Patricio Mendoza-Araya

Islanding Detection in Microgrids Using Harmonic Signatures

In recent years, there has been a growing interest in incorporating microgrids in electrical power networks. This is due to various advantages they present, particularly the possibility of working in either autonomous mode or grid connected, which makes them highly versatile structures for incorporating intermittent generation and energy storage. However, they pose safety issues in being able to support a local island in case of utility disconnection. Thus, in the event of an unintentional island situation, they should be able to detect the loss of mains and disconnect for self-protection and safety reasons. Most of the anti-islanding schemes are implemented within control of single generation devices, such as dc-ac inverters used with solar electric systems being incompatible with the concept of microgrids due to the variety and multiplicity of sources within the microgrid. In this paper, a passive islanding detection method based on the change of the 5th harmonic voltage magnitude at the point of common coupling between grid-connected and islanded modes of operation is presented. Hardware test results from the application of this approach to a laboratory scale microgrid are shown. The experimental results demonstrate the validity of the proposed method, in meeting the requirements of IEEE 1547 standards.

Lab-Scale TCR-Based SVC System for Educational and DG Applications

Motivated by the development of power semiconductor technologies, flexible ac transmission systems (FACTS) devices and their penetration in the field of electrical power systems, an educational challenge in complementing theoretical knowledge with practical experience is recognized. In this paper, the design and implementation of a lab-scale hardware and software setup is presented. Three small-scale devices, including a static VAr compensator (SVC) unit, a transmission line model, and a substation, are developed. The SVC unit is validated by obtaining its operating characteristic. The lab setup is presented as a platform to carry out different experiments related to the SVC operation. Safety considerations in the design are discussed. Steady-state and dynamic analysis are presented showing the consistency between theory and practice. The potential use of small SVC units on low-voltage distributed generation schemes is discussed.

V2G integration and experimental demonstration on a lab-scale microgrid

Electric and plug-in hybrid-electric vehicles are soon likely to be integrated as bidirectional energy storage elements with the electric grid or local microgrids. This paper discusses the interfacing of a plug-in vehicle with a lab-scale microgrid, and how this integration was successfully achieved with a power electronics converter that utilizes a power-following droop controller. Simulations, which are verified with experimental results obtained with two electric research vehicles and a lab-scale microgrid, demonstrate that for both single and three-phase cases the imbalances created by vehicle charging and discharging meet, or nearly meet the required power quality and phase imbalance standards. The power-following droop control is validated as an effective way of supporting the microgrid during transients as well as maintaining, in the long term, a desired charging rate. Fast charging is also briefly introduced as part of the future work.

Stability Analysis of AC Microgrids Using Incremental Phasor Impedance Matching

Abstract—The concept of a microgrid is emerging to be a technically viable approach for meeting reliable supply of electricity with increased availability in the presence of large-scale grid disturbances induced by severe weather events, as well to integrate various types of electricity sources and storage devices close to consumer loads. The existing approaches to studying and ensuring the stability of microgrids are largely incapable of providing the structural certainty to promote true plug-and-play operation, particularly with changing network conditions. Thus, there is a need and an opportunity to develop a stability criterion that can truly promote the plug-and-play capabilities of a microgrid. This article proposes a novel stability criterion that uses an impedance matching approach in a microgrid environment. Analytical and simulation results show stability boundaries that can be used in the grid-tied and islanded cases.

An alpaca fiber processing solution based on Solar energy for an isolated location in Chile following a co-construction approach

Sustainable development of rural communities requires defining development strategies that respect human nature and the environment, guaranteeing the involvement of the affected community. The aim of this paper is to analyze a case study where a co-construction methodological approach was applied to productive projects in isolated rural communities. This project has the particularity of using local renewable energy resources to satisfy the energy demand of the productive process. The co-construction approach was implemented from the kick-off of the project to the operation and evaluation stages. In this specific case, the proposed methodology required that the community became involved in the decision-making process from the beginning of the project. The methodology was applied in the General Lagos region in the north of Chile, within the framework of the sustainable development project “Ayllu Solar.” The results showed that high levels of community engagement could be achieved through the involvement of the community since the beginning of sustainable development projects.

Combined economic and stability analysis of a microgrid: A co-optimisation approach

Both economics and stability analysis are critical to operate electricity networks in an efficient and secure manner, especially in the context of microgrids, where more complex stability phenomena may arise. In this vein, we propose a combined economic and stability model implemented through a hierarchical approach, where a master problem determines the economic system dispatch regardless of stability considerations and then a slave subproblem attempts to stabilize the masters solution through the optimization of control gains. If the economic dispatch solution determined by the master problem cannot be stabilized by slaves adjustments of control gains, a feasibility cut is generated and added to the master problem to calculate a new, more stable dispatch solution (master and slave are run iteratively). We demonstrate that control gains can be co-optimized with power outputs of generating units (in real time) to obtain more economically efficient and secure dispatch solutions and therefore that economics and stability analysis can be combined in a single framework by using advanced optimization techniques.

Impacts of using microwave oven transformers on micropower distribution grids

The Microformer project aims to develop electricity distribution systems from discarded electronic waste, by using a microwave oven transformer (MOT) as the main component. Even though this project has seen a few practical applications so far, and there is some knowledge on the behavior of the lone transformer, a thorough study on the behavior of the MOT on a larger distribution system coexisting with other transformers has not been carried out. This paper presents a study of the impact of MOTs on distribution grids, using a 12-bus lab-scale microgrid. The grid is populated with MOTs and configured to show typical characteristics of a distribution system (e.g. unbalance). Model simulations and lab-scale experiments are carried out for the 12-bus system. The results are presented as a series of recommendations for future grid developments using MOTs, which include derating and modifications of MOTs depending on their use within the grid, and technical adequacy of the Microformer solution as a function of distribution line length, among others.

Dynamic phasor models for AC microgrids stability studies

This paper develops a dynamic phasor based model for single-source microgrids aimed at studying small-signal stability. The modeled microgrids comprise distributed generators and loads operating on a droop-control strategy. The model provides a convenient set of variables to represent the system dynamics which are readily compatible with phasor representation in magnitude and phase angle coordinates. Stability of both a grid-tied microgrid and standalone microgrid are studied. Analytical results show interesting stability boundaries in the closed form that can be used for design and operation of microgrids, supported by simulation results. The model may be readily extended to include the effects of reactive power control, power factor control, etc.

Small signal impedance measurement in droop controlled AC microgrids

Stable operation of microgrids is highly influenced by characteristics of generators due to their small size and inertia and fast and variable dynamics. Recent work has shown that microgird stability can be determined by analysis of small signal impedances at the point of interconnection. The purpose of small signal impedance measurement is to verify the analytical models of single devices and to provide measured impedances where analytical models are not available, so that stability may be established. Small signal impedance measurement typically involves in-situ injection of currents or voltages superimposed upon the operating system. In droop-controlled microgrids, since the frequency is a function of the power demand, the injection has to be independent of the frequency. In this paper an injection approach is proposed using a three phase buck converter. Analytical models using dynamic phasors are compared to measurement results obtained in a laboratory microgrid. The injection method and the incremental phasor models of passive loads are verified and small signal impedance measurements of an islanded and grid-connected microgrid are obtained including a voltage source PWM converter.