Table of Content

28 March 2023, Volume 56 Issue 3

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Special Contribution

Analysis of China’s Power Demand Situation in the Last Three Years of the “14th Five-Year Plan” Under the New Situation

SHAN Baoguo, LIU Qing, ZHANG Lili, ZHENG Haifeng, ZHANG Chenglong, WU Shanshan, XUE Wanlei

2023, 56(3):  1-11.  DOI: 10.11930/j.issn.1004-9649.202302048

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The new situation, such as the construction of the Chinese modernization, implementation of the “double carbon” strategy, construction of the new power system, and promotion of power market-oriented reform, will profoundly affect future power demand situation in China. With full consideration of the changing trend of macroeconomics, technological progress, energy transformation, power market, climate and temperature and other factors affecting power demand under the new situation, the medium and long-term power demand forecasting model coupled with “economy-energy-electricity-environment” is adopted to analyze the growth trend of the China’s power demand in the last three years of the “14th Five-Year Plan” (2021-2025) under three scenarios. The results show that in 2023, 2024 and 2025, China’s total social electricity consumption will be 9.1 to 9.3 trillion, 9.4 to 9.7 trillion and 9.7 to 10.1 trillion kilowatt-hours respectively, with an annual growth rate of 5.2% to 6.0% in the “14th Five-Year Plan”.

New Utilization of Renewable Energy and Its Key Technologies Under the Dual-Carbon Target

Reserch on Low-Carbon Optimal Operation of Offshore Oil and Gas Micro Integrated Energy System

LI Qian, HUANG Haitao, YAN Xiaobin, LIAO Changjiang, PENG Xin, ZHANG Anan

2023, 56(3):  13-22.  DOI: 10.11930/j.issn.1004-9649.202209070

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At present, the human-free and low carbonization of offshore oil and gas platforms has become a development trend. In order to meet the low-carbon operation of unmanned oil and gas platforms, this paper constructs an offshore oil and gas micro energy system considering the access of renewable energy to realize the low-carbon operation of offshore oil and gas platforms. Firstly, considering the uncertainty of renewable energy, a hybrid energy storage system is constructed, which consists of a low carbon operation module of floating power to gas-associated gas storage（FP2G-AGS）, and an offshore oil and gas micro energy system with renewable energy access and hybrid energy storage system is established. Secondly, considering the matter-energy flow of the system, a heterogeneous flow coupling model is established, and the coupling relationship of each system unit is analyzed. Considering the uncertainty of source and load, a stochastic fuzzy economic optimal scheduling model is constructed to realize the coordinated optimization of the system. Finally, the feasibility and effectiveness of the proposed model and method are verified through numerical simulation.

Simulation and Analysis on the Solar-Assisted Direct-Expansion PVT Heat Pump Hot Water System in Lingang

LIU Wenjie, PENG Cihua, YAO Jian, JIA Teng, DAI Yanjun

2023, 56(3):  23-29.  DOI: 10.11930/j.issn.1004-9649.202209105

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The solar-assisted direct-expansion PVT (photovoltaic-thermal) heat pump is a novel and efficient technology to utilize the solar energy comprehensively. The simulation model of the solar-assisted direct-expansion PVT heat pump hot water system on Matlab platform was developed based on the energy balance, and the effect of the varying environmental conditions and different configurations was investigated. Based on the data of environmental conditions in Lingang, we simulated the hot water supply performance of the systems with different configurations on typical days in different seasons, besides the year-round variation of the electricity generation benefits. The COP of the hot water system increases with the decreasing theoretical displacement of the compressor, however, the needed heating time of the system increases; the year-round electricity generation benefits decrease when the theoretical displacement of the compressor decreases.

Whole Life Cycle Economic Assessment of Renewable Energy-PEM Electrolyzer Hydrogen Production

YUAN Tiejiang, ZHANG Hong, YANG Yang, WANG Zhengyi

2023, 56(3):  30-35,46.  DOI: 10.11930/j.issn.1004-9649.202104040

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The high investment and operation costs as well as the negative impact of stochastic power input on production efficiency and durability restrict large-scale application of electrolyzer based hydrogen production. Firstly, the life-cycle cost model of the PEM electrolytic hydrogen production system is established, where the efficiency decay and the impacts of the random input power on the durability of the electrolyzer are considered. Then, the life-cycle revenue and economic assessment models are established considering the hydrogen sale profits and the equivalent environment profit. Finally, the proposed model and method were verified by simulations with the actual data, in order to provide a theoretical basis for the large-scale application of the PEM electrolyzer hydrogen production technology.

Self-evolving Power Smooth Control Method for Offshore Wind Power Cluster Based On Deep Reinforcement Learning

SONG Weiye, LIU Lingyue, YAN Jie, WANG Hangyu, HE Shukai, HAN Shuang, WANG Minghui, LIU Yongqian

2023, 56(3):  36-46.  DOI: 10.11930/j.issn.1004-9649.202206099

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The offshore wind speed has a high spatial-temporal correlation, which aggravates the power fluctuation of the whole wind farm and poses significant challenges to the power system, especially when large-scale offshore wind power is integrated. Smoothing control of large-scale offshore wind power clusters is a key solution to mitigating the above problems. However, most existing methods are inefficient and difficult to support higher frequency control and are susceptible to wind power forecast errors and the deviation of actual action from the optimal control command. Therefore, this paper proposes a new control framework for “offline-training, online-optimization and self-evolution”, and establishes a deep-reinforcement-learning-based model for the smoothing control of the active power of offshore wind power clusters. Firstly, a short-term revenue function for cluster power smoothing control is proposed to solve the optimal command based on the Markov decision process model. Secondly, a long-term revenue policy function for power policy calibration is proposed to effectively correct the control deviation according to the historical feedback data. Finally, a deep neural network model is established for the mapping between the state of the agent, the control benefit and the control decision to realize the training and solution of the agent based on the deep deterministic policy gradient algorithm. The results show that the proposed method can reduce the power fluctuation by 20% and control the power loss within 5% under the given wind condition of 7.5 m/s average wind speed.

Experimental and Performance Analysis of Direct Expansion Solar Assisted Heat Pump System for Space Heating

MA Guangbai, YANG Zhaohui, SU Shiqiang, DAI Yanjun

2023, 56(3):  47-54,63.  DOI: 10.11930/j.issn.1004-9649.202210104

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A direct expansion solar assisted heat pump (DX-SAHP) system for space heating with solar heat collector/evaporator and fin evaporator in parallel is constructed, the thermal cycle process of the system is analyzed, an experiment platform of the system is set up. The experimental results show that the DX-SAHP heating system can obtain high performance under different operating conditions. The highest COP can reached 6.88. Compressor frequency, solar irradiance and ambient temperature all affect the heating capacity and COP of the system. The COP of the system running with solar collector/evaporator is nearly 30% higher than that of the fin evaporator under constant frequency, and nearly 45% under conversion frequency. The system has better performance under conversion frequency operation mode.

Power System

Research on the Improvement Method of OPGW Ground Uneven Icing Calculation Model under Micro-terrain

ZHU Yongcan, SHU Xin, TIAN Yi, XIE Songlin, ZHANG Ye, LIU Yupeng

2023, 56(3):  55-63.  DOI: 10.11930/j.issn.1004-9649.202210098

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At present, there are many studies on the calculation model of equivalent ice thickness of overhead line under uniform ice cover, but there is a lack of research on OPGW ground ice covering with large cross-section and large unit length weight, especially the applicability of the equivalent ice thickness calculation model under microterrain. In this paper, the three-tower and two-gear OPGW ground wire model under three typical terrains (hillside, mountain top and pass) is established by finite element software, and the error analysis of the equivalent ice thickness model of traditional transmission lines is carried out by combining the equivalent ice thickness model considering the deflection angle of the insulator string, and the results show that the traditional ice thickness calculation error is large when the equivalent ice thickness is small. However, with the increase of the average equivalent ice thickness, the ice thickness calculation error decreases significantly. Based on the above analysis results and the function relationship between the average equivalent ice thickness and the axial tensile force and inclination angle of the insulator string, an ice thickness error optimization calculation method is proposed, and the relative error of the improved ice thickness can be controlled within 10%.

Multi-fault Repair and Optimization Strategy of Distribution Network Based on Fault Adjacency State

YU Aiqing, DING Liqing, WANG Yufei, LI Hao

2023, 56(3):  64-76.  DOI: 10.11930/j.issn.1004-9649.202103145

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According to the relationship between faults and topology of the distribution network as well as the coupling between repair and recovery, a multi-fault repair and optimization model of distribution network based on fault adjacency state is established in this paper. In the stage of emergency repair, the electrified state matrix of load nodes is established based on the power supply type. The electrified state matrix of the fault adjacent load is proposed by extracting the electrified state of the fault adjacent load. The fault adjacency state is obtained by extending the electrified state matrix of the fault adjacent load, then the faults are classified. The optimal repair task at each stage is determined by the alternate update of repair and fault adjacent state. During the reconstruction calculation period, the node voltage based adaptive ordered ring matrix for the ring network is set up as the solution space of the algorithm. Then, the Levy coefficient quantum particle swarm optimization was applied using the decreasing cosine function and Levy flight to improve the quantum particle swarm optimization algorithm. The practicability and the effectiveness of the proposed methods are verified by simulation on PG&E69 bus system.

Semantic Segmentation Model for Transmission Tower Point Cloud Based on Improved PointNet++

HUANG Zheng, GU Xu, WANG Hongxing, ZHANG Xingwei, ZHANG Xin

2023, 56(3):  77-85.  DOI: 10.11930/j.issn.1004-9649.202206087

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Aiming at the existing problem that the point cloud extraction accuracy of transmission lines is not high and cannot meet the needs of autonomous and refined inspection by unmanned aerial vehicles, an improved PointNet++ semantic segmentation method for transmission tower point cloud is proposed, which realizes the segmentation of wires, ground wires, drainage lines, insulators and towers. Firstly, the parameters of the classic PointNet++ model are adjusted to make the model more suitable for the point cloud data of transmission towers in terms of feature extraction quantity and receptive field; then, the kernel point convolution is used as the point cloud feature extraction algorithm to further improve the model's ability to detect point cloud features; finally, for the data imbalance problem in the point cloud data, the focal loss is used as the loss function, so that the categories with a small proportion can be fully trained. In order to verify the effectiveness of the proposed method, experiments are carried out on the point cloud dataset composed of 2284 transmission towers. The experimental results show that the average F₁ value of the improved algorithm reaches 97.26%, which is 3.95 percentage points higher than that of the classic PointNet++.

Influence of Excitation Mode Difference on RAM Generator Overcurrent Protection Setting

LI Runpei, GUI Lin, WU long, XIE Xiaorong, WANG Xiangheng

2023, 56(3):  86-93.  DOI: 10.11930/j.issn.1004-9649.202211023

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The rotating asynchronous machine (RAM) system in the power stations of China General Nuclear Power Group (CGN) includes three types of generators —i.e., Shangdian generator, Zhongchuan generator and Remeng generator. The Shangdian generator is under self-shunt excitation, and the other two types are under phase compound excitation. When setting the overcurrent protection of RAM generators with different excitation modes, the power stations don’t consider the influence of excitation difference on value setting and delay time setting of overcurrent protection, and there may be dangers of overcurrent protection refusal and protection mismatch with other abnormal condition protections (malfunction). In this paper, the PSACD models of RAM generators with different excitation modes are established. The influence of excitation difference on the short circuit current decay process of RAM generator is illustrated by theoretical analysis and simulation, and the correctness of simulation analysis is verified by prototype experiment. Based on the theoretical analysis and simulation results, the setting value and delay time of RAM generator overcurrent protection under different excitation modes are set reasonably, which has been applied in the power stations of CGN.

Multi-objective Optimal Allocation of Reactive Compensation and OLTC in Active Distribution Network

TIAN Yu, HUANG Jing, XIE Xiao, WANG Ruoxin, SHEN Danqing, HE Lina, YANG Kaifan, CHEN Ruke

2023, 56(3):  94-99.  DOI: 10.11930/j.issn.1004-9649.202206133

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In order to cope with the power flow fluctuation of the active distribution network and improve the economy and security of the active distribution network operation, a multi-objective optimal configuration model integrating the investment layer and the multi-period simulation operation layer is established with the goal of minimizing the investment cost, network loss and voltage offset. At the same time, in order to further determine the optimal allocation scheme that meets the actual needs, a dynamic weighted multi-objective solution method is proposed to obtain the optimal solution set. The effectiveness of the proposed method is verified by a simulation example.

A Bi-LSTM-Based Transformer Fault Diagnosis Method Considering Feature Coupling

LI Gang, MENG Kun, HE Shuai, LIU Yunpeng, YANG Ning

2023, 56(3):  100-108,117.  DOI: 10.11930/j.issn.1004-9649.202209055

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Power transformer is one of the key equipment to ensure the safe and stable operation of the power system, but the existing fault diagnosis methods cannot fully exploit the feature interaction within the equipment and have poor sensitivity to the changes of operating conditions, which has limited the improvement of fault diagnosis accuracy and reliability. To address the above problems, a transformer fault diagnosis method is proposed based on bi-directional long short-term memory (Bi-LSTM) considering feature coupling. Firstly, the initial transition sequence of feature state is determined based on the equipment operation mechanism; then, a deep neural network fault diagnosis model is constructed with consideration of complex dependencies to mine the feature coupling relationship for refined condition assessment; finally, the simulation results have verified the support role of the priori feature sequence for the fault diagnosis model. The proposed method improves the fault diagnosis effectiveness, and can provide a reference solution for intelligent and refined maintenance of power equipment.

A Multi-vector Power Theory Framework and Reactive Current Compensation Strategy for Three-Phase Non-sinusoidal Distribution Networks

SUN Jia'an, LI Lin

2023, 56(3):  109-117.  DOI: 10.11930/j.issn.1004-9649.202301017

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The increasing complexity of distribution-level source, network, load and storage have been deteriorating voltage imbalance and distortion issues. Therefore, the traditional power theories cannot meet the conversation law and would lead to the limitation of power compensation. A Multi-vector Power Theory (MPT) based reactive current compensation strategy for three-phase non-sinusoidal distribution networks is proposed. The frequency domain decomposition results of voltage and current are employed to establish the basis vector and form the voltage and current vectors, and the geometric product of the two vectors is defined as the multi-vector power. It is proved that the multi-vector power theory meets the conservation law. Then two types of reactive current detection performance improvement strategies aiming at Unity Fundamental Power Factor (UFPF) and Perfect Harmonic Cancellation (PHC) are proposed. Comparing with 7 reactive component detection algorithms under different power theories developed by different working conditions, 5 algorithms with better results are selected to build reactive power compensation simulation models, and to design physical experiments to verify the algorithms. The results show that the UFPF on MPT achieves the lowest apparent power flowing into the system, and the PHC on MPT has the best comprehensive compensation for all non-active power, harmonics and unbalanced components.

Information and Communication

Design and Implementation of Low Voltage Power Communication System Based on Single Frequency Communication

ZHANG Peiling, ZHAO Keke

2023, 56(3):  118-127,136.  DOI: 10.11930/j.issn.1004-9649.202207044

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In order to improve the reliability of low voltage power line communication, a low voltage power line carrier single frequency communication system is proposed, which integrates the single frequency communication and low-voltage power line communication. Based on the physical layer of Q/GDW 11612—2016 standard, the system only needs to modify the data link layer, thus shortening the signal propagation time. At the same time, a fractional PLL based interval clock synchronization algorithm is proposed to avoid the excessive adjustment of the clock and realize the high-precision adjustment of the single frequency communication clock synchronization in the system. The simulation and actual measurement results show that the proposed clock synchronization algorithm has high clock accuracy; and the low voltage power line carrier single frequency communication system has a higher communication reliability compared with power line communication due to its integration of the complementary advantages of the two. It can be seen that the low-voltage power line carrier single frequency communication system is practical and reliable.

Digital Front End Technology for Long-Distance Power Line Communication

GAO Hongjian, XIE Hongwei, LU Xu, LIU Yao, ZHANG Lijun, CAO Yang

2023, 56(3):  128-136.  DOI: 10.11930/j.issn.1004-9649.202104048

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Since the power line communication (PLC) channel is not specifically designed for communication, there usually exists a large noise and/or a strong interference around the frequency band of a PLC system. It is not economical to change the structure of the analog front end (AFE) to improve the performance of the PLC system. Therefore, based on the equivalent complex baseband and Nyquist windowing technology, a new digital front end (DFE) structure is proposed. The windowing at the receiver end can not only effectively suppress the out-of-band narrowband interference and eliminate the impact of adjacent frequency PLC systems or wireless systems, but also reduce the complexity of the AFE and save design costs. The simulation results show that the Nyquist windowing is better for concentrating the energy of narrowband interference to the less subcarriers, which is convenient for detection and elimination of the narrowband interference, thus improving the performance of the system. In addition, the effectiveness of the proposed DFE technology is further verified through field tests.

Energy Storage System Control Strategy

Research on Optimal Control Strategy of Energy Storage for Improving New Energy Consumption

LIU Liantao, LIU Fei, JI Ping, LIN Weifang, ZHANG Xiangcheng, TIAN Xu, GAO Fei

2023, 56(3):  137-143.  DOI: 10.11930/j.issn.1004-9649.202110107

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To achieve the carbon peak and neutrality goals by improving the new energy consumption, a decoupling based optimal control method of energy storage is proposed. For the problem of solving the nonlinear model of optimal control, a linearization and simplification method based on decoupling is presented. Using the enumeration optimization and iterative load flow, the constraint of energy storage operation is compacted, which guarantees the objective of new energy consumption promotion and operation security constraints. The case analysis shows that the simplified linear model is consistent with the original nonlinear model and the difficulty of solving the high-order optimal control model is reduced. It ensures the fast and reliable decision of energy storage to promote the new energy consumption, and increases the comprehensive benefits of new energy and energy storage.

Optimal Operation Strategy of Energy Storage System in Photovoltaic-Storage Charging Station Considering Multi-mode Integration

SHI Shanshan, WEI Xinchi, ZHANG Yu, WANG Yufei, FANG Chen, WANG Haojing

2023, 56(3):  144-153,161.  DOI: 10.11930/j.issn.1004-9649.202210009

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A single operation mode of the energy storage system is difficult to meet various technical requirements of a photovoltaic-storage charging station. In view of this problem, this paper proposes an optimal operation strategy of the energy storage system in a photovoltaic-storage charging station considering multi-mode integration. Firstly, typical operation modes of the energy storage system in a photovoltaic-storage charging station are analyzed, and multi-mode integration of the energy storage system is designed on this basis. Secondly, operation models of the energy storage system in the photovoltaic-storage charging station under different modes are established to further propose an optimal operation strategy of the energy storage system in the photovoltaic-storage charging station with multi-mode integration. Finally, the proposed strategy is simulated and experimentally analyzed based on 24 h operation curves of a photovoltaic-storage charging station in Shanghai. The results show that the proposed strategy can reduce load fluctuation and energy-balance cost of the energy storage system, thus improving operating benefits of the photovoltaic-storage charging station.

Technology and Economics

Impact Analysis of Two-Part Tariff Policy Executive Mode on Market Resource Allocation Efficiency

YAO Jun, WU Yongfei, WANG Yali, HE Jiao, DAI Shuangfeng

2023, 56(3):  154-161.  DOI: 10.11930/j.issn.1004-9649.202103096

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In recent years, China has perfected the executive mode of two-part electricity price policy by increasing users’ options. This paper uses the social welfare model to analyze the impact of the implementation of the national adjustment two-part electricity price system on the efficiency of market resource allocation in the year of 2016. Results show that the relaxation of the change cycle of the two-part pricing system can reduce the basic electricity price burden of enterprises, who have stopped production or half stopped production. However, it is not beneficial to the efficient production enterprises, which is not conducive to promoting the survival of the fittest in enterprises as a whole, and reduces the long-term utility of the whole society. The empirical results also show that The change of the two-part electricity price policy led to the decline of the total social welfare, which was reflected in the drop of the load rate by 7%. Meanwhile, it also reduces the fairness among users, which is reflected in the capacity utilization rate dropping by 30.6%. We believe that simply adjusting the executive mode of the electricity price policy is not conducive to the optimal allocation of power resources, and all enterprises should adopt the fair electricity price policy at the same time.

Dynamic Low-Carbon Dispatching Method of Power System Based on Improved Carbon Emission Flow Theory

CHEN Jiaxing, WANG Chunling, LIU Chunming

2023, 56(3):  162-172.  DOI: 10.11930/j.issn.1004-9649.202208104

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At present, power systems are facing great pressure of carbon reduction. With the development of smart grids, the participation of demand-side resources in power-system scheduling can further reduce carbon emissions of power systems. Therefore, this paper proposes a dynamic low-carbon two-stage optimal scheduling method considering demand response in a day-ahead market. In the first stage, the carbon market transaction cost on the power generation side is calculated based on a metering model of dynamic carbon emission of generation units. On this basis, an optimization model for low-carbon economic scheduling of a power system is established to obtain an initial schedule. In the second stage, based on the improved carbon emission flow theory of power systems, the real-time carbon emission and cost of users are calculated. Moreover, demand response with carbon price as a signal is considered to establish a low-carbon economic optimal dispatch model to optimize load distribution to further reduce carbon emission of the system. On this basis, a final schedule can be obtained. Finally, the improved IEEE 14 node system is used as an example to calculate and analyze carbon emissions and total operating cost of the system. The simulation results show that the proposed model and method can reduce carbon emissions of the system, thus verifying their feasibility and rationality.

Multi-layer Embedded Optimization of Microgrid Capacity Considering Price and Incentive/Compensation Coupling Mechanism

ZHU Xianhui, HU Xu, SHI Nan, ZHANG Yao, ZHONG Jingwen

2023, 56(3):  173-186.  DOI: 10.11930/j.issn.1004-9649.202209052

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This study proposes a collaborative optimization idea of source and load sides by combining multiple response mechanisms to fully tap the ability of two-way interaction between supply and demand sides to stabilize the difference between source and load in the microgrid. This idea is based on the complementary relationship between the advantages and disadvantages of price response and incentive/compensation response. Firstly, an upper and lower bi-level optimization model of demand-side response is constructed at the load end of the inner layer. The upper layer divides the peak and valley periods according to the net load curve and optimizes the time-of-use (TOU) tariff with the objective of minimizing the sum of the absolute value of the net load in each period of the microgrid. The lower layer optimizes the incentive/compensation coefficient with the satisfaction indexes consisting of electricity comfort and economy, which takes into account the enthusiasm of the flexible load to participate in dispatching. Secondly, a source-end capacity optimization model considering economy and reliability is built in the outer layer. Finally, the optimization models of both the source and load are coupled through the multi-layer embedded mechanism, and a solution model is constructed, which combines the multi-objective particle swarm optimization (MOPSO) algorithm and the particle swarm optimization–imperial competition algorithm (PSO-ICA). Simulations show that the proposed method can improve the economy and reliability of the microgrid on the basis of meeting the needs of users due to the advantages of the demand-side comprehensive response mechanism and solution model structure.