This paper demonstrates how reactive power injection from distributed generators can be used to mitigate the voltage/VAR control problem of a distribution network. Firstly, power flow equations are formulated with arbitrarily located distributed generators in the network. Since reactive power injection is limited by economic viability and power electronics interface, we formulate voltage/VAR control as a constrained optimization problem. The formulation aims to minimize the combined reactive power injection by distributed generators, with constraints on: 1) power flow equations; 2) voltage regulation; 3) phase imbalance correction; and 4) maximum and minimum reactive power injection. The formulation is a nonconvex problem thereby making the search for an optimal solution extremely complex. So, a suboptimal approach is proposed based on methods of sequential convex programming (SCP). Comparing our suboptimal approach with the optimal solution obtained from branch and bound method, we show the trade-off in quality of our solution with runtime. We also validate our approach on the IEEE 123 node test feeder and illustrate the efficacy of using distributed generators as distributed reactive power resource.

Voltage/VAR Control in Distribution Networks via Reactive Power Injection Through Distributed Generators

Distributed generation (DG) connected to distribution networks affects the currents or power flows in the networks; thus, node voltages that are strongly related to power flows also are changed. As the voltage must be within permitted limits to comply with utility and customer requirements, this effect should be assessed prior to DG connection. At the distribution level there are a number of attributes that can influence the voltage profiles; therefore, this assessment requires detailed distribution operation models. To provide reliable voltage evaluation results, a new probabilistic methodology is proposed in this paper. The distribution system operation uncertainties including daily time varying load, stochastic DG power production, network configuration, and voltage control devices operation are all taken into account. A probabilistic load flow method based on an efficient algorithm is used to handle uncertainties in loads and DG output power and voltage control devices operation. Accordingly, a probabilistic network reconfiguration model is employed to take stochastic network configurations for service restoration or load balancing into consideration. The proposed probabilistic method provides a better knowledge of the voltage effects and can be used for evaluating the level of DG that might be accepted on a distribution network. The models developed can also be used for assessing impact of voltage mitigation equipment on distribution operating performance. Test results of a modified IEEE feeder test system demonstrate the performance of the proposed method.

Stochastic Evaluation of Voltages in Distribution Networks With Distributed Generation Using Detailed Distribution Operation Models

An improved control scheme based in droop characteristic for microgrid converters

A meta-heuristic firefly algorithm based smart control strategy and analysis of a grid connected hybrid photovoltaic/wind distributed generation system

Due to the increasing penetration of distributed generation, storage, electric vehicles, and new information communication technologies, distribution networks are evolving toward the smart grid paradigm. For this reason, new control strategies, algorithms, and technologies need to be tested and validated before their actual field implementation. In this paper, we present a novel modular distributed infrastructure, based on real-time simulation, for multipurpose smart grid studies. The different components of the infrastructure are described, and the system is applied to a case study based on a real urban district located in northern Italy. The presented infrastructure is shown to be flexible and useful for different and multidisciplinary smart grid studies.

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A Flexible Distributed Infrastructure for Real-Time Cosimulations in Smart Grids

As a consequence of the growing importance of distributed generation (DG) it's very important to study the distribution network behavior. In this paper, voltage profile and gradient are analyzed taking in account power in-feed/out-feed of DG. The influence of reactive power requirements on the network voltage levels, based in the comparison of software simulation results with real-life behavior, are also studied. This paper equally analyzes the impact of DG on the substation transformers taps changers, with and without DG. Finally, it's analyzed the impact of DG on protection systems functioning in a 60 kV network.

F. Bastiao

Papers

Impact of distributed generation on distribution networks