In the energy development trend of 'clean energy replacement and electricity replacement'， as the carrier for transmission and distribution of electric energy， power grid is an important part of the energy supply system， and the important foundation and guarantee of the modern economic development and social progress， moreover is the core subject of energy Internet. This paper analyzes the history of power grids in North America， Europe， and Russia over hundred year history， and summarizes the general development rule of typical synchronous power grids in the world from traditional grid to modern power grid， isolated grid to interregional and international large-scale interconnected grid， which provides references for the development of China's power grid. Based on the analysis of China power grid development history and the study of power grid interconnection evolution feature integrating renewable energy features， this paper proposes the future development patterns of China's energy interconnection based on the synchronous grid framework， combining the electric power demand， the energy exploration， and the development trend of electricity flow scale， which can be an important foundation for the construction of the global energy internet.
At present， the energy Internet has become the main development direction of power system in our country. The construction of the energy Internet will change the energy utilization status and the management pattern. In the perspective of demand side management， this paper studies the new control strategy under energy Internet. Traditional demand side management controls parts of the load by related protocol based on the interaction between the grid and the users. The development of energy Internet makes the information interaction between users more important and frequently. At the same time， the access of various generation forms of energy makes the demand side management more important. This paper proposes a new demand side management method for energy Internet， which uses the user-side sound communications infrastructure to add the power control module in the intelligent measurement equipment for each user. Through the game theory in this module， each user makes his energy plan according to those of other users which make his payment minimum， so as to obtain all the user's energy consumption plans， and realize the minimum peak-average ratio of system operation and power generation cost under the overall energy consumption plan. At last， the example simulation results prove the validity of the load management mode.
The integration of Northwest renewable power resources in Northwest area is mainly restricted by the transmission capability of the Northwest-Xinjiang power corridor. In order to make reasonable development planning of the Northwest renewable power resources， this paper studies the relations of the integration of renewable power resources to the transmission capability of the Northwest-Xinjiang power corridor and the power system's security and stability. We adopt PSD-BPA electromechanical transient simulation program to analyze the impact of wind power integration in Xinjiang Hami， Gansu Hexi Corridor and PV power integration in Gansu Jinchang， Qinghai Qaidam on the transmission capability of the Northwest-Xinjiang power corridor and the power system's security and stability. The results indicate that the Hami wind power's integration and the Hami wind power units' control mode have small influence on the transmission capability of the Northwest-Xinjiang power corridor， but the Hami wind power's integration will decrease the power system's stability； the Gansu wind power and PV power's integration will increase the transmission capability of the Northwest-Xinjiang power corridor and the power system's stability； the Qinghai PV power's integration will decrease the transmission capability of the Northwest-Xinjiang power corridor and the stability of the first corridor of the Northwest-Xinjiang power corridor， but the total integration amount of the renewable power resources will be greatly increased. According to the analysis results， it is suggested that the development scale and the scale ratio of the Gansu and Qinghai PV power resources should be reasonably made， and the development proportion should be paid attention. Meanwhile， the suitable security and stability control measures should be made when the power system has large scale wind power and PV power's integration.
According to the wind power curtailment problem caused by the shortage of peak regulation capacity of power system with large-scale wind power integration in China， this paper proposes the charging and discharging strategy of energy storage battery with large capacity to improve the peak regulation capacity and reduce the wind power curtailment loss. Based on the proposed energy storage constant power charging and discharging strategy， we establish a mathematical model for capacity and layout optimization of energy storage power plants， and adopt genetic algorithm to solve the model. This model takes the minimum total costs as optimization objectives including the investment and operation costs of energy storage power plant， network loss， and the sum of wind power curtailment caused by the shortage of peak regulation capacity and wind power channel blocking.It also considers the benefits resuled from the electricity price gap between peak and valley periods and the benefits of carbon emission reduction of wind power， and meets the security operation constraints of power grid as well. Finally， we use IEEE RTS79 system to analyze the layout optimization of energy storage and verify the effectiveness of the method. The application of this method can provide technical solution scheme for the wind power curtailment problem in the area of large-scale wind power integration.
Due to its feasibility， demand side response and storage device can be used as virtual reserve resources to guarantee the security of power system with intermittent wind power penetration. In order to evaluate the impact of virtual reserve resource on the economy and environmental protection of the system， this paper establishes two different kinds of electricity dispatching models with wind power penetration for traditional thermal reserve and virtual fast reserve respectively. With the consideration of system risk brought by renewable energy generation， electricity market and unit parameters， we combine the interval two-stage stochastic optimization model with CVaR risk theory. The uncertainties of supply side and demand side are integrated with optimization function though interval value and probability， which can reflect the risk preferences of decision makers. The example analysis shows that the proposed hybrid optimization algorithm can effectively optimize the different spinning reserve modes of power system with wind power penetration， and make better trade-off between system cost and risk. The results show that making full use of storage battery and demand response as virtual reserve resources can efficiently reduce the system cost and CO2 emission.
In traditional electromechanical-electromagnetic transient simulation， the equivalent methods of electromagnetic side system in electromechanical side mainly include current source， Norton equivalent circuit， power source etc. This paper analyzes the error mechanism of current source equivalent of electromagnetic side system in electromechanical side， and points that only transmitting the current information including magnitude and phase cannot ensure the right calculation for electromechanical side during the fault in electromagnetic side. In combination with the voltage and power constraints of the interface， we propose a equivalent method which is different from the current source. With using a step information on the electromechanical side， this method changes the calculation method of electromechanical side network from the way with the current source equivalent directly involved into iterative solution， which can solve the calculation accuracy problem of current source equivalent method caused by can't ensuring the power transmitting of the interface. An electromechanical-electromagnetic transient hybrid simulation platform of IEEE-39 node system with two DC links is built in PSCAD/EMTDC environment based on PSCAD+C. The simulation result shows that the proposed current source equivalent method can significantly improve the simulation accuracy of electromechanical side during fault.
This paper analyzes the error forming principle of traditional dq-120 algorithm when the fault current containing decaying DC component and its display form. On this basis， an improved dq-120 algorithm is proposed combined with Prony algorithm. The improved algorithm can reduce the model order for the dq-120 calculation results of fault current based on the assumption that the fault current contains DC component， simplify the calculation of traditional Prony algorithm and improve the immune level of dq-120 algorithm to the DC component. With using PSCAD/EMTDC simulation software， we build an electromechanical-electromagnetic hybrid transient simulation model of IEEE 39-node system with a DC link. The simulation result shows that， compared with traditional dq-120 algorithm， the improved algorithm improves the phasor extraction accuracy of current during fault， so as to improve the accuracy of electromechanical-electromagnetic hybrid transient simulation during fault as well as the whole simulation process.
This paper analyzes the mathematical principle of the electromagnetic transient simulation detailed model of modular multilevel converter （MMC） arm based on the Thevenin's equivalent principle. It is found that when the network structure changes caused by fault or switch of breakers during simulation process， the calculation error may be introduced when using trapezoidal integration method because of the mutation of the capacitor current. To solve the problem， this paper proposes a method to eliminate the calculation error through solving the non-state variable after the mutation. We compare the capacitor voltage before and after the elimination of the calculation error at the moment of switch changing in PSCAD/EMTDC， and verify the correctness and validity of the method. Meanwhile， we establish a single-terminal 101-level MMC-HVDC simulation system， whose results verify the correctness of the proposed improved calculation model.
Due to the special characteristics of microgrid， the operation， dispatch and control in microgrid are significantly different from those in the traditional power grid. It is a challenging subject to determine the best strategies of the decision-making parts in microgrid in order to balance and optimize the profits of related parties. Game theory， a multi-target optimization method for complex subjects， is expected to be a powerful tool to solve the key problems of microgrid. This paper reviews the typical applications of game theory in microgrid from the aspects of power source， network， load， and price policy， etc.， and discusses the future applications of game theory in microgrid， including the microgrid-type power sellers， the interaction between the microgid and main grid， the electric permeability of the sustainable energy， and the construction of the communication network， which can play positive roles in promoting the studies of game theory in microgrid.
To make a better choice of the model of the power system dispatching plan with the random characteristics of wind power， this paper compares three economic dispatch wait-and-see models based on wind power scenario. The difference between two kinds of objective functions are compared and analyzed， which are ‘the minimum distance to the mean of wind power’ and ‘the minimum adjustment amount of dispatching plan’. Based on the power balance equation， we deduce and compare the dispatching plans obtained by three models and the regulation ability and adjustment amount for coping with the actual possibility of wind farm scenarios. Finally， taking the IEEE 24 node system as the example， we compare and analyze the simulation results of three models from the aspects of operating cost， adjusting ability， adjusting range， abandoning air volume， and so on. The analysis results show that the model with the minimum adjustment as objective has obvious advantages in robustness， economy and computation speed compared with other two models. The proposed three economic dispatch models and the comparative analysis results can provide important references for the dispatching plan optimization of the wind power system scheduling schemes.
The power system operation is constrained by a multitude of factors， and the load-carrying capacity is relatively low if only with reliability as the criterion for evaluation. Aiming at the problem， through the analysis of the annual duration load curve， this paper proposes the maximum load-carrying capacity evaluation method of transmission line based on economy and reliability coordination. By coordinating the reliability and economy of power system， the annual average load-carrying capacity of existing lines can achieve the highest level. In the evaluation， the annual maximum load of the system meeting the reliability constraint is firstly calculated. Then the parts on duration load curve that are greater than the annual maximum are cut as overloads， and load-cutting compensation is given according to the way of interruptible load. Besides， customers also get compensation from the reserved parts on duration load curve as outage cost based on expected energy not supplied （EENS）. The growth of economic costs of reliability composed of the these two compensations are compared with the economic efficiency growth brought by electricity sale of grid， whose result shows that as long as the growth of economic costs of reliability is relatively lower， there will be still likelihood for the improvement of the maximum annual load-carrying capacity in evaluation system. The proposed method is applied in IEEE RTS 79 system， and the result shows that this evaluation method has higher results than those of traditional security assessment， which can further develop the utilization of lines and make full use of the available capacity of transmission line.Symbol`@@
The existing droop control methods for the voltage source converter based multi-terminal high voltage direct current （VSC-MTDC） system can reasonably distribute the unbalanced power of DC network among the converter stations， but neglect the bearing capacity of AC system in converter system， and cannot flexibly adjust the power output variation of converter stations according to the transient responses of the AC systems. Therefore， this paper proposes an improved droop control method for VSC-MTDC system considering the adjusting ability of AC grid. The improved method can adaptively modify the slope coefficient of droop control based on the frequency deviation of the AC grid， which can distribute the unbalance power in the DC grid more flexible and reasonable without changing the controller structure. Compared to the droop control method with fixed slope coefficient and the adaptive droop control method with considering power margin， the proposed improved control method is proved to be more effective and superior on the RTDS （real-time digital simulator） platform.
Due to differences of the relay protection status and external characteristics among generators derived from distribution of the wind speed and collection network， the conventional single-machine aggregation model cannot offer high accuracy of fault ride-through behaviors of real wind farms in all scenarios. This paper proposes a dual-machine model that is more applicable for doubly-fed induction generator （DFIG） wind farms， based on a reverse modeling method and the delicately-designed macroscopic parameters. First， we analyze the effect of over-current protection on controllability of the wind farm. Considering the power-source nature of DFIGs， the Crowbar dynamic during a large disturbance has a great impact on accuracy of the simulated power response， whereas the peak current level decides whether Crowbar is activated. Thus the current level proves to be the critical factor that generates incoherency among DFIGs， based on which the generators can be grouped. Naturally， description of the incoherency can be implemented by a dual-machine model， and its macroscopic parameters can be adjusted according to control parameters and the wind resources， so as to smoothly set the level of distribution factors that produce incoherency. In order to improve practicability of the proposed model， a reliable parameter-identification procedure is presented， which extracts macroscopic parameters reflecting power responses with the maximum probability. Simulation verifies drawbacks of the single-machine aggregation model and performances of the novel model. With the ability to consider features of wind resources， the proposed model remarkably improves accuracy of wind farms' power modulation behaviors， adjacent synchronous generators' power-angle dynamics， and the motor-type loads' voltage dynamics.
To make up for the drawback that clustering method based on Euclidean Distance considering all dimensions of load curves is weak in load shape similarity， this paper proposes a two-step clustering algorithm combined with load shape characteristic index for power load curve. First， this algorithm obtains the preliminary clustering result by using clustering method based on the Euclidean Distance of load curves and selects the clustering method and number through cluster evaluation index. Second， this algorithm uses supervised learning algorithm to reclassify load based on load shape characteristic index. Then， different clustering algorithms are compared. At last， we propose the suggestions for the application of the clustering results. The example results show that the proposed two-step clustering algorithm can make up for the weakness of traditional clustering algorithm in load shape similarity. Support vector machine （SVM） algorithm has better performance in the second-step classification. The proposed algorithm has practical significance.
This paper researches the optimal allocation problem of distributed generation （DG） in distribution network， and establishes a multi-objective optimal configuration considering investment benefit， voltage quality and power loss comprehensively based on fuzzy membership technique， which can effectively solve the excessive optimization problem caused by different magnitude of targets. We improve a new bionic intelligent algorithm-fruit fly optimization algorithm （FOA） and introduce the operation of attraction and repulsion into the algorithm optimization process by following the chemotaxis of bacteria in foraging process to improve the population diversity and reduce the possibility of falling into local optimum. The simulation results of IEEE 33 node system show that， compared with the traditional FOA and particle swarm optimization （PSO） algorithm， the improved fruit fly optimization algorithm （IFOA） has a great advantage in search speed and accuracy and can quickly and effectively search the optimal configuration， which verify the validity and rationality of the improved algorithm.
Ice shedding occurs frequently on overhead transmission line in ice area. The line vibration caused by ice shedding may reduce the structure safety of transmission tower. In order to implement the experiment simulation for the ice shedding of transmission line under multi-operating conditions， this paper develops a new nonlinear simulation experiment system of ice shedding for overhead transmission lines based on bus architecture design， which consists of ice shedding simulation module， ice shedding control module and data acquisition module. The ice shedding simulation module establishes the fundamental environment of the experiment， which can design according to different transmission line conditions. The ice shedding control module sets the time sequence of ice shedding， which can accurately simulate different ice shedding conditions according to the time sequence. The data acquisition module acquires the dynamic tension in real time， and adopts binocular stereo vision technology for the measurement of ice shedding jump track of the overhead conductor. The system has a higher lever of automation and a good control precision， which can effectively obtain the dynamic tension and ice shedding track during ice shedding.
The scientific layout and construction of charging infrastructure for electric taxis is of great significance to the promotion of electric taxis. Taking into account the importance of time value to taxi drivers with the purpose of maximizing the benefits， this paper adopts the annual cost of construction and operation maintenance of charging station， the annual time cost of taxi to the charging station， the annual waiting time cost of charging and the annual cost of distribution network loss to establish the total annual cost objective function in the whole society， and takes the safe operation of distribution network as the constraints of charging station layout planning to construct model. We apply adaptive adjustment strategy in the quantum genetic algorithm to solve the model with combining Voronoi diagram method. Then， we divide the service areas of charging station based on Voronoi diagram， and adopt the queuing theory M/G/c model to perform the optimization configuration of charging station， so as to realize the location of electric taxi charging station. Finally， the example analysis of 36-nodes road network and 33-nodes distribution network verifies the effectiveness and practicality of the model.
The study on the power loss calculation method for modular multilevel converter based high voltage direct current （MMC-HVDC） transmission system has great importance to the design and optimization of HVDC transmission system. This paper proposes a practical power loss calculation method for MMC-HVDC. Firstly， we construct the power loss calculation models for MMC-HVDC and each component according to the topology of MMC-HVDC and the parameters of components， and exactly solve the loss data of MMC-HVDC and its components under different operating conditions through simulation calculation. Then， we use data fitting method to obtain the loss calculation formula convenient for engineering application. Finally， according to the VSC-HVDC transmission system in Xiamen， we compare the results of the proposed loss calculation formula with the practically measured results. The results show that the loss of MMC-HVDC calculated and evaluated by the proposed fitting formula can meet the engineering accuracy requirements.
Credible capacity is an important index to evaluate the capacity value of distributed generation. According to the characteristics in western region of abundant wind power/hydropower located in the terminal of distribution network， distributed generation dispersedly accessing to the grid and the weak grid structure， this paper proposes the wind power credible capacity evaluation method considering grid constraint under the different operation strategies in local grid and intergration grid， adopts the local power grid scheduling and global credible capacity two-step algorithm to calculate the equivalent load capacity of system， and quantitatively analyzes the effect of grid connection in multiple types of power enrichment area on system adequacy. Taking a certain water-enriched regional grid in western region as example， we calculated the capacity credible of wind power， at the same time researched the influence of three different operation modes of local and external power system on the overall adequacy of system， and proposed relevant operation suggestions.
In the background of low-carbon power system， this paper analyzes the influence of distributed generators （DGs）， energy storage systems （ESS）， EV chargers on carbon emission of smart distribution network. Considering the access of DGs， ESS and EV chargers on smart distribution network， a life-cycle theory of carbon emission flow is proposed， then the emission model and simulation method is established， showing that the carbon emission during the operation period accounts for the largest proportion in the life-cycle carbon emission of smart distribution network. The influence of the single or common access of DGs， ESS， and EV chargers on carbon emission of distribution network during the operation period was simulated and analyzed. Suggestions for the low-carbon operation mode of smart distribution network is proposed. The IEEE 33-node distribution system is used to validate the feasibility of the method.
In allusion to the uncertainty of photovoltaic power station output and the difficulty to accurately describe the probability distribution function of output， this paper adopts distributional robust linear optimization method to study the capacity limit of grid-connected photovoltaic power station. We establish the distributional robust linear optimization model for the capacity limit of photovoltaic power station based on the constraint conditions of system operation. The solar radiation intensity is taken as random variable in the model， whose bound and expectation are used to describe the uncertainty of photovoltaic power station output. The model is transformed to certain linear programming problems via duality theory， which is easy to be solved. We verify the model in a modified Garver's 6-bus system. The results show that the capacity limit of grid-connected photovoltaic power station varies under the effect of factors such as the grid-connected access position， and solar traditional variation range. The optimization result obtained by distributional robust optimization method is better than that obtained by cassette robust optimization， and the proposed model can provide flexible calculation results between optimization and robustness， thereby the practicality and effectiveness of the model are proved.
