Abstract:The grid?connected inverter?interfaced distributed generation transforms the power supply mode of the system from the original single power supply to a multi?power supply, which brings many challenges to the traditional relay protection, and may cause the protection device to fail or malfunction. This paper takes the inverter?interfaced distributed generation with low voltage ride?through characteristics as the research object and analyzes its influence on relay protection after it is connected to the distribution network. A multi?objective programming model considering the capacity and comprehensive cost of the inverter?interfaced distributed generation is constructed and also takes into account current protection, node voltage and location constraints without increasing the investment cost of the distribution network relay protection. The particle swarm optimization algorithm is used to analyze an example in the IEEE33?node system. The results show that the configuration scheme of the inverter?interfaced distributed generation considering the current protection constraints can ensure the regular operation of the original protection device of the system when the fault occurs, which verifies the necessity of considering the current protection.

Abstract:With the advancement of carbon?neutral goal and the deepening of electricity market reform, it is of practical significance to study multi?agent game on power generation side of electricity wholesale market to improve renewable energy permeability. Aiming at asymmetric market position, a Cournot?Bertrand hybrid game model considering market share preference with carbon transaction cost is established. Performing mathematical reasoning and numerical analysis, equilibrium characteristic value and local stability region are given. Finally, the influence of carbon emission coefficient, horizontal difference parameter and market share preference parameter on equilibrium is studied. Simulation examples show that with the decrease of horizontal difference parameter, market profits are significantly reduced, and electricity output of thermal power generation suppliers shows a U?shaped trend. Considering market share preference, profit?seeking power generation suppliers will take the competitive strategy of controlling power supply and raising electricity price to maximize profits.

Abstract:In the intelligent frequency control strategy with large?scale wind power grid?connected system, only considering the CPS control criterion can easily cause the frequency off?limit in a short time, which seriously affects the control effect of the intelligent AGC control strategy. This paper proposes a multi?objective collaborative reward function reinforcement learning algorithm (TOPQ?MORL) intelligent frequency control strategy, which constructs a collaborative reward function that takes into account the multi?dimensional frequency control performance evaluation criteria, and realizes the coordinating evaluation of multi?dimensional frequency control performance standards on the time scale .The TOPQ learning strategy is used to optimize the action space of the agent globally, which effectively solves the problem of poor calculation efficiency of the Q function linear weighted multi?objective reinforcement learning algorithm under the traditional greedy strategy. The simulation results of the AGC control model of the standard two?region interconnected power grid shows that the intelligent AGC control strategy proposed in this paper can effectively improve the frequency control performance and improve the frequency quality of the system on the full?time scale obviously.

Abstract:In response to the problems of high cost and excessive fault current under fault conditions in existing hybrid DC circuit breaker topologies, this paper proposes an improved current limiting DC circuit breaker topology based on the existing traditional DC circuit breaker topology. The current?limiting branch of the topology was connected to the circuit after the fault occured, effectively limiting the rise of fault current. The transfer branch consisted of thyristor and IGBT in series to reduce the number of IGBT.A pre?charged capacitor was used to provide the reverse voltage for the thyristor, and a pre?charged scheme was proposed. The operation principle was analyzed based on the proposed topology, and then the parameters were designed. Finally, a simulation model was built in PSCAD/EMTDC, compared with the breaker with traditional topology, to verify the reliability and economy of the proposed topology.

Abstract:As the front end for users, the stable and safe operation of distribution networks are directly related to the reliable power supplies. However, the large amount of branches in 10 kV distribution networks makes the transmission conditions more complicated. When a fault occurs, it is difficult to determine its specific location, which will affect the power supply. In order to solve this, this paper uses particle swarm optimization (PSO) to improve artificial fish swarm optimization (AFSA). The feasibility of AFSA?PSO algorithm is tested by a case study, where it is applied in a standard distribution network model to verify its practicality and superiority. The results show that the AFSA?PSO algorithm can accurately reflect the single and multiple point failures in distribution networks, and this algorithm is better in both iteration times and convergence speed.

Abstract:The rapid development of intermittent new energy sources such as photovoltaics and wind power has increased the demand for energy storage in microgrids. Shared energy storage and flexible load scheduling can optimize load curves and reduce energy storage costs. To this end, a two?stage robust dispatching optimization method for microgrid considering shared energy storage and flexible load is proposed. Firstly, flexible loads are scheduled in advance based on demand response in the day?ahead scheduling stage. Then, in order to compensate for the decision?making in the day?ahead stage, the charging and discharging status of the shared energy storage is modified hourly through the cloud platform during the day. In most cases, the prediction information considering the uncertainty is near the expected value. In order to seek the balance between the economy and robustness of the microgrid operation, a two?stage robust model based on the expected scenario is adopted, and the column?and?constraint generation (C&CG) algorithm is used to obtain the robust and feasible solution. Simulation results show that the flexible load and shared energy storage can be effectively coordinated to adapt to the uncertainty of renewable energy and load demand, while maximizing the benefits of the microgrid, thus effectively balancing robustness and economy.

Abstract:With the proposal of "double carbon" goal, many new energy sources are connected to the power grid, and the flexible DC transmission system represented by modular multilevel converters (MMC) has been widely used in engineering. Electromagnetic transient simulation plays an essential role in the planning and operation of the MMC system, but the accuracy of the large?step electromechanical transient simulation needs to be improved, and the small?step electromagnetic transient simulation takes too long to meet the development needs of MMC. Therefore, based on the basic idea of the hybrid simulation, the MMC detailed equivalent model is divided into AC and DC parts, the interface equivalent model is established, and the data interaction algorithm is proposed, so as to realize the long?step simulation of AC system and small?step simulation of DC system. The simulation verification of the MMC system based on PSCAD/EMTDC shows that the simulation accuracy of the hybrid simulation method is obviously improved compared with the large?step electromechanical transient simulation, and the simulation time is greatly shortened compared with the small?step electromagnetic transient simulation.

Abstract:Overhead distribution poles are widely distributed with large quantity. However, the poles are prone to overturning under extreme weather conditions, which threaten the power supply of local areas or even the entire distribution line. How to apply scientific and effective methods to simulate and analyze the anti?overturning ability of poles has now become a key technical issue in the construction and transformation of distribution networks. To address the problem, this paper takes 10 kV reinforced concrete poles as an example, the load and internal force considering meteorological conditions are calculated first. Then, based on the FLAC3D software, a simulation modeling and analysis method for the anti?overturning ability of distribution poles is proposed. Finally, a calculation analysis of example is carried out in combination with soil parameters in a certain area of Henan. The deformation damage process of the foundation under extreme weather conditions is analyzed in detail and the load?displacement curve is drawn. The contribution of this research can provide technical support for the installation and reinforcement of distribution poles.

Abstract:This paper analyzes the influences of the attenuation of high frequency signals by the HVDC transmission lines and line boundaries on the current HVDC transmission line protections. The frequency characteristics of boundary and line are also studied. The traditional traveling wave protection approaches based on the derivative of electrical quantity generally have poor tolerance to transition resistance. To solve this, a single?ended protection method based on the second?order micro?component of electrical quantity is proposed, where the transient fault component information after the second?order differential transformation will be amplified, and the difference of second?order differential variables inside and outside the boundary are utilized to judge the fault. In the proposed DC protection scheme, full line protections can be realized only by the single?ended fault transient information. The simulation analysis is carried out in PSCAD/EMTDC, and the results show that this criterion can accurately distinguish internal and external faults, and select fault poles, which indicates its strong ability to withstand the influence of transition resistance and long transmission lines, thus can realize full?line quick action.

Abstract:With a large number of renewable energy stations connected to power grid, their stochastic power outputs have a great impact on the reactive power and voltage control of power system. To this end, a sample robust reactive power optimization approach is proposed considering the power output uncertainty of renewable energy stations. Firstly, considering the variation of generator active power output caused by the random output fluctuation of renewable energy stations, an uncertain reactive power optimization model of power system is established. Secondly, based on the sample robust optimization method, the optimization model is transformed into a two?level optimization model. The upper?level model searches for the generator terminal voltages, transformer ratios and number of shunt capacitor switching groups that minimize the active power network loss under the average worst?case scenario. The lower?level model searches for the worst scenario in the box uncertainty set near each sample point. Next, in order to consider the correlation between the power output of the same type of renewable energy stations, the sample points in the independent normal space are transformed into the sample points in the relevant original sample space by using the relationship between Nataf transform and its inverse transform. Then, the column and constraint generation algorithm is used to solve the two?layer optimization model alternately and iteratively. Finally, through the analysis and calculation of the modified IEEE 39 bus system and the actual Guizhou power grid, the correctness and effectiveness of the proposed method is verified.

Abstract:In order to avoid the frequent occurrence of cable cutting accidents in urban construction, the cable path should be located scientifically and reasonably. Taking three core cable as the research object, locating characteristic point and locating characteristic value K are introduced as the judgment basis of magnetic induction intensity above the cable, and the cable laying path is determined by the distribution characteristics of magnetic field around the cable. Then, the factors affecting the change of magnetic field around the detection points?wire core position, cable buried depth, laying spacing and different paths are analyzed by using this criterion. Simulation results show that the value of K can reflect the change of magnetic field environment around the cable well. The characteristic points appear near the top of the cable. Finally, the accuracy and feasibility of the criterion are verified by finite element and experiments. The principle of the proposed method is simple and portable, which provides an important reference for realizing intelligent and modern cable path positioning.

Abstract:In order to study the intrusion range and degree of subway stray current into the AC power grid, a mathematical model of stray current which is based on the degradation of insulation performance of rail insulation fasteners under actual operation is established, and the stray current leakage of each sleeper is derived. The subway stray current is discretized into a finite point current source according to the number of sleepers, and the Green's function is solved based on the complex image method. The ground potential distribution calculation model caused by the subway stray current is also established, and the commercial grounding software CDEGS based on the boundary element is deployed to verify the method accuracy. The influence of traditional sensitive factors, such as stray current leakage and soil structure, on the ground potential distribution along the urban rail line and the surrounding ground potential fluctuations under the operation of multiple trains in a multi?line transportation hub area are discussed.

Abstract:Aiming at the potential large number of controllable loads on the demand side of the community integrated energy system, an optimal dispatch model of the community integrated energy system with energy storage considering the demand side controllable load is proposed. Firstly, the framework of the integrated energy system is analyzed and a mathematical model including modules of energy production, conversion, and storage is established. Secondly, three types of load response models are established according to the response types of demand?side electric and thermal controllable loads. Finally, with the goal of minimizing the comprehensive operating cost of the community integrated energy system in a dispatch cycle, an optimal dispatch model of the community integrated energy system considering the controllable load is constructed. The simulation results of calculation examples show that the participation of controllable loads and energy storage equipment has a positive impact on improving system economy and can effectively reduce the peak?to?valley difference of system load, and therefore verify the rationality of the model proposed in the paper.

Abstract:Real?time monitoring and timely diagnosis of transmission line faults are the prerequisite for the safe operation of transmission lines. Due to the complex shooting environment of transmission line images, individual detection or segmentation can not meet the real?time requirements, and it is difficult to extract small parts and occluded parts in the picture. In order to more accurately locate the target position, detect and segment small parts and occluded parts in the picture, an improved fully convolutional instance?aware semantic segmentation （FCIS） simultaneous detection and segmentation method for transmission line components is proposed. This method introduces the idea of region of interest (ROI) Align algorithm into the FCIS model, and proposes position sensitive inside/outside?region of interest (PS2?ROI) Align, which uses bilinear interpolation method to effectively solve the problem that the ROI in the input image feature map does not match the position information in the original image. And the gradient backpropagation algorithm is used to solve the problem of poor detection and segmentation accuracy due to the difficulty in extracting the features of small fittings and occluded fittings in the image. The detection and segmentation experiment was carried out on the transmission line detection and segmentation data set of this structure. The results showed that the small targets that could not be detected and segmented in the modified figure had indicators and masked detection segmentation. Compared with other detection models, the FCIS model has the highest mean average precision (mAP), which is 1.73% higher than before improvement.

Abstract:Traditional microgrids have problems such as lack of interaction among users and low utilization rate of renewable energy. Considering the operation mode of photovoltaic (PV) output and energy storage (ES) in smart buildings under different climatic conditions, this paper proposes a micro?grid operation mode based on multi?agent interaction to optimize the user's energy cost of the micro?grid and improve the ability to absorb renewable energy simultaneously. First, this paper compares and analyzes the classic operation mode of microgrid and the multi?agent interactive operation mode, and studies the energy consumption behavior of each agent in different modes; Then, the contract price is set flexibly to improve the efficiency of the energy interaction between the smart building operators and the electric vehicle (EV) charging station (CS) operators in the microgrid, and the energy flow inside the microgrid under the multi?agant interaction mode is analyzed; Finally, considering the impact of environments on PV output, the energy cost of users in the microgrid under different operating modes and the microgrid’s capacity of renewable energy consumption are analyzed. The simulation results show that the multi?agent interaction mode of the microgrid increases the consumption rate of renewable energy from 67.83% of the classic operation mode to 100% when the light conditions are sufficient, and at the same time optimizes the energy cost of smart building operators and CS operators.

Abstract:With the rapid development of distributed generation, energy storage and intelligent ring network cabinets in the distribution network, the active and intelligent distribution network provides strong support for its island operation. To solve the problem of islanding of active distribution network (ADN) after a fault in the upper?level power grid, a robust optimal partition model is established with the consideration of the least comprehensive loss of load outage. The comprehensive loss of power outage takes into account the compensation cost of cutting off the interruptible load and the load loss cost caused by non?agreement blackout. The loss cost is modeled by piecewise linearization technique, and a unified linear constraint is constructed by adding logical variables. In order to avoid the frequent switching on and off of any load in the island operation scheme, the continuous state constraint of load power failure and its linearization method are proposed. Further, considering the uncertainty of the output characteristics of distributed energy in ADN, the deterministic model is transformed into a two?stage robust optimization model, and the flexible adjustment scheme of robust adjustment coefficients is introduced to adjust the scheme conservativeness. At the same time, the model is solved based on duality theory and column generation algorithm. Cases studies verify the effectiveness of the proposed model and method.

Abstract:The quantitative analysis and formation mechanism of the decomposition products of (CF₃)₂CFCN/CO₂ mixture under breakdown discharge have some defects. Therefore, the decomposition products of (CF₃)₂CFCN/CO₂ gas mixture after multiple AC breakdown discharge are quantitatively detected by gas chromatography-mass spectrometry, and the difference of product contents are analyzed in this paper. In addition, based on density functional theory, the decomposition and product formation path of (CF₃)₂CFCN/CO₂ mixed gas and the stability of (CF₃)₂CFCN are analyzed from microscopic view. The enthalpy change and reaction rate of each reaction at different temperatures are calculated. The research shown that the decomposition products of (CF₃)₂CFCN/CO₂ mixed gas are mainly CO, CF4, C₂F6, C₃F8, CF₃CF₂CF₂CF₃, C₂F4, C₃F6, CF₃C≡CCF₃, CF₂=CFCF₂CF₃, CF₃CN, C₂F5CN, C₂N₂ and HF, and the decomposition products are mainly small molecular compounds. The volume fractions of saturated and unsaturated fluorocarbons trend to decrease with the increasing carbon atoms number, and the total volume fractions of saturated fluorocarbons are relatively larger. The increasing temperature accelerate the decomposition of (CF₃)₂CFCN to generate CF₃ radicals. The relevant results reveal the decomposition characteristics of (CF₃)₂CFCN/CO₂ mixed gas under AC breakdown discharge, which provides a reference for the application and maintenance of mixed gas.

Abstract:In order to study the breaking mechanism of 10 kV overhead insulated lines by lightning, an ablation model of insulated conductors is established based on COMSOL, and the ablation status of the conductors when suffering lightning current and power frequency short?circuit current is simulated respectively. Then the force model of the conductor is established to analyze the conductor force when ablating. Simulation results indicate that, the lightning current only leads to one perforation on the conductor insulation layer. The power frequency arc can ablate and fuse the insulated wire in 1.3 s without considering the effect of external forces. The mechanical simulation results of the insulated conductor show that the tension of the conductor suffers abrupt changes at the ablation site, and the electromotive force between the wires and the electromagnetic thrust of the arc act on this site. Combined with theoretical analysis, it is concluded that the main reason for the line breakage caused by lightning is the combined action of heat and mechanics, which results in plastic deformation and brittle fracture. The simulation research provides a reference for lightning protection of 10 kV overhead insulated conductors.

Abstract:At present, the communication of most substations is based on the IEC 61850 standard, but its performance is lagging behind modern communication technology, which hinders the comprehensive transition of the substation to intelligent lightweight communications. To this end, a communication mapping method is proposed, which combines the confident binary object representation (CBOR) format and maps the IEC 61850 standard to the constrained application protocol (CoAP). Firstly, a COAP mapping URI and request method of commonly used IEC 61850 services are given. Secondly, the COAP subscription mode is expanded to resolve the IEC 61850 to COAP mapping requirements. Finally, the communication mapping model is set to verify the effectiveness of the proposed method. Compared to existing WS?SOAP and HTTP mapping schemes, COAP+CBOR requires only 44% and 18% of information size, 71% and 85% communication time, which alleviates the problem of limited equipment and network resources in the power grid.

Abstract:Aiming at the problem of fault location errors caused by the uncertainty of travelling wave velocity, this paper proposes a new fault location method that requires no wave velocity and transmission line radian information. Firstly, a denoise method through multi?scale wavelet transform for the fault signal is described. Secondly, the arrival time parameters of initial traveling wave at different buses are measured. Furthermore, the influences of wave speed and radian of transmission line are eliminated by those time parameters in fault distance expressions. In addition, this paper compares the different fault location results with and without transformers. The simulation results show that although the error will be larger when considering a transformer, this method has higher accuracy and reliability in most cases.

Abstract:The application of ultrasonic sensing technology is expected to achieve online monitoring of cable partial discharge. Therefore, it is necessary to study the acoustic frequency and amplitude attenuation rules of partial discharge in a certain type of cable. Taking the YJV?185 mm2 type 10 kV XLPE power cable as research object, this paper carries out simulation calculations of two sets of different frequency acoustic sources and a set of "needle?hole" partial discharge experiment. The frequency and amplitude attenuation rules of partial discharge acoustic signals in the cable are studied. Research results show that the attenuation law of acoustic waves in multi?layer complex media is inconsistent with that in a single medium. The influence of the frequency composition of the sound source on the detectable sound frequency and amplitude of the cable surface cannot be ignored. The acoustic source model of the "needle?hole" partial discharge in the cable can be approximated as a Gaussian pulse with a bandwidth of 1 MHz, a peak time of 1μs, and a frequency in the range of 0~1.5 MHz. The radial attenuation coefficient of the "needle?hole" partial discharge acoustic signal in the cable sample is about 8.17 dB/mm, the axial attenuation coefficient on the cable surface is about 0.43~0.52 dB/mm, and the detectable acoustic frequency range on the cable surface is 0~40 kHz. The center frequency of high sensitivity sensors is recommended to be designed at 20~40 kHz, while the design of distribution density of distributed detection sensors require specific research on specific issues.

Abstract:In order to improve the accuracy and reliability of circuit breaker test robot wiring, a locating method with background augmentation and improved YOLOv4 on the basis of binocular vision and deep learning object detection technology is proposed in this paper. Background mixed shear method is adopted in the proposed method to solve the low generalization ability and accuracy problems caused by insufficient training background features. Therefore, the accuracy and reliability of wiring under the background disturbance such as different test sites and people walking are increased. Furthermore, the backbone of YOLOv4 is replaced to Mobiledets to optimize the reasoning period of the object detection model. So that the efficiency of robot wiring is improved. Simulation and test results show that the accuracy of detection model based on the proposed method is 99.9%, the robot wiring accuracy is 98.8%, and the wiring time is reduced by 57 s. Comparison and analysis indicate that, the method proposed in this paper is superior to other methods in robot wiring accuracy and time, which can provide technical support for the practicability of breaker robot test platform.

Abstract:Residual current operated circuit breaker directly affects the safety and reliability of low?voltage distribution system. In order to study the reliability of residual current operated circuit breaker, the performance degradation process is studied by using the modeling method based on degradation distribution, and its service life is predicted. Firstly, the failure mechanism of residual current operated circuit breaker is analyzed, and then the accelerated degradation test of residual current operated circuit breaker is designed and implemented. The reliability analysis model that the degradation quantity obeys the normal distribution is established, and the parameters in the model are estimated by the least square method, so as to evaluate the reliability of residual current operated circuit breaker and draw the reliability curve.

Abstract:With the continuous expansion of UHV AC/DC interconnection scale, on?line high?precision and fast transient stability assessment (TSA) is very important for the safe operation of power grid. To this end, a TSA method based on gating spatial temporal graph neural network (GSTGNN) is proposed and the time adaptive method is used to improve the accuracy and speed of TSA at the same time. Firstly, in order to reduce the impact of dynamic topology on TSA after fault removal, GSTGNN is used to extract and fuse the key features of topology and attribute information of adjacent nodes to learn the spatial data correlation and improve the evaluation accuracy. Then, the extracted features are input into the gated recurrent unit (GRU) to learn the correlation of data at each time, and adjust the stability threshold to quickly output accurate evaluation results. Meanwhile, in order to avoid the influence of the quality of training samples, the improved weighted cross entropy loss function with K nearest neighbor (KNN) idea is used to deal with the unbalanced training samples. Through the analysis of an calculation example, it is verified from the data visualization that TSA method can effectively improve assessment accuracy and shorten assessment time.

Abstract:Aiming at the problem of large?scale air conditioner loads participating in the frequency regulation of renewable energy power systems, a frequency regulation method based on model?free adaptive control (MFAC) is proposed. Firstly, a multiarea interconnected power grid model including large?scale wind power generation is established. The wind power generation system participates in power grid frequency regulation through virtual inertia control. Secondly, the equivalent thermodynamic parameter (ETP) model is used to build fixed?frequency and variable?frequency air conditioner models, and the frequency regulation model of air conditioner loads is established through large?scale air conditioner aggregation. Then, the automatic generation controller (AGC) and air conditioner controller (ACC) of multiarea interconnected power grid are designed based on the MFAC algorithm, of which the advantages are completely data?driven, no model parameters, strong anti?interference ability and suitable for nonlinear time?varying systems, thereby realizing the control of large?scale air conditioner loads participating in the frequency regulation of renewable energy power systems. Simulation studies are carried out in a three?area interconnected power system. The simulation results obtained under the conditions of load disturbance, wind power fluctuation and ambient temperature change show that the proposed MFAC frequency control algorithm can control large?scale air conditioner loads and effectively suppress the frequency fluctuation caused by wind powers and load disturbances.

Abstract:The frequency source of the power clock synchronization system is affected by factors such as changes in the external environment or self?aging, and there will be frequency drift problems, which can not maintain long?term stability. A low?cost crystal oscillator frequency taming calibration scheme based on Beidou pulse per?second signal and improved Kalman filter algorithm is proposed. Firstly, take the Beidou second pulse signal as the time reference and use Kalman filter to eliminate the random error contained in the reference; Secondly, in view of the divergence of Kalman filtering prediction results and large errors, the RBP neural network is used to correct the filtering errors online in real time to improve the filtering performance; At the same time, aiming at the problem of jumping outliers in Beidou pulse per?second, an outlier detection and weighted correction method is proposed based on innovation change rate. Experimental results based on simulation data show that the proposed method can effectively improve the frequency accuracy and stability of the frequency source of the power clock synchronization system, and has strong adaptability to jump outliers.

Abstract:The smart meter clock battery can provide power for the clock chip in the meter during the power down state, and premature undervoltage of the clock battery is one of the common faults of the meter in recent years. To this end, through the analysis of the constant temperature degradation data of the clock battery, an empirical method to test and predict the battery power in the meter is proposed. Then, based on the domestic new dual?core smart meter with operating system, a management core operating system application is design for on?line power monitoring of the clock battery in the meter. This application regularly detects the battery power of the clock, gives an approximate battery life estimate, and reports abnormal conditions. The experimental analysis shows that the application can effectively monitor the battery capacity.

Abstract:To deal with a variety of operation modes of distribution network and ensure the selectivity and sensibility of feeder protection, the recording device is introduced to the feeder and installed at proper position to record operation status of feeders in various operation mode. First, the recording files will be analyzed after being uploaded to protection setting & recording data management system. Second, the fault position will be identified with the help of network topology analysis. Third, according to installation of recording device and recording time sequence, the recording data weight is calculated. Last, the protection setting will be revised by multiple regression algorithm. The protection settings will be linked to recording characteristic data and feeder operation modes to join into feeder recording character map, which is a helpful investigation of the optimization of distribution network setting management work.