Flexible Power System Research Articles

Digital Transformation of Energy Companies: A Colombian Case Study

The United Nations established 17 Sustainable Development Goals (SDGs), and the fulfillment of the 7th, defined as “Ensure access to affordable, reliable, sustainable, and modern energy for all”, requires energy industry transitions and digital transformations, which implies that diverse stakeholders need to move fast to allow the growth of more flexible power systems. This paper contains the case report that addresses the commercial digital transformation process developed at AES Colombia, through the implementation of a modern platform based on specialized applications that use Industry 4.0 tools. The Chivor hydropower project, a 1000-MW powerplant that covers 6% of Colombia’s demand, which is owned by AES Colombia and constitutes its primary asset, is first described. Then, a description of Colombia’s complex market (energy matrix, trading and dispatch mechanisms, and future projects) is presented. Then, the methodology followed for the digital transformation process using modern tools is described. The project, conceived as a broad framework, comprises applications for the management of hydrological, operational, and market information, commercial information systems and platforms to facilitate consultation and analysis by different users. Such an innovative project in the Latin American context has been developed in order reduce risks and to contribute to a sustainable energy supply for the future.

Flexible CNT/S-GO composite film without current collector for high-energy density lithium-sulfur batteries

Lithium-sulfur batteries are well-known for their higher theoretical energy density, low cost, and environmental friendliness, making them an ideal next-generation energy battery to replace conventional lithium batteries. Here we introduce an easy-to-form composite flexible film of CNT/S-GO with no current collector. The composite film is fabricated by a simple process that is coating slurry on the surface of hydrophobic sapphire. This composite film exhibits excellent flexibility; the electrochemical measurement results show that the modified membrane exhibits an initial discharge specific capacity of 1050 mAh·g−1 at 0.1 C. In addition, at 0.5 C, the specific capacity remains around 800 mAh·g−1, and after 200 cycles, the capacity retention rate is 82.4%. The flexible battery based on the flexible cathode shows well mechanical and electrochemical performance in the folded state, and the electrode exhibits well cycling performance, which highlights the practical application of our carefully designed electrode in the flexible power system. In this paper, a cheap and simple method for high-energy flexible lithium-sulfur batteries has been provided.

Interface covalent bonding endowing high-sulfur-loading paper cathode with robustness for energy-dense, compact and foldable lithium-sulfur batteries

Lithium-sulfur batteries are promising candidates for powering flexible devices with high energy densities. To realize both high areal and volumetric capacity of lithium-sulfur batteries, while maintaining flexible and mechanically robust characteristics, is challenging for their portable energy storage applications. Herein, interface covalent bonding was demonstrated to design densely-packed graphene/CoS2/nano-sulfur hybrid papers with flexible and robust characteristics for energy-dense, compact and foldable lithium-sulfur batteries. The as-designed paper cathodes showed excellent cycling stability with a low decay rate of 0.044% per cycle over 800 cycles at 1 C, as well as high reversible areal capacity (4.11 mAh cm−2) and volumetric capacity (1240 Ah L−1). Meanwhile, the assembled batteries performed a high gravimetric/volumetric energy density (363.5 Wh kg−1/378 Wh L−1) under high sulfur loading (5.6 mg cm−2) and lean electrolyte/sulfur ratio (E/S: 5 μL mg−1). Furthermore, durable pouch cells based on as-designed integrated paper cathodes showed negligible performance decay even at a folding angle of 180°, highlighting their practical applications for flexible power systems.

Adaptive power sharing in flexible frequency, flexible voltage hybrid power system

Adaptive power sharing in flexible frequency, flexible voltage hybrid power system

Adaptive power sharing in flexible frequency, flexible voltage hybrid power system

Hybrid power systems (HPS) are small clusters of distributed generation, storage system along with load. Intertied hybrid systems have been anticipated the better interconnection of the various hyb...

The Role of Biomass Gasification in the Future Flexible Power System – BECCS or CCU?

In this work we study if biomass gasification for production of advanced biofuels also can play a role in managing variability in the electricity system. The idea is a CCU/power-to-gas concept to enhance methane production from biomass gasification. The suggested process is flexible in that CO2 not used for methane production can be stored through a BECCS concept that implies negative GHG emissions. For this purpose, rigorous models of three different gasification process configurations were simplified through surrogate modeling and integrated into a dynamic optimization model of regional electricity systems. The results show the diverse advantages of flexible operation between CCU and BECCS and that it is economically beneficial for the system to invest in gasification at the investigated levels of CO2 charge. The gasification option also provides value for low-priced electricity and thus stimulate increased investments in renewable electricity generation, which indicates the importance of considering geographical diversities in the assessment and highlights the importance of studying this type of concept with a time-resolved model. It is clear that the BECCS option is the most used, however, the limited quantities of CO2 used for the CCU option has a large impact on the investments made in the electricity system.

Assessing new block order options of the EUPHEMIA algorithm: An optimization model for the economic dispatch problem in power exchanges

To implement the process of European power markets’ integration, a market-clearing algorithm has been developed among European power exchanges under the title EUPHEMIA (Pan-European Hybrid Electricity Market Integration Algorithm), being a strictly economic dispatch algorithm and providing several options and products to market participants. This paper proposes an optimization-based methodological framework for the optimal economic dispatch problem in power exchanges, further enhancing the EUPHEMIA algorithm’s block order module. More specifically, through the development of a mixed-integer linear programming (MILP) model and utilizing an iterative process, it quantifies the impacts of the proposed new options to the optimal energy mix, the wholesale prices, and on the market players’ economic performance. The model considers all the current market products of the EUPHEMIA algorithm, as well as introduces new market products such as the flexibility provision of the main aspects of block orders (minimum acceptance ratio, price offer, and block time limits), the modification of existing block orders (exclusive groups), the development of new linkage structure (linked block orders with parallel relationship), as well as the activation of mixed schemes combining existing types of block orders into new integrated forms. The developed optimization framework has been assessed in the Greek interconnected power system, including its interconnections with neighboring power systems. The proposed methodological approach suggests a robust and systematic methodological formation to provide useful insights on policy issues and ongoing debate regarding the shaping of more efficient market designs and structures to deal with the new operational challenges of low-carbon flexible power systems.

Improved dielectric properties of PVDF nanocomposites with core–shell structured BaTiO 3 @polyurethane nanoparticles

Polymer nanocomposites with improved dielectric permittivity and high breakdown strength are extremely desirable for the flexible electronic devices and power systems. The compatibility of fillers and polymer matrix is important in determining the dielectric and breakdown strength properties. The core–shell structure concept is useful to improve the compatibility of fillers with polymer matrix. Herein, an organic thermoplastic urethanes (TPU) polymer shell was successfully grafted on the surface of barium titanate (BaTiO3, BT) and such a TPU shell improved the permittivity and breakdown strength of TPU@BT/PVDF polymer nanocomposites greatly. The permittivity of TPU@BT/PVDF nanocomposites with 12 wt% fillers at 102 Hz was up to 13.5, which was 1.5 times higher than that of pure poly(vinylidene fluoride) (PVDF). The improvement of the dielectric properties could be attributed to the enhanced interfacial polarisation between BT nanoparticles and TPU shell. Besides, the compatibility of BT nanoparticles and PVDF matrix was improved after the introduction of TPU shell. Accordingly, a highest breakdown strength value about 373 MV/m was obtained for the TPU@BT/PVDF nanocomposites with 7 wt% fillers. The core–shell strategy could be extended to a variety of inorganic fillers to improve the dielectric and breakdown strength properties of polymer nanocomposites.

Computational experiment design for operations model simulation

Computer simulations that demonstrate the value of novel approaches are crucial to developing more flexible and robust power systems operations with high penetrations of renewable energy at multiple geographic and temporal scales. However, optimization-based simulations that depend on forecast data often face challenges in evaluating performance, reproducing results, and testing under realistic simulation scenarios. In this paper, we develop scientific computing best-practices for the validation and reproduction of power systems operational models. We then employ two case studies to demonstrate the proposed validation and reproduction framework.

Flexible Power System Defense Strategies in an Isolated Microgrid System with High Renewable Power Generation

This work develops an underfrequency preventive control strategy for an islanded power system with a high penetration of wind power generation. First, the preventive control strategy uses the frequency nadir forecasting module to analyze the frequency stability under largest diesel generator tripping (N-1) contingency events. If predicted frequency nadir is too low, four frequency support methods are then analyzed and used for preventing potential frequency stability problem. They include generator rescheduling (GR), the use of battery energy storage system (BESS), direct load control (DLC) and emergency demand response program (EDRP). In terms of the GR method, the optimal diesel generator dispatch is obtained, with sufficient frequency stability and minimal fuel cost and start-up cost. In the BESS method, the optimal instantaneous power output from BESS is obtained based on its frequency support capability. With the DLC or EDRP method, the optimal contract-based load-shedding or the load-reduction to provide frequency support is obtained, respectively. Then, the operating costs of each method to support frequency are analyzed. The research methods and simulation results are very useful to the low-frequency protection of actual power systems with high renewable power generation. This work proposed a complete defense strategy in a microgrid system. It combines GR, BESS, DLC and EDRP. Therefore, the system operators have many options to implement their defense strategies, based on the operating costs of various methods. In other words, the proposed defense strategy provides a more flexible solution for the protection of micro grids with a high renewable power penetration. Therefore, the solution considers the system safety and economical aspects.

Flexibility requirement for large-scale renewable energy integration in Indian power system: Technology, policy and modeling options

Reliable and stable power system operation requires flexibility, in addition to capacity adequacy. Traditional system components either have limited flexibility to suppress extensive system variation, or their role is limited due to lack of proper regulatory provisions and inefficient market design. Large-scale integration of renewable energy (RE) resources (e.g., solar, wind) imposes additional variability and uncertainty to the existing system and thus enhances flexibility need. There are various solutions to the problem. Revamping system operation protocol with existing resources, retrofitting current power-generating assets, network expansion, etc. can provide flexible service. Investing in a new type of resources like energy storage and demand-side response (DSR) however, needs aggressive policy interventions and market mechanisms. Identifying suitable flexible resources and designing appropriate policy structures require long-term system planning. Traditional methods in this regard need to evolve to consider the operation-scale impact of large-scale RE integration at the planning stage such that long-term carbon emission reduction targets can be met. The approach towards transitioning into a flexible energy system can differ according to its present status. This paper focuses on the Indian power sector’s perspective, which has ambitious RE integration goals. With a fast-evolving system configuration, flexibility related challenges are high in India due to weak infrastructure, inefficient regulatory policies, and aggregated planning methods. This article presents the current status of the Indian power system detailing existing technology types, regulatory norms, and future targets. It further details a comprehensive review of relevant technical options, market mechanisms and planning approaches for transitioning into a flexible power system for India. Comparative analysis with international experiences highlights the need for a major paradigm shift. A short-term transition towards becoming a flexible system can focus on developing adequate transmission infrastructure, exploit available pumped hydro storage potential and retrofitting existing coal-fired power plants. On longer-term, innovating market mechanisms and regulatory changes should drive investment into emerging flexible resources like DSR, storage, etc. Planning for this transition should be designed using improved modeling and planning approaches which should focus on the interlinking of different sector-specific models.

Uncertainty-based unit commitment and construction in the presence of fast ramp units and energy storages as flexible resources considering enigmatic demand elasticity

Abstract In recent years, and with rapid rise of climate change, many countries have established multifield policies to drive more renewable resources into the power system. The increasing electricity generation by renewable resources gives rise to various structural issues like uncertainty and variability in modern power systems. Here, facing the abovementioned issues will be one of the most pressing problems in future energy systems and leads to define a new feature namely as power system flexibility. A novel framework for considering the enhancement of flexibility in the power system is presented in this paper. So, an innovative structure is suggested for flexibility improvement based upon unit commitment problem as well as construction of flexible fast ramp generating units. Here, an innovative formulation for uncertainty based flexible unit commitment and construction in combination with demand response resources i.e. (UBFUCCDRRs) is suggested. There are several uncertain resources affecting the UBFUCCDRRs. Here, one of the foremost imperative issues is the uncertainty of demand side resources. This paper considered, the price-elasticity of electrical consumption, as an uncertain, unavailable and hard to estimate parameter which is modelled using Z numbers as a possibilistic-probabilistic methodology. Moreover, the supply side resources uncertainty considered with Monte Carlo simulation methodology. In the modern smart grids, DRRs, fast ramp resources and energy storages can be considered for compensating the variability and uncertainty of renewable energy resources. Actually, with an increasing thrust towards renewable integration across the globe, energy storage as one of the most important flexibility resources has the potential to manage demand and supply dynamics. The energy storage is mostly used to adjust the timing of electricity supply by storing electricity at the lowest price level and discharging at an expensive time. So the energy storage plays an important role in reducing costs and increasing flexibility at the same time. Therefore, this paper sheds light on the various issues of future flexible power systems with significant amounts of non-dispatchable and uncertain renewable energy capacities. UBFUCCDRRs 's primary goal is to determine the optimum flexibility value as a key problem while achieving the operation and investment costs at the lowest possible level. The results indicate improvement of the flexibility index with cost adjustment. In order to trace the capability of the suggested framework, several cases are modeled on a modified standard 10-unit system.

Grid-Forming Inverters: A Critical Asset for the Power Grid

Increasing inverter-based sources reduces the system’s inertia resulting in possible frequency stability issues. Understanding low-inertia systems and their stability properties is of crucial importance. This article introduces fundamental ways to integrate high levels of renewable energy (RE) and distributed energy resources (DERs) in the power system while creating a more flexible power system. Using RE and DER in the distribution system has many advantages such as reducing the physical and electrical distance between generation and loads, bringing sources closer to loads contributes to the enhancement of the voltage profile, reduction in distribution and transmission bottlenecks, improved reliability, lower losses, and enhances the potential use of waste heat. A basic issue for high penetration of DER is the technical complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local measurements eliminating the need for fast control systems. The key issues addressed in this article include using inverter damping to stabilize frequency in systems with low or no inertia, autonomous operation, methods for relieving inverter overload, energy reserves, and their implementation in photovoltaics (PV) systems. This article provides important insight into the interactions between inverter bases sources and the high-power system. The distinction between grid-forming (GFM) inverter and grid-following (GFL) inverter is profound. GFM inverters provide damping to frequency swings in a mixed system, while GFL inverter can aggravate frequency problems with increased penetration. Rather than acting as a source of inertia, the GFM inverter acts as a source of damping to the system. On the other hand, the application of inverters in the power system has two major issues. One is the complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local measurements. The other is the potential of high overcurrent in GFM inverters and techniques for explicitly protecting against overloading. To exploit the innate damping of GFM inverters, energy reserves are critical.

Reduced switches multilevel inverter integration with boost converters in photovoltaic system

Multilevel inverters (MLIs) are developed to meet medium voltage and high power applications in flexible power systems. The conventional configuration of multilevel inverter requires more switches and has limitation to its wide range application. This paper reports the performed work on 1-phase 7-level reduced switch multilevel inverter (RS MLI) in photovoltaic (PV) system. RS MLI configuration integration with PV system which uses less number of switching components for specified number of voltage output levels as compared to that of conventional multilevel inverter topology. To performed enhanced operation of PV cells and maximize the solar energy extraction an incremental conductance based maximum power point tracking scheme is used. To improve the quality of RS MLI output parameters mainly total harmonic distortion and switching losses, selected harmonic elimination based genetic algorithm method is consider for control the gating pulse of PV based RS MLI. This work is performed using MATLAB/SIMULINK software.

Portable Self-Charging Power System via Integration of a Flexible Paper-Based Triboelectric Nanogenerator and Supercapacitor

To meet the energy demand for flexible and miniaturized green electronics, it is highly desirable to develop a portable, cost-effective, lightweight, and sustainable power source through a facile and environment friendly approach. Herein, we report a portable, flexible, and low-cost self-charging power system (SCPS) consisting of a paper-based triboelectric nanogenerator (P-TENG) with high output power density as the energy harvester and a paper-based supercapacitor (P-SC) with a great areal capacitance as the energy storage device. A cellulose paper/polypyrrole composite with a low sheet resistance of 7.8 Ω sq–1 replaced the conventional metal electrodes and positive friction material in the P-TENG, as well as the capacitive material in the P-SC. The portable SCPS is capable of driving various miniaturized electronics such as a temperature/humidity indicator, thus demonstrating its potential as a sustainable power source for flexible and miniaturized green electronics.

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics.

Implantable bioelectronics represent an emerging technology that can be integrated into the human body for diagnostic and therapeutic functions. Power supply devices are an essential component of bioelectronics to ensure their robust performance. However, conventional power sources are usually bulky, rigid, and potentially contain hazardous constituent materials. The fact that biological organisms are soft, curvilinear, and have limited accommodation space poses new challenges for power supply systems to minimize the interface mismatch and still offer sufficient power to meet clinical-grade applications. Here, recent advances in state-of-the-art nonconventional power options for implantable electronics, specifically, miniaturized, flexible, or biodegradable power systems are reviewed. Material strategies and architectural design of a broad array of power devices are discussed, including energy storage systems (batteries and supercapacitors), power devices which harvest sources from the human body (biofuel cells, devices utilizing biopotentials, piezoelectric harvesters, triboelectric devices, and thermoelectric devices), and energy transfer devices which utilize sources in the surrounding environment (ultrasonic energy harvesters, inductive coupling/radiofrequency energy harvesters, and photovoltaic devices). Finally, future challenges and perspectives are given.

Flexibility Services to Minimize the Electricity Production from Fossil Fuels. A Case Study in a Mediterranean Small Island

The design of multi-carrier energy systems (MESs) has become increasingly important in the last decades, due to the need to move towards more efficient, flexible, and reliable power systems. In a MES, electricity, heating, cooling, water, and other resources interact at various levels, in order to get optimized operation. The aim of this study is to identify the optimal combination of components, their optimal sizes, and operating schedule allowing minimizing the annual cost for meeting the energy demand of Pantelleria, a Mediterranean island. Starting from the existing energy system (comprising diesel generators, desalination plant, freshwater storage, heat pumps, and domestic hot water storages) the installation of solar resources (photovoltaic and solar thermal) and electrical storage were considered. In this way, the optimal scheduling of storage units injections, water desalination operation, and domestic hot water production was deduced. An energy hub model was implemented using MATLAB to represent the problem. All equations in the model are linear functions, and variables are real or integer. Thus, a mixed integer linear programming algorithm was used for the solution of the optimization problem. Results prove that the method allows a strong reduction of operating costs of diesel generators also in the existing configuration.

Experimental investigation of theoretical stability regions for ultra-low frequency oscillations of hydropower generating systems

With the increasing momentum towards flexible power systems based on renewables, the role of hydropower has great importance, especially for providing balancing power. In this paper, a fundamental study on the operating stability of hydropower generating systems is conducted to reveal the practical characteristics for the newly emergent issue of ultra-low frequency oscillations. A unique study methodology is adapted by combing the theoretical analysis and the physical model experiment. In this paper, first, the set-up of the integral experiment platform for the transient processes of the pumped storage plants is presented. Second, a mathematical model of hydropower generating systems is built, and the theoretical stability analysis is conducted based on the Routh-Hurwitz criterion and the stability margin region. The model experiments related to the frequency stability of hydropower generating systems were conducted with reference to the stability region from theoretical analysis. The results demonstrate the sustained ultra-low frequency oscillations and frequency instability of hydropower units in experiments for the first time. Attenuation characteristics of the oscillations are theoretically derived based on the stability margin region, and then quantitatively identified by experiments. The experiment accorded with theoretical stability region within a reasonable tolerance that corresponded to the ±0.1 stability margin.

Optimal Energy Routing in Microgrids With IEC 61850 Based Energy Routers

The concept of energy Internet (EI) is very promising due to its ability to integrate distributed generators and storage devices. Energy routers (ERs) enable highly efficient, reliable, and flexible power system operation. To dynamically control and optimize energy flow in EI, an extensive communication is required. Considering the diversity of generators and ERs, it is crucial that such communication is achieved in a standardized and interoperable way. In this paper, an improved energy routing algorithm and its impact in EI operation are demonstrated. Furthermore, a full communication solution is developed for ERs and their interaction with grid operator. This paper proposes an International Electrotechnical Commission (IEC) 61850 communication-based power routing algorithm in microgrids. Optimal selection of source and routing path is achieved according to the proposed algorithm and communicated to the ERs via IEC 61850 based communication. The effectiveness of the proposed IEC 61850 communication-based routing algorithm is verified on network emulation platform comprising of IEC 61850 emulator tools and network simulator tool.

Flexible, reliable, and renewable power system resource expansion planning considering energy storage systems and demand response programs

This study presents a flexible, reliable, and renewable power system resource planning approach to coordinate generation, transmission, and energy storage (ES) expansion planning in the presence of demand response (DR). The flexibility and reliability of the optimal resource expansion planning are ensured by means of appropriate constraints incorporated into the proposed planning tool where thermal generation units, ES systems, and DR programs are considered as flexibility resources. The proposed planning tool is a mixed-integer non-linear programming (MINLP) problem due to the non-linear and non-convex constraints of AC power flow equations. Accordingly, to linearise the proposed MINLP problem, the AC nodal power balance constraints are linearised by means of the first-order expansion of Taylor's series and the line flow equations are linearised by means of a polygon. Additionally, the stochastic programming is used to characterise the uncertainty of loads, a maximum available power of wind farms, forecasted energy price, and availability/unavailability of generation units and transmission lines by means of a sufficient number of scenarios. The proposed planning tool is implemented on the IEEE 6-bus and the IEEE 30-bus test systems under different conditions. Case studies illustrate the effectiveness of the proposed approach based on both flexibility and reliability criteria.