Distributed generation (DG) is expected to become more important in the future generation system. The current literature, however, does not use a consistent definition of DG. This paper discusses the relevant issues and aims at providing a general definition for distributed power generation in competitive electricity markets. In general, DG can be defined as electric power generation within distribution networks or on the customer side of the network. In addition, the terms distributed resources, distributed capacity and distributed utility are discussed. Network and connection issues of distributed generation are presented, too.
Low voltage dc microgrids have been widely used for supplying critical loads, such as data centers and remote communication stations. Consequently, it is important to ensure redundancy and enough energy capacity in order to support possible increments in load consumption. This is achieved by means of expansion of the energy storage system by adding extra distributed energy storage units. However, using distributed energy storage units adds more challenges in microgrids control, since stored energy should be balanced in order to avoid deep discharge or over-charge in one of the energy storage units. Typically, voltage droop loops are used for interconnecting several different units in parallel to a microgrid. This paper proposes a new decentralized strategy based on fuzzy logic that ensures stored energy balance for a low voltage dc microgrid with distributed battery energy storage systems by modifying the virtual resistances of the droop controllers in accordance with the state of charge of each energy storage unit. Additionally, the virtual resistance is adjusted in order to reduce the voltage deviation at the common dc bus. The units are self-controlled by using local variables only, hence, the microgrid can operate without relying on communication systems. Hardware in the loop results show the feasibility of the proposed method.
With the rapid increase in distributed generation (DG), the issue of voltage regulation in the distribution network becomes more significant, and centralized voltage control (or active network management) is one of the proposed methods. Alternative work on intelligent distributed voltage and reactive power control of DG has also demonstrated benefits in terms of the minimization of voltage variation and violations as well as the ability to connect larger generators to the distribution network. This paper uses optimal power flow to compare the two methods and shows that intelligent distributed voltage and reactive power control of the DG gives similar results to those obtained by centralized management in terms of the potential for connecting increased capacities within existing networks
This paper introduces a new magnetically coupled single-switch nonisolated dc-dc converter with a high-voltage gain. The topology utilizes magnetic coupling for boosting its output voltage, but unlike other converters with coupled magnetics, its voltage gain is increased by reducing its magnetic turns ratio. The name "Trans-inverse (Tx -1 )" is thus used for representing this inverse operating principle of the converter. The converter draws a continuous current from the source and is, hence, suitable for many types of renewable sources. Its leakage energy from the coupled magnetics has further been recycled and transferred to the load by an integrated regenerative snubber circuit. Its inclusion of dc-current-blocking capacitors has also helped to prevent core saturation, which, together with other performance features, has been verified experimentally.
This paper presents a model for use in the problem of multistage planning of energy distribution systems including distributed generation. The expansion model allows alternatives to be considered for increasing the capacity of existing substations, for installing new ones, for using distributed generation, and for the possible change to feeders in terms of addition and removing feeders sections; combining, subdividing, and load transfer between feeders; and replacement of conductors. The objective function to be minimized is the present value of total installation costs (feeders and substations), of operating and maintaining the network, and of distributed generation. The model takes operational constraints on equipment capacities and voltage limits together into account with logical constraints, aimed at reducing the search space. This paper presents: (1) an extension to the linear disjunctive formulation to represent the inclusion, exclusion, and replacement of branches and (2) a generalization of constraints related to the creation of new paths which can be applied in more complex topologies. The resulting mixed integer linear model allows the optimal solution to be found using mathematical programming methods, such as the branch-and-bound algorithm. The validity and efficiency of the model are demonstrated in Part II of this paper.
This review paper is focused on the impact of distributed generation (DG) on distribution system protection. The integration of DG is transforming the traditional radial distribution system into a multi-source system that requires protection that is capable of maintaining proper coordination under bi-directional and variable power flow conditions. The multiple types of DGs with different short circuit characteristics mean that the protection must also be effective under conditions of unpredictable fault currents. New grid code requirements demand that DGs remain connected under fault conditions to provide grid support and improve system reliability and security of supply. A discussion is given of the traditional protection techniques for the distribution system and the shortcomings of such techniques when DGs are integrated into the system. The paper also presents a wide survey and review of recent techniques proposed by various researchers to mitigate the effects of DG integration on the performance of distribution system protection. Centralised and distributed techniques have been proposed that include deployment of intelligent smart devices and communication systems to enhance and provide novel ideas for solving the protection problem. The implementation challenges of these techniques are discussed and proposals for the future given.
The Solid-state transformer (SST) has been proposed by researchers to replace the regular distribution transformer in the future smart grid. The SST provides ports for the integration of storage and distributed generation (DG), e.g., photovoltaic (PV), and enables the implementation of power quality features. This paper proposes a SST topology based on a quad-active-bridge (QAB) converter which not only provides isolation for the load, but also for DG and storage. A gyrator-based average model is developed for a general multiactive-bridge (MAB) converter, and expressions to determine the power rating of the MAB ports are derived. These results are then applied to analyze the QAB converter. For the control of the dc-dc stage of the proposed QAB-based SST integrating PV and battery, a technique that accounts for the cross-coupling characteristics of the QAB converter in order to improve the regulation of the high-voltage-dc link is introduced. This is done by transferring the disturbances onto the battery. The control loops are designed using single-input single-output techniques with different bandwidths. The dynamic performance of the control strategy is verified through extensive simulation and experimental results.
In this paper, a novel high step-up dc-dc converter for distributed generation systems is proposed. The concept is to utilize two capacitors and one coupled inductor. The two capacitors are charged in parallel during the switch-off period and are discharged in series during the switch-on period by the energy stored in the coupled inductor to achieve a high step-up voltage gain. In addition, the leakage-inductor energy of the coupled inductor is recycled with a passive clamp circuit. Thus, the voltage stress on the main switch is reduced. The switch with low resistance R DS(ON) can be adopted to reduce the conduction loss. In addition, the reverse-recovery problem of the diodes is alleviated, and thus, the efficiency can be further improved. The operating principle and steady-state analyses are discussed in detail. Finally, a prototype circuit with 24-V input voltage, 400-V output voltage, and 200-W output power is implemented in the laboratory to verify the performance of the proposed converter.
In this paper a technical review of parallel operation of power electronics inverters for load sharing conditions in distributed generation (DG) network is presented. Emphasis is given to parallel operation of Active Power Filters (APFs) as they are widely used to mitigate load current disturbances into DG networks. Discussions on recent advances in control strategies as applied to APFs are presented.
This paper introduces a versatile Y-source boost dc/dc converter intended for distributed power generation, where high gain is often demanded. The proposed converter uses a Y-source impedance network realized with a tightly coupled three-winding inductor for high voltage boosting that is presently unmatched by existing impedance networks. The proposed converter also has more variables for tuning the required gain and, hence, more degrees of freedom for meeting design constraints. These capabilities have been demonstrated by mathematical derivation and experimental testing. For the experiments, a 300-W prototype has been built in the laboratory using silicon carbide devices for better efficiency. The prototype has been tested with a regulated power supply, before operating it with a high-temperature proton-exchange-membrane fuel cell. Results obtained confirm the practicality and performance of the proposed converter.