Nowadays, the global energy internet is popular, and building the VPP （virtual power plant） is an important step to construct the global energy internet and an important means to relieve the energy shortages and environmental pollution in China. Therefore, its really important to understand and grasp the key technologies and operation principles of VPP. The purpose of this paper is to provide the theoretical and practical experience for the VPP construction in China by analyzing its operating mode. Firstly, based on the statement of VPP in other literatures, the detail concept and typical features of VPP are definitely summarized, and according to the different functions, the VPP is divided into two categories： CVPP （commercial virtual power plant） and TVPP （technical virtual power plant）. Then, the relationships between energy internet and VPP are expounded in detail from different perspectives, such as physical structure, information model, market roles and so on. And then, we summary the operation principle and condition of the typical demonstration project of VPP in Germany. An last, according to the current development level of power distribution system and the relevant policies of power system reform in China, we discuss the application prospect of VPP in China, and propose the suggestions on the key issues to be resolved, which can provide a theoretical basis for the builders and decision maker of VPP.
Energy supply side reform plays an examplary and leading role in reform in other areas. With using the energy Internet thinking, this paper analyzes the main problems existing in Chinas energy supply system for a long time, including extensive development model and less consideration of user needs, lack of Internet platform to coordinate and optimize energy supply, low comprehensive utilization level and incomplete energy trading system. The application of energy Internets user thinking, platform thinking, integrated thinking and big data thinking can effectively promote the management level, coordination and optimization, multi-energy complementary and the perfection of energy trading system of energy supply, which can provide innovative ideas for the energy supply side reform.
Under the background of global energy internet, renewable energy represented by wind power insertion into the power system brings new challenges to the security and stability of the system operation and puts forward higher requirements to the configuration of reserve capacity. For this reason, this paper proposes the optimization model of reserve capacity taking the minimum cost expectations on both sides as the objective function. Considering the interruptible load in the demand response and the uncertainty factors such as the deviations of wind speed prediction and load prediction, we set up the allocation principle of reserve capacity that can satisfy the requirements of economy and reliability. Finally, we solve the improved 10-units test system with using the genetic algorithm based on Monte Carlo stochastic simulation. The economy of reserve capacity optimization decision with considering demand response is better, which is obtained through the example. Compared with traditional reserve capacity configuration, the bilateral reserve capacity configuration can achieve the optimal allocation of resources within the system as a whole, and improve the absorption of wind power generation as well, which can achieve the optimum security and economy of power system.
The multi-carrier system is hybrid energy network which takes electric, natural gas, heat and others as power conversion hubs through energy hub （EH）, and is a development trend of the future energy interconnection structure. This paper discusses the structure and operation mechanism of multi-carrier system, and proposes the planning-operation co-optimization model of gas-heat-electricity co-generation network with taking EH as dispatching hub. This model takes the minimum total cost of planning and construction, scheduling and operation, reliability and other aspects as the objective function. The model considers the constraint conditions that the system can meet the network constraints of each energy system, the energy balance of EH, etc., it is a mixed integer optimization problem in which the objective function and the constraint condition both contain nonlinear terms. Therefore, we adopt linearization and large-scale optimization method to solve the model, in order to make the planning and operation of multi-carrier system to achieve the optimal. Finally, we compare and analyze different situations in example simulation, such as coupling and non-coupling planning, and coupling system considering different types of components, whose results verify the superiority and effectiveness of the proposed model and processing method.
According to the problem of wind power absorption in grid, this paper proposes a mathematical model for pumped storage units participating in peak shaving. We construct a stochastic programming model of wind power-thermal power-pumped storage association system, which takes wind curtailment cost as one of the economic indicators and wind speed and load as uncertain variables. When dealing with the constraint condition of opportunity, we adopt bootstrap sampling to estimate confidence interval, in order to improve the accuracy. Finally, we carry out the simulation test on the IEEE 30-bus system to analyze the economical efficiency under the condition of different wind power and pumped storage capacity. The results show that with the rising of wind power installed capacity from 300 MW to 400 MW, wind curtailment cost increases and the demand of pumped storage capacity and reserve capacity also goes up. When the wind power installed capacity arrives at the level of 400 MW and pump storage capacity raises to 90 MW, the economic cost can be reduced by 5% compared with that in the case without pumped storage in scheduling. Meanwhile, the number of start-up （shut-down） thermal power units is reduced from 2 to 1. Example shows that according to the different wind power installed capacity, the rational allocation of pumped storage capacity and the coordinative peaking of multiple sources can achieve the purpose of the wind power absorption at the least cost.
Accurately evaluating the economic life of a transformer not only plays an important role in appropriately scheduling its secure and economic operation, but also provides the basis for determining its replacement strategy. Considering the characteristics of the transformer failure rate in its life cycle, the Arrhenius-Weibull model which is widely employed for describing the transformer temperature aging failure is firstly presented to model the loss failure stage in the failure rate bathtub curve. And a transformer age reduction factor is introduced to characterize the effect of transformer maintenance. Then, the opportunity costs are calculated through comprehensively considering the economic factors of the transformer maintenance and replacement. Finally, the opportunity costs of the transformer maintenance and replacement are used as the criteria for determining the optimal replacement timing of the transformer. A sample example is served for demonstrating the essential features of the presented method.
The application of life cycle cost （LCC） management in network planning is an important part of the management system in a power company. According to the LCC management theory, with taking the life cycle of equipment as planning research period, this presents a LCC-based method for comparing multiple network planning schemes in transmission network planning. Through the analysis on the LCC composition of planning scheme, this paper suggests a whole process analysis model in view of costs in different network planning stages. The proposed method is applied in the planning scheme selection of the 500 kV long-range network planning in Zhejiang. The simulation results show that this method can improve the scientific nature of power grid planning and implement the coordination and unification of each stage in the LCC process of power grid.
According to the issue that the application depth of the method and model in each link of life cycle asset management （LCAM） of power grid enterprises is not unified and its convergence and coordination are not enough, this paper analyzes the key business of power grid asset management and its decision-making demands. Based on the technical solutions of life cycle cost （LCC）, risk assessment, priority ranking and asset wall method, we propose a method framework for whole process asset management decision-making, which runs through the whole process of power grid asset life cycle including network planning and management plans, procurement and engineering construction, operation and maintenance, decommissioning and/or disposal of assets. The proposed method framework makes clear the implementation of decision-making methods in each link, and provides framework and foundation for unifying the technical methods and models of power grid asset whole process management and solving the issues of mismatched and uncoordinated methods in each business link and bad actual business integration.
To reduce the operation cost of grid-connected microgrid and give assistance to load shifting in power grid, this paper proposes an economic dispatch model of grid-connected microgrid with considering load interruption. The model regards microgrid as an intermediate link and establishes a new load interruption compensation mechanism. Floating compensation price is introduced to reflect user satisfaction, which is affected by interrupting power and time. We select a typical microgrid consisting of wind turbines, photovoltaic cells, micro turbines, fuel cells, storage battery and interruptible load as example, adopt Cuckoo-Search algorithm to solve the model, obtain the optimal interrupting combination, dispatch result and operation cost, as well as the limit interrupting energy. The results show that the model and algorithm are feasible and can create remarkable economic revenue for all participants.
To deal with the optimized dispatching of a microgrid working in the isolated island mode, taking economic efficiency and reliability into consideration, this paper adds comprehensive evaluation into the economic dispatching model of traditional microgrid to get optimal dispatching scheme with different targets. At first, we construct the optimized dispatching model of microgrid with taking the lowest operation cost and the lowest load deficiency rate as target function, based on the microgrid with cogeneration structure. And then, considering the conflict between different targets, we apply multi-objective PSO （particle swarm optimization） algorithm combined with dispatching strategy to solve the proposed optimized dispatching model in MATLAB, in order to obtain a series of Pareto solutions. At last, we use the comprehensive evaluation model based on the application of analysis hierarchy process to evaluate the Pareto solutions, and provide the optimal scheduling scheme for decision makers combining with real-time demand analysis. We verify the feasibility and practicability of the proposed model through the analysis example of an isolated microgrid.
When using the method of current-voltage three-electrode method to measure the power frequency grounding resistance of overhead line tower, the ground wire has a role in separating the measuring current into the tower grounding grid, which can affect the measurement accuracy of grounding resistance. This paper establishes a shunting model of measuring current into the tower grounding grid for overhead ground wire, and analyzes the degree of the ground wire shunting, the factors affecting the shunting effect and its influence law. The results show that： （1）the share of the ground wire shunting can reach more than 60%； the effect of shunting is more obvious when the grounding resistance of the measurement tower is greater, the grounding resistance of the non-measurement tower is smaller and the measurement tower is the first two tower from the substation； （2）only considering the effect of shunt size on grounding resistance measurement is not enough, ignoring the phase angle difference between the ground wire shunting and the measuring current can also cause big errors, which will make the measuring value of the grounding resistance higher.
Ice shedding, which can cause wire breaking, hardwire failure and flashover, is one of the common disasters for transmission line. In order to study the vibration mechanism of ice shedding, this paper constructs the model of transmission in the finite element software ANSYS, which considers the stiffness of ice and simulates two typical forms of ice-shedding with using the element birth and death method, including the shock-load-induced ice-shedding of a single conductor and one subconductor ice-shedding from bundle conductors. Then, we study the influences of line parameters and external load on the ice shedding through numerical simulation. The results show that： （1） during the shock-load-induced ice shedding, the influences of wind loads should be considered when the span is large； （2） the ice shedding rate and jump height increase with the increase of shock loads； （3） during the one subconductor ice shedding from bundle conductors, the vibration of one subconductor can accelerate the process of ice shedding of the whole span, so the wind loads should be considered； （4） the number and distribution of subconductors have influences on ice-shedding rate； （5） arranging a spacer near the middle of the span will reduce the jump height； （6） the simulation results will not be safe without considering the stiffness of ice. The research results can provide reference for the design of transmission lines.
With the DC voltage level upgrading and transmission capacity increasing, the voltage source converter based high voltage direct current （VSC-HVDC ） plays a more important role in the optimal allocation of large capacity resources over a long distance. In the previous studies, the technology performance of VSC-HVDC was analyzed by using the virtual small grid and electromagnetic transient simulation software. The study results of the dynamic performance validation for the actual AC grid were reported rarely. In this paper, the DA simulation model in line commutated converter based high voltage direct current （LCC-HVDC ） and VSC-HVDC simulation models developed newly by PSD-BPA are introduced and the technical characteristics of these models are analyzed firstly. On this basis, aimed to the Tibetan AC weak power grid, the transient recovery characteristics of receiving-end grid with large disturbance impact are compared under two different power transmission programs. The simulation results can provide technical support to apply VSC-HVDC to improve the disturbance characteristics of weak -receiving-end grid and grid stable level.
Variable speed pumped storage （VSPS） with full-size converter （FSC） can be an effective measure for automatic frequency control and renewable energy generation fluctuation balance. This paper mainly studies the modeling and control strategies of the machine-side and grid-side converter, based on the introduction of the overall structure of VSPS with three-level FSC. On a basis of the given reference power generated by the need of grid operation, we propose the control strategy of active power and reactive power for FSC-VSPS under generator mode and motor mode. According to the proposed model of FSC-VSPS units, we adopt the Fourier transform method based on impulse response to present the spectrum characteristics of units. Compared with the spectrum characteristics of wind power fluctuation, this paper describes the effectiveness of control effect of the VSPS system with FSC to the power fluctuation caused by renewable energy. Finally, we simulate and verify the effect of VSPS units with FSC on the restrain action of wind power output fluctuation.
Relay protection equipment is the first defense line for the safety of power grid, so the risk assessment of relay protection system is of great significance for the reliable operation of power grid. In order to solve the uncertainty of the data statistics of relay protection system, this paper adopts soft hierarchical model to establish the risk assessment model of relay protection. Firstly, based on the definition of risk, we point the risk factors, including the accident probability and accident loss of relay protection equipment. Secondly, we use state evaluation model to calculate the equipment failure rate and assignment method to calculate the loss caused by relay protection equipment failure. Then, we use fuzzy information granulation algorithm （soft algorithm） to process the data of accident probability and accident loss, calculate the risk and adopt fuzzy ranking method to sort the risks of multiple regions, which can provide theoretical basis for risk managers to make right decision. Finally, we use the actual data in a certain area to prove the correctness and effectiveness of the proposed fuzzy information granulation algorithm for the risk assessment of relay protection.
With the development of new energy technology in the field of distribution network, the distributed generation （DG） connected to distribution network has become a hot research area. It will appear weak loops and non-PQ nodes in the distribution network with DGs compared with the traditional distribution network, and the traditional power flow calculation method only can be used for PQ nodes and radial network. In order to solve the distribution network reconfiguration problem after DG connection, this paper uses superposition theory to solve the weak loop during switching process, and improves power flow calculation method based on forward-backward sweep method which can make the nodes in DG involved in the power flow calculation. Combining the advantages of crisscross optimization （CSO） algorithm and particle swarm optimization （PSO） algorithm, we propose crisscross particle swarm optimization （CPSO） algorithm to optimize the reconfiguration problem of distribution network with DG. Finally, the simulation is based on typical distribution network with 33 nodes with considering DG access modes of PI node, PV node, PQ（V） node, whose results show that the reasonable access of DG in distribution network can reduce the network loss and improve the voltage quality.
n view of the imbalanced phenomenon of energy caused by the geographical location and seasonal variation, this paper proposes a normalized control strategy with bidirectional transmission based on voltage source converter-high voltage direct current （VSC-HVDC） system, which can contact grid by partition to realize the complementary advantages. Firstly, the control system determines the reference value of transmission power between AC and DC system through normalizing the droop characteristics on both sides of voltage source converter. Then, we obtain the transmission power of DC transmission line through comparing the size and direction of the reference value of the transmission power between the two ends of DC transmission line. Finally, it achieves bidirectional transmission and power balance between two grids by controlling the DC voltage at both ends of DC line. We design three different work situations and carry out simulation study in real time digital simulator （RTDS）. The simulation results verify the effectiveness of the proposed control strategy, which realizes the low carbon power dispatching.
Aiming at the distributed new energy with problems of large output randomness and high planning complexity in distribution network planning, this paper proposes a risk planning model of distribution network with distributed new energy. The model takes the minimum cost as the objective function, determines the maximum value of the new distributed new energy output through the load capacity of the network, comprehensively considers system power supply shortage and other network risk factors and carries out the risk planning of distribution network with distributed new energy. A method for the infeasible solution repair of Genetic Algorithm is proposed during the solving process which is similar to communication network broadcast. The effectiveness of the risk planning model is verified through its application in a 10 kV network planning in Anhui Province, which contains distributed photovoltaic power generation and run-of-river hydropower station.
After the implementation of controlled islanding on unstable system, the separation surfaces split the whole system into two or more power islands. It is necessary that effective correction control measures are adopted to ensure the stable operation of each island. This paper proposes rapid real-time correction control strategy based on the bidirectional power flow tracing algorithm and DC flow algorithm of separation surface. Through the power flow tracing algorithm of separation surfaces, we obtain the adjustment object （generator and load） and quantity of island, and check the result with using DC flow algorithm to maintain transient stability under the condition that the islands satisfy the security and stability constraints. Simulations on the New England 39-bus system validate the effectiveness and flexibility of the proposed approach.
Extraction steam parameters of extraction condensate heating unit are often higher than the heating network required, which resulted in a great loss of heat. High back pressure unit makes use of exhaust heat for heating, thus increasing heating capacity and reducing heating steam extraction. There are two main methods of high back pressure heating retrofit for large steam turbine, which are single-rotor mode and double-rotor interchange mode. For the study of different forms of economy and applicability, taking a 350 MW unit as an example,this paper constructs an off-design calculation model of high back pressure heating turbine using Ebsilon simulation software. We comparatively analyze the economic efficiency and energy consumption in heating season and non-heating season under two modes based on the theory of unit fuel consumption. The results show that in heating season,the electricity output of double-rotor interchange mode is 2 000 MW·h higher, the average coal consumption rate is 0.24 g/kW·h lower and the maximum heating capacity is 6.48 MW lower compared with that of single rotor mode. In non-heating season, the exergy efficiency of double-rotor interchange mode is better than that of single-rotor mode. However,the advantage of double-rotor interchange mode in heating season is not obvious and double-rotor interchange mode requires replacing rotor twice a year. Therefore, in order to reduce cost, single-rotor mode is the first choice for high back pressure heating retrofit of large-scale cogeneration unit.
Heat recovery from exhaust steam based on absorption heat pump can be used for heating, which has remarkable energy saving effect. Taking a 300 MW direct air-cooled heating unit as an example, this paper constructs the calculation model for heating unit performance based on heat pump with exhaust steam heat recovery, analyzes the influence of heating load on the heating supply system with heat pump, and studies the peak regulation capability of the unit with heat pump heating supply system. The results show that the performance coefficient of absorption heat pump with heat recovery from exhaust steam is 1.73, and the exergy efficient of heat pump heating supply system increases by 15.6 % compared with that of the traditional system. The heat pump heating supply system can save extraction steam of 64.7 t/h, and the net power increment is 11.1 MW. With the increase of heating load, the recovery exhaust steam increases in heat pump heating supply system, which saves more extraction steam of turbines； while the net power increment increases and subsequently decreases. The peak regulation capability is improved by heat pump recovering heat from exhaust steam.
