Showing papers on "Stand-alone power system published in 2018"

Forecasting of photovoltaic power generation and model optimization: A review

Abstract: To mitigate the impact of climate change and global warming, the use of renewable energies is increasing day by day significantly. A considerable amount of electricity is generated from renewable energy sources since the last decade. Among the potential renewable energies, photovoltaic (PV) has experienced enormous growth in electricity generation. A large number of PV systems have been installed in on-grid and off-grid systems in the last few years. The number of PV systems will increase rapidly in the future due to the policies of the government and international organizations, and the advantages of PV technology. However, the variability of PV power generation creates different negative impacts on the electric grid system, such as the stability, reliability, and planning of the operation, aside from the economic benefits. Therefore, accurate forecasting of PV power generation is significantly important to stabilize and secure grid operation and promote large-scale PV power integration. A good number of research has been conducted to forecast PV power generation in different perspectives. This paper made a comprehensive and systematic review of the direct forecasting of PV power generation. The importance of the correlation of the input-output data and the preprocessing of model input data are discussed. This review covers the performance analysis of several PV power forecasting models based on different classifications. The critical analysis of recent works, including statistical and machine-learning models based on historical data, is also presented. Moreover, the strengths and weaknesses of the different forecasting models, including hybrid models, and performance matrices in evaluating the forecasting model, are considered in this research. In addition, the potential benefits of model optimization are also discussed.

Modeling and Integration of Flexible Demand in Heat and Electricity Integrated Energy System

Abstract: This paper is focused on utilizing customers’ flexible energy demand, including both heat demand and electricity demand, to provide balancing resources and relieve the difficulties of integrating variable wind power with the combined heat and power. The integration of heat and electricity energy systems providing customers with multiple options for fulfilling their energy demand is described. Customer aggregators are introduced to supply downstream demand in the most economical way. Controlling customers’ energy consumption behaviors enables aggregators to adjust their energy demand in response to supply conditions. Incorporating aggregators’ flexible energy demand into the centralized energy dispatch model, a two-level optimization problem (TLOP) is first formed where the system operator maximizes social welfare subject to aggregators’ strategies, which minimize the energy purchase cost. Furthermore, the subproblems are linearized based on several reasonable assumptions. Optimal conditions of the subproblems are then transformed as energy demands to be described as explicit piecewise-linear functions of electricity prices corresponding to the demand bid curves. In this way, the TLOP is transformed to a standard optimization problem, which requires aggregators to only submit a demand bid to run the centralized energy dispatch program. All the parameters pertaining to the aggregators’ energy consumption models are internalized in the bid curves. The proposed technique is illustrated in a modified testing system.

Implementation of a Grid-Integrated PV-Battery System for Residential and Electrical Vehicle Applications

Abstract: A new control approach of integrating a solar photovoltaic (PV) with a battery storage is presented to a single-phase grid for residential and electric vehicle application. The main purpose of the proposed work is to feed a continuous power to the grid, thereby enhancing the viability of the battery energy storage support connected to the system. The charging and discharging of the battery achieve power leveling and load leveling along with increased reliability of the system. The multifunctional voltage-source converter acts as an active power filter and performs the harmonics mitigation along with reactive power compensation. In the proposed system, a unique control is developed for resynchronization of the grid during reconnection of the grid after the mitigation of a failure. The overall control of the system is adaptable under various practically occurring situations such as disconnection of the PV array, the battery, and the grid from the system. The detailed design and control of the proposed system are presented. The validity of the proposed system is performed through a laboratory prototype developed for a power rating of 2.2 kW connected to the utility grid. The performance of the system is found satisfactory under various disturbance, and the recorded results have been demonstrated.

Voltage regulation mitigation techniques in distribution system with high PV penetration: A review

Abstract: The share of power generated from solar photovoltaic (SPV) is increasing drastically worldwide to meet the ever increasing energy demands. The power generated from the solar PV is mainly connected to low voltage (LV) distribution systems. However, the power generated from solar PV is intermittent in nature as a results it creates a problem in grid stability and reliability. The technical impacts of high PV penetration into distribution systems are mainly on the current and voltage profiles, quality of power, power balancing, protection, losses in system, power factor, etc. To address aforesaid issues lot of research is required, therefore an extensive literature review is performed considering the current status, impacts and various technical challenges due to high PV contribution. In addition, the proposed study also provides the insights to the possible solutions for voltage rise problem due to high PV penetration in LV distribution system.

Wireless Charging of Electric Vehicles in Electricity and Transportation Networks

Abstract: Wireless charging station (WCS) enables in-motion charging of the electric vehicles (EVs). This paper presents the short-term operation of WCS by capturing the interdependence among the electricity and transportation networks. In the transportation network, the total travel cost consists of the cost associated with the travel time and the cost of utilized electricity along each path. Each EV takes the path that minimizes its total travel cost. In the electricity network, the changes in WCS demand as a result of changes in the traffic flow pattern impacts the price of electricity. The changes in the price of electricity further affect the charging strategy of the EVs and the associated traffic flow pattern. The coordination between electricity and transportation networks would help mitigate congestion in the electricity network by routing the traffic flow in the transportation network. The presented formulation leverages decentralized optimization to address the economic dispatch in the electricity network as well as the traffic assignment in the transportation network. The presented case studies highlight the merit of the presented model and the developed algorithms for the coordinated operation of WCS in electricity and transportation networks.

An MPC-Based ESS Control Method for PV Power Smoothing Applications

Abstract: Random fluctuation in photovoltaic (PV) power plants is becoming a serious problem affecting the power quality and stability of the grid along with the increasing penetration of PVs. In order to solve this problem, by the adding of energy storage systems (ESS), a grid-connected microgrid system can be performed. To make this system feasible, this paper proposes a model predictive control (MPC) based on power/voltage smoothing strategy. With the receding horizon optimization performed by MPC, the system parameters can be estimated with high accuracy, and at the same time the optimal ESS power reference is obtained. The critical parameters, such as state of charge, are also taken into account in order to ensure the health and stability of the ESSs. In this proposed control strategy, communication between PVs and ESS is not needed, since control command can be calculated with local measured data. At the same time, MPC can make a great contribution to the accuracy and timeliness of the control. Finally, experimental results from a grid-connected lab-scale microgrid system are presented to prove effectiveness and robustness of the proposed approach.

Optimal Operation of Battery Energy Storage System Considering Distribution System Uncertainty

Abstract: We present a novel control strategy of charging and discharging batteries in a distribution system to optimize the energy transaction cost. With an increased proportion of renewable energy in a distribution system, the real demand curve may significantly deviate from the forecast curve, which can lead to an increased challenge for an energy distribution company in making an effective purchase plan. The proposed strategy aims at tracking the total forecast demand curve, and can mitigate risk and encourage demand-side bidding. In this paper, short-term load forecasting, wind power forecasting, and solar power forecasting are performed. To optimize profit, the optimal operation of energy storage systems in a distribution system was developed and solved in a two-level framework considering forecast uncertainties in day-ahead operation and mitigating the net demand gap in real-time operation. To quantify the risk mitigation and profits, the purchase strategies for uncertain and certain demand that occurs on the next day were compared. The promising results show that optimal operation of a battery energy storage system can reduce the energy cost and the transaction risk for an energy distribution company.

Benchmarking of Constant Power Generation Strategies for Single-Phase Grid-Connected Photovoltaic Systems

Abstract: With a still increase of grid-connected photovoltaic (PV) systems, challenges have been imposed on the grid due to the continuous injection of a large amount of fluctuating PV power, like overloading the grid infrastructure (e.g., transformers) during peak power production periods. Hence, advanced active power control methods are required. As a cost-effective solution to avoid overloading, a constant power generation (CPG) control scheme by limiting the feed-in power has been introduced into the currently active grid regulations. In order to achieve a CPG operation, this paper presents three CPG strategies based on a power control method (P-CPG), a current limit method (I-CPG), and the perturb and observe algorithm (P&O-CPG). However, the operational mode changes (e.g., from the maximum power point tracking to a CPG operation) will affect the entire system performance. Thus, a benchmarking of the presented CPG strategies is also conducted on a 3-kW single-phase grid-connected PV system. Comparisons reveal that either the P-CPG or I-CPG strategies can achieve fast dynamics and satisfactory steady-state performance. In contrast, the P&O-CPG algorithm is the most suitable solution in terms of high robustness, but it presents poor dynamic performance.

Performance of Interconnection Protection Based on Distance Relaying for Wind Power Distributed Generation

Abstract: This paper proposes a method to analyze and improve the performance of interconnection protection based on distance relaying for wind power distributed generation (DG) in distribution systems. Of particular importance is distance protection that uses the concept of prefault voltages as reference quantities found to have issues with intermittent behavior of wind power DG. This concept is normally used in different distance protective relaying applications in order to increase the fault resistance coverage capability of the distance relays as well as to ensure selectivity, dependability, and security under extreme undervoltages. The main contributions of this paper are to analyze this issue and propose a method to enhance the performance of distance protection to mitigate this issue. In this methodology, several case studies are investigated with different penetration levels, weather patterns, and configuration topology of DGs under both normal operating conditions as well as fault conditions. Results for a case study are given.

On Charging Scheduling Optimization for a Wirelessly Charged Electric Bus System

Abstract: The introduction of wirelessly charged electric buses (WCEBs) into current public transportation system attracts many attentions in recent years. As the wireless charging technology enables energy transfer from power transmitters to electric vehicles (EVs) on road, it provides a promising solution to reduce the huge cost of battery with large size and long charging time, which are two critical impediments for EV applications. However, the system cost of WCEBs is huge. Under the dynamic electricity demands and the fluctuating electricity prices, the system operating electricity cost highly depends on the charging schedule. In this paper, according to the typical day-ahead electricity market, we explore an optimal charging scheduling scheme in a WCEB system to minimize the system operating electricity cost, while the characteristic of WCEBs is considered. The price of electricity fluctuates with the accumulated energy demands in both spatial and temporal domains. We first present a day-ahead reserved wholesale electricity determination algorithm, in which, the average speeds of WCEBs are presumed. Then, we propose an optimal charging scheduling algorithm, in which the WCEB charging schedules in slots are optimized sequentially. Both the reserved electricity and the predicted speeds in the slot are used. Simulation results demonstrate the efficiency of our proposed WCEB charging schedules.

Optimal Wind Power Uncertainty Intervals for Electricity Market Operation

Abstract: It is important to select an appropriate uncertainty level of the wind power forecast for power system scheduling and electricity market operation. Traditional methods hedge against a predefined level of wind power uncertainty, such as a specific confidence interval or uncertainty set, which leaves the questions of how to best select the appropriate uncertainty levels. To bridge this gap, this paper proposes a model to optimize the forecast uncertainty intervals of wind power for power system scheduling problems, with the aim of achieving the best trade-off between economics and reliability. Then, we reformulate and linearize the models into a mixed integer linear programming (MILP) without strong assumptions on the shape of the probability distribution. In order to invest the impacts on cost, reliability, and prices in a electricity market, we apply the proposed model on a two-settlement electricity market based on a six-bus test system and on a power system representing the U.S. state of Illinois. The results show that the proposed method can not only help to balance the economics and reliability of the power system scheduling, but also help to stabilize the energy prices in electricity market operation.

Effects of Front-End Converter and DC-Link of a Utility-Scale PV Energy System on Dynamic Stability of a Power System

Abstract: This paper presents a method for small-signal dynamic studies of power systems including utility-scale PV energy systems considering the effects of dc-side components. Existing methods commonly model a PV energy system as a dc source connected to a grid-tied inverter. This paper shows that the dc components of a PV energy system can also contribute in the dynamics of the power system in the range of small-signal studies. The paper first develops the model of a PV energy system by merging the submodels of dc- and ac-side components. Then, a method to obtain the augmented model of the power system including a PV energy system will be explained using a study system. The study system consists of a PV energy system in parallel with a synchronous generator connected to a grid. Then, based on eigenvalue analysis, verified by time-domain simulations, it is shown that the dc-link capacitor, front-end converter, and its controller can introduce oscillatory modes in subsynchronous range of frequencies. Furthermore, it is shown that the damping of the sensitive modes can significantly vary with respect to the parameters of the dc-side components.

Effects of large scale penetration of renewables: The Italian case in the years 2008–2015

Abstract: Italy has experienced a revolution in the electricity production mix in the years 2008-2015, when a large scale deployment of intermittent renewables caused a high volatility of electricity prices, stopped the investments in both fossil and renewable power plants and caused a high degree of uncertainty in matching electricity demand and supply. The current legislation gives renewable energy the priority of dispatchment, producing a significant decrease of the operational hours of all kinds of power plants, which caused economic problems to utilities, that had started investments in new high efficiency combined cycles before 2008, and reduced the overall efficiency of fossil fired power generation. In order to restore the opportunities for further investments in renewable energy systems, it is very important to develop long term policies and interventions to improve the capacity to balance the electricity demand and supply.

Hybrid Energy System for Upgrading the Rural Environment

Abstract: Off-grid hybrid energy systems are attractive options for supplying electricity to rural areas in all aspects like, reliability, sustainability and environmental protection. It is especially best option for communities living far in the interior areas, where grid extension is not appropriate. Ethiopia is also facing the same problem. Many villages are very far from the grid. Therefore, off grid hybrid systems will supply those villages. This work presents the photovoltaic, wind turbine, battery bank and diesel generator based off grid system, which is sized and simulated for the rural community of Addis Border village in the Southern Regional State of Ethiopia. Primary load demand of 142kWh/day, peak load of 26kW, deferrable energy requirement of about 27kWh/day, and deferrable peak load of 3.6kW are involved during modeling of the proposed stand alone power system.

Challenges in meeting all of India's electricity from solar: An energetic approach

Abstract: India's electricity requirements will continue to grow with its increasing population and urbanization. Climate change, increased carbon emissions, and the depletion of nonrenewable energy resources have forced India to shift to renewable energy resources. India's solar potential is large enough to provide 100-percent of its current electricity requirements if photovoltaic arrays and energy storage infrastructure of sufficient size is deployed. In this paper, we modeled the dynamics of net electricity input and output from a photovoltaic electricity (PV) system as it is built out to provide the entire electricity demand by 2050. The results showed that building a PV system large enough to meet the nation's entire electricity demand by 2050 is possible; however, it will require a rapid increase in the deployment of solar PV and the associated storage infrastructure over the next few decades. Such rapid expansion of the PV system will require substantial electricity allocation away from general societal use and towards building the photovoltaic system equipment and integrating it with existing infrastructure. This will lead to a short-term lack of electricity supply for general use by society.

Methods of SoC determination of lead acid battery

Abstract: Lead acid batteries are typically used in the automotive industry, where they provide a high current pulse to start the vehicle, in traction applications, where they undergo periodic deep discharge and charge, and in stationary applications, where they remain in charged state most of their life. They are used also in hybrid electric vehicles (HEVs) and in remote area power supply systems (RAPS), where they remain in a state of about 50% of charge during their operation. In this state, these batteries can be charged or discharged with high effectivity. In all these applications, it is necessary to monitor and report the battery state of charge (SoC) instead of simply monitoring the battery voltage.

Impact of the Uncertainty of Distributed Renewable Generation on Deregulated Electricity Supply Chain

Abstract: Active districts are districts that have a system in place to coordinate distributed energy generation and external grid to meet the local energy demand. They are now widely recognized as a clear opportunity toward distributed renewable integration. Despite apparent benefits of incorporating renewable sources in an active district, uncertainty in renewable generation can impose unprecedented challenges in efficient operation of the existing deregulated electricity supply chain, which is designed to operate with no or little uncertainty in both supply and demand. While most previous studies focused on the impact of renewables on the supply side of the supply chain, we investigate the impact of distributed renewable generation on the demand side. In particular, we study how the uncertainty from distributed renewable generation in an active district affects the average buying cost of utilities and the cost-saving of the active district. Our analysis shows that the renewable uncertainty in an active district can: 1) increase the average buying cost of the utility serving the active district, termed as local impact and 2) somewhat surprisingly, reduce the average buying cost of other utilities participating in the same electricity market, termed as global impact . Moreover, the local impact will lead to an increase in the electricity retail price of active district, resulting in a cost-saving less than the case without renewable uncertainty. These observations reveal an inherent economic incentive for utilities to improve their load forecasting accuracy, in order to avoid economy loss and even extract economic benefit in the electricity market. We verify our theoretical results by extensive experiments using real-world traces. Our experimental results show that a 9% increase in load forecasting error (modeled by the standard deviation of the mismatch between real-time actual demand and day-ahead purchased supply) will increase the average buying cost of the utility by 10%.

A Novel Power Distribution System Employing State of Available Power Estimation for a Hybrid Energy Storage System

Abstract: This paper presents a novel power distribution system (PDS) algorithm to be employed in a hybrid energy storage system (HESS). PDS is responsible for sharing the demand power between energy storage modules, which are battery and ultracapacitor (UC) in this study. The challenge in designing PDS is in assigning the power-share between these modules. A state of available power technique is proposed based on the prediction of the power limitations for a predefined time frame in the future. Another PDS based on the UC state of charge is developed. Various design variables are defined that affect the performance of the PDS. The genetic algorithm optimization technique is employed to determine the design variables. The proposed PDS techniques along with an energy storage system (ESS) consisting of a single battery and a basic PDS system is studied on a 12-kW electric motorcycle during the standard FTP and the New York City Cycle (NYCC) driving cycles. Battery lifetime, vehicle range, and regenerative braking energy recovery functions for the proposed methods compared with the ESS are improved by 2.6 times, 25%, and 29%, respectively. The results suggest that employing the proposed novel PDSs improves the performance of the HESS significantly.

Comparison of flexibility options to improve the value of variable power generation

Abstract: As the share of variable generation in power systems increases, there is increasing value in more flexible use and generation of electricity. The paper compares the economic value of several flexib...

Available Transfer Capability Evaluation in a Deregulated Electricity Market Considering Correlated Wind Power

Abstract: Evaluation of available transfer capability (ATC) is a complicated process involving the determination of the total transfer capability (TTC) and the existing transfer commitments (ETC). Considering the uncertain renewable generation such as wind power will bring more challenge to this process. Previously the uncertainty of wind power is considered either in the ED model or the following TTC calculation, but not included in two process simultaneously. Therefore, the ATC output may not be accurate since the uncertainty impact two problem simultaneously. To consider the uncertainty and correlation of wind power in both ISO’s ED and ATC evaluation, this paper proposes a bi-level optimization framework in which the ATC evaluation is formulated as the upper level problem and the ED is the lower level. The bi-level model is first converted to a mathematic program with equilibrium constraints (MPEC) by recasting the lower level problem as its Karush-Kuhn-Tucker (KKT) optimality conditions, and then transformed to a mixed-integer linear programming (MILP) problem which can be solved by existing optimization tools. Case studies on the PJM 5-bus and IEEE 118-bus systems are presented to verify the proposed methodology and the impacts of correlation of wind power on ATC are analysed.