In the context of the “double carbon” goal, higher requirements have been put forward for energy conservation and emission reduction in the energy and agricultural fields. As a product of the deep coupling of energy and agriculture, the Agricultural Energy Internet is an important means to achieve “carbon neutrality”. This paper proposes an accounting method for the carbon cycle of the Agricultural Energy Internet and an optimal operation strategy for the Agricultural Energy Internet that takes into account agricultural flexible loads and carbon trading. Firstly, this paper constructs an accounting model for carbon emissions of photovoltaic generation and cogeneration in agricultural parks. Secondly, taking the lowest daily operating cost of the park as the objective function, considering the constraints of equality and inequality, an optimal scheduling model is constructed. Finally, the optimization model is simulated by taking the agricultural energy internet of a certain park as the research object, the carbon emissions in the park are calculated in detail, and the correctness of the carbon model is verified by comparing with other agricultural parks. The results show that the optimal scheduling strategy can effectively reduce the carbon emissions of agricultural parks and achieve “carbon neutrality”.
Ensuring sufficient generation capacity is a necessary condition for the safety of power system and the stability of power market. It is one of the core issues to be concerned in the development of power industry. With the global low-carbon energy transition, the adequacy of generation capacity of power system is facing severe challenges. Various capacity mechanisms have been implemented internationally to deal with relevant problems. Combined with the process of European energy transition and power market reform, this paper combs the construction background, development context and current situation of its capacity mechanism, focuses on the strategic reserve mechanism recommended in Regulation (EU) 2019/943, and introduces the implementation details of the mechanism in Finland, Germany and Belgium. Under the double carbon goal, China’s coal-fired power will change from the main power supply to the regulatory and supporting power supply, and there is an urgent need for capacity mechanism to ensure its safe and stable transformation. This paper combs the current situation and problems of China’s coal-fired power capacity mechanism, points out that the strategic reserve mechanism has good applicability, analyzes the key problems of implementing the mechanism, and provides decision-making reference for the construction of domestic capacity mechanism.
Because DC system usually adopts overhead line for DC transmission, its failure rate is high. When a single-pole short-circuit grounding fault occurs in the system, the unbalanced power of the fault pole can be transferred to the non-fault pole through the real-bipolar wiring mode. The unbalanced power can be divided into self-absorption and collaborative absorption according to the power margin of the converter station. For the self-absorption situation, fault ride-through can be realized by power transfer between sending end bipolar converter stations. For the situation of collaborative absorption, the coordinated control strategies between converter station and energy dissipation resistance are designed. Considering the limited input time of energy dissipation resistance, unbalanced power in DC System is reduced by sub-sequent generator cutting. Finally, the effectiveness of the proposed control strategy is verified in PSCAD. The simulation results show that the strategy can effectively avoid the expansion of fault range and ensure the safe operation of the system.
DC circuit breaker is the core equipment for the stable operation of the DC transmission system. In order to design a DC circuit breaker which can solve DC fault detection and isolation and has reclosing function, a kind of current-limiting hybrid high voltage DC circuit breaker with reclosing function (RFL-HDCCB) is proposed. RFL-HDCCB topology utilizes the symmetry of current-limiting branch, which not only realizes the bi-directional fault-current breaking function, but also can complete the reclosing function. Whether it is a transient failure or a permanent failure, the recloser function can be realized to restore the normal power supply of the system. By studying and analyzing the working principle of RFL-HDCCB in stages, the parameters of RFL-HDCCB are designed, and finally, the PSCAD software is used to build the system simulation model for verification. The simulation shows that, compared with the traditional circuit breaker, the proposed HVDC circuit breaker with RFL-HDCCB topology can not only effectively reduce the rise rate of fault current and reduce the energy consumption requirements of lightning arrester, but also reduce the breaking pressure of mechanical switch, and has obvious current-limiting capacity, which reflects the rationality of the proposed scheme.
DC circuit breaker(DCCB)is an effective means to solve the problem of DC side fault clearing of VSC-HVDC grid, and hybrid DCCB is currently one of the most mature technical routes. The development speed of the DC side fault of VSC-HVDC grid is fast and its process is complex. The study of the transient current (TC) characteristics of hybrid DCCBs in this case has important reference value for the design and development of DCCBs. Considering the real control and protection logic of VSC-HVDC grid after short-circuit fault and the action sequence of AC breakers and DCCBs, this paper analyzes the time-varying characteristics of the paths of the TC of DCCBs, deduces the expression of each development stage of TC, proposes the typical waveform of TC stress of each branch of DCCB. It provides a basis for the selection and the parallel number design of IGBT devices in DCCB. At the same time. Aiming at the problems that the TC stress of the main branch of the DCCB is severe and there is no effective improvement method, a TC suppression method of DCCB based on damping resistors in converter station is proposed. The results of electro-magnetic transient simulation show that the proposed method can effectively suppress the TC of the main branch of DCCB after faults.
The 5 000 MW power collected by Zhangbei UHV substation put into operation at the end of 2020 is new energy. From the perspective of uncertainty of new energy output, the power flow of Zhangbei-Beijingxi line will change between 0 MW and 5 000 MW. Aiming at the uncertainty, a complete set of UHV hierarchical controllable shunt reactor (CSR) is applied for the first time. It solves the contradiction between reactive power compensation and limiting overvoltage on different requirements of shunt reactor in UHV transmission system, reduces reactive power loss, improves the flexibility of system regulation, and creates favorable conditions for the export of new energy in Zhangbei area. In the process of realizing the application of the first UHV CSR demonstration project, a series of innovative achievements have been made in integrated design and equipment development. The project selection starts with the problems of frequent and large voltage fluctuation on the UHV channel of new energy export. In the integrated design, the intensive design concept of CSR and thyristor valve lays the foundation for economy. These innovative achievements in the power system test stage and more than one year of actual operation of the UHV CSR are analyzed and summarized, and the optimization direction is put forward.
The existing robust optimization methods for energy storage dispatch in the field of user-side peak load shifting lack the research on robust optimal scheduling of energy storage considering nonlinear multi-objective optimization model. When the range of energy storage output is directly limited by the load uncertainty, the conventional column and constraint generation algorithm cannot solve this kind of model. Aiming at these problems, considering the user-side load, battery energy storage and other constraints, a robust optimization model of energy storage system dispatch with net load variance and user-side power expenditure as optimization objectives is established, while the uncertainty of user load and new energy output is also taken into consideration. Since the decision-making and optimization results of the second stage will affect the value range of the decision-making in the first stage, it is necessary to improve the generation algorithm of columns and constraints to solve this kind of robust optimization problem. With the sub-problem solving steps in each iteration of the original column and constraint generation algorithm expanded by considering the objective function and some constraints as multiple sub-problems, solving multiple sub-problems in each iteration can effectively broaden the application scope of the algorithm. In the end, the simulation results are presented to verify the effectiveness of the method, which can be successfully applied to nonlinear multi-objective robust optimization problems without losing the performance advantages of the conventional algorithm.
A multi-mode coordinated control strategy is proposed for isolated AC/DC hybrid microgrid, which considers load state and the charge state of the energy storage subnet. In the state judgment level, the charged state of energy storage is divided into five modes, and the network operating conditions corresponding to the six power interaction states between subnets under each mode are planned in detail. The priority of energy storage subnets participating in power interaction among subnets changes with the state of charge. Power mutual-aid level controls the transmission power of bidirectional interlinking converters between subnets. At the local level, droop control is used to keep the subnet autonomous. This strategy can reduce unnecessary power interaction losses, and prevent the energy storage subnets from losing power regulation ability due to excessive charge and discharge in advance. Simulation models on the MATLAB/Simulink and RT-LAB verify the real-time effectiveness of the proposed control strategy.
With the increase of renewable energy penetration, the volatility and intermittence brought by distributed renewable energy will be transferred to the main network, which will affect the safe operation of the system. The study of uncertainty optimization method plays a certain guiding role in the actual operation of the system. However, the traditional stochastic optimization and robust optimization methods do not meet the unpredictable requirements of the actual operation of the system. In this paper, a multi-stage stochastic programming model considering the uncertainty of distributed renewable power generation is established with the goal of minimizing the expected cost of daily operation. The pre-scheduling decision can be made at each stage according to the realization of the previous uncertain information, which will not be affected by the future uncertain information, and is in line with the actual operation law of the system, and meets the unexpected requirements. In order to avoid the disaster of dimensionality in solving multi-stage stochastic programming problems, the stochastic dual dynamic programming algorithm is used to solve the problem. The simulation results show that, compared with the traditional deterministic model, the optimal scheduling decision tree obtained by multi-stage stochastic optimization has wider decision space than the single decision scheme obtained by deterministic optimization. The scheduling decision can be updated according to the implementation and decision of the uncertain information in the previous stage, and the operating cost of the system can be reduced.
At present, the interaction among the indices is usually not considered in the multi-index evaluation of planning schemes for park-level integrated energy system (PIES), which results in the evaluation results are not general, and even have some problems. Therefore, an improved VIKOR method considering the interaction of indices is proposed for the planning schemes of the PIES. Firstly, the evaluation index models of PIES are established from the four aspects of economy, reliability, environmental protection and energy efficiency, and then the comprehensive evaluation system is constructed. Then, on the basis of the conception of the dual hesitant fuzzy set and fuzzy measure, the classical VIKOR method is improved, and each index is weighted by fuzzy measure, so that the interaction between each evaluation index is fully considered when evaluating the planning schemes. Finally, an example is given to verify the rationality and objectivity of the proposed method.
At present, a prominent problem in the state estimation of distribution system is the lack of real-time measurements, which makes it difficult to realize the observability of the whole network. In order to provide accurate basic data for distribution management system (DMS), an alternating-iteration state estimation method based on pseudo measurement modeling using deep neural networks (DNN) is proposed. Firstly, the steady-state model of voltage source converter (VSC) and the real-time measurement model of hybrid distribution system are presented. Then the historical measurements are used to train DNN off-line and establish pseudo-measurement models of power injection on load buses. Finally, alternating-iteration state estimation is carried out for AC and DC areas. Only the estimated states of VSC branches need to be exchanged, thus ensuring the consistency of the boundary states. Test results show that the proposed method can accurately estimate the states of hybrid distribution system under low coverage of real-time measurements.
In order to meet the economic premise and minimize the risk of large area outages caused by the coupling of failures in power and communication networks in extreme scenarios, this paper proposes a robust extended planning model with two layers (main layer and sub-layer) of cyber-physical cooperation, taking into account the structural convergence and functional coupling characteristics of the dual network. Firstly, the main-layer model for cooperative optimization of dual-network line and communication service routing is established with the objectives of economy and minimum loss of load under extreme scenarios; in the sub-layer model, the multiple fault sets of power/communication lines are constructed taking into account the common cause failure modes caused by line structure coupling, and the impact of communication failure on the emergency dispatch of power system is considered, and the calculation model of minimum loss of load under the worst extreme scenarios is established based on the max-min criterion. Then, the column and constraint generation algorithm is used to decouple the two-layer model. Finally, simulation analysis is conducted on the basis of IEEE 14-node information physical system. The results show that the collaborative planning model proposed in this paper can optimize the dual-network structure with economical and reasonable investment, reduce the impact of fault cascade in communication system, and improve the resistance of the coupled system to face extreme events.
In order to solve the problems of the increasing power loss of network, power reverse transmission, voltage out-of-limit and so on, caused by the continuous increase of distributed photovoltaic penetration in distribution network, according to the cluster division of distributed photovoltaic generation, an output evaluation method of distributed photovoltaic cluster considering renewable energy accommodation and power loss of network is proposed. Firstly, the modular index based on electrical distance and active-power balance index are used as comprehensive division indices, and the distributed photovoltaic generation in distribution network is divided into clusters by using genetic algorithm. Then, on the basis of the cluster division results, considering the regulation effect of energy storage and the constraints of network security and stability, the output evaluation method of distributed photovoltaic cluster is proposed with the lowest economic cost of distribution system including the power-loss cost of network and distributed photovoltaic generation. Finally, the feasibility and effectiveness of the evaluation method proposed in this paper are proved by simulation analysis on an actual 41-node system in Yangzhou. The proposed method can provide output evaluation data of distributed photovoltaic cluster according to the demand of dispatching center.
Aiming at the problems of voltage violation, harmonic distortion and three-phase imbalance in distribution network, this paper studies the optimal scheduling model and its solution algorithm of distributed photovoltaic generation in distribution network from the perspective of comprehensively improving power quality. Firstly, the control scheme of reactive power, harmonic current and unbalanced power compensation of the grid-connected inverter of distributed photovoltaic generation is analyzed. On this basis, taking the three-phase power and harmonic current output of schedulable distributed photovoltaic generation as control variables, combined with the three-phase fundamental and harmonic power flow equations of distribution network, an optimal power flow model considering the improvement of power quality is established. Then, a two-stage optimization algorithm with alternating iteration of power flow calculation and optimization calculation is proposed to reduce the variables of the nonconvex nonlinear optimal power flow model and convert it into a convex quadratic constrained quadratic programming model, so as to achieve efficient solution. Finally, a case study is carried out on a 162-node three-phase distribution network. The results show that, after the scheduling of distributed photovoltaic generation according to the solution of optimal power flow model, the problems of harmonic distortion, three-phase imbalance and voltage violation of distribution network have been effectively improved, and the computational efficiency of the two-stage optimization algorithm also meets the distribution network scheduling requirements, which verifies the effectiveness of the proposed optimal scheduling method for distributed photovoltaic generation in improving the power quality of distribution network.
In order to solve the economic dispatch problem of a typical retailer coping with the stochastic risk brought by the distributed generation and demand-side fluctuation, a bi-level optimization model with the introduction of random variables is proposed. In this model, the upper-level sub-problem aims to simulate the market clearing process of electricity and reserve auxiliary services, where market clearing price and market clearing electricity are the decision variables, while the lower-level sub-problem is formulated to minimize the costs of purchasing under time-of-use pricing given by the simulation of market clearing. The model is converted into a deterministic model by chance-constrained programming, and the equilibrium solution is obtained by iterations between the upper and lower layers, where the CPLEX solvers are employed to address the upper and lower level sub-problems, respectively. Finally, the impact of different confidence level on the decision carried out by retailers is clarified through the analysis of the numerical simulation of the bi-level optimization model. It is verified that the model can effectively reflect the impact of the decision-making behavior of retailers on the market clearing process.
In recent years, power grid companies have formed a standard cost system for the operation and maintenance of transmission, transformation and distribution equipment assets, which lays the foundation for adapting to cost supervision and auditing and scientifically allocating resource input. However, the assets of distribution network equipment are large, the content and frequency of operation and maintenance work are cumbersome, and the cost structure of operation and maintenance is ambiguous. As a result, the rationality of operation and maintenance cost allocation is still insufficient, and it is still unable to support lean cost management. Aiming at the problem of distribution network operation and maintenance cost allocation, an optimal allocation model of operation and maintenance cost of distribution network equipment asset, which is based on AHP and entropy weight method, is proposed. Firstly, according to the key influencing factors of the distribution network operation and inspection cost, an evaluation index system for cost optimization configuration is established. Then, taking into account the rationality and effectiveness of the cost input, the entropy weight method is used to weight the optimal configuration evaluation index, and an optimal configuration model of operation and maintenance cost of equipment assets in the regional distribution network is constructed to reasonably and effectively allocate the regional operation and maintenance cost. Finally, taking 14 prefecture-level units in a province as an example, the validity and practicability of the model are verified. The model can reasonably optimize the distribution of operation and maintenance cost in the distribution network, and find the problems in the existing distribution ratio, which has a certain reference for the formulation of the actual operation and maintenance cost strategy of the distribution network.
