Abstract:In order to solve the problem of refusal or misoperation in the staged current protection of the existing centralized photovoltaic power station, a simulation model for the boosted grid connection of the centralized photovoltaic power station is established, which combines the control target of the inverter and the output characteristics of the photovoltaic itself. The analytical expression of the steady-state short-circuit current provided by the photovoltaic side is derived. On the basis of expressions, the adaptability of traditional fault analysis and protection schemes is analyzed one by one when fault occurs on the overhead line, the collection cable, and the current collection line respectively. In view of the shortcomings of the original backup protection when the overhead line fails, the distance protection at the downstream collecting station side is proposed to replace the original staged current protection. For the existing protection scheme, it is difficult to distinguish the collecting line fault from the collecting cable fault. Then, inverse time protection scheme is proposed. PSCAD simulation results show that the proposed protection scheme can reliably operate on common fault types.

Abstract:Since quintessential probabilistic photovoltaic (PV) models like Weibull and Beta distribution are not able to reflect accurately the changes of PV station's output characteristics in different scenarios, a data-driven scenario generation model for distribution system is proposed. The model which is based on the algorithm of local density clustering (LDC), takes into account the correlation of multiple PV stations and the influence of external conditions, thus realizing the accurate modeling of multiple PV stations' output power. Firstly, LDC is used to classify historical data into several clusters. Secondly, kernel density function and copula function are utilized to build joint probabilistic density functions (PDF) in each cluster, and the data of joint PDF are processed by applying Latin Hypercube Sampling (LHS). Then, the samples are used for probabilistic power flow calculation to set up the model which estimates operational condition of distribution network. Finally, the stability of model is analyzed, and influence of sampling size on model is also discussed. It is shown that the proposed method in the paper improves the accuracy of modelling for PV station's output in distribution network, and it also reduces the error of probabilistic power flow calculation.

Abstract:The high proportion of grid-connected photovoltaics (PVs) leads to a dramatical increase of supraharmonic emissions at distribution network. The influence of supraharmonic interaction between grid-connected PVs and distribution network is much more remarkable than that in single PV grid-connected system. So the high proportion of grid-connected PVs reduces the stability of the grid. In order to reveal the characteristics of supraharmonic emission at high proportion of PVs grid-connected, the effect of PVs connecting to grid on supraharmonic emission is discussed. Firstly, the propagation of supraharmonic current at high proportion of grid-connected PV is described. Considering background harmonic emission of grid and control circuits of PVs, a mathematic model is built to calculate the value of supraharmonic currents and summarize the law of supraharmonic propagation at high proportion of grid-connected PVs. On the basis of the model built by PSCAD simulation platform, the supraharmonic emission from individual PVs is obtained. The model is also used to show the influence of backgrounds and PVs on supraharmonic emission. The last but not the least, the model is verified, based on measured date of concentrated PV access in Quanzhou city, Fujian Province.

Abstract:As wind power industry develops rapidly, the control strategy for active power of wind farms tends to be regional. In order to regulate reasonably the active power of wind powercluster and increase the amount of wind power accommodation for reducing the number of wind turbines, a stratified active power control strategy for wind power cluster considering ordered wind turbines is proposed. Firstly, according to the location of wind farms and ultrashort term prediction of wind power, the wind power of regions are divided into three control layers, namely wind farm group layer, wind farm layer and wind turbine layer. The wind farm group layer and wind farm layer are optimized to increase the accommodation of wind power by rolling optimization at different time scales. The wind turbine level calculates and ranks the control capacity scores of each turbine by selecting the evaluation indexes that affect the control ability of the wind turbines, combining the entropy method and the membership function. In this way, the number of control times of the wind turbines is reduced. Finally, the data of actual wind farms in Shanxi power grid are used to analyze by GAMS and Matlab platform. The results show that the proposed control strategy reduces the number of wind turbine control times while improving the wind power accommodation.

Abstract:Virtual power plants integrate distributed power generations into a whole to feed power to the grid by utilizing advanced technologies such as intelligent measurement, network communication, and intelligent decision-making, which is expected to become a supporting framework for large-scale new energy generation integrating into grids. The goal of the virtual power plant constructed is to maximize the economic benefits of grid-connection. At the same time, considering the adverse effects of the uncertainty of new energy output on the power grid, fluctuation factor parameters and mechanism for reward or punishment are introduced to limit the fluctuation of grid-connection power. On this basis, the energy storage system and interruptible load are used as scheduling resources to consume the new energy power generation completely. Finally, the particle swarm algorithm is used for optimizing under the constraints. The calculation results show that the method can effectively suppress the fluctuation of the grid-connected power virtual power plant on the basis of consuming all the new energy generation, and greatly improve the friendliness of new energy access.

Abstract:China has formed a cluster of renewable energy bases through the UHV DC group delivery mode, and the renewable energy consumption is constrained by the DC power transmission capacity and the new energy grid-connected power. Firstly, in order to improve the ability to absorb new energy and distinguish it from the traditional rigid cut-off control of the feeder, the necessity of using the rapid control characteristics of new energy (wind power, photovoltaic) inverters to incorporate new energy power control into the emergency control of the grid is analyzed. New energy power control can effectively reduce the impact, improve the fine level of control, and realize the decoupling control ability of active and reactive power. Secondly, for new energy equipment control, communication status and active and reactive power control capabilities, the technical requirements for including new energy in emergency control communication delay and controllable power real-time sensing are studied, the system architecture is designed, the applicable scenarios are studied, and the application scenarios are proposed. The specific implementation methods and corresponding control strategies are presented. Finally, based on the actual power grid, simulations verify the effectiveness of the proposed control architecture and control method, which can effectively improve the DC transmission capacity and the grid-connected power of renewable energy.

Abstract:The access of photovoltaics changes the structure and power flow of distribution network, thus collapsing traditional pattern by single-phase power supply. The change of system flow inevitably affects the voltage quality, economic indicators and safety of distribution network. Considering the impacts that photovoltaic access to distribution network brings, a multi-objective optimization method based on interactive decision mathematical model is proposed. Firstly, it takes into account the comprehensive factors including different access capacities, dense and decentralized access of photovoltaic which affect the voltage and line loss. Then, the optimal model of photovoltaic access is established. Finally, from the impact of access to photovoltaic on the key indicators of distribution network, the most optimal solution for photovoltaic access is found. By the analysis of De 31 Dedubei, the proposed multi-objective optimization method provides a theoretical basis for the planning and design of photovoltaic power generation projects.

Abstract:As a mature power flow control device, power phase shift transformer can effectively balance the power flow distribution and improve the power supply capacity of power grid. It also has the advantages of low investment cost and high operation reliability. Firstly, the structure characteristics of phase shift transformer and the principle of power flow control are analyzed. Then, based on the real-time digital simulation platform, the detailed electromagnetic transient model of dual core symmetrical phase shift transformer is established. The power flow fluctuation and the control characteristics of the phase shift transformer are studied under the put-in situation and the power flow regulation mode respectively. The results show that the proposed model can effectively control the power flow distribution. Finally, according to the actual operation situation of power grid, the application scenarios of phase shift transformer in power grid are summarized, which provides reference for the large-scale application of power flow control technology in China's power grid.

Abstract:With the rapid development of distributed renewable energy and the popularization of DC loads such as electric vehicles and data centers, the operation and management of AC distribution networks are confronted with challenges. DC power distribution system has a broad application prospect because of its flexible and controllable power flow, closed loop operation and various power supply modes. However, compared with the control of AC system, the control of DC distribution system is more complicated. As the only indicator to measure the active power balance of DC distribution network, the stability control of DC voltage is very important to the reliable operation of DC distribution system. Firstly, the typical topology structure and the DC voltage levels of DC distribution system is introduced. Secondly, the control technology of power electronic converter of key equipment in DC distribution network is introduced. Then, the traditional voltage control strategies of DC distribution network are sorted out, and some improved voltage control strategies of DC distribution network are deeply analyzed and summarized. Finally, it looks forward to and points out the problems that need to be paid attention to and solved in DC distribution network voltage control. Ideas and references for further research on DC voltage control in DC distribution network are provided.

Abstract:Hardware-in-the-loop simulation (HILS) is an effective method to improve the accuracy of current large-scale power grid system simulating, and enhances reliability of the high voltage direct current/new energy device verification. First of all, on the basis of the basic architecture and its advantages of HILS for power systems, the technical characteristics and application of HILS in traditional power system are introduced, such as improving the accuracy of primary system modeling and reliability of secondary system controling. Then, the challenges of HILS application in the power system are analyzed and the key technologies for these problems solution are proposed, such as the flexible architecture technology for accessing multi-heterogeneous data models, the equivalent and the control system modeling of power system, and the universal interface technology for control object integration. Finally, from the perspectives of deep research on traditional technologies and new technologies development, the trend of hardware-in-the-loop simulation for power systems is discussed to provide valuable suggestions for development and validation of related platforms.

Abstract:With the large-scale development of wind power, it increases rapidly the number of directly-driven permanent magnet wind turbines connected to the grid, thus which threatens the safety and stability of operation in the power grid. The low voltage ride-through (LVRT) is the primary problem in terms of the safety of wind power connected to grid. The corresponding strategies for wind farms with directly-driven permanent magnet synchronous generator (D-PMSG) are provided from the present researches of LVRT technology for traditional wind farms and other new energy power plants. A review of mainstream LVRT technologies suitable for the features of wind farms with D-PMSG is reported. The mechanism and application of each technology are introduced. The advantages and disadvantages of different technologies are compared, and then corresponding suggestion on the future application is given out. The trend of LVRT technology is discussed. The economic and technical challenges for current large-scale grid-connected wind farms are pointed out for further research.

Abstract:The commutation failure is one of the most common faults in high voltage direct current transmission (HVDC) systems. In China, the control and protection system of ultra-high voltage direct current is provided with the logic of starting active DC blocking to avoid negative influence of continuous commutation failure. However, the possibility of DC blocking which is caused by the continuous commutation failure poses a certain threat to the safety and stability of operation in the power grid. The suppressing HVDC continuous commutation failure has received more attention by researchers around the world. However, the influence of harmonic on the HVDC continuous commutation failure has not been reported thoroughly yet. The method of commutation voltage-time area is applied to analyze commutation process for HVDC transmission, after which harmonic control parameters of additional control loop are obtained. In the recovery process, the influence of commutation failure on voltage dependent current order limiter is taken into account, and a method for reducing failure rate of HVDC continuous commutation with additional harmonic control is proposed. Finally, based on the CIGRE HVDC standard test system, the effectiveness of the proposed control method is verified by PSCAD/EMTDC.

Abstract:Blockchain is an important supporting technology for new information infrastructure and it is widely used in power system. According to the requirements of decentralization and trusted data exchange in power system application scenarios, the adaptability and technical architecture of power blockchain technology are analyzed. On this basis, the construction principles and specifications of blockchain technology facilities are discussed from the aspects of construction requirements, high availability of computing resources, distributed storage, multi plane network and service-oriented platform. In terms of computing resources, the design method of high-performance self-organizing blockchain all-in-one machine is proposed. In terms of network resources, a multi-plane architecture of blockchain data center in business plane, storage plane and management plane is proposed. In the aspect of service-oriented middle platform, a three-tier management system of resource management layer, blockchain management layer and platform management layer is proposed. The last but not the least, the feasibility of the research content is verified through the power information security supervision and management system.

Abstract:There are risks of frequency and voltage security and stability due to the on-going replacement of conventional synchronous power plants by intermittent generation and DC transmission. Prompt and effective emergency regulation after faults can prevent blackouts. An online pre-decision method for emergency regulation of frequency and voltage security and stability considering running condition of equipment is proposed. Considering the influence of system protection, unit primary frequency regulation, automatic generation control and automatic voltage control on node injection after failure, the quasi-steady state mode after failure is automatically identified, and the frequency and voltage pre-decision-making model with the goal of minimizing comprehensive control cost is constructed. A check plan is formed through the enumeration and combination of measures, and the check plan screening is realized based on the rapid estimation of the measure adjustment amount. The iterative search of the pre-decision strategy taking into account the frequency and voltage safety issues is realized, and the specific equipment and control quantities are given. After the actual fault occurs, emergency control is carried out by matching the fault and the post-fault problem to reduce the risk of grid accidents. The effectiveness of the method is verified by an actual grid calculation example.

Abstract:With the deepening reform of electric power enterprise and the development of big data technology, traditional power supply companies and integrated energy service enterprises have to change the present extensive marketing mode for offering rapid response to consumers' requirement. In order to improve the accurate identification of potential customers in integrated energy services, this paper marks the tags of potential customers, and proposes an improved parallel K-means clustering algorithm based on spark memory computing platform. Firstly, the selection of initial cluster center and the evaluation of sample influencing factors are improved. Secondly, based on the optimized weight of factors, cluster analysis is carried out on the data setting to identify the potential customers of integrated energy services. Finally, the recent transaction data of integrated energy service enterprises are collected, and the experimental results are carried out on a multi-node physical machine. The results show that the accuracy of improved K-means clustering model is boosted. In terms of executive effectiveness, the algorithm with high concurrency has better parallel ability than that with single thread.

Abstract:Fast and reliable location of single-phase-to-ground fault is an important technical mean to improve the reliability of power supply in distribution network. However, the faults of cable combustion are really common in the situation of long time over voltage, and it is difficult to locate the faults by traditional single-phase-to-ground fault positioning technology. Firstly, the adaptability of line wave spacing technology in the single-phase-to-ground fault location of distribution network is discussed. Then, it is used to analyze the fault characteristics of transient zero-mode and line-mode traveling waves by modulus analysis method when single-phase-to-ground faults occur in distribution lines, and a method of double ended traveling wave fault location based on the time difference of zero-mode and line-mode is proposed. Finally, on the basis of simulation model of distribution network, the effectiveness and superiority of the proposed algorithm are verified by the comparision of single-phase-to-ground fault location among proposed algorithm and other algorithms. The simulation results show that the proposed algorithm is not affected by transition resistance and traveling wave-head reflection. Also it is with no need of time synchronization, and has a good prospect for engineering application.

Abstract:Energy-intensive enterprises have great potential in consuming curtailed wind power. While there are few decision making methods to support the regulation capacity or intended regulation curve report of enterprises. Thus, on the basis of benefit analysis of energy-intensive enterprise taking part of the regulation, a decision making model which is intended to maximize both the benefit of involved energy-intensive enterprise and the consumption of curtailed wind power is proposed. Besides, the decision making method for the energy-intensive enterprise is put forward and NSGA-Ⅱ is employed for calculation in the model. A proper compromised solution is picked with application of additional constraints and satisfaction index. Finally, the effectiveness of the proposed method is verified through case analysis.

Abstract:Nowadays it is the primary objective to improve energy efficiency of distribution network planning. However, it is focused on economic efficiency by most traditional models of distribution network planning. Therefore, a model of distribution network planning for optimal energy efficiency in power system is proposed. On the basis of the data for coal consumption, the factors are discussed such as the power loss of distribution network and the planning of distributed enregy, and these factors reflect comprehensively the energy efficiency of distribution network system. An improved algorithm of particle swarm optimization (POS) is used for the solution process in the proposed model by adding inertia weights, and this algorithm improves the convergence speed the accuracy at the same time. A radiation network shape strategy is also carried out to correct results individually. IEEE 33-bus examples are selected for verification. The calculation results show that the model with fast convergence and high stability, effectively improves the energy efficiency level of the distribution system, and it makes sure that the results of distribution network planning are reasonable. The present method is verified for its effectiveness of distribution network planning.

Abstract:It has been reported that frequency domain spectroscopy (FDS) is sensitive to moisture content for oil-paper insulation. In order to reflect the characteristics of frequency domain dielectric spectrum about damp-affected defect in transformer oil paper insulation bushings, comparative study for the influence of voltage value and frequency value on dielectric loss from 0.001 Hz to 1 kHz is carried out. The results show that the value of tan δ increases slightly with time at the same value of test voltage in the first stage of the process of rising damp. At the same time, an increase of the value of tan δ is seen with the increasing test voltage. In the second stage of the process of rising damp, the value of tan δ increases remarkably with time, and reaches its peak at the time point of 120 h. At the third stage of the process of rising damp, the value of tan δ decreases with time. The value of tan δ in the whole process does not exceed the values of standard, and the value of standard is suggested to be reduced. In the low frequency band from 0.001 to 0.01 Hz, it is easy to distinguish the damp-affected bushings from the non-damp-affected bushings by frequency domain dielectric spectrum, especially at the frequency of 1 mHz. Therefore, it is recommended that FDS low-frequency test is used for insulation diagnosis.

Abstract:Because of the excellent hydrophobicity and hydrophobicity migration, silicone rubber composite insulators have an out-standing anti-pollution flashover performance, so they are often selected as the first choice to deal with pollution flashover accidents. However, in some special industrial dust areas, creepage and electric erosion occurs on the surface of composite insulators after short-term operation, which eventually develops into insulation failure. In order to study the corrosion failure process of composite insulators operated in special industrial dust areas, the samples of composite insulators from a special industrial park are taken, and the pollution degree and pollution composition, pollution flashover voltage gradient, hydrophobicity, and microscopic properties of samples are tested. Furthermore, the failure process of the insulators is analyzed. The results show that the equivalent salt deposit density (ESDD) of insulators is about 0.1~0.2 mg/cm², and the pollution composition is similar to that in chemical industry pollution area. With natural pollution on the surface, the hydrophobicity of the insulators is great, but the hydrophobicity loss, recovery, and migration properties cannot meet the operation requirements. The cause of insulation failure is the decrease of hydrophobicity caused by corona discharge. The decrease of hydrophobicity leads to electric erosion of the umbrella skirts, and finally develops into insulation failure.

Abstract:Power transformer is one of the most important equipments in power transmission, and it is of great significance to detect the aging state of transformers. In order to effectively evaluate the aging condition of oil paper insulation in transformers, the dielectric properties of oil-paper insulation under different aging degrees are studied by frequency domain spectroscopy (FDS). Besides, the relationship between the characteristic parameters and aging time is established by Havriliak-Negami (H-N) model. Then, this method is applied to the field transformer test. The results show that with the deepening of aging degree, the FDS curve increases significantly in the middle frequency band, but does not change significantly in the high and low frequency bands. The overall curve is in the shape of 'jujube nucleus'. According to the H-N model, the characteristic parameters have a good correspondence with the aging degree. This method that evaluates the aging condition of transformers is verified by the application of the field transformer.

Abstract:To simplify the sequence control process, voltage source converter based high voltage direct current transmission system requires that VSC valve group has the ability to complete online entry process when direct current (DC) side is on the short-circuit condition. For this requirement, the key points of online entry for voltage source converter based high voltage direct current valve group based on hybrid MMC are described firstly. Secondly, the key strategies of valve group online entry are analyzed by the control characteristics and DC side equivalent circuit of hybrid MMC, and an implemental scheme based on DC modulation degree is proposed. On the short-circuit condition of DC side, control objectives can be realized including smooth converter deblock, fast DC current transfer, reliable bypass switch breaking and effective sub-module voltage balance. Finally, the effecs of valve group online entry strategies are verified by real-time digital simulations.

Abstract:The non-coherence of the disturbed power system may lead to inaccurate dynamic equivalence and affect the analysis of power system safety and stability. For this reason, a quantitative analysis method for power system coherence considering the influence of damping torque is proposed. Firstly, based on the single pendulum equation, it gives a derivation of the dynamic equivalent system period characteristic expression after the power system is disturbed, and the correlation between the dynamic equivalence and the coherence of the power system is discussed. Secondly, in the scenario of determined faults, a motion period estimation method is put forward based on the upper and lower boundaries in the rotor trajectory of the equivalent system. A quantitative index is proposed by comparing the estimated and the measured periods. Then, the influence of damping torque is deeply studied, and the quantitative evaluation index of system dynamic damping characteristics is proposed based on the estimation period. Finally, the simulation examples of two typical systems show that the methods and indicators proposed are effective and reliable, which provide a reference for evaluating the safety and stability of the power system.

Abstract:Efficient and reliable fault classification is beneficial to guide the dispatchers in finding and removing the fault quickly, thus restoring system power supply promptly, so the classification is of great significance for ensuring the safe and reliable operation of the system. A fault classification method based on deep belief network is proposed to overcome deficiencies of traditional fault classification, such as shallow intelligent methods' dependence on signal processing technology and artificial experience, and the lack of feature extraction and expression for complex power system. The raw data of each phase current- voltage and zero sequence current-voltage are taken as the network input, and the features of fault state are automatically learned and extracted from the original time-domain signals to realize the fault type identification. The simulation results of the IEEE 39-bus system and real fault cases of power grid show that the proposed fault type identification method has good capability of fault feature extraction. Besides, the proposed method keeps the original characteristics of data in the process of dimensionality reduction, and it is not affected by factors including transition resistance, fault time, fault location and load size. Therefore, it identifies fault types more accurately than other traditional artificial neural networks do.

Abstract:The voltage source converter based high voltage direct current transmission (VSC-HVDC) project has entered the era of ultra-high voltage (UHV). Electric field equalizing design of the existing VSC valve cannot meet the requirement of UHV. In order to reduce the electric field density of the top tubular busbar of ±800 kV VSC valve, the modeling technologies of PTC Creo and ANSYS are applied for the three-dimention complex valve tower modeling to analyze electrostatic field finite elements. By adding a top shield plate equalizing connected with the top tubular busbar, the peak electric field densities of the top sub modules and tubular busbar are reduced obviously. The parasitic capacitance parameters of the valve tower are extracted. The influence of the top shield plate on the voltage distribution of sub-modules under the switching impulse is analyzed. The influence of distance among electric field equalizing parts on the distribution of peakelectric field is studied. The optimal electric field equalizing design of ±800 kV VSC valve is obtained, and the experiment of impulse voltageon valve tower prototype is tested. The proposed optimization measurement improves the stable operation of VSC valve in UHV application, and provides a design reference for the application of VSC valve in subsequent UHV VSC-HVDC projects.

Abstract:In order to improve the low voltage ride through (LVRT) capability of doubly-fed induction generator (DFIG), a tracking control method for grid side converter (GSC) based on state-dependent Riccati equation (SDRE) technique is proposed. The grid code requires that wind farms should inject reactive power to support voltage recovery during LVRT process. In order to improve the supporting capacity of the nonlinear state-regulator on reactive power, nonlinear reactive power tracking controller is designed in GSC of DFIG, and the state feedback control law is obtained through solving state dependent Riccati equation. On the basis of maintaining the stability of DC link voltage in LVRT process, the reactive power regulation capability of GSC is fully utilized to provide reactive power support for the power grid to avoid voltage deterioration. Finally, a 9 MW DFIG-based wind farm is built by Matlab/Simulink. The simulation results show that the proposed GSC control method has good transient performance and effectively improves the LVRT capability of DFIG through simulation verification under three phase ground faults.

Abstract:During the operation of the power system, when a large load is suddenly lost and exceeds generator adjust capability, the frequency increases, meanwhile the frequency and power oscillate or even cause power system collapsing. In the isolation grid power system with only a few generators, the regulation capacity of the generators is limited, and the conventional load need serve as production tasks and cannot participate in frequency control. The isolation grid system lacks effective frequency control method. An electronic load device based on thyristor control is proposed, and the working principal of the device and the mechanism that can be applied to the suppression of the isolation grid frequency oscillation are analyzed. The working control strategy of the electronic load is introduced and the effects of different parameters are studied by the real time digital simulation system (RTDS). The results show that the electronic load device can participate in primary frequency control by means of the load dynamic control, which provides a new control idea for the suppression of frequency oscillation in the isolated network.

Abstract:Under the premise of safe operation, to improve the economy and environmental protection of thermal power units, a combustion optimization framework is proposed, based on the historical operation data, combustion adjustment data and real-time running data. In this framework, steady-state detection, on-line calculation of boiler efficiency, data mining, nonlinear modeling, intelligent optimization and other techniques are adopted, and basic control references and real-time control increments are obtained. After reliable communication and undisturbed configuration with DCS, these results can participate in the real-time control optimization of boiler combustion, according to the running state of the thermal power unit. It has been applied in coal-fired power plant, realizing analysis of combustion states, automatic optimization of setpoints and improvement of boiler efficiency in a wide range of load. Based on the framework, the technical elements can be expanded and optimized, and it can be applied to various types of boilers and control systems.

Abstract:With the increase of renewable energy and DC external power supply capacity, it is more and more important to ensure the frequency safety of the power system. A simplified frequency simulation model is proposed, which includes the synchronous generator, governor and load model, and takes the voltage variation affecting the load response into account. The model is used to simulate the frequency response of the power system under the actual and expected faults. It shows that the simulation accuracy meets the requirements while compared with the calculation results of the BPA detailed model. The simplified model is used to evaluate the current and future frequency security situation of East China Grid. It is pointed out that the frequency security of East China Grid is facing severe challenges in 2025. The primary frequency response services of the conventional synchronous generator need to be improved and the proportion of DC external power supply injecting power needs to be limited to ensure the frequency safety of the power system. It is also suggested that the renewable energy should provide virtual synchronous generator control and primary frequency control to realize the friendly connection of new energy generating units to the grid and meet the needs of the grid development in the future.

Abstract:The existing power grid security risk assessment methods do not fully consider the impact of different primary equipment, load importance and secondary system performance. Grid static security risk assessment method considering the influence of secondary system based on the improved severity model is proposed. Firstly, the effects of hidden faults of relay protection, automatic reclosing success rate and automatic load-cutting devices on risk assessment are analyzed, and corresponding risk assessment model is established. Then, by quantifying the importance of lines, buses and loads, a risk index quantification method of the improved severity model is proposed which introduces the importance degree factor into severity model. The proposed method is applied to the improved IEEE-RTS79 testing system. It is verified that the proposed model and method can effectively identify the weak links in the power system, and are more in line with the system reality than traditional risk assessment methods. The proposed method can provide a reference for power system operation, maintenance, and risk management.