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Modular multilevel converter (MMC) tends to cause resonance instability in interconnected systems. Current studies on the stability of MMC mainly focus on high-voltage and large-capacity power systems, while the impedance modeling process of MMC ignores the harmonics of the submodule (SM) capacitor voltages and the influence of voltage feedforward control. The applicability of the MMC impedance model with fewer submodules is doubtful. According to the circuit structure and control mode, the AC-side sequence impedance model of the MMC is established, which takes into account the capacitor voltage balance control of submodules and voltage feedforward control. Based on the RT-Lab control hardware-in-loop (CHIL) test platform, the MMC impedance frequency scanning was carried out to verify the accuracy of the impedance modeling method. The influence of control parameters in different frequency bands on the impedance characteristics of MMC was studied. The AC terminal voltage feedforward causes phase lag in the mid-/high-frequency range and increases the risk of resonance. In the low-frequency range, the dynamics and control of capacitor voltages reduce the impedance magnitude of MMC. Using the resonance phenomenon of an MMC connected to a weak grid as an example, the high-frequency resonance mechanism caused by control parameters is analyzed from the perspective of the negative damping effect. The simulation results show that the detailed wideband impedance model can improve the accuracy of the stability analysis results.

In this paper, based on the pseudo-totem pole (PTP) circuit, a family of five-level PTP dual boost converters (PDBC) is proposed. Dual boost converter has some unique advantages such as no bridge arm shoot-through risk and no switch body diode reverse recovery problem, so that it has a good application prospect. Compared with conventional three-level PTP converters, PDBCs has higher power density, higher efficiency, and low voltage and current stress. The topological derivation process, working principle, modulation and strategy of the topology are analyzed firstly. Further, the number of power devices, the switches voltage and current stress of the proposed topology is analyzed. Finally, a representative five-level PDBC experimental prototype is designed with AC input 220V/50Hz, DC output 400V/1kW, and peak efficiency of 98.27%. The experimental results show that the five-level PDBC proposed in this paper has higher efficiency and verify the correctness of the topology.

Maximizing two-way arterial bands often plays a critical role in signal coordination along urban arterials. With an increasing number of signals involved, the arterial bands tend to shrink to some extent resulting in inefficient arterial signal coordination, and not all vehicles fully take advantage of the arterial bands to travel through the entire corridor. In response to that, system partition is a technique for handling arterials with many signals. Rather than designing end-to-end signal coordination, efficient arterial signal coordination is highly reliant on traffic origin and destination (OD) patterns on the arterial, which have been difficult to obtain using conventional data collection methods. The emerging big data sources, such as connected vehicles, provide great potential to gather such invaluable OD information for improving arterial signal coordination. This research proposes an easy-to-implement OD-based partition technique to improve arterial signal coordination by utilizing vehicle trajectory data automatically collected from connected vehicles. The proposed signal timing technique was tested using an arterial with 17 signalized intersections in Orange County, California. The results demonstrated that the OD-based partition technique improved the arterial average travel speed by 2.7% and 12.1% for the eastbound and westbound directions, respectively. At the same time, the proposed technique shortened the arterial average travel time by 2.6% and 11.1% for the eastbound and westbound directions, respectively. The total travel time was shortened both for the main-street and side-street major traffic flows.

Based on the working principle of high-speed electromagnetic repulsion mechanism, the main factors influencing the motion characteristics of the repulsion mechanism and their variation rules are analyzed and verified through calculation and simulation. Because of its fast moving speed and large kinetic energy of moving parts, it will produce large operating impact and bounce. Buffer performance is of great significance to the safe and reliable operation of high-voltage circuit breakers. Moreover, aiming at the above problems, this article studies the repulsive mechanism and its buffer problem. First, the mathematical model of the electromagnetic repulsive opening mechanism is established, and the electromagnetic repulsive force of the electromagnetic repulsive opening mechanism is deduced. The simplified model of the electromagnetic repulsive mechanism and the finite element simulation mesh are divided, and the discharge circuit model of the energy storage capacitor is designed. Then, the simulation results show that as the repulsion disk spacing, radius, storage, capacitor voltage, turn ratio, and other parameters adjust, the peak value of electromagnetic repulsion force increases, which can reach more than 60 kN, and the displacement of the mechanism can reach 84 mm within 5.5 ms. Finally, the drop weight contrast test is carried out. When the landing height is 300 mm, 500 mm, and 700 mm, respectively, the energy absorption rate of the buffer in the three groups of tests is higher than 85%. Through the speed curve simulation after the installation of buffer, it is verified that the elastic clay buffer is suitable for the buffer mode of fast switch, and a high-speed buffer device based on the elastic clay material is proposed.

Among the distribution network faults, single-phase grounding faults have the greatest probability. The faults are often accompanied by arcs in the grounding point soil. This type of fault current has a small amplitude and seldom can obtain field record data. A soil arc grounding fault is tested on a realistic-distribution-network-experimental-platform (RDNEP), and it is concluded that the soil-arc-grounding-fault (SAGF) has three main characteristics: hysteresis, nonlinearity, and asymmetry. By comparing with the characteristics of common arc models, it is pointed out that common arc models cannot accurately fit the characteristics of SAGF. This paper proposes and establishes a double exponential function arc model. Through the comparison of simulation waveforms with experimental data, it is verified that the numerical simulation method proposed in this paper can simulate the development process of SAGF more accurately. Furthermore, the equivalence of RDNEP is verified on the real distribution network system (RDNS). On this basis, analyzed the arc characteristic changes of different SAGF development cycles. Finally, by studying the applicability of the proposed model in simulating ground faults in grass and gravel roads, it is verified that the model proposed in this paper has a strong generalization capability. The research has laid a theoretical foundation for a detection algorithm that is based on the characteristics of SAGF.

The study of ground motion effects at river valley sites is an important guide to site selection and seismic design. In this paper, FLAC3D numerical simulation is used to explore the influencing factors of a river valley site. By selecting four influencing factors with different input ground motion spectrum characteristics, ground motion intensities, site slope angles and depth-to-width ratios, orthogonal test forms are designed to determine the calculation conditions, and numerical simulation analysis is conducted. The study obtains the ranking of influencing factors for the top section of the slope, slope section and valley bottom section at different locations of the river valley site. The main influencing factor is the spectral characteristics of the input ground motion; the main influencing factor of the slope section and the valley bottom section is also the spectral characteristics of the input ground motion; and the overall analysis of the amplification effect pattern of the trapezoidal valley site shows that the amplification effect of the valley bottom site is the smallest and that the amplification of the slope top site is the largest.

The invention belongs to the field of large power grid transient frequency control strategies, and particularly relates to a wind/thermal power combined frequency control method based on a virtual weight coefficient. The method comprises the following steps: establishing a comprehensive frequency response model; constructing a robust comprehensive frequency response model containing RES; performing inertia control analysis; and performing frequency secondary response analysis. According to the invention, a robust comprehensive frequency response model containing virtual inertia support and steady-state frequency secondary support is constructed; the power contribution of a fan under different time scales can be controlled by detecting the frequency change rate of the system; an additionalfrequency secondary support control strategy establishes a function relationship between a fan virtual inertia coefficient and system frequency sensitivity; the method dynamically responds to the full-time-scale frequency requirement of the system, achieves the power grid transient state and steady state comprehensive frequency expectation control performance under the wind power high permeability, improves the safe and stable operation level of a power grid, provides double-frequency support for the power grid under the transient state/steady state full-time scale, and further guarantees thesafe and stable operation of the power grid and a unit.

Dividing wall column (DWC) is an advanced technology which could decrease energy consumption. As the vertical wall inserted in DWC increases the degree of freedom of systems, the control becomes more difficult than the conventional columns. In this study, the mixture glycols (1, 2-propanediol+ 1, 3-butanediol+ 1, 4-butanediol) were taken as feed, an optimized DWC structure was proposed, and three control structures for DWC were tested by ± 10% feed disturbances. The temperature control structure (CS1) was hard to control the system while composition control structure (CS2) and flow rate-composition cascade control structure (CS3) had good performance on controlling the DWC. It showed that CS3 was superior to CS2, as CS3 could stabilize the DWC within 4 hours, and the maximum deviations of the three products, namely 1, 2-propanediol, 1, 3-butanediol and 1, 4-butanediol, were 0.07%, 1.44%, and 0.46% respectively, while CS2 could realize the stability within 7 hours, and the corresponding numbers were 0.35%, 2.78%, and 0.41%, respectively.

The increasing global energy and environmental problems are encouraging to the development and utilization of renewable and clean energy in various countries. Wind power is one of the major source in large-scale renewable energy applications. However, the frequency regulation becomes a critical issue while the technology is spreading. Research on the frequency modulation (FM) technology of wind turbines and its control strategy for future power grids become significant. The paper proposes a novel coordinated frequency control strategy with the synchronous generator to solve the unmatched state between the output power of the doubly-fed wind turbines (doubly-fed induction generators) and the grid frequency, combined with the frequency response characteristics of the synchronous generator. The FM coordination strategy is formulated by the modulation coefficient from current wind speed and operation mode of each wind turbine. By coordinating the FM output of the doubly-fed wind turbine and the synchronous generator within the allowable range of frequency deviation, it will achieve the dual goal of reducing the frequency regulation pressure of the synchronous generator and indirectly reducing the abandoned wind volume of the wind turbine. The simulation is carried out on the MATLAB/SIMULINK platform. The results show that the presenting variable coefficient frequency modulation strategy could significant smooth the wind power fluctuation, and allow the reserve power of the doubly-fed wind turbine can fully engaged in frequency modulation which will reduces the frequency modulation pressure of the synchronous generator in the system.

The essence of the mathematical model of disconnectors' multiple reignition arc is the repeated breakdowns of SF6. In this study, the kinetic properties of microparticles are studies based on the streamer discharge theory, and a fluid arc mathematical model applied in centimetre clearance is established. Ultra-High Voltage (UHV) disconnector manufactured by Pingao Electric Co. Ltd of Henan Province is selected as the object and the resistance change process of contact clearance multiple reignition arc is simulated by finite difference method-finite element method-flux corrected transport self-programming in MATLAB based on the chamber structure and operating characteristics. UHV gas-insulated switchgear very fast transient overvoltage (VFTO) test platform is built to gain the characteristics of VFTO waveforms generated by the disconnector's operation. Compared with simulation results, the test data shows that the fluid arc mathematical model can scientifically explain the dynamic development process of microparticles in the contact clearance and the calculation results are consistent with the test data. In addition, the arc fluid mathematical model combines the structure and operating characteristics of the switch with the development process of microparticles, which can better guide the design of the switch, and provide a theoretical basis for the suppression of VFTO with the disconnector itself.

The single input single output (SISO) system with known strong interference is widely used in various occasions. Due to its strong interference, the control accuracy is hard to guarantee. To solve ...

In this article, we take a 126 kV single-break vacuum circuit breaker as the research object and study the application of high-energy-density PM motor in the high-voltage circuit breaker for the first time. The PM motor maintains maximum power density and torque density during the start-up phase. Note that most of the faults of high-voltage circuit breakers are mechanical faults. We designed a set of mechanical fault prediction systems for high-voltage circuit breakers. We present the prediction method of the opening and closing action curve of the high-voltage circuit breaker. It is inspired by Chaos Ant Colony Algorithm (CAS) and an optimized Long- and Short-Term Memory (LSTM) cycle neural network. We constructed the main structure of the neural network expert system and established the fault prediction model of the high-voltage circuit breaker, based on the LSTM cycle neural network, optimized by CAS. We used the improved least-square method to achieve the operation accuracy of the phase control switch. Finally, we completed the development and experiment of the prototype.

The peak load regulation ability of thermal power unit is closely related to the deep peak load regulation mode of thermal power unit and the peak load regulation strategy of power system. Meanwhile, the deep peak-load regulation ability is affected by many factors. In order to meet the increasing demand for peak load regulation, it is necessary to study the economy of deep peak load regulation of thermal power units under the condition of large-scale wind power grid connection from the perspective of thermal power enterprises, wind power enterprises and society. In this paper, taking full account of the current deep peak load regulation capacity and coal consumption cost control strategy of thermal power units, considering the economy of the deep peak load regulation stage of thermal power units, a unit combination optimization model with the joint constraint of "deep peak load regulation and coal consumption" is established, and the coordinated operation scheme of each thermal power unit after the wind power unit is connected to the system is arranged as a whole.

With the fast increasing of new energy, the voltage stability control ability of the AC/DC hybrid grid is seriously insufficient and the voltage stability margin of the network is greatly reduced. The dynamic reactive power allocation strategy for AC/DC grid with a lot of new energy is studied in this paper. Firstly, the sensitivity analysis method of AC/DC hybrid system is presented. Then a dynamic reactive power allocation evaluation index considering both steady and transient characteristics is determined. And an optimization model for AC/DC grid with new energy considering both steady and transient processes is established. Finally, a dynamic reactive power allocation strategy based on quantum genetic algorithm is proposed. The proposed strategy is applied to the actual power grid, and the calculation and comparative study prove the effectiveness and practicability of the strategy.

In order to study the cold dielectric recovery characteristics of high voltage SF 6 circuit breaker, a mathematical model is established for the airflow field and electric field inside the circuit breaker arc extinction chamber, and numerical calculation and analysis were made for electric field intensity and airflow characteristics. The variation curve of the electric field non-uniform coefficient $f$ with the contact open distance is obtained by electric field calculation; the electric field calculation result is introduced into the flow field, while the spatial distribution dynamic characteristics like pressure, mass density were analyzed through the flow field, and the critical breakdown field strength of contact gap is calculated according to the stream theory; Based on the electric field calculation result, the circuit breaker arcing chamber structure is a slightly uneven electrical field, the breakdown voltage of the SF 6 gas under different pressures is calculated by breakdown voltage empirical formula of SF 6 gas under slightly uneven electrical field. The results show that the dielectric recovery strength is affected by the open distance of the circuit breaker, the nonuniformity coefficient of the electric field structure and the particles number density of SF 6 gas. Near the open distance of 3mm, there is a sharp point in the electric field nonuniformity coefficient, the minimum particles number density of SF 6 gas between the arc contacts, and the low breakdown voltage of SF 6 gas, which is the relatively weak area of SF 6 dielectric insulation strength in breaking process. Under the same conditions, the higher the pressure of arc extinction chamber, the higher the recovery strength of the dielectric. The dielectric recovery strength at 0.5MPa is 71.4% to 0.7MPa. The analytical method of this paper provides a new idea for the study of dielectric recovery characteristics of SF 6 and its alternative gas.

Environmental-friendly insulating medium C 5 F 10 O has attracted wide attention due to its good insulation properties, but there are still few researches on the discharge decomposition of C 5 F 10 O. Based on density functional theory, the discharge decomposition characteristics of C 5 F 10 O are simulated in this paper. Firstly, the possible discharge decomposition paths of C 5 F 10 O are analyzed and the energy required for different decomposition paths is calculated. Secondly, the synthetic path of C 5 F 10 O decomposition products is discussed, and the energy variation of the synthesis pathway is calculated. Finally, the ionization parameters of C 5 F 10 O discharge decomposition products were calculated and the insulation properties were analyzed. The results show that the C-C bond in the molecular structure of C 5 F 10 O is the most likely to break, and the process of C 5 F 10 O discharge decomposition to form CF 3 CFCOCF 3 ·and CF 3 · radical is the most likely to occur. In the decomposition products of C 5 F 10 O, C2F6, C 5 F 10 and CF4 are easy to be generated, while C3F6, C6F14 and C 3 F 8 are relatively difficult to be generated. The ionization energy of C 5 F 10 O discharge decomposition products is greater than 11eV, which has a strong insulating ability, certain insulation strength can be guaranteed in GIS/GIL.

Converter transformer bushing as a piece of important power equipment in HVDC transmission, need to withstand AC voltage, DC voltage, and polarity reversal voltage during operation, the complexity of the operating conditions leads to high requirements on the insulation performance of the converter transformer bushing. The dry-type SF 6 gas-insulated DC bushing meets the requirement of no oil in the valve hall, is the bushing of the current mainstream converter transformer, and it uses SF 6 gas as the upper additional insulation. Analyze the electric field distribution in SF 6 gas of converter transformer bushing under different voltages, Especially important for the design of SF 6 gas internal voltage equalization device. This paper selects ±400kV dry-type SF 6 gas insulated bushing as the research object, establishes a simulation analysis model, and uses the finite element analysis method to calculate the electric field intensity distribution of the converter transformer bushing under different voltages. Mainly analyze the distribution law of electric field intensity in SF 6 gas. The results show that under DC excitation, the distribution of equipotential lines in SF 6 gas is relatively concentrated, and the electric field intensity near the top of the capacitor core is the highest. Under the condition of polarity reversal, the electric field intensity in SF 6 gas showed a downward trend.

In recent years, C 5 F 10 O has attracted wide attention as a potential alternative gas of SF 6 , and its decomposition characteristics have become a research hotspot. To this end, this article analyzes the thermal decomposition characteristics of C 5 F 10 O/CO 2 mixed insulating medium. Firstly, the saturated vapor pressure characteristics of the mixed insulating medium are obtained by using the Riedel vapor pressure equation and the basic law of vapor-liquid equilibrium, and the application schemes of the mixed insulating medium under different temperature limits are discussed. Secondly, the possible decomposition reaction of C 5 F 10 O was analyzed. The reaction energy of each reaction was calculated by using density functional theory, and the thermal decomposition path of C 5 F 10 O was determined. Finally, the Dalton law of partial pressure, the law of mass action, the quasi-neutral conditions of charge, and the stoichiometric equilibrium conditions are used to establish a mathematical model, and the particle number density of C 5 F 10 O/CO 2 high-temperature plasma at pressure of 0.1mpa and temperature of 300 ∼ 30000K was obtained, and its electronegativity was discussed. The results show that: at 0.1MPa and 248K, the mixed insulating medium with C 5 F 10 O mole fraction below 9% can keep the gas phase. The lowest path of energy required for decomposition of C 5 F 10 O is C 5 F 10 O → CF 3 COCFCF 3 → CF 3 CFCO → CF 3 CF → CF 3 . The decomposition products have strong electronegativity. The research results can lay a theoretical foundation for arc simulation of C 5 F 10 O/CO 2 mixed insulation medium, insulation characteristics and other problems, and provide reference for the research of C n F 2n O type alternative medium.

The insulation strength of high-voltage switchgear opening and closing break is the basis to ensure its safe operation, and it is also one of the important factors affecting its successful closing and breaking. In order to study the break insulation characteristics of the mixed gas of perfluoroisobutyronitrile (C 4 F 7 N) and carbon dioxide (CO 2 ), Build a test and research platform for dynamic insulation characteristics of C 4 F 7 N/CO 2 mixed gas break of the prototype circuit breaker closing-opening process under no-load high DC voltage, Measure the base pressure of 0.7MPa arc extinguishing chamber, the dynamic breakdown voltage of pure SF 6 , 5%C 4 F 7 N/95%CO 2 , 9%C 4 F 7 N/91%CO 2 and 13%C 4 F 7 N/ 87%CO 2 mixed gas, study mixed gas break insulation strength changes. The results show that, compared with pure SF 6 , C 4 F 7 N/CO 2 mixed gas break dynamic breakdown voltage dispersion is greater, the expected penetration time is longer than SF 6 ; increase the content of C 4 F 7 N in the mixed gas, The rate of change of the dielectric strength of the mixed gas break is improved.

During the breaking process of the self-blasting circuit breaker, the pressure characteristics greatly affect the action characteristics of the valve and the pressure in the expansion chamber, thus affecting the arc blowing effect. Therefore, a 550kV single-break selfblasting circuit breaker is taken as the research object. Based on the theory of magnetohydrodynamics (MHD), a two-dimensional transient model considering arc radiation is established, and the numerical calculation of the breaking process under two typical breaking conditions with short- circuit current of 63kA and 40kA and arcing time of 12ms is completed. The pressure and temperature distribution in the expansion chamber, and the action characteristics of the valve are obtained. Besides, combined with the test conditions, the 63kA short-circuit current, the pressure and temperature characteristics under short, medium and long arcing conditions are studied, and the valve action time under different conditions is obtained. The results show that the maximum temperature of the arc core region is 33219K at 63kA, which is about 3332K higher than the 40kA condition. The maximum pressure in the expansion chamber is 2.94MPa under the condition of 63kA and 2.36MPa at 40kA. The check valve is mainly affected by the temperature and pressure in expansion chamber side under the two breaking conditions, and the force received on the side of the cylinder is substantially same. The action time of the check valve under 63kA is 0.06ms earlier than the 40kA, and relief valve advance acts 0.05ms. Corresponding to different arcing time, the action time of check valve is 16.38ms, 16.28ms and 16.48ms and the time of relief valve is 17.52ms, 17.42ms and 17.67ms.

The physical parameters such as saturated vapor pressure, specific heat at constant pressure and viscosity of C 5 F 10 O, C 6 F 12 O and their CO 2 gas mixtures are calculated. The Joback group contribution method and the Thodos method are used to calculate the specific heat at constant pressure and viscosity of the gas mixtures. The results show that the saturated vapor pressures of C 5 F 10 O/CO 2 and C 6 F 12 O/CO 2 mixtures with C 5 F 10 O and C 6 F 12 O gases mole fractions above 3% are significantly lower than SF 6 , and the applicable range are smaller than SF 6 . The specific heat at constant pressure of C 5 F 10 O/CO 2 and C 6 F 12 O/CO 2 mixtures with C 5 F 10 O and C 6 F 12 O gases mole fractions below 9% are similar to CO 2 , and are higher than SF6, which can absorb more energy, lower viscosity than SF6, and have better mobility. The calculation results can provide basic data for the study of the gases ratio of C 5 F 10 O/CO 2 or C 6 F 12 O/CO 2 gas mixtures used in high- voltage circuit breakers and switch, as well as the calculation of gases temperature rise inside the equipment and simulation of gases flow characteristics.

The phenomenon of DC magnetic bias in the ultra/UHV DC transmission has a very important influence on the stable operation of the transformer. The vibration method can be used to monitor the vibration characteristics of the transformer in real time. Therefore, The principle of transformer DC magnetic bias generation and its influence on transformer vibration is analyzed, and a transformer prototype vibration information acquisition and test platform is built. Under the simulated transformer DC bias state, air and load experiments are carried out respectively and vibration signals are collected. The vibration signal of different working conditions is extracted by Fourier algorithm. The vibration signal characteristic analysis method based on "frequency band-energy ratio-Euclidean distance " is proposed. The research results show that can effectively analyze the vibration signal of the transformer under DC bias state can be analyzed effectively by means of "frequency band-energy ratio-Euclidean distance" method, which can diagnose the vibration characteristics of the transformer.

Combining load characteristics of 126kV high voltage circuit breaker, a design scheme of high power density permanent magnet motor is proposed. A control strategy with different control parameters in different travel stages of motor operating mechanism of high voltage circuit breaker is proposed, in order to satisfy the requirement that the control system can effectively control the speed of motor operating mechanism in the whole movement process. The experimental results show that the requirements of the opening and closing time and speed of 126kV vacuum interrupter can be satisfied. The opening and closing time have good stability.

Sub-synchronous oscillation may occur when the wind-thermal-bundled system sent out via AC/DC transmission (WTBH) is integrated in power grid. Causing large-scale wind-turbine tripping, even lead the system to collapse. First, in this study the mechanism of sub-synchronous oscillation of this system is analysed. Second, the influencing factors such as the ratio of the wind-thermal-bundled installed capacity, the series compensation parameters of AC transmission line, the different operating conditions of wind power etc., are analysed, which can cause different degree impact on the sub-synchronous oscillation. Finally, the system is simulated under the Power Systems Computer Aided Design (PSCAD) environment. The results show that under the same conditions, the higher series compensation, the greater transmission capacity of the AC line, the greater risk of the sub-synchronous oscillation. Under the condition of full load, the greater proportion of installed capacity of Doubly fed Induction Generator (DFIG) is, the less risk of sub-synchronous oscillation; Under the lower wind speed condition, reducing the number of wind turbine can eliminate the risk of sub-synchronous oscillation, and the oscillation frequency vary with the number of wind turbine.

In order to ensure the high-efficient and stable operation of the MMC-HVDC transmission system, it is necessary to analyse the failure mode and failure mechanism of MMC-HVDC in detail. First, this article briefly introduced the MMC-HVDC system working principle. Then, we deeply analyse characteristic investigation under internal AC bus fault including single-phase ground fault and two-phase short circuit fault. It is proved theoretically that when asymmetrical fault occurs in AC bus, negative sequence components will appear in the system and cause double frequency fluctuations in the active power. Finally, a simulation model of modular multilevel converter DC transmission is built in the PSCAD/EMTDC electromagnetic transient simulation platform, which validates the correctness of the theoretical derivation, and provides a basis for the research of system protection strategy.