Multi-energy Flow Calculation Research Articles

Multi-energy flow calculation in integrated energy system via topological graph attention convolutional network with transfer learning

Multi-energy flow (MEF) calculation plays a key role in integrated energy system (IES) analysis. However, its practical implementation is challenged by the high computational burden and frequently changing topology. To mitigate these issues, the topological graph attention convolutional network with transfer learning (TGACN-TL) is proposed for MEF calculation in IES with electrical, natural gas, and heating networks. Specifically, the topological physics information is embedded in TGACN to improve the MEF calculation accuracy. Besides, the attention mechanism is leveraged by TGACN to capture and represent intricate graphical patterns inherent in the MEF data, thereby preserving essential graphical structure features. Furthermore, transfer learning is applied to utilize previously learned topological knowledge, facilitating adaptation to new electricity network topologies through updating partial model's parameters. The simulations demonstrate that the proposed TGACN with transfer learning achieves superior MEF calculation accuracy, maintaining robust performance across diverse conditions of uncertainty and topological variations.

A comprehensive methodology for optimal planning of remote integrated energy systems

Rational planning for remote integrated energy systems is of great importance for demand guarantee and sustainable development of remote areas. A critical challenge is that comprehensive factors, e.g., technical, economic, environmental, and social, which are inherently intertwined, should be properly evaluated and balanced in terms of social benefits. In addition, the feasibility of each planning scheme can only be verified based on their local electrical conditions by employing multi-energy flow calculations. Thus, this paper develops a comprehensive methodology for the optimal planning of remote integrated energy systems taking into account the uncertainty of renewable energy, where a multi-criteria decision-making procedure is designed, including the candidate set construction, remote integrated energy systems modeling, multi-energy flow calculation of the candidates, index definition and selection, and the optimal scheme determination. The methodology is applied to a case study in Lankao County, China. The optimal scheme, selected by the proposed multi-criteria decision-making procedure from 432 candidates, shows the best comprehensive performance, which is verified by different ranking methods. The optimal scheme can rank in the top 13% of each aspect on average, with economic and environmental aspects ranking in the top 2%. The methodology can help decision-makers find reasonable solutions for energy system planning in remote areas.

Bi-level modeling and multi-energy flow calculation of main grid and microgrid cluster based on electro-thermal coupling analysis

In this study, considering the characteristics of multi-energy coupling and multi-level interconnection, a bi-level steady-state physical model is developed. Both decomposed and unified solution methods are employed for the energy flow calculation under the bi-level and multi-energy coupling structure. A numerical study is executed to examine the validity of the algorithms. In addition, the load change within the microgrid and the system operation state under both on-grid and off-grid modes are examined. According to the simulation results, compared with the unified solution method, the decomposed method has faster solution speed and higher data privacy protection, and is more adaptive to the further expansion of the scale of the interconnected microgrids. The microgrids can realize energy interaction and energy mutual aid through grid-connecting operation or inter-network interconnection.

Probabilistic multi-energy flow calculation method for integrated heat and electricity systems considering correlation of source–load power

There are many types of sources and loads in the electricity-heating coupling integrated energy system, and there are correlation characteristics between different energy sources, between loads, and between energy sources and loads, and the uncertainty of source and load is becoming more and more significant. In this regard, a calculation method of electricity-heating coupling probabilistic multi-energy flow considering the correlation and uncertainty of input variables is proposed in this paper. Firstly, the uncertainty probability models of wind power generation, photovoltaic generation, solar heat pump, heat load, and electricity load are established respectively; Secondly, the triangular fuzzy number is proposed to describe the correlation between variables, and the fuzzy correlation model of random variables of source and load is established by means of Gauss–Hermite integral and Nataf inverse transformation; Finally, the output state variables are fitted using the cumulant method and Cornish–Fisher series expansion to obtain the probability distribution of the output variables. The feasibility and effectiveness of the proposed method is verified by using an electricity-heating coupling integrated energy system. At the same time, the influence of fuzzy correlation intervals and coefficient changes on the probability distribution of output variables, and the influence of heat load fluctuations on the nodal voltage probability distribution of the power supply system are analyzed.

Unified calculation of multi-energy flow for integrated energy system based on difference grid

The comprehensive utilization of electricity, gas, and heat energy is an important way of energy transformation. However, different energy forms follow different physical laws, which brings great challenges to the collaborative analysis and optimization of the integrated energy system (IES). In this paper, a unified time-domain model of IES is developed based on the two-port network equivalence theory. First, the unified linear equations for IES are derived according to the basic dynamic models of electricity, gas, and heat networks. Second, a unified model of the multi-energy branch based on the finite difference scheme is proposed. The complex internal information of the branch is transformed into equivalent transfer matrixes of initial and boundary conditions. Finally, combined with the network topological equations, a multi-energy flow calculation model is established. Numerical simulation results show that the proposed modeling method has higher computational efficiency than the traditional finite difference method.

A non-intrusive probabilistic multi-energy flow calculation method and its application in operation risk analysis of integrated energy systems

With the deep coupling of electricity, heat, and gas systems, the uncertainties in renewable energy sources and loads significantly impact the energy flow distribution of integrated energy systems. Probabilistic multi-energy flow calculations considering these uncertain factors have become essential for risk analysis, optimal management, and operational control. However, it is still difficult to efficiently and accurately deal with the diverse and large numbers of correlated random variables. This paper proposes a non-intrusive probabilistic multi-energy flow calculation method and explores its application in the operation risk analysis of integrated energy systems. The probabilistic multi-energy flow model is established considering the uncertainties and correlations of renewable energy sources and loads. The proposed model is solved within the sparse polynomial chaos expansion framework based on Bayesian compressive sensing. Thus, the probabilistic density functions of the risk indices of each subsystem can be obtained. On this basis, the conditional value-at-risk method is employed for the operation risk analysis. The feasibility and advantages of the proposed method are verified using a typical integrated energy system test case.

A composite voltage stability index for integrated energy systems based on L-index and the minimum eigenvalue of reduced Jacobian matrix

The closer interdependency of subsystems in integrated energy systems (IESs) and the continuous increase of electricity/gas/heat loads have brought great challenges to the stable operation of IESs. In response to the static voltage stability problem of IESs, this paper proposes a composite voltage stability index (CVSI) based on the minimum eigenvalue of a reduced Jacobian matrix and the known L-index. First, a unified multi-energy flow model for integrated electrical, natural gas and heating system is established, which comprises the steady-state modeling of each energy subsystem and coupling components in IESs. Then, an integrated multi-energy flow calculation method based on the Newton–Raphson algorithm is developed to solve the unified steady-state model of IESs. On the basis, the unified Jacobian matrix after multi-energy flow convergence can be obtained. Moreover, a reduced Jacobian matrix considering the impacts of multi-energy state variables on the reactive power of electrical power system (EPS) is constructed. Afterward, the CVSI is proposed, which combines the minimum eigenvalue of the constructed reduced Jacobian matrix and the L-index derived from bus voltage calculation formula. The proposed CVSI takes both the voltage stability margin of whole system and the voltage stability of electrical buses into consideration. Finally, numerical simulations are exploited to verify the effectiveness and applicability of the proposed voltage stability index.

Probabilistic Multi-Energy Flow Calculation of Electricity–Gas Integrated Energy Systems With Hydrogen Injection

Probabilistic multienergy flow (PMEF) analysis is the fundamental of planning and operation of integrated energy systems (IES) considering uncertainties. The injection of hydrogen will make the PMEF calculation more complex and can deeply affect the distribution of energy flows. This article studies an efficient PMEF calculation method which can obtain the probabilistic information of electricity–gas IES with hydrogen injection. First, the steady-state model of electricity–gas IES with hydrogen injection is established, in which the gas network with hydrogen injection is formulated in compact matrix form. Second, the Jacobian matrix for the steady-state model of electricity–gas IES with hydrogen injection is derived. Third, the cumulant method and Nataf transformation are applied to calculate the PMEF considering the correlations. Finally, case studies are carried out on a coupled IES, which consists of modified IEEE 33-bus electricity system and 11-node gas system. The results demonstrate that the proposed PMEF method can reduce computational time greatly while keeping high computational accuracy when compared with the Monte–Carlo simulation method.

Topological partition based multi-energy flow calculation method for complex integrated energy systems

Multi-energy flow (MEF) calculation is essential for analyzing integrated energy systems (IES) with electricity, gas, and heat. However, for some hybrid-topology IES, conventional MEF calculation methods are hard to converge due to the complex topological structure. To this end, this paper proposes a topological partition based MEF calculation method. First, based on topological structure, the proposed method divides the original system into multiple blocks with only radial or looped topologies, and solves each block with suitable algorithms. This improvement can accelerate the calculation process and broaden the initial solutions range. Second, the proposed method sets the proper balance node of each block such that the convergence of each block becomes independent. This enables the non-convergent blocks can be identified easily. Third, the proposed method sets isobarometric nodes to get equivalent topology reconstruction, which makes the MEF calculation applicable for certain complex systems. Finally, a case study on the IES of Yangzhong City shows the effectiveness of the proposed method.

A data-driven method for operation pattern analysis of the integrated energy microgrid

• Consider uncertainty of load and source in Integrated Energy Microgrid (IEM). • Suitable for analyzing operation patterns of IEM under all operation modes. • Use kernel PCA and enhanced K-means technology etc., to analyze operating scenarios. • Multi-energy flow calculation and real system to acquire comprehensive operating data. • Economy, security, and energy-saving rate of operation patterns are demonstrated. The variability of renewable energy generation and diverse load demands have led to diverse operation patterns of the integrated energy microgrid (IEM). However, there is a lack of systematic analysis of operation patterns from massive operational scenarios. Considering the uncertainty of the load and renewable energy, this paper proposes a data-driven method to identify the normal and extreme operation scenarios, then extracts all potential operation patterns of the IEM. Furthermore, the evaluation indices for the extracted operation patterns are given to quantify the economy, security, and energy-saving rate. The proposed method involves the normalization, kernel principal component analysis (KPCA), the enhanced K-means, and uniform manifold approximation and projection (UMAP) techniques. The effectiveness and superiority of the proposed method are verified by comparison with a conventional method using principal component analysis (PCA) and K-means algorithms under a modified industrial park testbed. The testbed combined with a 14-bus modified distribution power system and an 11-node heat system employs the simulation under isolated and grid-connected operating circumstances. The results show that the accuracy and effectiveness of the proposed method to identify extreme scenarios are better than that of the conventional method. In addition, the extracted operation patterns with no duplication in energy allocation and the performance of these patterns in economy, security, and energy-saving rate are demonstrated.

Multi-Energy Flow Calculation Considering the Convexification Network Constraints for the Integrated Energy System

To alleviate environmental pollution and improve the energy efficiency of end-user utilization, the integrated energy systems (IESs) have become an important direction of energy structure adjustment over the world. The widespread application of the coupling units, such as gas-fired generators, gas-fired boilers, and combined heat and power (CHP), increases the connection among electrical, natural gas, and heating systems in IESs. This study proposes a mixed-integer nonlinear programming (MINLP) model combining electrical, natural gas, and heating systems, as well as the coupling components, such as CHP and gas-fired generators. The proposed model is applicable for either the radial multi-energy network or the meshed multi-energy network. Since the proposed MINLP model is difficult to be solved, the second-order cone and linearized techniques are used to transform the non-convex fundamental matrix formulation of multi-energy network equations to a mixed-integer convex multi-energy flow model, which can improve the computational efficiency significantly. Moreover, the potential convergence problem of the original model can also be avoided. A simulation of IEEE 14-node electrical system, 6-node natural gas system, and 23-node heating system are studied to verify the accuracy and computational rapidity of the proposed method.

Multi-energy flow calculation based on energy cell and parallel distributed computation

To deal with the deep penetration of renewable energy in the power grid and energy coupling in the distribution and consumption part, improve energy efficiency, and construct the regional integrated energy system (IES) with multiple self-sufficient cells, energy cell has attracted widespread interest. However, the different management systems, diversified energy features, and information barriers increase the difficulties of unified energy flow calculation of IES. Based on the theory, this paper proposes a parallel distributed computing method for multi-region IES with electricity network being considered as a dividing surface. First of all, the basic principle of energy cell is proposed and the large-scale IES is divided into several energy cells according to the energy balance ability and geographic location. Then virtual nodes are added at the boundaries of the energy cells and the adjustment factors are introduced to ensure system convergence. Moreover, the extended Jacobian matrix was constructed to calculate muti-energy flow (MEF) in a single energy cell and decoupled energy cells can be computed in parallel through the limited information exchange of virtual nodes. Finally, two cases are utilized to verify the performances of the proposed energy method. Comparing with the integrated method and the decomposed method, the proposed method in this paper has better abilities in calculation efficiency and accuracy.

An integrated multi-energy flow calculation method for electricity-gas-thermal integrated energy systems

The modeling and multi-energy flow calculation of an integrated energy system (IES) are the bases of its operation and planning. This paper establishes the models of various energy sub-systems and the coupling equipment for an electricity-gas-thermal IES, and an integrated multi-energy flow calculation model of the IES is constructed. A simplified calculation method for the compressor model in a natural gas network, one which is not included in a loop and works in constant compression ratio mode, is also proposed based on the concept of model reduction. In addition, a numerical conversion method for dealing with the conflict between nominal value and per unit value in the multi-energy flow calculation of IES is described. A case study is given to verify the correctness and speed of the proposed method, and the electricity-gas-thermal coupling interaction characteristics among sub-systems are studied.

Rapid energy flow calculation method for integrated electrical and thermal systems

The specific solution methodologies adopted for solving multi-energy flow problems involving integrated energy systems (IESs), such as integrated electrical and thermal energy systems, suffer from a number of deficiencies, such as the choice of iterative initial values when using Newton–Raphson method, poor numerical stability and computational efficiency issues. While the computational complexity of the district heating system model increases dramatically as the scale of the system increases. As such, the development of a new solution algorithm suitable for application to the complex models of large IESs is urgently required. Therefore, this paper proposes a rapid multi-energy flow calculation method for integrated electrical and thermal energy systems. Firstly, an equivalent function of the pipeline pressure drop equation is derived to avoid the iterative and simultaneous solution of crucial pipeline parameters. Secondly, a linear equation is introduced to decouple and transform a typical ring district heating system into a collection of radial district heating systems, which can be rapidly solved with high-precision. Numerical applications of the proposed approach to the Barry Island system verify that the approach provides accurate and highly efficient multi-energy flow calculations.

IEC 61970 standard based common information model extension of electricity-gas-heat integrated energy system

Power system, natural gas system, and thermal system are traditionally managed by different types of companies, resulting in information islands among different systems. In order to break the information islands phenomenon and realize the unified management of electric-gas-heat integrated energy system, this paper thoroughly analyses the composition and characteristics of the electricity-gas-heat integrated energy system and extends the common information model by using object-oriented modeling concept based on the IEC 61970 to meet the needs of integrated energy systems, such as multi-energy flow calculation, optimal scheduling, and operational control. The complete extended model of natural gas system, thermal system, coupling links and multi-energy storage systems is built. In addition, the attributes of key classes in the electricity-gas-heat integrated energy system are described, such as the classes of natural gas source, natural gas transporting unit, natural gas pipeline, natural gas load, motor-driven compressor, power-to-gas unit, power-to-heat unit, natural gas storage system, thermal storage system and hydrogen storage system. The extended common information model of electricity-gas-heat integrated energy system is built under the Rational Rose platform and an example verification is carried out to generate XML file and partial code of header file and source file in order to test the rationality of the extended common information model.

Fast Decoupled Multi-energy Flow Calculation for Integrated Energy System

In recent years, as a promising option to improve the overall efficiency of energy utilization and absorptive capacity of renewable energies, the integrated energy system (IES) has raised great interest in academies and industries. Multi-energy flow (MF) calculation, which differs from the traditional power flow calculation, plays a basic role in analyzing IES. MF calculation based on Newton-Raphson method has been proposed in literature, but its calculation efficiency is not high. In this paper, a fast decoupled MF (FDMF) calculation method for IES is proposed. Its main idea is to replace the original Jacobian matrix of MF calculation based on Newton-Raphson method with a diagonal and constant Jacobian matrix by the transformation. The simulations demonstrate that the proposed FDMF method can increase the calculation efficiency by at least 4 times with high calculation accuracy.

A Decomposed Solution of Multi-energy Flow in Regional Integrated Energy Systems Considering Operational Constraints

Abstract With the technology development of energy conversion, multi-energy flow containing electricity, gas and heat is becoming tightly integrated in regional integrated energy systems (RIESs). Interactions and complementarities of various energy systems can bring more environmental and economic benefits but also security problems. This paper studies a decomposed solution of multi-energy flow considering operational constraints, the energy coupling part is analyzed with the concept of energy hub (EH). Multi-energy flow calculation is verified in case study under conditions of different disturbance in EH, showing the necessarily of operational constraint concern. In addition, a multi-energy flow regulation is discussed utilizing gas load-pressure sensitivity analysis.

Generalized Energy Flow Analysis Considering Electricity Gas and Heat Subsystems in Local-Area Energy Systems Integration

To alleviate environmental pollution and improve the efficient use of energy, energy systems integration (ESI)—covering electric power systems, heat systems and natural gas systems—has become an important trend in energy utilization. The traditional power flow calculation method, with the object as the power system, will prove difficult in meeting the requirements of the coupled energy flow analysis. This paper proposes a generalized energy flow (GEF) analysis method which is suitable for an ESI containing electricity, heat and gas subsystems. First, the models of electricity, heat, and natural gas networks in the ESI are established. In view of the complexity of the conventional method to solve the gas network including the compressor, an improved practical equivalent method was adopted based on different control modes. On this basis, a hybrid method combining homotopy and the Newton-Raphson algorithm was executed to compute the nonlinear equations of GEF, and the Jacobi matrix reflecting the coupling relationship of multi-energy was derived considering the grid connected mode and island modes of the power system in the ESI. Finally, the validity of the proposed method in multi-energy flow calculation and the analysis of interacting characteristics was verified using practical cases.