Future Electric Power Research Articles

Strategic management of residential electric services in the competitive market: Demand-oriented perspective

This paper aims to empirically investigate consumers’ preference structures and their willingness to pay for key features of future residential electric power services that they have not experienced in the regulated market. Using a choice experiment based on conjoint survey and applying a mixed logit model, we quantitatively estimate individual utility functions for certain important attributes such as type of service-providing company, installation of smart meter devices, introduction of E-prosumer groups, relaxation of progressive electricity billing system, and share of renewable energy in the generation mix. The analysis reveals that households prefer installation of smart meter devices and introduction of E-prosumer groups, and are willing to pay 10,044 KRW/year (USD 8.97/year) and 5,222 KRW/year (USD 4.66/year), respectively, for these services. However, households dislike the participation of privately-owned companies under the competitive market structure, owing to the possibility of a rise in the electricity price.

Engineering Support for Handling Controller Conflicts in Energy Storage Systems Applications

Energy storage systems will play a major role in the decarbonization of future sustainable electric power systems, allowing a high penetration of distributed renewable energy sources and contributing to the distribution network stability and reliability. To accomplish this, a storage system is required to provide multiple services such as self-consumption, grid support, peak-shaving, etc. The simultaneous activation of controllers operation may lead to conflicts, as a consequence the execution of committed services is not guaranteed. This paper presents and discusses a solution to the exposed issue by developing an engineering support approach to semi-automatically detect and handle conflicts for multi-usage storage systems applications. To accomplish that an ontology is developed and exploited by model-driven engineering mechanisms. The proposed approach is evaluated by implementing a use case example, where detection of conflicts is automatically done at an early design stage. Besides this, exploitable source code for conflicts resolution is generated and used during the design and prototype stages of controllers development. Thus, the proposed engineering support enhances the design and development of storage system controllers, especially for multi-usage applications.

A Z-Source-Based Bidirectional DC Circuit Breaker With Fault Current Limitation and Interruption Capabilities

DC microgrids have some attractive characteristics, which have being investigated to utilize in future electrical power systems. However, they have several essential challenges, such as limiting and interrupting fault current, which should be rectified to have high-performance dc microgrids. In this paper, an efficient dc bidirectional fault current limiter and interrupter (FCLI) based on Z-source topology is proposed to overcome some of the challenges in dc microgrids. The FCLI is a multifunction device, by which power flow direction control, circuit breaking, fault current limiting, and interrupting in a dc system can be handled. Analytical analysis of the FCLI is discussed in detail for different operation modes. Performance of the proposed FCLI in the different operation modes is evaluated using some simulations and experiments. The results confirm high capability of the device to realize appropriate operation in dc systems. Fast response time of fault current limitation and interruption, simple and reliable structure, and negligible conduction loss are the main features of the proposed FCLI.

Analysis of Microgrid Contributing to Hour-ahead market operation through Marginal Day-ahead market Price-Based Demand Response

Abstract: In Japan, 53 GW Photovoltaic (PV) systems will be introduced in future electric power system in 2030 year. It will raise issues of insufficient supply capability and reserve capacity to utility operator to ensure supply-demand balance. On the other hand, Microgrid that located in demand side will be expecting to actively response the incentive signal sent by the utility operator so as to contributing to demand-supply adjustment. In this paper, based on revised IEEJ-EAST-10 Generators simulation model that included of 22GW PV generations and 5GW Microgrids, we analyzed the effect and potential contribution capability of microgrid to electric power system demand-supply adjustment in hour-ahead electricity market through Price-Based Demand Response. Firstly, we analyzed the impact of day-ahead market marginal price on optimal scheduling of Micorgrid. Secondly, we analyzed the impact of optimal scheduling of Micorgrid on Utility operator in Hour-ahead market operation. Lastly, we evaluated the contribution capability of microgrid to electric power system demand-supply adjustment in hour-ahead electricity market that included the improvement of partial-load operation of coal thermal power plant, Utility side load-leveling, and reserve capacity provided by Microgrid.

Energy savings in data centers: A framework for modelling and control of servers’ cooling

Aiming at improving the energy efficiency of air cooled servers in data centers, we devise a novel control oriented, nonlinear, thermal model of the servers that accounts explicitly for both direct and recirculating convective air flows. Instrumental to the optimal co-design of both geometries and cooling policies, we propose an identification methodology based on Computational Fluid Dynamics (CFD) for a generic thermal network of m fans and n electronic components. The performance of the proposed modelling framework is validated against CFD measurements with promising results. We formalize the minimum cooling cost control problem as a polynomially constrained Receding Horizon Control (RHC) and show, in-silico, that the resulting policy is able to efficiently modulate the cooling resources in spite of the unknown future computational and electrical power loads.

Frequency response services designed for energy storage

Energy Storage Systems (ESS) are expected to play a significant role in regulating the frequency of future electric power systems. Increased penetration of renewable generation, and reduction in the inertia provided by large synchronous generators, are likely to increase the severity and regularity of frequency events in synchronous AC power systems. By supplying or absorbing power in response to deviations from the nominal frequency and imbalances between supply and demand, the rapid response of ESS will provide a form of stability which cannot be matched by conventional network assets. However, the increased complexity of ESS operational requirements and design specifications introduces challenges when it comes to the realisation of their full potential through existing frequency response service markets: new service markets will need to be designed to take advantage of the capabilities of ESS. This paper provides new methods to analyse and assessing the performance of ESS within existing service frameworks, using real-time network simulation and power hardware in the loop. These methods can be used to introduce improvements in existing services and potentially create new ones. Novel statistical techniques have been devised to quantify the design and operational requirements of ESS providing frequency regulation services. These new techniques are demonstrated via an illustrative service design and high-resolution frequency data from the Great Britain transmission system.

A New Approach for Soft Synchronization of Microgrid Using Robust Control Theory

Microgrid is the main part of future electrical power systems, called “smart grids”. In this context, the synchronization of a microgrid with utility or other microgrids will be a crucial and commonplace task during power system operation. Based on robust control principles, a new approach for synchronizing microgrids with utility was presented in this paper. Uncertainties of the dynamic model of microgrids were considered as multiplicative perturbations. Based on the uncertain model, a robust controller was designed by means of $\mu$ synthesis analysis so that the robust stability and performance of the system could be maximized. The simulation results confirmed the effectiveness of the proposed control strategy.

Future energy and electric power systems and smart technologies

In this paper, we describe, first, the present status and the tasks toward the future of energy systems in Japan from the viewpoint of 3E+S. 3E+S means energy security, environmental conservation, economic efficiency, and safety. Second, we describe the future energy society in 2030 and 2050, respectively. We introduce a large picture of the total energy system considering the energy resources, conversion, transportation, storage, consumption, control, and system architecture. For the image of 2030, the Japanese government has already announced the middle‐term (2030) energy demand and supply on July 16, 2015. For 2050, we assume three cases regarding the renewable energy installations: the status quo of 2030 covering 22–24% of the total consumption, and 50 and 100% of the total consumption. In the last section, we describe smart technologies to support the envisioned society in 2030 and 2050. We also introduce the reference architecture model. To achieve 80% reduction of greenhouse gas (GHG) emission in 2050, the innovations at the consumer side, such as the large‐scale renewable energy resources and storage installations, utilization of electrified vehicles, distributed energy management systems including virtual power plants, and system integration, will become very important in addition to innovations at the supply side. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Role of pump hydro in electric power systems

This paper provides an overview of the expected role that variable speed hydro power plants can have in future electric power systems characterized by a massive integration of highly variable sources. Therefore, it is discussed the development of a methodology for optimising the operation of hydropower plants under increasing contribution from new renewable energy sources, addressing the participation of a hydropower plant with variable speed pumping in reserve markets. Complementarily, it is also discussed the active role variable speed generators can have in the provision of advanced frequency regulation services.

A Distribution Level Wide Area Monitoring System for the Electric Power Grid–FNET/GridEye

The wide area monitoring system (WAMS) is considered a pivotal component of future electric power grids. As a pilot WAMS that has been operated for more than a decade, the frequency monitoring network FNET/GridEye makes use of hundreds of global positioning system-synchronized phasor measurement sensors to capture the increasingly complicated grid behaviors across the interconnected power systems. In this paper, the FNET/GridEye system is overviewed and its operation experiences in electric power grid wide area monitoring are presented. Particularly, the implementation of a number of data analytics applications will be discussed in details. FNET/GridEye lays a firm foundation for the later WAMS operation in the electric power industry.

Interpreting and implementing IEC 61850-90-5 Routed-Sampled Value and Routed-GOOSE protocols for IEEE C37.118.2 compliant wide-area synchrophasor data transfer

Flexibility and adaptability requirements of future electric power grids for integrating distributed energy resources (DERs) call for the development of wide-area monitoring, protection and control (WAMPAC) applications, utilizing synchrophasor measurements provided by the phasor measurement units (PMUs).IEEE C37.118 is the most utilized protocol for real-time exchange of synchronized phasor measurement data. In order to fulfill some gaps not addressed in IEEE C37.118, and also to harmonize with the IEC 61850 power utility automation standard, the IEC 61850-90-5 technical report has been developed. IEC TR 61850-90-5 introduces a mechanism for transfer of digital states and time synchronized phasor measurement data over wide-area networks between PMUs, phasor data concentrators (PDCs) and WAMPAC applications in the context of IEC 61850.This work interprets the IEEE C37.118.2 and IEC 61850-90-5 Routed-Sampled Value and Routed-GOOSE protocols and describes the design and implementation of a library named Khorjin with the functionality of (1) an IEEE C37.118.2 to IEC 61850-90-5 gateway and protocol converter and (2) an IEC 61850-90-5 subscriber and traffic parser.The main contribution of this work is the development of Khorjin library using only standard C libraries (i.e. independent from any operating system). This is allowing the use of the library in different platforms.The design requirements and functionality of the Khorjin library has been tested in the KTH SmarTS Lab real-time hardware-in-the-loop (HIL) simulation environment to assess its conformance to the functional requirements of IEEE C37.118.2 and IEC 61850-90-5 standards.

The melting process of a freezing molten salt pipe of concentracted solar power plant

Concentrated solar power plants are potential to provide based load power of the future electrical power system. Commercial concentrated solar power plants using molten salt as the heat transfer fluid and the energy storage medium have been built and show great promising. However, due to high freezing point, the molten salt has a freezing possibility and may block the pipe. In practical, an electrical heat tracing is installed along the flow path of the molten salt to protect against freezing. Once the molten salt is freezing inside the pipe, the electrical heat tracing can be used to melt the molten salt. This paper studied the melting process of a molten salt (60% NaNO3 and 40% KNO3, referred to as Solar Salt) inside a horizontal pipe by an electrical heat tracing. The molten salt is a binary mixture, its freezing point (511 K) is higher than melting point (494 K). A solid-liquid mixture mushy zone exists between the melting point and the freezing point during the melting process. The enthalpy method was used to simulate the solid-liquid phase change phenomenon of the molten salt. The effect of the natural convection inside the pipe was also considerate. The effect of the installation position and the heating power of the electrical heat tracing on the melting process and the melting time were studied. During the heating process, the molten salt close to the electrical heat tracing melts first and forms a mushy zone. With the assistance of the natural convection, the molten salt in the mushy zone flows upward and gathers in the upper zone of the pipe. Thus, the upper zone of the pipe has a higher liquid fraction than the lower zone, which results in a liquid fraction gradient inside the pipe. The results show than the installation position of the electrical heat tracing effects the gradient of the liquid fraction during the melting process. The increase in the angle between the gravity and the installation position, γ , increases the liquid fraction gradient. It takes a same time to completely melt the molten salt when γ equals to 30° and 60°. When γ is 90°, due to a larger liquid fraction gradient, it needs more 5 min than γ is 60°. Therefore, large γ should be avoided for the practically installation of the electrical heat tracing. The results also show that the melting time is 165 min for a 35 W/m heating power, 85 min for 70 W/m, and 51 min for 140 W/m. Increasing the heating power from 35 W/m to 70 W/m can shorten 48.5% of the melting time, while increasing the heating power from 70 W/m to 140 W/m can only shorten 40% of the melting time. This is because a higher electrical heating power increases the liquid fraction gradient of the mushy zone during the melting process. Thus, the percentages of the shorten melting time decreases with the increases of the heating power. This study gives practical reference to the choose and the installation of the electrical heating tracing of the molten salt pipe.

Toward Distributed/Decentralized DC Optimal Power Flow Implementation in Future Electric Power Systems

This paper reviews distributed/decentralized algorithms to solve the optimal power flow (OPF) problem in electric power systems. Six decomposition coordination algorithms are studied, including analytical target cascading, optimality condition decomposition, alternating direction method of multipliers, auxiliary problem principle, consensus+innovations, and proximal message passing. The basic concept, the general formulation, the application for dc-OPF, and the solution methodology for each algorithm are presented. We apply these six decomposition coordination algorithms on a test system, and discuss their key features and simulation results.

Upcoming Challenges of Future Electric Power Systems: Sustainability and Resiliency

Going back and taking a quick glance at the history of developed countries prove that prosperity of any society is tightly intertwined with resiliency and sustainability of its preliminary infrastructures. Surely, in modern societies, electricity is among the most important infrastructures whose resiliency and sustainability is a key driving force toward development of the society. This is verified by the fact that, since the industrial revolution, per capita electricity consumption has taken as a key index showing the level of economic development and standard of living in a country. This paper focuses on the concept of resiliency and sustainability of electric power systems. The paper, initially, introduces the concept and evaluation procedure of power systems resiliency. Then, it strives to introduce the most challenging issues faced by resilient and sustainable power grids. The challenging issues are electricity load growth, energy crisis, environmental emissions and climate changes, unexpected events, aging infrastructures, and cyber challenges. Then, the most effective solutions proposed by power industry scientists and engineers are discussed. The solutions are asset management, renewable energy resources, demand response, controlled islanding and micro grids, and automation, self-healing , and monitoring systems. Finally, a typical sustainable and resilient power system is described.

Control Design for PMM-Based Generator Fed by Active Front-End Rectifier in More-Electric Aircraft

The future aircraft electrical power system is expected to be more efficient, safer, simpler in servicing and easier in maintenance. As a result, many existing hydraulic and pneumatic power driven systems are being replaced by their electrical counterparts. This trend is known as a move towards the More-Electric Aircraft (MEA). As a result, a large number of new electrical loads have been introduced in order to power many primary functions including actuation, de-icing, cabin airconditioning, and engine start. Therefore electric power generation systems have a key role in supporting this technological trend. Advances in modern power electronics allow the concept of starter/generator (S/G) which enables electrical engine start and power generation using the same electrical machine. This results in substantial improvements in power density and reduced overall weight. One of the potential S/G solutions is to employ a permanent magnet machine (PMM) controlled by active front-end rectifier (AFE). Operation of the PMM as a generator at wide range of speed that is dictated by the engine and electrical loads connected to the aircraft bus require careful design of the controllers. Corresponding plant models are derived and verified with simulations using developed models in Matlab/Simulink. The relevant controllers are designed based on the derived plants and operating points. The controllers are tested with Simulink models and experimentally using a scaled prototype of the investigated generator system.

Agent-Based Distributed Security Constrained Optimal Power Flow

The need for the coordination of distributed energy resources in the future electric power system provides motivation to move from the current highly centralized control of resources toward a more distributed control structure. This paper presents an agent-based fully distributed dc security constrained optimal power flow (DC-SCOPF) approach. The algorithm is based on a multi-agent system, in which geographically distributed network entities are designated as agents with local sensing, communication, and computation abilities as envisioned for a smart grid. This distributed approach is based on solving the first order optimality conditions associated with DC-SCOPF formulation through an iterative process. At each iteration, each agent updates a few local variables through simple computations, and exchanges information with its neighboring agents. In particular, the updates for each agent incorporate local information such as the Lagrange multipliers, as well as enforcing the supply/demand balance through a local innovation term. Also, the performance is evaluated using the IEEE test systems with 14 and 57 buses and a 944-bus system consisting of eight IEEE 118-bus systems. Finally, analytical arguments concerning the convergence of the proposed method to the optimal solution of the DC-SCOPF are provided.

The future electric power system: Impact of Power-to-Gas by interacting with other renewable energy components

The storage of fluctuating energy production is a major challenge on the pathway to a fully renewable electricity supply. This paper investigates the impact of the storage technology Power-to-Gas (PtG) in the implementation of the Energiewende. A detailed cost optimisation model based on data from an existing system in an actual German region describes the optimal composition and application of energy supply technologies. The electricity demand of the region can be covered with 100% renewable energy (RE) at a levelised cost of electricity (LCOE) of 11ct/kWhel. A 100% RE supply is possible with or without PtG. However, long-term energy storage system such as PtG reduce the LCOE of the energy system significantly. We conclude that the capital expenditures (CAPEX) of PtG must at least reach values below 2500€/kWel to compete with short-term solutions such as Li-ion batteries. Beside PtG this investigation identifies several system components with extensive impact on LCOE and demand of long-term energy storage, such as Power to Heat (PtH), wind turbine technology and hydropower. The combination of such influences increases the impact of each of them on the LCOE. Several energy system components can positively influence the implementation of the Energiewende, PtG is one of them.

Model Predictive Heating Control for Electric Vehicles Using Load Prediction and Switched Actuators

Thermal management of electric vehicles in low-temperature environments poses an interesting control problem. While thermal control of the cabin is vital for passenger comfort, energy consumption and battery aging always remain an essential concern. Since more reliable information about the short-term future electrical power flow is becoming available by more sophisticated cruise control systems and map information, on-line model predictive thermal management systems can utilize this knowledge to improve battery life maintaining passenger comfort. In this contribution, such a model predictive heating control is proposed based on an on-board capable fast gradient method to solve the nonlinear optimization problem. Direct control of simple electronic switches by the proposed method reduces the need for dedicated PWM controllers embedded within the heating actuators and allows for a cost-efficient and easy realization.

Profit maximization algorithms for utility companies in an oligopolistic energy market with dynamic prices and intelligent users

Dynamic energy pricing provides a promising solution for the utility companies to incentivize energy users to perform demand side management in order to minimize their electric bills. Moreover, the emerging decentralized smart grid, which is a likely infrastructure scenario for future electrical power networks, allows energy consumers to select their energy provider from among multiple utility companies in any billing period. This paper thus starts by considering an oligopolistic energy market with multiple non-cooperative (competitive) utility companies, and addresses the problem of determining dynamic energy prices for every utility company in this market based on a modified Bertrand Competition Model of user behaviors. Two methods of dynamic energy pricing are proposed for a utility company to maximize its total profit. The first method finds the greatest lower bound on the total profit that can be achieved by the utility company, whereas the second method finds the best response of a utility company to dynamic pricing policies that the other companies have adopted in previous billing periods. To exploit the advantages of each method while compensating their shortcomings, an adaptive dynamic pricing policy is proposed based on a machine learning technique, which finds a good balance between invocations of the two aforesaid methods. Experimental results show that the adaptive policy results in consistently high profit for the utility company no matter what policies are employed by the other companies.

Experimental validation of smart distribution grids: Development of a microgrid and electric mobility laboratory

Abstract The development of the Smart Grid concept is the pathway for assuring high reliability, control and management requirements in future electric power distribution systems. The Smart Grid can be defined as an electricity network supported by an intelligent infrastructure, both hardware and software, capable of accommodating high shares of Distributed Energy Resources. Within this line, a Smart Grid laboratorial infrastructure was developed, being dedicated to advanced research and demonstration activities. The adopted laboratorial architecture was developed according to the Microgrid concept, where Electric Vehicles are regarded as active and flexible players. Following the laboratory implementation, this paper provides a detailed description of its infrastructure and experimental capabilities, presenting and discussing different experimental set-ups and associated results.