Mahmoud Kabalan

Large Signal Lyapunov-Based Stability Studies in Microgrids: A Review

Microgrid stability studies have been largely based on small-signal linearization techniques. However, the validity and magnitude of the linearization domain are limited to small perturbations. Thus, there is a need to examine microgrids with large-signal nonlinear techniques to fully understand and examine their stability. Large-signal stability analysis can be accomplished by Lyapunov-based mathematical methods. These Lyapunov methods estimate the domain of asymptotic stability of the studied system. In this paper, a survey of Lyapunov-based large-signal stability studies of microgrids is given. Moreover, this paper covers large-signal studies of individual generator and load types in microgrid settings. Stability studies of dc/ac droop controlled inverters, ac/dc and dc/dc converters, and motor drives are explored. The survey shows that few large-signal Lyapunov-based studies have been completed on either individual systems or microgrid systems. This paper highlights the aspects that make Lyapunov-based microgrid stability studies interesting and valuable. This paper also recommends areas that future research could address to improve large-signal stability studies of microgrids.

Community engagement for the development of a micro-hydroelectric site in Ifugao, Philippines

Micro hydroelectric systems have been implemented in Ifugao, Philippines over the past few years. These approaches adopted a top-down approach where the local government or NGO implements a system within a rural community without proper community engagement. The authors of this paper believe that community engagement is paramount for the success of any rural development project. It gives the community a sense of ownership and empowerment during the implementation and usage of any project. The authors adopted a bottom-up approach for a planned micro-hydroelectric system in the village of Duli, Ifugao Philippines. The community was selected after multiple trips to various communities across the region. Duli was selected because the community members showed enthusiasm and exhibited the ability to present income generating activities for electric energy such as a welding shop, tailoring facility and bakery. The authors then worked with the community to develop a business plan for the construction, implementation and maintenance of the system. Multiple meetings were held with community members to present ideas and obtain feedback to develop the business plan as the community sees fit. Community surveys were held to get a better understanding of the local community population and layout. Moreover, a socio-economic and socio-cultural analysis was completed in order to guide the business plan development. A terrain and household mapping survey was completed to guide the engineering design work that served as a basis to estimate the system cost. The paper provides the steps carried out by the authors to complete the work and presents the lessons learned from the experience.

Solar photovoltaic versus micro -hydroelectricity: A framework for assessing the sustainability of community-run rural electrification projects

One of the crucial steps in meeting the Millennium Development Goals (MDGs) is access to reliable and affordable energy. The majority of the people without access to clean and reliable energy sources live in rural areas. The advent of renewable energy technologies, such as solar photovoltaic (PV), wind and micro-hydroelectricity has allowed electricity to be generated independently of the national utility grid. The sustainability of such off-grid energy projects is crucial to foster socio-economic development of these local communities. Many studies have addressed the sustainability of rural electrification projects post-completion using indicators. However, these studies are fairly extensive and do not provide pre-implementation insights into the best rural electrification technology. In this study, we present a more holistic approach to decision making by analyzing two off-grid renewable technologies - solar photovoltaic (PV) and micro-hydroelectricity (MH) using a village in Ifugao Province in the Philippines as a case study. An analysis of social, technical, environment, economic and political (STEEP) dimensions that impact the success of the project is presented. A measure of the technologys potential to bring about positive change, termed total impact (TI), is estimated. Micro-hydroelectricity was projected to be a better alternative in this location.

Electrical load controller for rural micro-hydroelectric systems using a programmable logic controller

Micro-hydroelectric systems convert the energy of moving water into electric energy. In rural settings, micro hydroelectric systems are run at full power at all times to avoid the cost of expensive electromechanical controls. That in turn causes the generator to produce its maximum rated power. If the electric energy supply and demand are not matching, the generator eventually fails. Electronic load controllers have been proposed in the literature to better match the demand and supply. In this paper, an electrical load controller is implemented using a programmable logic controller (PLC). PLCs are used in industrial applications and can withstand high levels of dust, dirt and moisture making them very suitable for micro-hydroelectric applications. The proposed controller monitors the frequency of the generator. It will dynamically balance the system power by incrementing or decrementing the power rating of a resistive heating load. The controller was experimentally tested in a lab using a micro-hydroelectric emulator. The emulator includes a 13.8 kW generator, a 10 Hp motor, a motor drive and the PLC controller. The results showed that the PLC controller is a viable load control system for such an application.

Failure analysis of micro-hydroelectric sites in the province of Ifugao, Philippines

Micro-hydroelectric power has the promise of supplying clean renewable energy for remote communities at a cost-effective price. However, previous attempts of implementation suffered from a high failure rate and proved to be unsustainable. This paper presents a failure analysis of multiple micro hydroelectric sites that were built in the province of Ifugao, Philippines. The analysis was done by completing field trips to the failed sites and performing a technical examination of the neglected hydroelectric facilities. Moreover, interviews with multiple community members and officials were held to understand the social, culture and economic context of these systems. The interviews also focused on including female community members to get a gender neutral overview of the community. The study showed that multiple technical, economic and social factors can lead to the failure of the implementation of this technology. A relatively successful micro-hydroelectric system in the province is highlighted to provide a comparison with the other failed sites. The aim of the paper is to provide an insight on the best practices for the future development of micro-hydroelectric systems. The study showed that a sustainable micro-hydroelectric system should address the three pillars of sustainability - social, economic and technical.

Optimizing a virtual impedance droop controller for parallel inverters

This paper explores a previously developed frequency and voltage droop control scheme via virtual impedance emulation. Previously, the control scheme utilized a Kalman observer to extract the fundamental voltage and frequency which increased the complexity of the control loop. This paper investigates the use of a second-order generalized integrator-frequency locked loop (SOGI-FLL) to accomplish the same task in a straightforward fashion. Moreover, a linear quadratic Gaussian (LQG) servo controller was used to implement the control scheme instead of the LQG optimal control approach used formerly. The performance of the modified control algorithm was studied using Matlab/Simulink simulations under various linear and non-linear load conditions. Furthermore, two inverters were operated in parallel to assess the load-sharing capability of the modified control method. Simulations showed that the optimized control scheme kept output voltage and frequency within acceptable levels. Additionally, simulations exhibited the load sharing capability of the control scheme.

Exploring the effect of grid impedance on the large signal stability of an inverter using Lyapunov functions

This paper investigates the large signal stability of a DC to AC inverter using a Lure-type Lyapunov function. The Lyapunov function is systematically calculated for an inverter modeled as an electrostatic machine. The calculated Lyapunov function takes into account the impedance between the inverter and the grid. The stability of the inverter was studied under three scenarios: purely inductive, slightly resistive and purely resistive grid impedance. Simulation results show that the grid impedance has a pronounced effect on the large signal stability of inverters.

Large signal stability analysis of a DC/AC droop controlled inverter connected to an infinite bus

The large signal stability of a dc/ac inverter connected to an infinite bus is explored. The study aims to understand if a droop controlled inverter can lose synchronism with an infinite bus. Specifically, the analysis is completed using Lyapunov-based mathematical techniques. The 13th order mathematical model of a droop controlled inverter connected to an infinite bus is generated. An algorithm is used to estimate the domain of asymptotic attraction of the system. The effect of system parameters on the domain of attraction are explored. Moreover, the effect of control parameters are studied. Results suggest that a droop controlled inverter requires a long fault time or large transient to lose synchronism with the infinite bus. Numerical results validated the estimated domain of attraction.

A framework for community survey and management plan for community-run electrification projects: Duli, Philippines as a case study

The sustainability of rural electrification projects depends on intertwining social, economic, cultural and technical factors. Understanding the socioeconomic and sociocultural environment of the target community is vital before any project. In this paper, a framework for gaining insights into the rural community of Duli, Ifugao province, Philippines is presented. The framework consists of a questionnaire containing 65 questions that covers various areas such as lifestyle, financial income and expenditure, energy usage and cooking and lighting habits. The questionnaire also probes the communitys engagement and excitement towards the project. On the other hand, the steps for developing a management plan for a community-run cooperative (co-op) system are covered. The community members form the general assembly that is responsible for electing the board of directors. The general assembly also sets the constitution and by-laws of the co-op. The board of directors is responsible for hiring the management team that oversees the daily operation and maintenance of the system. Proper financial and technical oversight is ensured by having clear responsibilities and tasks for each member of the management team. The community survey and co-op business plan developed here can serve as guidelines for future rural electrification projects.

Open source photovoltaic system performance modeling with python

Several tools exist for modeling the annual energy output of photovoltaic (PV) solar systems. However, open source frameworks are not widely available and tend to be procedural. Moreover, they are oriented toward the modeling of the solar resource instead of the optimization of PV system design. Open source software allows for peer revision, collaboration and rapid development. Furthermore, localized optimizations are possible such as adaptation to local requirements or different weather data formats. In this paper, solpy, an object oriented open source python implementation, is presented. This software is capable of using historic or forecasted weather data to predict system performance as well as validate certain design constraints such as system voltage and conductor sizing. The developed software, solpy, compares favorably against NREL PV Watts and System Advisor Model.