Local Utility Grid Research Articles

A Road Test for Vehicle-to-Grid Tech: Utrecht leads the world in using EVs for grid storage

Unlike those you may have grown accustomed to seeing, many of these stations don't just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Heuristic Greedy Scheduling of Electric Vehicles in Vehicle-to-Grid Microgrid Owned Aggregators.

In on-grid microgrids, electric vehicles (EVs) have to be efficiently scheduled for cost-effective electricity consumption and network operation. The stochastic nature of the involved parameters along with their large number and correlations make such scheduling a challenging task. This paper aims at identifying pertinent innovative solutions for reducing the relevant total costs of the on-grid EVs within hybrid microgrids. To optimally scale the EVs, a heuristic greedy approach is considered. Unlike most existing scheduling methodologies in the literature, the proposed greedy scheduler is model-free, training-free, and yet efficient. The proposed approach considers different factors such as the electricity price, on-grid EVs state of arrival and departure, and the total revenue to meet the load demands. The greedy-based approach behaves satisfactorily in terms of fulfilling its objective for the hybrid microgrid system, which is established of photovoltaic, wind turbine, and a local utility grid. Meanwhile, the on-grid EVs are being utilized as an energy storage exchange location. A real time hardware-in-the-loop experimentation is comprehensively conducted to maximize the earned profit. Through different uncertainty scenarios, the ability of the proposed greedy approach to obtain a global optimal solution is assessed. A data simulator was developed for the purposes of generating evaluation datasets, which captures uncertainties in the behaviors of the system’s parameters. The greedy-based strategy is considered applicable, scalable, and efficient in terms of total operating expenditures. Furthermore, as EVs penetration became more versatile, total expenses decreased significantly. Using simulated data of an effective operational duration of 500 years, the proposed approach succeeded in cutting down the energy consumption costs by about 50–85%, beating existing state-of-the-arts results. The proposed approach is proved to be tolerant to the large amounts of uncertainties that are involved in the system’s operational data.

Active Fault Current Limitation for Low-Voltage Ride-Through of Networked Microgrids

With the continuously increasing penetration of networked microgrids (MGs) on the local utility grid (UG), MGs face the challenge to avoid increasing system fault currents during low-voltage ride-through (LVRT). To solve this challenge, an active fault current limitation (AFCL) method is proposed with three parts: 1) a novel phase angle adjustment (PAA) strategy is conducted to relieve the impact of MGs output fault current on system fault current; 2) the current injection (CI) strategy for LVRT is formulated to fit the function of PAA; 3) a novel converter current generation (CCG) strategy is developed to achieve a better voltage support ability by considering network impedance characteristics. The proposed AFCL method is applied to the back-to-back converter, as a connection interface between MGs and UG. Extensive tests and pertinent results have verified the improvements of proposed AFCL method with better LVRT performance, while the networked MGs output fault current does not increase the amplitude of system fault current.

Grid Integration of Solar and Solar/Wind Hybrid Mini-Grid Projects: A Case of Solar/Wind Hybrid Mini-Grid Project Implemented by AEPC

Alternative Energy Promotion Center (AEPC) has been scaling up renewable energy technologies through Mini-grid power supply in Nepal’s off-grid areas in order to fulfill community electricity demands for both households and electricity-based enterprises. It is likely that, in some of the off-grid renewable energy (RE) mini-grid service areas, Nepal Electricity Authority (NEA) grid line might reach in near future. The objective of this study is to highlight success stories of solar and solar/wind mini-grids implemented by AEPC and for their longer-term sustainable operation grid integration policy of isolated mini-grid systems will require. Till the date AEPC has successfully electrified more than 20 rural communities through solar and solar/wind hybrid mini-grid systems. Some of these isolated mini-grid projects will seek grid interconnections in near future due to NEA distribution system expansion trend. When the isolated mini-grids will be connected to the national grid power network in future, the mini-grid can feed surplus electricity to the local utility grid line and will receive deficit electricity from the local utility grid system to serve the consumers connected to the local grid network. The methodology applied to this study is assessment of existing solar and solar/wind mini-grid projects, technological intervention required for grid integration, reviewing grid-connection policy of distributed renewable generations in the country and recommendation of relevant policy option for grid connection of rural mini-grids. Grid integration of isolated solar and solar/wind mini-grids will have positive impacts to the sustainability of the present isolated mini-grids, will help in retaining existing mini-grids end users, energy produced by mini-grid systems will be optimally utilized, the existing mini-grid power will contribute to stabilize weak national grid electrical parameters. The outcome of the study will recommend need of policy options as well as technological interventions in order to do grid integration of solar and solar/wind hybrid mini-grid systems in Nepal.

Privacy-Preserving Collaborative Operation of Networked Microgrids With the Local Utility Grid Based on Enhanced Benders Decomposition

In this paper, a privacy-preserving decision-making framework is developed for a collaborative operation of networked microgrids and the local utility grid, where the distribution system operator (DSO) interacts with microgrid master controllers (MCs) in a leader-followers fashion. First, the paper models the decision-making in the collaborative operation presented as an integrated mixed-integer second-order cone programming problem which satisfies various technical and operational requirements in a look-ahead manner. Then, the integrated optimization problem is decomposed into a master problem and a set of subproblems in order to decentralize the decision-making process of DSO and MCs. The master problem is solved by DSO for optimizing the local utility grid operation, and the subproblems are solved independently by MCs for optimizing the operation of individual microgrids. We propose an enhanced Benders decomposition algorithm to guide the iterations between the master problem and subproblems. In particular, an enhanced approach is introduced in the Benders decomposition algorithm for generating valid cutting planes from mixed-integer linear programming subproblems. Mathematically, the proposed algorithm can find the globally optimal solution after a finite number of iterations. Accordingly, DSO and MCs manage to collaborate on making operational decisions that would maximize the social welfare without compromising independent decision-making and privacy provisions. Numerical experiments are conducted on a simplified two-bus system and a modified IEEE 123-bus system. The results validate the efficiency, the robustness, and the scalability of the proposed collaborative decision-making framework in power systems.

Single Phase Grid-tie Inverter Design Using PLL and MPPTTechniques

This paper focuses on designing and implementing a grid-tie inverter, which can convert DC voltage from the PV systems into an AC voltage using pulse width modulation technique. The proposed inverter is synchronized with the local grid to provide an alternate solution for the energy generation. To obtain the maximum power from the inverter maximum power point tracking technology is used. Using MPPT, approximately 95% power efficiency was achieved. Boost converter is designed to boost the voltage from solar panels to 240V. Phase locked loop circuit is utilized to synchronize the output frequency of the inverter with that of the local utility grid. Phase locked loop circuit uses phase detector to detect the phase difference between the reference (utility grid) frequency and the quiescent (required) frequency set in Voltage Controlled Oscillator. This quiescent frequency is converted to match with the reference frequency. This converted or synchronized frequency is then used as a reference for pulse width modulation controller to generate Pulse Width Modulation waveform. Using PLL, phase or frequency matching between utility grid’s electricity and inverter’s electricity was achieved in just 0.6 seconds. In the end, filtering system is designed using LMS filter and KALMAN filter to remove the noise from inverter output. A total of -22.63 dB total harmonic distortion was achieved using Kalman filter and were proved to be better than LMS filter. The simulation results provided in this report show the efficacy of the proposed grid-tie inverter.

Development and Demonstration of a Novel Reversible SOFC System for Utility and Micro Grid Energy Storage

AbstractEnergy storage is a critical component to supply local energy generation for both grid and off‐grid connected facilities and communities, enabling localized grid independent energy secure power in cases of emergencies or unreliable traditional grid use. The high cost and energy security of importing fuel to islanded grids has led to a growing need to generate power onsite with alternative and renewable energy technologies while reducing facility costs of importing electrical power. However, utility grid operators are being faced with the challenges of intermittent and variability in energy production from renewables. Therefore, energy storage is crucial to balance micro and utility grids, improve efficiency, reduce fuel consumption, and provide critical power in the event of power outages. There has been particular interest in reversible solid oxide fuel cells (RSOFCs) in the energy sector for electricity, energy storage, grid stabilization and improvement to power plant system efficiency due to favorable thermodynamic efficiencies of high temperature steam electrolysis. Boeing has been active in the development of a fully integrated, grid tied RSOFC system for micro grid and commercial utility energy storage using Sunfire fuel cell technology. In this system, excess grid energy or curtailed power generated by renewables is sent to the system operating in electrolysis mode to produce H2. The H2 is stored and then used in the system's fuel cell mode to provide supplemental power to the grid during peak hours or as needed. As part of this program, Boeing has developed a H2 storage and compression system, power distribution system, and master controller to interface with RSOFC subsystems. Sunfire developed a reversible solid oxide cell module with a power output of 50 kW in SOFC mode and 120 kW input in electrolysis mode producing 3.5 kg H2 hr−1. The system was demonstrated while connected to the local utility grid and operated in a microgrid test environment. This paper will discuss the development, integration, and demonstration of the RSOFC system.

Performance investigation of a Q-V-based Lyapunov finite time VSC control for grid interactive photovoltaic system

A photovoltaic (PV)-based voltage source converter (VSC) system, integrated with local load and utility grid is presented in this paper. The PV-VSC control hence considered on the reactive power (Qpv) and DC side VSC voltage (V2) errors, obtained from the measured parameters at point of common coupling (PCC) and DC side VSC capacitor respectively. The unmodelled dynamics of the phase-locked loop system (PLL) is averted for the proposed control approach as it is designed directly from instantaneous reactive power and DC voltage. A Lyapunov function-based finite time nonlinear Q-V controller is proposed to provide robustness with efficient error convergence during various micro grid operation disturbances. The performance evaluation of the proposed control during utility grid fault has been studied in MATLAB/m-file script. Validation of the proposed control is further obtained in MATLAB/Simulink environment. A conclusion is being carried out from simulation studies where the Lyapunov-based control is found efficient and robust compared with conventional PI control and feedback linearisation-based control (FLC).

Review and retrofitted architectures to form reliable smart microgrid networks for urban buildings

Smart microgrid initiatives for recent urbanisation at power distribution level need an integrated and interoperable environment that can work collectively with local energy systems and utility grid. This is achieved through the design of an architecture by using contemporary information and communication technology. System architecture provides a common work process that span across all the critical subsystems of a building for better informed decisions with reduced human interventions. Two key aspects of architecture development are, the way of its presentation and network reliability. The architecture should be clear in its presentation for the understanding of various stakeholders and possess fault tolerant communication mechanisms to have high network reliability. Considering aforementioned aspects, this study presents review of state-of-the-art architectures developed by IEEE-1547, ISA-95, National Institute of Standards and Technology, IEC-61850 for smart microgrids formation and suggests retrofitted architectures to improve architecture clarity by presenting in a more lucid way and network reliability by the concept of redundant communication paths.

Analysis of measured and simulated performance data of a 3.2 kWp grid-connected PV system in Port Elizabeth, South Africa

This paper analyzes and compares the actual measured and simulated performance of a 3.2kWp grid-connected photovoltaic system. The system is located at the Outdoor Research Facility (34.01°S, 25.67°E) at the Nelson Mandela Metropolitan University (NMMU), South Africa. The system consists of 14 poly crystalline silicon modules connected in two strings of 7 series-connected modules, each facing north at a fixed tilt of 34°. The data presented in this study were measured in the year 2013, where the system supplied a total of 5757kWh to the local electric utility grid. The performance of the system was simulated using PVsyst software using measured and Meteonorm derived climate data sets (solar radiation, ambient temperature and wind speed). The comparison between measured and simulated energy yield are discussed. Although, both simulation results were similar, better comparison between measured and predicted monthly energy yield is observed with simulation performed using measured weather data at the site. The measured performance ratio in the present study is 84% which is slightly higher than values of 74%, 81.5%, 67.4%, 70% and 64.5% reported is Khatkar-Kalan (India), Dublin (Ireland), Crete (Greece), Karnataka (India) and Malaga (Spain), respectively.

Control technique for enhancing the stable operation of distributed generation units within a microgrid

This paper describes a control technique for enhancing the stable operation of distributed generation (DG) units based on renewable energy sources, during islanding and grid-connected modes. The Passivity-based control technique is considered to analyze the dynamic and steady-state behaviors of DG units during integration and power sharing with loads and/or power grid, which is an appropriate tool to analyze and define a stable operating condition for DG units in microgrid technology. The compensation of instantaneous variations in the reference current components of DG units in ac-side, and dc-link voltage variations in dc-side of interfaced converters, are considered properly in the control loop of DG units, which is the main contribution and novelty of this control technique over other control strategies. By using the proposed control technique, DG units can provide the continuous injection of active power from DG sources to the local loads and/or utility grid. Moreover, by setting appropriate reference current components in the control loop of DG units, reactive power and harmonic current components of loads can be supplied during the islanding and grid-connected modes with a fast dynamic response. Simulation results confirm the performance of the control scheme within the microgrid during dynamic and steady-state operating conditions.

Evaluation of a Hybrid Energy Storage Module for Pulsed Power Applications

Before pulsed power systems can be fielded in either mobile or small footprint stationary applications, the prime power source must be optimized for both size and operational efficiency. In large footprint laboratories, prime power supplies are connected to a local utility grid to charge intermediate storage systems. In mobile platforms, alternative energy sources, such as electrochemical batteries or supercapacitors, must be used to backup smaller fossil fuel generators. The prime power source used in a pulsed power system must store high energy, to maximize the number of shots stored, and be able to source high power to recharge the intermediate store as fast as possible. Finding a single electrochemical energy storage device that has the right energy and power density for most applications is nearly impossible. Therefore, usage of batteries, which possess high energy density, along with electrochemical capacitors, which offer high power density, in a hybrid energy storage module (HESM) configuration is a promising way of combining both of these features into a single supply. Usage of this topology reduces the stress on the batteries, thereby prolonging their life, and also increases the instantaneous power capabilities of the system. This paper presents the design and validation of an actively controlled HESM built using commercial off the shelf power electronics and simple control strategies.

Hybrid Train Power with Diesel Locomotive and Slug Car–Based Flywheels for NOx and Fuel Reduction

AbstractAn energy-storage flywheel consists of a large inertia wheel sharing a common shaft with a motor generator (MG) set and with magnetic bearings to support the entire rotating assembly. Flywheels mounted on a special slug car are charged from the local utility grid and from regenerative-braking events. Usage of these power sources reduces fuel consumption and the related NOx emission by the locomotive-mounted Diesel generator sets (DGS). The flywheel-supplied power can replace the DGS-supplied power in one or more of the eight fixed power settings (notches), plus idle and reverse, which are common to most locomotives either for line-haul or switchyard service. The slug cars have separate traction motors to be driven by the flywheel systems so that the flywheel power and DGS power are electrically and physically decoupled. A system model is presented that includes the train dynamics coupled with the electromechanical models for the flywheels and traction motors. The modified Davis equation is employe...

OPERATING A 250 KW LANDFILL GAS FIRED MICROTURBINE AT A 0.4 HECTARE RESEARCH AND DEMONSTRATION GREENHOUSE

A 250 kW landfill gas-fired microturbine system was installed at a 0.4 ha research and demonstration greenhouse located at the Burlington County Resource Recovery Complex in Columbus, NJ. The landfill gas is scrubbed of sulfur (H 2 S), compressed, and chilled (to remove moisture and siloxanes) prior to combustion in the turbine. Waste heat contained in the exhaust gasses is reclaimed using a gas-to-liquid heat exchanger. The captured waste heat is used to help heat the greenhouse and is distributed through the hot water heating system. The electricity generated by the turbine is used to power electrical equipment (including the supplemental lighting system) in the greenhouse facility. Excess electricity is exported to the local utility grid. The exported electricity provides a separate revenue stream in addition to the crops produced in the greenhouse. Furthermore, every 1000 kWh of electricity produced generates a renewable energy credit that can be sold to third parties to satisfy requirements for renewable energy portfolios. The microturbine uses the relatively low energy content landfill gas (-17.1 MJ m -3 ) at a rate of approximately 51.9 L s -1 and converts it into 220 kW of electricity (yearly average). Approximately 30 kW of electricity is required to operate the equipment, primarily the compressor and chiller (parasitic losses). In addition, approximately 1.16 GJ h -1 of heat energy is recovered. The estimated annual run-time percentage is 80% or higher. This paper includes operational data as well as a discussion of potential management strategies for operating the equipment as economically as possible. Since grid electricity prices fluctuate rapidly depending on demand, time-of-day, season, etc., and crop requirements change depending on weather conditions, crop stage, harvesting schedule, etc., the operational management of the combined heat and power equipment and greenhouse equipment can be quite challenging. Consequently, decision support tools for growers and operators were developed.

Short term scheduling of multiple grid-parallel PEM fuel cells for microgrid applications

This paper presents a short term scheduling scheme for multiple grid-parallel PEM fuel cell power plants (FCPPs) connected to supply electrical and thermal energy to a microgrid community. As in the case of regular power plants, short term scheduling of FCPP is also a cost-based optimization problem that includes the cost of operation, thermal power recovery, and the power trade with the local utility grid. Due to the ability of the microgrid community to trade power with the local grid, the power balance constraint is not applicable, other constraints like the real power operating limits of the FCPP, and minimum up and down time are therefore used. To solve the short term scheduling problem of the FCPPs, a hybrid technique based on evolutionary programming (EP) and hill climbing technique (HC) is used. The EP is used to estimate the optimal schedule and the output power from each FCPP. The HC technique is used to monitor the feasibility of the solution during the search process. The short term scheduling problem is used to estimate the schedule and the electrical and thermal power output of five FCPPs supplying a maximum power of 300 kW.

Small Modular Power System for Clean Energy Generation

The overall goal of this project is to design, develop and demon-strate a 50-kW modular gasi fication system for grid-connected combinedheat and power using forest residue.Building on the success of the previous 12.5-kW small modularbiomass project, this new project will result in the development anddemonstration of a 50-kW small modular biopower (SMB) system de-signed for a parallel connection to the local utility grid and capable ofcontinuous operation. This project will support the goal of a commer-cially viable small modular biopower system.A SMB system will be designed and developed and tested in atwo-phase program. The first phase involves a one-year R&D programto design, fabricate, and factory test a 50-kW system. During secondphase, this new first of its kind unit will be grid-connected, and fielddemonstrated in California for two years.The SMB system shall be designed to meet or exceed The CaliforniaAir Resources Board (CARB) emission standards, including nitrogen ox-ides, volatile organic compounds, and particulate matter, for a combinedheat and power distributed generation system. The engine/generator setwill be capable of operating 24 hours per day, 6 days per week.This project supports the Public Interest Energy Research (PIER)program objectives of improving cost competitiveness of the biomassenergy conversion technologies and reducing environmental risks andcost of electricity.

Small Modular Power System for Clean Energy Generation

ABSTRACT The overall goal of this project is to design, develop and demonstrate a 50-kW modular gasification system for grid-connected combined heat and power using forest residue. Building on the success of the previous 12.5-kW small modular biomass project, this new project will result in the development and demonstration of a 50-kW small modular biopower (SMB) system designed for a parallel connection to the local utility grid and capable of continuous operation. This project will support the goal of a commercially viable small modular biopower system. A SMB system will be designed and developed and tested in a two-phase program. The first phase involves a one-year R&D program to design, fabricate, and factory test a 50-kW system. During second phase, this new first of its kind unit will be grid-connected, and field demonstrated in California for two years. The SMB system shall be designed to meet or exceed The California Air Resources Board (CARB) emission standards, including nitrogen oxides, volatil...

Case Study of Austin Energy's 200-kW Fuel Cell

ABSTRACT In the spring of 2001, Austin Energy decided to pursue a commercial fuel cell demonstration project to determine the issues involved with either a customer or the utility owning, installing, operating and maintaining this technology. A significant component of this project included understanding the issues associated with distributed generation connected to the local utility grid and how this would impact both the customer and the grid. An added benefit would be to provide a fuel cell education site that is accessible to other Austin Energy customers and the general public. The site selected for the project is the city-owned Rebekah Baines Johnson Health Center, which houses the city health clinic. Because the Health Center had existing redundant 1,000,000 Btu per hour boilers for Heating, Ventilating, Air Conditioning, (HVAC) desiccant drying, and building heat along with a domestic hot water heater, the site presented an opportunity for using the waste heat generated by the fuel cell power plan...

Case Study of Austin Energy’s 200-kW Fuel Cell

In the spring of 2001, Austin Energy decided to pursue a com-mercial fuel cell demonstration project to determine the issues involvedwith either a customer or the utility owning, installing, operating andmaintaining this technology. A significant component of this project in-cluded understanding the issues associated with distributed generationconnected to the local utility grid and how this would impact both thecustomer and the grid. An added bene fit would be to provide a fuel celleducation site that is accessible to other Austin Energy customers andthe general public.The site selected for the project is the city-owned Rebekah BainesJohnson Health Center, which houses the city health clinic. Because theHealth Center had existing redundant 1,000,000 Btu per hour boilers forHeating, Ventilating, Air Conditioning, (HVAC) desiccant drying, andbuilding heat along with a domestic hot water heater, the site presentedan opportunity for using the waste heat generated by the fuel cell powerplant in a combined heat and power application.Using a federal grant of $200,000 from the Climate Change Pro-gram administered by the U. S. Department of Defense, Austin Energyinstalled a 200-kW UTC Power Model PC25™C fuel cell. This fuel cellwas the first in Texas to feed electric power into the utility grid. Com-mercial operation began July 2, 2002.The issues to be worked through in many areas proved to be dif fi-cult, but doable, and many lessons have been learned along the way. Theperformance results have been impressive proving that this technologyis not only technically viable in commercial applications but reliable aswell.

PERFORMANCE EVALUATION AND ECONOMIC ANALYSIS OF A GRID CONNECTED PHOTOVOLTAIC SYSTEM IN A MULTIFAMILY RESIDENTIAL BUILDING

A 2.5-kW photovoltaic (PV) system with battery storage to supply emergency power was designed and installedin a 1200-ft2 apartment unit in collaboration with the Greensboro Housing Authority (GHA) to test the performance of agrid-connected PV system. The power generation system was interconnected with the local electric utility grid to allow forthe grid to be used as a supplemental source of electric power. The highest monthly normalized electricity yield was observedduring the study period in May and June (119.04 and 119.44 kWh/kWp, respectively). The yearly PV system conversionefficiency was calculated to be 4.28% for the year of 2003 based on the local solar radiation data. Assuming a 25-year usefullife on equipment, based on the findings from the test of the system, the electricity that was produced cost approximately$0.4661 per kilowatt-hour (kWh). This cost is much higher than the unit price of electricity (about 8 cents per kWh) chargedby the local utility. The future cost for the solar electricity with reduced cost and improved performance was also analyzed.