12.2% of peak demand. In the developing countries like India, DGs may widely be used to supply electric loads in integration with the grid. Some of the factors that must be taken into account in the planning process of expanding distribution system with DG are: the capacity of DG unit, best location and technology, the network connection, capacity of existing system, protection schemes, among others. Different methodologies and tools have been developed to identify optimal places to install DG capacity and its size. These methodologies are based on: knowledge-based approaches, optimization programs or heuristic techniques. The computer aided techniques have been employed for the purpose of mathematical modeling and implementation of the various approaches for the optimal placement of DGs in order to reduce losses and the improvement in voltage profiles. References reveal that many heuristic techniques like genetic algorithm (GA), tabu search algorithm, ant colony search algorithm and fuzzy logic have been used for optimal placement of DG, which requires extended computational time, and large memory size. Naturally, a more efficient approach is the need of the hour. Therefore, an analytical method and the application of particle swarm optimization (PSO) technique have been proposed in the present work for optimal placement of DGs to minimize the system losses, improvement in voltage profile and maximization of benefits. The PSO technique is computationally efficient and is a metaheuristic as it makes few or no assumptions about the problem being optimized and can search very large spaces of candidate solutions. It does not require that the optimization problem be differentiable as is required by classical optimization methods. Considerable amount of work on the sizing and siting of DGs have been reported in the literature, however some of the research gaps need attention of the researchers. Analytical methodology, PSO based algorithm and hybrid approaches have been applied to different configurations of DGs in different distribution systems. The results obtained have been compared for the validation of the proposed approaches. Optimal placement of DG units in the distribution systems reduces the energy losses, improves the voltage profile, releases the transmission capacity, decreases equipment stress, and defers transmission and distribution upgrades. For even a small distribution network, the selection of the best DG allocation plan among the different possibilities needs computationally arduous efforts. Least loss method is one of the criteria to select the appropriate bus for DG placement, consequently, to reduce the search space and thus, to save the computational time to attain an optimal solution. To cater this requirement, an analytical approach has been developed for calculating the optimal size and location of type-I DGs in radial distribution system. The developed algorithm has been successfully applied to a 33-bus and 69-bus distribution test systems. The obtained results have been compared with the results obtained using PSO technique and loss sensitivity approach. The proper allocation of DG units in distribution system plays a important role in achieving economical, technical, and qualitative benefits. Depending on their location, DG units may improve or worsen the system performance. The reduction of real power losses, improvement in voltage profile, diminution of harmonic pollution, enhancement in reliability, and deferral of network upgrade have been reported as the primary aims for DG placement in the literature. Most of these DG allocation techniques are well suited to allocate DGs injecting real power output. Since these existing techniques, do not incorporate the integration of type-I DG in reactive power compensated network. In this work optimal placement of type-I DG is integrated in reactive power compensated network in distribution systems. The reactive power of the network is compensated by the optimal placement of Capacitor. An analytical approach has been developed in this work to determine the optimal size, location and optimal power factor to achieve the objective by compensating the active and reactive powers. The objective function, considering the real power system loss has been minimized. The constraints on power flow equations, on bus voltages, on line loadings, and on sizes of DG and Capacitor have been considered. As distributed generation is defined as the generation of electricity by facilities that are sufficiently smaller than the central generating plants so to allow interconnection at nearly any point in a power system. The maximum DG installed capacity limits have been considered as 30%. The proposed approach has been applied to a 33-bus distribution test system, and also to a 69-bus distribution test system. In the proposed work, optimal power factor of DG has also been evaluated, and the effect of variation of power factor on the system losses has been analyzed. The results of the analytical approach have been compared with the results obtained based on other approaches like PSO and GA. As the capital cost of Capacitor is too less as compared to capital cost of DG. The integration of type-I DG in reactive power compensated network provides more economy to the system. The existing literature reveals that, the optimal placement of the DG in the distribution systems is for reduction of power losses, Improvement in system voltage profile, maximization of DG capacity, minimization of investment and diminution of harmonic pollution. The optimal placement of different types of DGs i.e., type-I DG, type-II DG, type-III DG and type-IV DG in the distribution system have not been given due consideration in the techniques reported. Hence, a realistic mathematical approach considering different types of DGs has been proposed here. Therefore, in this work suitable mathematical formulations have been developed for the optimal placement of different types of DG sources with various system constraints to minimize the system losses. The PSO based algorithm has been developed for the proposed approach and the obtained results are also verified with analytical approach results. Most of the optimal placement techniques to allocate multiple DGs use heuristic approach only, and do not take the advantage of analytical approach. The analytical techniques may not be appropriate for optimal placements of multiple DGs alone. To fill this void, a hybrid approach has been developed in this work for optimal placement of multiple DGs of multiple types. In this approach the sizes of multiple DGs are evaluated at each bus and the optimal locations and power factor are determined by PSO technique. The objective function has been minimized under operating constraints. The proposed hybrid approach is tested on 33-bus and 69-bus test systems and the obtained results are compared with the results obtained using PSO. The distribution system planners effort to supply economical and reliable electric power to the customer. It is important to design, operate and maintain the power system with lowest cost and highest benefit. Loss reduction and improvement in voltage profile are two important goals for electrical distribution companies. These companies work on various technologies and optimization programs to achieve economic benefits. They provide electricity with high quality and also prevent interruptions in distribution systems. The impact of DG on system operation depends highly on its location in the distribution system. Installation of DGs at improper locations would lead to increase in energy loss and loading of distribution feeders. For this reason, an optimization method must be used to find optimal DG location and size considering the costs and benefits to the customer and the utility. Optimal DG placement is a multivariable optimization problem with different operating constraints on DG in distribution system. Therefore, mathematical formulations for optimal sizing and siting of DGs and Capacitors in the distribution systems have also been developed in this work. The cost of electricity sold to the electricity market, loss reduction revenue, operating costs of DGs, constraints on number of DGs and Capacitors, maintenance costs and the payback period have been considered in this optimization. The developed formulation is a mixed-integer non-linear optimization problem and their solution has been obtained by a hybrid technique based on PSO approach. The various contributions made through this work are summarized as follows:  An analytical approach has been developed for optimal placement of type-I DG in the distribution system and the obtained results are compared with PSO technique and loss sensitivity approach results to validate the developed algorithm,  An analytical approach has been presented for optimal placement of type-I DG in reactive power compensated networks in a distribution system. The optimal power factor has also been considered in this work,  A PSO based algorithm has been proposed for optimal placement of different types of DGs sources i.e., type-I DG, type-II DG, type-III DG and type-IV DG in the distribution system and the results are validated with analytical approach,  An hybrid approach consisting of analytical method and PSO technique has been developed for optimal allocation of the multiple DG units in the distribution networks, comparison has been made with the developed PSO algorithm,  An objective function has been developed for the cost benefit analysis for DG placement in distribution network. This objective function has been maximized using PSO technique for the profit, taking the initial costs, operating costs, maintenance costs of DGs and Capacitors, cost of grid power, cost of DG power, present worth factor and payback period into consideration.