Dynamic Energy Flow Research Articles

Vehicle-to-Grid Power Transfer Method for Electric Vehicles using off-board charger

This article explores a power transfer technique from vehicle to grid (V2G) via the construction of an off-board charger for electric cars (EVs). The charger accommodates several charging modes, such as grid-to-vehicle (G2V), vehicle-to-vehicle (V2V), and vehicle-to-grid (V2G), facilitating efficient and adaptable energy management. In G2V mode, the charger utilizes grid power to recharge electric vehicle batteries, whilst V2V mode enables direct energy transfer between electric vehicles, circumventing the grid. The novel integration of G2V and V2V modes enables the concurrent use of grid electricity and energy from other electric vehicles, therefore diminishing grid reliance and enhancing power efficiency. The system has a three-phase pulse width modulation (PWM) rectifier that sustains a constant DC link voltage and attains a unity power factor on the grid side, therefore adhering to the IEEE 519 standard for total harmonic distortion (THD). Furthermore, a half-bridge bidirectional DC/DC converter guarantees consistent charging and discharging currents, hence improving the reliability and efficiency of the charging process. This holistic strategy enhances dynamic energy flow and grid stability while providing possible economic advantages to electric vehicle owners and operators via the integration of renewable energy sources and sophisticated management algorithms for improved energy use and storage.

A generalised dynamic energy flow model in multi‐energy network

A generalised dynamic energy flow model in multi‐energy network

Interaction energy flow paths analysis of PMSG-based wind power integrated systems during LVRT and its parameter adjustment strategy

To solve the problem of oscillation instability in permanent magnetic synchronous generator (PMSG)-based wind power connected systems during low-voltage ride through (LVRT) process, a parameter adjustment strategy based on interaction energy path optimization is proposed in this paper. Firstly, a modular state-space model of PMSG under fault transient conditions is constructed, and the system is divided into five subsystems. Then, the dynamic energy function of subsystems reflecting the oscillation stability of the system is derived. Based on that, the dynamic energy flow path is described considering the introduction of LVRT control. On this basis, the interaction energy between LVRT control links and subsystems is analyzed, and the coupling mechanism of voltage support and damping characteristics in the LVRT process is explained. Further, aiming at the optimal change rate of the total interaction energy in the LVRT process, the adjustment strategy of LVRT control parameters is constructed to meet voltage and damping requirements. Finally, a PMSG-connected system model is built on the MATLAB/Simulink platform to verify the effectiveness of the adjustment strategy. The results show that the proposed method can effectively improve the damping level under the fault transient condition, as well as supporting system voltage.

A comparative study of demand-side energy management strategies for building integrated photovoltaics-battery and electric vehicles (EVs) in diversified building communities

This study compares four developed energy management strategies for a grid-connected photovoltaic-battery (PVB) system in a district energy system comprising four diverse building communities: campus, residential, office, and commercial. The proposed demand-side energy management scenarios include maximizing photovoltaic self-consumption, cost minimum strategy under time-of-use and two peer-to-peer (P2P) strategies (a Mid-Market Rate (MMR) and a novel demand response (DR) based P2P strategies). Besides, Monte Carlo integrated Markov Chain simulation method was applied to calculate the load distribution of integrated electric vehicles in diversified building communities, and P2P price was generated considering dynamic supply-demand ratio. In term of dynamic energy flow, energy cost and grid interaction, dispatch results of proposed management strategies were simulated and compared in detailed. The results demonstrate that compared to the mainstream MSC and TOU operation strategies, P2P strategies, especially the DR based P2P strategy, effectively alleviate pressure on the utility grid by actively responding to peak electricity demand and utilizing excess renewable energy generation from other communities. It is worth noting that the choice of strategy depends on the role of the building community, whether as a consumer or a prosumer. This study offers insights for decision-makers and stakeholders in managing grid-connected PVB district energy systems in diverse building communities.

Phase change material window for dynamic energy flow regulation: Review

The phase change material (PCM) window is a promising technology for enhancing the thermal regulation capabilities of transparent facades by dynamically regulating the energy flow between indoor and outdoor environments. By storing and releasing thermal energy during phase transitions, PCM windows can effectively regulate indoor temperature and reduce heating or cooling loads. This study examines 53 research studies published within the last decade. These studies are analyzed based on geographic distribution, PCM material types, research methods, and performance indices. The PCM windows are categorized according to the PCMs integration measures, which include direct infill to the window cavity, embedding within window frames, and integration with built-in heat exchangers to preheat or precool the vent air. The light, thermal, and energy performances of these innovative PCM windows are summarized and discussed. Moreover, the potential of dynamic designs for PCM windows to enhance the light and thermal regulation abilities through flexible arrangement of PCM components is recognized as promising. However, a comprehensive assessment of their performance and energy-saving potential still need to be fully explored. This review identifies potential challenges and limitations associated with PCM window studies and applications, highlighting the need for future investigation to fully explore the benefits of dynamic designs and renewable energy utilization. These findings provide valuable insights for researchers and practitioners seeking to optimize the use of PCM windows in building envelopes.

Stability analysis for sub‐synchronous oscillations in multi‐DFIGs connected system considering the interaction between generators

AbstractIn order to reveal the multi‐DFIGs interaction mechanism in DFIG wind farms (DFIG‐WFs), this paper proposes a method based on dynamic energy flow path for stability analysis of sub‐synchronous oscillations in multi‐DFIGs connected system. First, the detailed dynamic energy model of DFIG‐WFs is established considering the inter‐DFIGs coupling effect, and the energy flow paths among multi‐DFIGs are revealed. From this, the interaction energy coefficient is defined to describe the effect of multi‐DFIGs interaction on the system stability, which can be divided into two items: the inter‐DFIGs induction coefficient and the inter‐DFIGs circulation coefficient. On this basis, how the differences in the parameters affect these coefficients are analysed. In this way, the effects of multi‐DFIGs interaction on the oscillation are clarified. Finally, a wind farm model is built in RT‐LAB for simulation verification. The results show that, the changes in DFIG parameters may have mutually exclusive effects on the two coefficients. When the parameters of DFIGs differ greatly, the circulation effect is dominant, which is mainly determined by the difference between DFIGs. If the parameters of DFIGs are similar to each other, the induction effect is dominant and the influence law of parameters is consistent with that of single equivalent model.

Dynamic energy flow analysis of electricity-heating based integrated energy system

With the development of integrated energy system, energy flow analysis of coupling energy network has attracted much attention. In this study, based on the unified energy path theory, energy flow analysis of electricity-heating coupled energy system is implemented considering different time characteristic of each system. Considering the instantaneous change process of heat transfer in the heating system, the dynamic model of heat network is constructed based on unified energy path theory. On this basis, the dynamic models of electric and heating systems are coupled, and the dynamic energy flow calculation method of the coupling system is proposed. Through a case study, the feasibility of the proposed model and calculation method are verified. In addition, the effect of heat source on the dynamic process of heat transfer in the heating system is analyzed.

A Multi-Rate Dynamic Energy Flow Analysis Method for Integrated Electricity-Gas-Heat System With Different Time-Scale

The integrated energy system (IES) combined electric power grid, natural gas network (NGN) and district heating network (DHN) is widely concerned because of its high efficiency and environmentally friendly. The accurate energy flow calculation of IES is the key to simulation analysis, operation optimization and control. This paper studies the dynamic energy flow of IES considering the different time-scale among the electric power, heat and gas networks. Firstly, a discretization method based on the delay characteristics of pipelines for DHN is proposed. By using this method, the selected temporal and spatial step sizes can be adaptively selected for thermal dynamic equation with application to different networks. Secondly, a discretization method for NGN is developed by considering the temporal step size of DHN as sampling period, so that the data interactions between two slow dynamic systems can be addressed in a same time series. Thirdly, a multi-rate energy flow calculation method with different temporal step sizes is presented for IES, which integrates the NGN and DHN considering different time-scale features to retain the state of IES as intact as possible. Simulation results illustrate the effectiveness of the proposed method, which provides dispatchers with more decision-making information.

Nonlinear Dynamic Energy Flow Calculation for Integrated Gas and Power System Based on Method of Lines

The rapid development of gas turbine (GT) and power-to-gas (P2G) technology promotes the integration of power systems (PS) and natural gas systems (NGS). To accurately describe the state distribution, this paper first introduces the model of integrated gas and power system (IGPS) governed by nonlinear partial differential-algebraic equations (PDAEs). A third-order method of lines (MoL) is proposed to solve the nonlinear partial differential equations (PDEs) in the natural gas system. The distribution of mathematical equations and variables in the energy flow model is then analyzed. The solution strategy for nonlinear dynamic energy flow calculation (EFC) in integrated gas and power system is then developed, including the equation set formulation, solvability analysis, and initial guess selection method. Finally, the accuracy and efficiency of the proposed method are verified through simulation in two different cases.

A network-based virtual slack bus model for energy conversion units in dynamic energy flow analysis

A network-based virtual slack bus model for energy conversion units in dynamic energy flow analysis

ОБЧИСЛЮВАЛЬНИЙ МЕТОД ВУЗЛОВОЇ ТРАНСФОРМАЦІЇ ПРОЦЕСУ ЦІНОУТВОРЕННЯ НА РИНКУ ЕЛЕКТРОЕНЕРГІЇ

The main attention in the article is given to the development of the method of nodal transformation of the pricing process in the electricity market. The sequence of implementation of the main constructive stages of its development and further use is given, such as: descriptions of the pricing process; formalization of the pricing process; development of computational procedures for building a simulation model of the pricing process. A distinctive feature of this method from the known and described in the scientific literature is the direct connection of the dynamic energy flow at all stages of the technological process of production, transmission and distribution of electricity with the economic flow. The computational procedures of the method are implemented using the discrete-event approach. The method is designed to build a simulation model of the pricing process in the electricity market, which along with a system of short-term price forecasting models in different market segments, becomes the key in the information and methodological support of multi-agent environment for the market agents interaction. References 13, figures 2.

Dynamic energy flow analysis of the heat-electricity integrated energy systems with a novel decomposition-iteration algorithm

Simulation and operation optimization studies on the integrated energy system have received extensive attention recently for its potential in improving energy efficiency and increasing grid integration of renewable energy, where the task of energy flow calculation serves as a fundamental tool to determine the network states. This paper investigates the models and methods for dynamic energy flow analysis of two strongly coupled networks in the integrated energy systems — the power grid and the heating network. First, the complicated coupling mechanisms of power grid and heating network are thoroughly analyzed and classified into four representative coupling modes. On this basis, the detailed dynamic energy flow analysis method for each coupling mode is developed. Second, a refined difference scheme is applied to discretize the partial differential equations describing the long-lasting temperature dynamics in the heating network. The high-dimensional dicretized model is then solved by a novel decomposition-iteration algorithm. Compared with existing methods, this algorithm avoids deriving the gigantic coefficient matrix of network equations and can improve the accuracy of energy flow results. Finally, considering the systematical error caused by neglecting the inertial and adjusting constraints of heat sources, a revision stage is firstly introduced to correct the heat power output of the slack source and help obtain more accurate energy flow results. Case study shows that the proposed methods take 3.21 s to obtain the dynamic energy flows of a coupled system consisting of a 118-node power grid and eight 35-node district heating networks over a 300-minutes simulation course, which is qualified to provide support for simulation and optimization related applications in practice.

A Robust Scheduling Methodology for Integrated Electric-Gas System Considering Dynamics of Natural Gas Pipeline and Blending Hydrogen

As smart grid develops and renewables advance, challenges caused by uncertainties of renewables have been seriously threatening the energy system’s safe operation. Nowadays, the integrated electric-gas system (IEGS) plays a significant role in promoting the flexibility of modern grid owing to its great characteristic in accommodating renewable energy and coping with fluctuation and uncertainty of the system. And hydrogen, as an emerging and clean energy carrier, can further enhance the energy coupling of the IEGS and promote carbon neutralization with the development of power-to-hydrogen (P2H) technology and technology of blending hydrogen in the natural gas system. Dealing with the uncertainty of renewables, a robust schedule optimization model for the integrated electric and gas systems with blending hydrogen (IEGSH) considering the dynamics of gas is proposed and the iterative solving method based on column-and-constraint generation (C&CG) algorithm is implemented to solve the problem. Case studies on the IEGSH consisting of IEEE 39-bus power system and 27-node natural gas system validate the effectiveness of the dynamic energy flow model in depicting the transient process of gas transmission. The effectiveness of the proposed robust day-ahead scheduling model in dealing with the intra-day uncertainty of wind power is also verified. Additionally, the carbon emission reduction resulting from the blending of hydrogen is evaluated.

A Novel RF Energy Harvester for Event-Based Environmental Monitoring in Wireless Sensor Networks

Perpetual energy source is the major research issue in the research community for energy-constrained wireless sensor network (WSN) and IoT applications. Radio-frequency (RF) energy harvesting has become a technology available round the clock due to increased communication activities. However, efficient RF energy harvesting for low-power regions [ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$PRF \leq (0 {\mathrm{ dBm}})$ </tex-math></inline-formula> ] is still a challenge. This article proposes a novel RF energy harvesting technique along with an intelligent dynamic energy flow control algorithm. The algorithm works with dedicated energy flow control hardware. It is also able to provide perpetual life time to the ultralow power sensor nodes. A close approximation of the size of the RF energy harvester array is proposed for the perpetual lifetime of the WSN node deployed with wake-up radio for event-based monitoring applications. The model is verified by mathematical analysis, simulation, and fabricated prototype results for the operability in the given system. It is found that the circuit provides improved dc output voltage over the previous benchmark at low power in the range of −20 to 0 dBm. The system can charge a 2.7 V, 350 F supercapacitor with the rate <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.16~\mu \text{V}$ </tex-math></inline-formula> /s at 0 dBm, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.125~\mu \text{V}$ </tex-math></inline-formula> /s at −6 dBm, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.08~\mu \text{V}$ </tex-math></inline-formula> /s at −20 dBm. To prove the utility of the proposed idea, an RF field survey is also conducted and found that the proposed circuit can harvest energy from high power region (≥ −6 dBm) for LTE850 and LTE 900 bands.

Study on the oscillation transmission paths in direct‐drive wind farm transmitted via flexible dc system based on dynamic energy flow

Concerning the sub-synchronous oscillation induced by the interaction among wind power converter, flexible DC converter and multiple control links, a method to study the oscillation transmission path based on dynamic energy flow is proposed. First, the system is divided into several subsystems according to different control links, and the dynamic energy model of each subsystem is built by using the first integration method. Then, the energy flows induced by different control links are determined according to the corresponding oscillation components. On this basis, the intersection of energy flows in each dynamic energy model is defined as an energy converging point. Thus, the energy flows between different energy converging points are obtained, and the oscillation transmission path of the interconnected system between different subsystems is determined. Finally, combining the parameters of a real direct-drive wind farm transmitted via flexible DC system, a test system is built in RT-LAB for simulation verification. The results show that the proposed method can describe the oscillation transmission paths between different control links quantitatively, and reveal the control links that make against the stability of system. Besides, studying the energy distribution in the oscillation transmission paths can contribute to further research on the control parameter setting and energy suppression, and lay the theoretical foundation for the design of supplementary compensation branches.

Dynamic energy flow analysis of integrated gas and electricity systems using the holomorphic embedding method

To perform efficient simulation of the integrated gas and energy system’s operation and explore the interaction between natural gas and electric power, an energy flow analysis tool with high accuracy and computational efficiency is needed. The commonly used steady-state analysis method is not applicable in computing the pipeline dynamics of natural gas networks, and it is computationally expensive for most transient analysis methods to obtain high-resolution solutions. In addition, conventional methods generate energy flow profiles at pre-set time intervals, which are not compatible with continuous-time applications. To bridge these gaps, this paper proposes a dynamic energy flow analysis method applied in integrated gas and electricity systems using the holomorphic embedding method. The system’s state equations are formulated using ordinary differential equations based on a simplified natural gas network model and are reconstructed by time-embedded holomorphic functions. By solving these functions, the continuous-time profiles of the energy flow of the whole system can be readily generated with a moderate computational burden, and the pipeline dynamics can be addressed. The simulation results of the case studies validate the improved computational performance of the proposed method over that of a conventional ordinary difference equation solver. In both small-scale and large-scale cases, the proposed method can capture the transient process in every state variable in response to disturbances accurately and efficiently.

The path-independent J-integral and the crack-extension energy-release rate

The equilibrium, path-independent J-integral is commonly interpreted as the rate of decrease in the potential energy of an elastic body, containing a crack, per unit area of the new surface created by crack extension. Such an interpretation encounters difficulties. The correct, contradiction-free description of the energy-release rate is the approach based on the dynamic energy flow into the crack tip. As a corollary, it leads to the correct quasistatic criteria for brittle-fracture propagation.

Fast Decomposed Method for Dynamic Energy Flow Calculation in Integrated Electricity and Heat System

Fast Decomposed Method for Dynamic Energy Flow Calculation in Integrated Electricity and Heat System

Energy transfer within the hydrogen bonding network of water following resonant terahertz excitation.

Energy dissipation in water is very fast and more efficient than in many other liquids. This behavior is commonly attributed to the intermolecular interactions associated with hydrogen bonding. Here, we investigate the dynamic energy flow in the hydrogen bond network of liquid water by a pump-probe experiment. We resonantly excite intermolecular degrees of freedom with ultrashort single-cycle terahertz pulses and monitor its Raman response. By using ultrathin sample cell windows, a background-free bipolar signal whose tail relaxes monoexponentially is obtained. The relaxation is attributed to the molecular translational motions, using complementary experiments, force field, and ab initio molecular dynamics simulations. They reveal an initial coupling of the terahertz electric field to the molecular rotational degrees of freedom whose energy is rapidly transferred, within the excitation pulse duration, to the restricted translational motion of neighboring molecules. This rapid energy transfer may be rationalized by the strong anharmonicity of the intermolecular interactions.

Equipment-Level Locating of Low Frequency Oscillating Source in Power System With DFIG Integration Based on Dynamic Energy Flow

In view of the complex correlation between Doubly Fed Induction Generator (DFIG) internal components and control links which makes it difficult to locate the oscillating source in the equipment level, a DFIG equipment-level oscillating source locating method based on dynamic energy flow is proposed. Firstly, the energy correlation topology network of DFIG internal components and control links is constructed. On this basis, the analytical expressions of dynamic energy flows of DFIG internal components and control links are derived. And then, through Partial Directional Coherence (PDC) analysis, the values of causality between dynamic energy flows of DFIG internal components and control links are calculated, and the diagram of DFIG internal oscillation transmission causality is depicted. Thus according to the distribution pattern of causality values in the causality diagram, the oscillation transmission route is identified and the oscillating source is located. Finally, simulation tests in Real Time Digital Simulator (RTDS) of IEEE 10-machine 39-bus system verify that, the proposed method can quantitatively describe the intensity of interaction between dynamic energy flows of DFIG internal components and accurately identify the oscillation transmission route and the oscillating source in the equipment level. The proposed method can accurately track the original control link/physical component that causes the system to oscillate. Therefore, this paper will facilitate research on DFIG parameter tuning and oscillation suppression measures for low-frequency oscillation in power system.