Abstract:Aiming at the problem of the impact of gas pressure and flow change on the small signal stability of power system for combined electricity and gas system, a small signal stability model of combined electricity and gas system considering the gas transmission delay, dynamic characteristics of natural gas pipeline and gas generator set is established. Firstly, the mathematical relationship of gas pressure changes to relevant eigenvalues and flow changes to relevant eigenvalues is derived under the delay of gas transmission to reveal the mechanism of the influence of gas status on the small signal stability of power system. Then the participation factor method of gas changes related oscillation mode is proposed. Through developing the participation factors of gas changes that affect the relevant oscillating modes, it is possible to quantitatively evaluate the influence of gas flow pressure and flow on the small signal stability of the system.The simulation results of CHP driven by natural gas access infinity system and the improved IEEE 9 node system with two CHPs show that the proposed model and method are correct and effective.

Abstract:The integrated energy system in the industry park is an important material carrier for Chinese comprehensive energy demonstration projects. Its optimal scheduling often takes into account multiple goals with different dimensions and orders of magnitude. Under the background, based on the actual engineering construction of Tongli comprehensive energy service center, a multiobjective optimal scheduling model of integrated energy in the industry park with the goal of considering the overall energy efficiency of integrated energy, integrated energy costs, and collaborative consumption of renewable energy is established. At the same time, the solution set of the Pareto plane is obtained by using the fixed step length of the objective function after unitization. The ideal solution is selected by the near ideal solution sorting method after the Pareto plane is drawn by interpolation fitting. Finally, the Tongli Park is selected as a case to verify the above model. On the Pareto plane, a ideal solution is chosen as the optimal according to the actual engineering requirement. The operation of the various equipment in the industry park is analyzed to provide theoretical and technical support for the future construction and development of the integrated energy system in the industry park.

Abstract:With the development of integrated energy system, the energy coupling degree is deepening. Especially the multienergy coupling price mechanism is formed on the energy selling side.An energy management optimization strategy based on noncooperative game is proposed for a comprehensive energy system with multienergy coupling pricing mechanism.Firstly, the energy cost model based on conditional value at risk (CVAR) is established according to the energy coupling price mechanism of the integrated energy system.Then, a noncooperative game model between users in a comprehensive energy system is established.The original problem is transformed into a quadratic programming problem with a single objective by constructing a potential function.It is proved that the equilibrium of pure strategy game exists and is unique.Finally, an example is analyzed to show the energyconsumption of users decreases somewhat and therefore verify the effectiveness of the proposed model and method.

Abstract:For the multiple time scale problem of energy routers, the impact of cyber physics interaction is considered and the energy router modeling based on cyber physics system is established. Then, an optimization scheduling method of energy router with multienergies is proposed based on the multiple time scale in this paper. Firstly, the cyber physics modeling of the energy router is established according to the relationship between cyber and physical factors. This model could reflect the relationships between individual constraint variables accurately, and provide the optimization decision basis. Secondly, a vertical structure data analysis method with the multiple time scale for the energy router is proposed by singular system theory. The method could effectively eliminate the influence of the time scale difference of data. In addition, a multiobjective optimization method for distributed energy routers based on multiagent particle swarm optimization (PSO) algorithm is proposed for interconnected energy routers. Eventually, the simulation results can verify the effectiveness of the proposed method.

Abstract:In order to solve the problems in active distribution network which incorporates wind power and energy hub, including the escalating power peakvalley fluctuation and wind curtailment, a model for power peakvalley regulation, as well as the wind power accommodation enhancement, is proposed by adjusting both the energy hub and energy storage on the demand side. Through analyzing the model of the sourceload storage on the demand side, the influence of both the wind power accommodation and the power peakvalley difference is assessed, then the equivalent load curve is obtained. The wind powerbased combined coolingheatingandpower weight coefficient is proposed according to the load change and wind power penetration rate during each period. The coupling operation mode of cooling and thermoelectricity in energy hubs is improved, and the level of the wind power accommodation is enhanced through the multienergy complementarity. Meanwhile, the coupling operation mode can also be improved via the proposed model and the EH to determine the charge and discharge controlling strategy of energy storage adapting the operation state of active distribution network. The power peak and valley can be suppressed via the vertically transfer of power, and the accommodation level of wind power can be improved. Finally, an improved IEEE 33node distribution system is included to simulate the model. The results show that this model can effectively improve the wind power accommodation in the active distribution network, along with the peak reduction and valley filling in power load.

Abstract:Standalone microgrid is an effective way to solve the problem of power supply in remote areas. However, standalone microgrid is lack of the support of large power grid and its frequency modulation capability and frequency stability are relatively weak. It is necessary to consider the frequency modulation in microgrid planning. Under the background, in view of the dual needs of peak modulation and frequency modulation, this paper proposes an investment optimization method of standalone microgrid that takes into account frequency modulation with hybrid energy storage. Firstly, the correlative mechanism and logical relationship of source and storage configuration parameters satisfying the requirements of frequency and peak regulation are studied. Then, an optimal allocation investment model of standalone microgrid is established with the objective of minimizing the total cost of system investment under the main constraints of wind abandonment rate and load power shortage rate. The model is solved by genetic algorithm. Lastly, an island microgrid is taken as the background for example analysis. The results show that the proposed method effectively considers demand of frequency modulation and peak modulation, and realize the integrated optimal allocation of source and storage.

Abstract:Aiming at the problem of multiagent interest game planning in the open environment of electricity market, a hierarchical planning model is proposed for Active Distribution Network with the coordination and interaction of "sourcenetworkload" multi agents based on the game theory, and the iterative search method and improved particle swarm optimization algorithm is applied to get the solution. The upper layer of the model considers the respective decisions of the source, network and load agents, and aims at achieving the equilibrium in the game mode for each interest body. The lower layer considers the DG(Distributed generation) reduction and OLTC(Onload Tap Changer)adjustment strategies from the active management level. The target of the lower layer is minimizing the expected value of annual load cutting of DG. In the upper layer, the iterative search algorithm is utilized to search the equilibrium solution of multiagents, and the improved particle swarm optimization algorithm is employed in the optimization process of each agent in the upper layer and the optimization process in the lower layer.Finally, an improved IEEE 33node example is simulated to verify the feasibility of the model. It also gives ideas and suggestions for the ADN planning game problem with multidecisions in the open environment of electricity market.

Abstract:The high renewable energy penetration power grid at sending end is widely distributed in China and their safety risks are existed and can not be ignored. Currently, there is no specific model and indicator system for its risk assessment while the traditional risk assessment method is also difficult to conduct a quantitative risk assessment. Under the background, a relatively complete evaluation index system is constructed for the high renewable energy penetration power grid at sending end, and a fuzzy comprehensive evaluation method is proposed based on the entropy weight method. The entropy weight method is utilized to determine the weight of each index. The degree of membership is determined by the improved triangular trapezoidal membership function and the comprehensive evaluation results are obtained through fuzzy comprehensive evaluation. This paper analyzes an example of the high renewable energy penetration power grid at sending end. The analysis results show that the proposed method can effectively evaluate the risk degree of the power grid at sending end and provide a basis and reference for the actual operation of the power grid.

Abstract:The home microgrid contains uncertain power sources and loads such as photovoltaics and electric vehicles. The lack of a reasonable energy management strategy can easily lead to instability of the household microgrid.In the V2G system, a model that simultaneously considers electric vehicles, houses, batteries, and renewable energy power generation systems is constructed. Under the restriction of electric vehicle charging and discharging strategy, a power production planning for the residence and for the microturbine is determined.Then a dynamic energy management is proposed. Finally, the proposed home microgrid energy management method is verified by simulation. By comparing the equivalent load and energy storage operation of the microgrid under the conditions of random charging, orderly charging and discharging of electric vehicles,the feasibility of proposed method is verified when the charging state of the battery is restricted.

Abstract:Shortterm load forecasting is of great significance for the economic dispatching and operation of power systems. In order to improve the accuracy of shortterm load forecasting, a shortterm load forecasting method based on kfold cross validation and Stacking ensemble is proposed. Firstly, the Pearson coefficient method is utilized to screen multiple features affecting shortterm load, and redundant features are eliminated. Secondly, the kfold validation crossvalidation method is applied to train the submodels of the first level, and the prediction results of each submodel are taken as new features to train the second level model. Thirdly, the results of the submodel are stacked, and the shortterm load forecasting results obtained by the second layer model. Finally, the validity of the proposed method is verified by the actual data set from New England. The simulation results show that the proposed kfold crossvalidation method can effectively improve the generalization ability of the model. Stacking fusion can not only improve the average accuracy of prediction, but also reduce the maximum prediction error, which is more advantageous than single model prediction.

Abstract:With the rapid growth of the number of electric vehicles, in view of the rough and inefficient operation and maintenance of the current DC charging station, a method based on risk assessment for the operation and maintenance of DC charging stations is proposed. Firstly, this paper establishes the operation and maintenance system. The consequences of the charging pile failure event to the user is defined as the loss of time (LOT) combining the fault parameters to establish the risk assessment model and realize system risk quantification. The risk tracking of the charging station is carried out by the energy not charged (ENC). The risk level of each station is evaluated while the operation and maintenance timing is determined. Secondly, the model of driving and charging of users is built. The dynamic traffic simulation is used to calculate risk indicators. Finally, the optimal operation and maintenance model of DC charging station aiming at economy and reliability is constructed to determine the maintenance duration of each station. The results is used to calculate the relevant risk indicators imitatively. Finally, a DC charging station optimization operation and maintenance model with the goal of economy and reliability is constructed to determine the operation and maintenance time of each station. The results of simulation examples show that compared with the current operation and maintenance work, this strategy can not only meet the operation and maintenance requirements, but also significantly improve the reliability of the system and improve the overall operation and maintenance efficiency.

Abstract:The rapid development of electric vehicles and windsolarstorage technologies play a key role in the distribution network planning. Firstly, the charging demand of electric vehicles is analyzed according to the demand for the car battery pack. Then, the electric vehicle load is calculated by considering the traffic flow provided by the charging stations, and a multiobjective planning model of distribution networks conductive with energy storage optimization strategy is proposed. In addition, a multiobjective function is constructed with the lowest planning cost, optimizing distribution network voltage and the best satisfaction with traffic network. This model also conducts a fixedcapacity location planning for the windsolarstorage and charging stations in the network, and utilizes the improved NSGAII algorithm embedded with the NDX crossover operator to solve the problem. Finally, a 33node power distribution system coupled with a transportation network is taken as an example to verify the model and method. The simulation results show that the proposed method can effectively improve the relevant indicators of distribution network planning and enhance the overall planning benefits.

Abstract:There are a large number of lowvoltage distributed smallcapacity photovoltaic power supply in the distribution network. Due to its large scale and limited realtime communication, its economy and operability of online adjustment can not be guaranteed. It is difficult to effectively use these reactive resources for auxiliary adjustment of the distribution network. Under the background, this paper proposes a lowvoltage photovoltaic participating in the reactive power operation mode optimization strategy of mediumvoltage grids based on cluster mode presets and online autonomous operation to make full use of the potential of lowvoltage distributed PVs (LVDPVs). Firstly, LVDPVs linked with the same transformer are assigned to a cluster and managed by a terminal platform. Secondly, the dayahead reactive power mode optimization is carried out aiming at compensating load reactive power demand within a feeder. Then, five cluster reactive power operation modes are designed and the dayahead prediction operation scenario is constructed. In addition, a cluster reactive power operation mode and parameter optimization model is established considering the optimal feeder reactive power balance and the minimum reactive power flow between clusters based on the scene characteristics. The improved particle swarm optimization algorithm is employed to solve the problem. Finally, examples verify the effectiveness of the proposed method.

Abstract:Paralleling existing cables with new is an effective way to attain the lowcost capacity expansion, which can make a full utilization of existing cable's transmission capacity. However, due to the difference in coupling effects among parallel cables, the load current may be unevenly distributed to reduce the load capacity utilization. On the background, a load distribution calculation method of parallel cables is proposed in view of the the basic equations of multiloop electromagnetic coupling between cable conductors and metal sheaths. Then the load capacity utilization of parallel cables with different layouts and phase sequence arrangements are analyzed, and application suggestions of phase sequence optimization of parallel cables are given. At last, the analysis conclusion is verified by a numerical simulation. The results show that the optimized phase sequence arrangements can improve the load capacity utilization of parallel cables effectively and take full advantages of the transmission capacity of cables.

Abstract:Frequency stability is a main criteria for determining the feasibility of a black start scheme. If the blackstart source is a hydropower unit, its water hammer effect will have a significantly negative impact on the frequency stability. It has been proved that the governor parameter optimization is an effective way to reduce the impact. Therefore, based on the characteristics of hydropower units and their governors, this paper selects out the main governor parameters that affect the frequency stability firstly. A multiscenario model of blackstart schemes is built to improve the suitability of optimized parameters. Then, a multiobjective multiverse optimization algorithm is employed to optimize the parameters globally and produces the Pareto optimal set. By adopting the fuzzy entropy method and multiattribute decision making based on gray relational model, the most satisfactory parameter combination is then chosen from the Pareto optimal set. Finally, a provincial power grid in southwest China is taken as an example, the validity and applicability of the method proposed in this paper are verified.

Abstract:In order to solve the distribution network in three dimensional space fault detection of optimal allocation problem of sensor nodes, the improved artificial fish algorithm is proposed based on the iot sensor effectively which realizes effective optimal allocation of space detection sensor nodes. Firstly, the MSP 430F 149 microprocessor chip is utilized to construct the space sensor node together with the monitoring computer to form the distribution station temperature monitoring system which realizes the effective collection, transmission and processing of the distribution station temperature detection data. Secondly, the traditional artificial fish swarm algorithm is improved through the initialization of artificial fish swarm and the improved gradient descent method. The field of view and the convergence accuracy of the algorithm is improved. Finally, an improved artificial fish swarm algorithm is applied to optimize the placement of sensor nodes. It is shown that the improved artificial fish swarm algorithm based on IoT sensors can effectively optimize the monitoring of substation space.

Abstract:Solid State Transformer (SST) is the central equipment of distribution network in Energy Internet, which controls the power flow actively. In this paper, a novel voltage and power balance control strategy for Cascaded HBridge (CHB) type SST is proposed, and the design method and operation mechanism of the control strategy are analyzed. Firstly, in order to solve the problem of unbalanced voltage on the DC side of CHB in the input stage, a voltage and reactive power balance control strategy that utilizes both active and reactive duty cycle modification are proposed. This method not only eliminates the coupling effect between the balance controller and the system controller, but also balances the voltage and reactive power of CHB capacitors. Secondly, the activeduty component of the input stage is taken as the power balance control feedback of the isolationstage and the correction is made to solve the problem of unbalanced power transferring of the dual active bridge DCDC converters due to the parameter differences. In addition, the coordination control of the front and rear controller is analyzed to improve the system transient performance. Finally, the feasibility and effectiveness of the control strategy are verified by simulation.

Abstract:To deal with the subsynchronous oscillation in the ACDC interconnecting system, the complex torque coefficient analysis based on the damping characteristic is utilized to investigate the mechanism of the Subsynchronous Oscillation in this paper. Firstly, a small signal model is built to derive the relationship between the variation of angular speed and the electromagnetic torque. Then, the impacts of the PI control parameters, VSC control strategy and DC line length on the oscillations are investigated, and the testing signal methodology is utilized to obtain the system damping characteristics. Finally, the analytical results are verified by the simulations performed in PSCAD/EMTDC. It can be concluded that SSOs are much easier to be triggered when the high proportional coefficient and low time constant are employed. The AC voltage control strategy at the sending end of VSC has the better SSO damping performance than the reactive power control strategy. Moreover, the damping performance could be improved by long DC transmission lines, which mitigates the DC voltage fluctuation in the HVDC system.

Abstract:Aiming at the problem of poor performance of traditional unified power quality conditioner (UPQC) control strategy, this paper proposes a hybrid control strategy combining passivity based control and nonlinear PI control, and establishes the EulerLagrange (EL) model of the unified power quality conditioner (UPQC). Firstly, the current innerloop passivity based controller is designed by injecting damping and the convergence of error energy is accelerated. Then, the nonlinear PI control is adopted and a voltage outer loop controller is designed to obtain more accurate expected current, effectively suppresses the static error, and makes the system has good dynamic and static performance. Finally, a simulation model of the unified power quality regulator is built in Matlab/Simulink. The simulation results based on the model verifies the feasibility of the proposed control strategy.

Abstract:The motor of a doublyfed induction machine (DFIM) driven multifunctional flexible power conditioner (FPC) can be treated as a doublyfed induction motor with a large rotating inertia and without mechanical load or a doublyfed induction generator without motor. It can regulate the active and reactive power rapidly to enhance the stability of power system. Based on the analysis of control strategy, a 10 kV·A excitation control system of FPC is developed. The proposed control method is experimentally running. Experimental results show that soft start can be implemented, and active/reactive power can be regulated independently. The excitation control system can be applied to a flywheel type FPC system.

Abstract:Peakload regulation capability of power systems can be improved by the rational utilization of thermal storage systems at the customerside, which can also promote the consumption of the renewable energy. A set of indicators, which considers the quantity, the intensity and the velocity of the potential power consumption, is proposed to direct the consumption of the abandoned wind power by distributed electric boilers with thermal storage (EBTS). The indicator set evaluate the consumption ability from three aspects, which includes day ahead level, hour level and realtime level. The indicator set not only provides data support for the instructions of the EBTS, but also provide the realtime operating state information of EBTS to operators. This paper introduce the thermal storage consumption system, and elaborate the application of the indicator set, of which effectiveness is validated through case studies.

Abstract:The metro stray current can flow through the neutral point of the transformer from the grounding grid in the soil, and then cause the transformer DC bias phenomenon. In order to effectively evaluate the influence of metro stray currents on transformers, a resistance model for the transformer DC bias caused by the stray current is established by considering the traction current in metro, the "railcurrent drainage netearth" metro system structure, and the DC bias current loop. Then the dynamic equation of transformer neutral point current with time and metro train position is established, and the neutral point current can be solved by the LU decomposition. The software CDEGS is utilized to build the train and transformer simulation model. The transformer neutral point current between the simulation results and the calculation results of the proposed modeling method are comparative analyzed, and the model error is small. Therefore, it can be effectively applied to the evaluation of transformers affected by metro stray current.

Abstract:Highspeed rail longdistance power lines have gradually realized full cable,and some highspeed rail power systems still use neutral point ungrounding. Therefore,when the system is singlephase grounded,it is often accompanied by intermittent arc grounding,which causes damage to some PTs. In order to solve the PT damage phenomenon of long cable line,the main reason of the PT burnout of highspeed long cable line is obtained through theoretical analysis without changing the grounding mode and line structure of the neutral point. Then,by constructing the simulation model,the railway is pointed out. In the longdistance cable line,the neutral point ungrounded system should be designed according to the ungrounded system for electrical equipment selection and insulation coordination. The electromagnetic PT with higher excitation point saturation should be selected. The PT rated voltage factor should be greater than 2.2 pu;The scheme is applied to a number of highlength cablelength cable distribution stations in Wuxi East,and good results have been obtained,which verifies the feasibility of the scheme.

Abstract:With the gradual opening up of the power market, the injection of outside lowprice electricity brings great challenges to the power purchase decision of receiving object. On the background, this paper classifies and sorts out the purchasing cost of different purchasing channels in the electricity plan and market, and then analyzes a series of constraints which needs to be considered in the acrossprovinces /and acrossregions power purchasing. Thus, a monthly trading decisionmaking framework is put forward for the electricity plan and market coordination with the acrossprovinces /and acrossregions trading. In addition, for the purpose of minimizing the total power purchase cost, the power flow safety constraints, on the ultra high voltage direct current (UHVDC) tie line and interprovincial transmission channel constraint are considered. Finally, the Hunan power grid is taken as an example. The influence of crossprovince and crossregion power purchase constraints on the power purchase results is discussed to verify the effectiveness of the proposed model.

Abstract:In the Northwest Economic Corridor region, the distribution lines with the low voltage ride through is built and parallel operates under high voltage lines in order to save the land occupation and improve the economic benefit. However, during the outage maintenance process of the low voltage line, the induction voltage and current generated by electrostatic effect and electromagnetic coupling of the multicircuit highvoltage transmission lines may threaten the safety of maintenance personnel. On this background, the normal operation of LuoshanLingzhou 330kV transmission line in Northwest China is taken as an example and an ATPEMTP simulation model is built in this paper. Then the variation of induction voltage and current on 380V line is compared and analyzed in the aspects of transmission line length, current magnitude, nominal height and the distance from the tower center. The magnitude of the current through human body is also calculated in different maintenance modes. The results show that the electrostatic induction voltage is mainly related to the nominal height of high voltage tower and the distance from the tower center. The electrostatic induction current is mainly affected by the nominal height of high voltage tower and the length of low voltage line. The electromagnetic induction voltage and current are influenced by the length of low voltage line, the magnitude of the operating current and the distance from the tower center. Comprehensively considered various recommended values of human physiological effects, the maintenance method of adding security grounding line is suggested to ensure the safety operation.