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The flexible interconnection system (FIS) in distribution transformer areas can improve the local consumption capacity of high penetration rate distributed photovoltaics and solve the problem of the high loading rate of distribution transformers. This paper presents an optimized grid‐forming control strategy for the FIS in distribution transformer areas. First, the DC side impedance small signal model of the FIS is built, and the reason for the stability difference of the FIS is analyzed when the active power flows in different directions. An optimized control structure is then presented based on the conventional grid‐forming control strategy. The theoretical analysis shows that the optimized grid‐forming control strategy can improve the stability of the FIS. Finally, the controller hardware‐in‐the‐loop experiments based on RT‐LAB confirm the effectiveness of the presented optimized control strategy. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The extensive deployment of Modular Multilevel Converters (MMCs) in AC/DC systems can lead to complex resonance issues. Impedance modeling forms the foundation for analyzing the stability of interconnected system. Existing investigations primarily address resonance concerns on the AC side of MMC. In the process of impedance modeling, the DC system is generally approximated as an ideal voltage source, thereby neglecting its dynamic impact on the impedance characteristic of MMC. Such simplification may result in inaccuracies within stability analysis findings. Based on the multi-harmonic linearization method, this paper introduces an impedance modeling approach that takes into account the characteristics of the DC port. Taking DC voltage control as a case study, the impedance model for the AC side of the MMC is established. The results of programming calculation and simulation measurement of sequence impedance are mutually verified. Finally, the MMC impedance responses determined by different DC port characteristics are analyzed. Significant alterations in MMC impedance characteristics are introduced by DC side resistance and capacitance, which may result in negative damping effects and a decrease in system stability margins. The DC side inductance has a relatively minor impact on MMC impedance responses. The analysis results show that the sequence impedance model of MMC considering DC port characteristics can improve the accuracy of stability analysis results. [ABSTRACT FROM AUTHOR]

The stability of an MMC AC/DC hybrid system shows differences with changes in its operating state. However, the time domain analysis method cannot quantitatively evaluate the dynamic characteristics of the system. In this paper, a small-signal model of an MMC AC/DC hybrid system is established to analyze the system stability under continuous changes of the parameters. First, the dynamic characteristics of the small-signal model and the time-domain simulation model are compared to verify the accuracy of the small-signal model. Second, the dynamic stability of the MMC under four typical operating states is analyzed, and the influences of the AC system capacity and impedance angle on the stability domain of the system are evaluated. Then, the modal analysis method is used to solve the dominant mode and participation factor of the critically stable system. In addition, the oscillation characteristics of the system are solved. Finally, the variation trend of the system stability dominated by the controller parameters and DC capacity is obtained. The obtained results show that the controller parameters of the MMC do not contribute to the system oscillation characteristics. The selection of the AC/DC capacity leads to differences in system stability. Under PV control, the MMC AC/DC hybrid system presents stronger stability, and the system is easily affected by low-frequency oscillation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The existing virtual inertia control increases the system's moment of inertia, which is beneficial to reduce the short-term frequency drop, but has no supporting effect on the steady-state frequency, and the fan is likely to cause negative power penetration of the system during the recovery of kinetic energy after discharge, resulting in a frequency twice. collapse. In order to realize the transient control performance of grid transient and steady-state frequency under high-permeability wind power, a robust integrated frequency response model with virtual inertia support and steady-state frequency secondary support is constructed. The model includes wind-fire with high wind penetration rate. The bundled DC delivery system and the 500 kV large-scale transmission grid with wind farms control the power contribution of the fan at different time scales with the system frequency change rate. The additional frequency secondary support control strategy establishes the wind speed and the virtual inertia of the fan. The relationship between the coefficient and the system frequency sensitivity function, the dynamic response system steady-state frequency requirement, the wind turbine is introduced into the wind farm virtual weight coefficient after the primary unit of the synchronous unit, and the stratified and step-by-step normal operation mode is provided to provide the transient/stable for the grid. Dual frequency support at full time scale. Based on PSCAD software, a robust integrated frequency control hardware-in-the-loop simulation platform is built to verify the correctness of the proposed method and analysis conclusions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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[AQ ID=Q1]) 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. [ABSTRACT FROM AUTHOR]

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 this problem, an improved generalized predictive control (IGPC) algorithm is developed. The IGPC firstly builds the difference equation CARIMA (Controlled Auto-Regressive Integrated Moving-Average) model of the SISO system and then treats the system as a two input single output (TISO) system and calculates its predictive vector, then transforms it into a SISO system and uses the TISO system predictive vector to calculate the SISO system control increment. A new parameter called phase coefficient is added to inhibit the control lag. Simulations are performed to make the comparison among the traditional GPC, PID control, velocity synchronization control (VSC), fuzzy adaptive PID control (FAPID), model-based robust PID control (BPID) and the IGPC. Results show that IGPC has best performance compared to the others. Finally, experiments are developed which proved that the IGPC algorithm has a higher accuracy in the SISO system with known strong interference than that of VSC. [ABSTRACT FROM AUTHOR]

• An improved virtual synchronous generator control strategy is proposed for the flexible interconnection system. • The DC side impedance small signal model is built. • The stability of the flexible interconnection system is analyzed mathematically. • The controller hardware-in-the-loop experiment is designed for verification. The flexible interconnection system (FIS) in the distribution transformer areas containing high-penetration distributed photovoltaics plays a significant role in balancing the load and improving new energy consumption. This paper proposes an improved virtual synchronous generator (VSG) control strategy for the FIS. Firstly, the impedance small signal model of the FIS is developed for analyzing the influence of the conventional VSG control strategy on the stability margin of the FIS in the case of bidirectional power flow. Then, the improved VSG control strategy is proposed based on the analysis, which can improve the stability of the FIS in the negative power direction. Finally, the controller hardware-in-loop experiments of the FIS verify the effectiveness of the proposed improved VSG control strategy. [ABSTRACT FROM AUTHOR]

This study has designed a set of motor operating devices for a 126 kV vacuum circuit breaker (VCB) to improve its reliability and controllability. A finite‐angle permanent magnet brushless motor (FAPMBM) with a multi‐slot stator structure and a dovetail rotor structure has been designed based on the torque and speed requirements of the motor. These requirements were determined by a dynamic analysis of the operating device and its short‐time, finite‐angle working characteristics. The work performance of the prototype motor has been evaluated in an online experiment with a 126 kV VCB, and based on this, a segmented control method has been designed. The motion process of the operating device has been divided into four stages in combination with the output torque demand of the driving motor. At each stage, the output torque of the motor has been changed dynamically to prevent contact collision, shorten the pre‐breakdown time, and make the circuit breaker work more reliably. The results show that the FAPMBM can meet the operating time and speed requirements of the interrupter for the operating device. In addition, the segmented control method improves the work reliability and optimizes the movement of the operating device, which helps the circuit breaker work intelligently. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Searching for SF6-substitute gaseous dielectrics is currently an urgent task for high-voltage circuit breaker (HVCB) insulation and arc extinction applications. Once leaked, SF6 will affect the Earth's climate on the order of decades to millennia. In this work, we developed a test method that supplies a series of extended pulse voltages to obtain the dynamic dielectric strength of C3F7CN/CO2 and C3F7CN/N2 gas mixtures that are potential SF6 alternative gases in an HVCB during its no-load closing-opening processes, by measuring the dynamic breakdown voltage between the contacts. We also investigated the closing pre-strike and opening insulation characteristics of these gas mixture HVCBs at different voltage polarities, C3F7CN concentrations and pressures during the processes. We experimentally found an obvious “low-voltage-breakdown” phenomenon and much higher dispersion in the dynamic breakdown voltage of C3F7CN gas mixtures compared with pure SF6. Moreover, the dispersion in closing was significantly higher than that in opening, leading to the closing pre-strike characteristics of an HVCB filled with C3F7CN mixtures that are inferior to SF6. The results not only provide a criterion via data but also evaluate the interruption gap design and give insight into the expected performance of the interruption chamber during breaking capacity tests. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Bi 2 Sr 2 CaCu 2 O 8+ x (Bi-2212) material, a high-temperature superconductor, holds significant promise for future high-field applications because of its multifilamentary, twistable production capabilities, coupled with a high upper critical field. Bi-2212 round wire (RW) is made by the powder-in-tube (PIT) technique, and Bi-2212 coils are usually being developed using the wind-and-react method and a high temperature and over-pressure (OP) heat treatment (50 atm, 890℃) is then required to achieve the high current performance. However, over-pressure (OP) heat treatment can lead to a reduction in wire diameter, compromising the stability of the coil structure. Addressing this issue, the pre-overpressure (pre-OP) heat treatment is used and proves effective in mitigating the reduction in Bi-2212 wire diameter. In this paper, to comprehensively investigate the impact of pre-OP heat treatment on the microstructure of Bi-2212 wire, a metallographic analysis of two kinds of Bi-2212 wires was carried out by the scanning electron microscope (SEM) and the ImageJ software. It was found that larger-area filaments experienced a greater reduction in area after pre-OP heat treatment, that pre-OP heat treatment increases the aspect ratio of filaments, and polygonal bundle structure helps maintain filament structure stability during pre-OP heat treatment. Additionally, the impact of pre-OP heat treatment on the performance of Bi-2212 wires was analyzed through critical current testing under high fields. [ABSTRACT FROM AUTHOR]

GIL/GIS bus is widely used in the field of power transmission and distribution, and the demand for lightweight is becoming more and more prominent. To reduce the weight of the bus and ensure the safety and reliability of the structure, a new 6σ robust design method of the GIL/GIS bus based on electric‐thermal‐mechanical co‐simulation is proposed. Taking a 550 kV/5000A bus as the initial structure, considering the uncertainty of product size and performance, a 6σ robust lightweight model of bus insulation electric field strength, current temperature rise, and mechanical stress multi‐performance co‐simulation is established. The finite element numerical calculation method is used to calculate and analyze the performance parameters of the bus. The Kriging surrogate model is used to form the response surface, and the optimal bus structure is obtained by genetic algorithm. The results show that after the robustness optimization, the performance of the bus meets the design requirements, the weight per meter decreased from 65.11 to 39.12 kg, and the lightweight effect is remarkable. Compared with the traditional deterministic optimization design, the reliability of the structure is improved. The new method of the GIL/GIS bus lightweight design proposed in this study has high feasibility and application prospects, which can provide new ideas for the development of gas‐insulated electrical equipment. © 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The fault detection time identified by relying on the over-voltage criterion of zero-sequence voltage often lags behind the actual occurrence time of ground faults, which may cause fault protection methods based on transient quantity principles to miss fault characteristics and lose their protection capability. To accurately estimate the time of occurrence of a single-phase-to-ground fault, this paper proposes a two-step dimensionality reduction algorithm for estimating the time of occurrence of a single-phase-to-ground fault in a distribution network. This algorithm constructs a filter based on Empirical Mode Decomposition (EMD) to establish a high-dimensional feature dataset based on the zero-sequence current of all feeders. After Principal Component Analysis and Hilbert Mapping Algorithm, the high-dimensional data are reduced to two dimensions to construct a two-dimensional feature dataset. The density-based clustering method is used to adaptively divide the data into two categories, fault data and non-fault data, so as to estimate the time of occurrence of the fault. The paper designs 11 sets of experiments including 7 common high-resistance grounding mediums to verify the accuracy of the fault time recognition of this algorithm. The accuracy of this algorithm is within 7.3 ms and it exhibits better detection performance compared to the threshold detection method. [ABSTRACT FROM AUTHOR]