Coordinated Voltage and Reactive Power Control of Power Distribution Systems with Distributed Generation

Distribution system voltage and VAR control (VVC) is a technique that combines conservation voltage reduction and reactive power compensation to operate a distribution system at its optimal conditions. Coordinated VVC can provide major economic benefits for distribution utilities. Incorporating distributed generation (DG) to VVC can improve the system efficiency and reliability. The first part of this dissertation introduces a direct optimization formulation for VVC with DG. The control is formulated as a mixed integer non-linear programming (MINLP) problem. The formulation is based on a three-phase power flow with accurate component models. The VVC problem is solved with a state of the art open-source academic solver utilizing an outer approximation algorithm. Applying the approach to several test feeders, including IEEE 13-node and 37-node radial test feeders, with variable load demand and DG generation, validates the proposed control. Incorporating renewable energy can provide major benefits for efficient operation of the distribution systems. However, when the number of renewables increases the system control becomes more complex. Renewable resources, particularly wind and solar, are often highly intermittent. The varying power output can cause significant fluctuations in feeder voltages. Traditional feeder controls are often too slow to react to these fast fluctuations. DG units providing reactive power compensation they can be utilized in supplying voltage support when fluctuations in generation occur. The second part of this dissertation focuses on two new approaches for dual-layer VVC. In these approaches the VVC is divided into two control layers, slow and fast. The slow control obtains optimal voltage profile and set points for the distribution control. The fast control layer is utilized to maintain the optimal voltage profile when the generation or loading suddenly changes. The MINLP based VVC formulation is utilized as the slow control. Both local reactive power control of DG and coordinated quadratic programming (QP) based reactive power control is considered as the fast control approaches. The effectiveness of these approaches is studied with test feeders, utility load data, and fast-varying solar irradiance data. The simulation results indicate that both methods achieve good results for VVC with DG

Coordinated Optimal Voltage Control in Distribution Networks with Data-Driven Methods

Voltage control is facing significant challenges with the increasing integration of photovoltaic (PV) systems and electric vehicles (EVs) in active distribution networks. This is leading to major transformations of control schemes that require more sophisticated coordination between different voltage regulation devices in different timescales. Except for conventional Volt/Var control (VVC) devices such on-load tap change (OLTC) and capacitor banks (CBs), inverter-based PVs are encouraged to participate in voltage regulation considering their flexible reactive power regulation capability. With the vehicle to grid (V2G) technology and inverter-based interface at charging stations, the charging power of an EV can be also controlled to support voltages. These emerging technologies facilitate the development of two-stage coordinated optimal voltage control schemes. However, these new control schemes pursue a fast response speed with local control strategies in shorter snapshots, which fails to track the optimal solutions for the distribution system operation. The voltage control methods mainly aim to mitigate voltage violations and reduce network power loss, but they seldom focus on satisfying the various requirements of PV and EV customers. This may discourage customer-owned resources from participating in ancillary services such as voltage regulation. Moreover, model-based voltage control methods highly rely on the accurate knowledge of power system models and parameters, which is sometimes difficult to obtain in real-life distribution networks. The goal of this thesis is to propose a data-driven two-stage voltage control framework to fill the research gaps mentioned above, showing what frameworks, models and solution methods can be used in the optimal voltage control of modern active distribution systems to tackle the security and economic challenges posed by high integration of PVs and EVs

Optimizing PV microgrid isolated electrification projects—A case study in Ecuador

Access to electricity for the rural and indigenous population of Ecuador’s Amazon Region (RAE) is considered a critical issue by the national authorities. The RAE is an isolated zone with communities scattered throughout the rainforest, where the expansion of the national grid is not a viable option. Therefore, autonomous electrification systems based on solar energy constitute an important solution, allowing the development of indigenous populations. This work proposes a tool for the design of stand-alone rural electrification systems based on photovoltaic technologies, including both microgrid or individual supply configurations. This tool is formulated as a Mixed Integer Linear Programming model including economic, technical and social aspects. This approach is used to design electrification systems (equipment location and sizing, microgrid configurations) in three real communities of the RAE. The results highlight the benefits of the developed tool and provide guidelines regarding RAE’s electrification.Peer ReviewedPostprint (published version

Integration of Energy Storage into a Future Energy System with a High Penetration of Distributed Photovoltaic Generation

Energy storage units (ESU) are increasingly used in electrical distribution systems because they can perform many functions compared with traditional equipment. These include peak shaving, voltage regulation, frequency regulation, provision of spinning reserve, and aiding integration of renewable generation by mitigating the effects of intermittency. As is the case with other equipment on electric distribution systems, it is necessary to follow appropriate methodologies in order to ensure that ESU are installed in a cost-effective manner and their benefits are realized. However, the necessary methodologies for integration of ESU have not kept pace with developments in both ESU and distribution systems. This work develops methodologies to integrate ESU into distribution systems by selecting the necessary storage technologies, energy capacities, power ratings, converter topologies, control strategies, and design lifetimes of ESU. In doing so, the impact of new technologies and issues such as volt-VAR optimization (VVO), intermittency of photovoltaic (PV) inverters, and the smart PV inverter proposed by EPRI are considered. The salient contributions of this dissertation follow. A unified methodology is developed for storage technology selection, storage capacity selection, and scheduling of an ESU used for energy arbitrage. The methodology is applied to make technology recommendations and to reveal that there exists a cost-optimal design lifetime for such an ESU. A methodology is developed for capacity selection of an ESU providing both energy arbitrage and ancillary services under a stochastic pricing structure. The ESU designed is evaluated using ridge regression for price forecasting; Ridge regression applied to overcome numerical stability and overfitting issues associated with the large number of highly correlated predictors. Heuristics are developed to speed convergence of simulated annealing for placement of distributed ESU. Scaling and clustering methods are also applied to reduce computation time for placement of ESU (or any other shunt-connected device) on a distribution system. A probabilistic model for cloud-induced photovoltaic (PV) intermittency of a single PV installation is developed and applied to the design of ESU

Distributed photovoltaic systems: Utility interface issues and their present status

Major technical issues involving the integration of distributed photovoltaics (PV) into electric utility systems are defined and their impacts are described quantitatively. An extensive literature search, interviews, and analysis yielded information about the work in progress and highlighted problem areas in which additional work and research are needed. The findings from the literature search were used to determine whether satisfactory solutions to the problems exist or whether satisfactory approaches to a solution are underway. It was discovered that very few standards, specifications, or guidelines currently exist that will aid industry in integrating PV into the utility system. Specific areas of concern identified are: (1) protection, (2) stability, (3) system unbalance, (4) voltage regulation and reactive power requirements, (5) harmonics, (6) utility operations, (7) safety, (8) metering, and (9) distribution system planning and design

Analysis, sizing and control of a micro-grid with photovoltaic generation and batteries, for residential applications in the city of Cúcuta, Norte de Santander (Colombia)

Currently, the Colombian electricity sector presents great opportunities for the implementation of electric power generation systems from unconventional energy sources such as photovoltaic solar energy, these opportunities arise from the need to strengthen the national energy matrix to be able to supply the increasing demand for electrical energy of the country, at the same time as the generation system, mainly dominated by generation of hydroelectric energy, is strengthened in front of environmental crises such as those experienced in the past. With this as a reference, the present work carries out a study for the implementation of micro-grid with photovoltaic generation systems and batteries for residential use, within the context of the actual Colombian electricity market, focused on the city of Cúcuta, Norte de Santander. Developing for this purpose a model of the microgrid in Simulink from MathWorks, and evaluating its performance for two particular case studies

A study of the solar energy systems and storage devices

Includes abstract.Includes bibliographical references.Following the 2008 severe electricity shortage in South Africa, domestic and industrial users faced incessant periods of blackouts. It is generally believed to be associated with lack of generation capacity. Since then research efforts have been directed towards boosting the generation capacity of the South African network by investing in a mix of power generation projects which include coal, nuclear and renewable energy schemes such as solar and wind. The renewable energy resources are considered a more viable option because of their many advantages such as lower greenhouse gas emissions, inexhaustible, reliable and even cheaper energy cost on the long term. Africa has huge potentials of solar power because of the abundance of direct sunshine in most days of the year. The rising cost of the fossil electricity has made the solar power an attractive option bearing in mind that the cost of the solar power has plummeted steadily in the past few years. Two main technologies are prevalent in the solar power research. These are photovoltaic (PV) systems and the concentrated solar power (CSP). The PV systems are made of solar panels and power electronic circuits. They are mostly economical in small residential units. The CSPs on the other hand which are made of solar field, thermal storage and steam turbine/generator units are economical only in large scale. In this thesis, a 2.5 kW Residential PV system and a 100 MW Molten Salt Power Tower Concentrated Solar Power were developed. The technical model of the photovoltaic panel and the power electronic circuits that connect it to the grid were also developed with Matlab/Simulink while the economic simulation of the PV, as well as the Concentrated Solar Power were carried out with Systems Advisor Model (SAM) using the climate data of Cape Town. The simulation results of this work compared the cost of PV electricity first with Renewable Energy Feed-in Tariff (REFIT) of National Energy Regulator of South Africa (NERSA), and then with the residential tariff charged by the City of Cape Town. Also the cost of electricity using CSP is compared NERSA`s REFIT. Finally the cost of PV electricity is compared with that of CSP. We therefore conclude that, with government incentives, CSP and PV are viable technologies however electricity produced by CSP is cheaper than that of the PV

High- and Low-Voltage Mitigation in Distribution Systems Using Residential Static Volt-Ampere Reactive Compensators

Power distribution systems are experiencing a fast transformation from simple one-way radial feeders to complex systems with multiple sources and bidirectional power flows. The rapid increase of Distributed Generation (DG) connected to the distribution system over the last decade, especially solar photovoltaic (PV), has been the key element to this transformation. The variable nature of PV-based DG has increased the complexity of voltage regulation in distribution systems. Electric Utilities are facing an increasing number of voltage issues in distribution systems with high penetration of DGs, leading customers to experience voltage levels outside of range A of the ANSI C84.1 standard. Electric Utilities have to expend resources, both human and economic, to mitigate the voltage issues caused by the interconnection of DG. The economic impact of voltage issues can be considerable in some cases. Conventional methods to mitigate voltage issues in distribution systems, such as the addition of voltage regulators and capacitor banks, could be ineffective in mitigating localized voltage issues caused by high levels of DG penetration. Other mitigation options, such as increasing the conductor size and the operating voltage of the feeder, are expensive. There is a clear need in the industry to locally solve voltage issues economically. In this dissertation, a new device, a Residential Static Volt-Ampere Reactive Compensator (RSVC), is proposed. The RSVC is used to mitigate low and high voltage issues by deploying them in a feeder with a high DG penetration level. This dissertation will investigate the interaction between solar inverters, voltage regulators and capacitor banks with the proposed RSVC. In order to reduce the number of buses to be analysed, the use of loss sensitivity factors will determine the candidate buses to host a RSVC. The results of this dissertation show that the use of RSVCs is able to mitigate low and high voltage conditions. Simulation results show that the RSVCs are able to control the voltage by absorbing and injecting reactive power according to the voltage seen at their terminals. Similar commercially available devices are not able to handle the injection and absorption of reactive power and are limited to handle either injection of reactive power or absorption of reactive power. The most common devices provide the capability of injecting reactive power