In this paper, the magnetic properties of ferromagnetic materials under sinusoidal and different harmonic conditions are obtained experimentally by building a complex working condition magnetic property test system; based on the idea of hysteresis loop equivalence, on the basis of the traditional equivalent elliptical loop (EEL) elliptical equivalence model, the influence of saturation magnetization is fully considered, and both the shape change of sinusoidal EEL and the shape factor of dynamic magnetization loss characteristics are effectively reflected and introduced. Based on the traditional EEL elliptical equivalent model, the shape factor which can reflect the shape change of the hysteresis line and accurately describe the dynamic magnetization loss characteristics is introduced to effectively characterize the shape of the saturated hysteresis line and establish a sinusoidal EEL loss model under saturated magnetic density, which improves the calculation accuracy of the EEL loss model under sinusoidal high magnetic density conditions. On this basis, the EEL loss model can be used to calculate the loss of the cores under the harmonic excitation by considering the influence of the local hysteresis loops caused by the distorted fluxes, and the hysteresis loops are decoupled to make the approximate equivalence between the main hysteresis loops and the local hysteresis loops. Finally, the experimental validation with the magnetic characteristic device verifies the accuracy and effectiveness of the proposed magnetic loss method.

The increase in renewable energy penetration rate may induce the risk of power supply interruption and reduce the operation reliability of the power system. The traditional mid-long-term reliability evaluation method is challenging to meet the time requirement of operation reliability evaluation. This paper proposes an efficient evaluation algorithm for power system operation reliability, which reveals the analytical function relationship between the power system operation reliability index and uncertain factors such as wind power output. It avoids repeated reliability calculation when uncertain factors change. Firstly, the distribution characteristics of wind power output are modeled based on the hidden Markov model. Then, the analytical function between the reliability index and wind power output is established by the state enumeration-polynomial chaos expansion method. Finally, based on the analytical function, the efficient operational reliability evaluation and weak links identification of the new energy power system under real-time wind power output are realized. Taking the modified IEEE RTS79 system as an example, the effectiveness of the proposed method is verified.

The arcing fault inside a converter transformer will result in a sudden rise of oil pressure inside the tank, which may lead to tank rupture or even serious explosion and fire, seriously threatening the safe and stable operation of the power system. This paper takes the actual 500 kV UHV converter transformer as the research object, and carries out numerical simulations on the ANSYS platform to obtain the spatial and temporal distribution characteristics of the oil pressure inside the converter transformer during the arcing fault. The simulation results show that the gas bubble grows dynamically during the arcing fault inside the equipment, the oil pressure rises abruptly with the pulsation of the gas bubbles and shows obvious fluctuation characteristics, and the spatial distribution of oil pressure inside the converter transformer is uneven. This study has certain reference significance for the converter transformer pressure reduction and explosion-proof and structure optimization.

With the promotion and development of China’s electricity market reform process, how to capture the maximum profits of all responding entities at the level of industrial parks so as to guide users to actively participate in demand response has become a new problem to be solved. Based on the situation that the market information disclosure is limited and users and aggregators being freely conclude contracts in the response process, this paper proposes an optimal game strategy from the perspective of aggregators and a revenue distribution method for users. Considering the interests of users in the industrial park, a multi-agent and two-tier game structure is established with incomplete information Bayesian game as the upper layer and cooperative game as the lower layer; and in order to maximize their own interests, the improved counterfactual regret minimization idea combined with heuristic algorithm is used to solve the game equilibrium to achieve a stable cooperative relationship in the park. Finally, a numerical example is used to verify the idea of the paper so that multiple comparison models are set up for the declaration strategy and income distribution in different scenarios. The results show that the strategy obtained under the proposed method can improve user income, and the reasonable selection of the benefit distribution mechanism can play a catalytic role in improving the enthusiasm of users to respond to their needs.

High temperature resistant metallized film capacitors (MFC) are urgently needed for high temperature applications in modern power electronic systems. While a large number of studies have shown that high temperature dielectric films have satisfactory energy storage properties, the self-healing properties are not yet known and this property is the key to determine whether high temperature dielectric films can be used in MFC. In this paper, the self-healing properties of three metallized high temperature dielectric films, namely, Polyethylene naphthalate (PEN), Polyether ether ketone (PEEK) and Polyimide (PI), at DC high voltage were investigated. The effects of external factors such as interlayer pressure, winding tension and temperature on the self-healing properties were specifically analysed. The results showed that PI is not suitable for application in MFC because of its high carbon content, which causes that is easy to breakdown and short-circuit in the experiment and lead to self-healing failure. The self-healing performance of PEEK is greatly affected by the interlayer pressure and winding tension. The winding tension and the number of winding layers should be considered after the application of PEEK in MFC. PEN has low carbon content and excellent aliphatic-aromatic alternating structure, and has shown excellent self-healing properties in various studies. From the perspective of self-healing, PEN is suitable as an insulating dielectric material for high temperature and strong electric field MFC.

With the increasing installed wind power capacity, the grid-connected wind turbines have a significant impact on the power system．In order to realize the stability analysis and calculation of the doubly fed induction generator (DFIG) wind power generation system during the low voltage ride-through (LVRT) period, it is necessary to establish a model of the DFIG wind power generation system which can accurately describe the external characteristics of the actual system. However, because the converter control system is a black box structure, its control model and control parameters are often difficult to obtain, so there is a significant deviation between the simulation model and the actual system. Therefore, in order to improve the accuracy of the model, this paper proposed a global parameter identification method which can consider LVRT sequential control of DFIG. Firstly, an accurate mathematical model of the system is established which takes into account the sequential control characteristics during LVRT period．Then, the best observations are selected based on the trajectory sensitivity method, and the multi-condition-step identification strategy is proposed. In addition, the global control parameters are identified with several groups of experimental data. Finally, waveform comparison and model verification are carried out under different voltage sag conditions. The verification results show that the proposed identification scheme can accurately simulate the external characteristics of actual DFIG wind generation system.

A novel single-stage three phase harmonic current injection Step-up/down (STHSUD) AC/DC converter is proposed in this paper. This proposal integrates a three-phase uncontrolled rectifier bridge combined with a post-stage Cuk module, and the low-frequency bidirectional switch is introduced to provide a path for the converter to feed back the harmonic current, so that the purpose of reducing the harmonic content of input current is achieved. Firstly, the topology and operating principle of the proposed converter are analyzed, its equivalent circuit is established, the voltage transfer ratio of the converter is deduced, and combined with hysteresis tracking control, the closed-loop simulation of the proposed converter is performed to prove the buck-boost capability. The control strategy is simple, and input current can be sinusoidal with high power factor. Finally, the experiments are carried out in the TMS320F28335 DSP digital control platform, and the experimental results verify the feasibility of the proposed topology.

When wind turbine generator (WTG) participates in system frequency response based on virtual synchronous generator (VSG) control, improper parameter may cause the rotor speed to fall below the limit value or the converter power to exceed the limit value. Moreover, few existing studies consider the impact of the dead zone of primary frequency regulation for WTG on system frequency response. Therefore, this paper proposes an optimized method for VSG control parameter of WTG that considers the dead zone and the physical constraint boundary of primary frequency regulation. Firstly, the modeling of the dead zone is considered more refined, and the whole process frequency response model of the WTG controlled by VSG is established. Secondly, the influence degree of WTG frequency regulation parameters on the whole dynamic trajectory of frequency response is studied by trajectory sensitivity analysis. The results show that the virtual damping coefficient plays a key role. On this basis, considering the different operating conditions of the WTG and the frequency dynamic response process of the system, the optimal value of virtual damping coefficient under the physical constraint boundary is obtained by taking the rotor speed constraint and the converter capacity limit as the conditions, which makes full use of the available frequency regulation capacity of the WTG. Finally, the system simulation model is built based on Matlab/Simulink simulation platform. The simulation results show that the proposed method can fully utilize the frequency regulation ability, which can avoid responding beyond the physical constraint boundary of primary frequency regulation and effectively improve the frequency stability of the system.

Electricity price forecasting is becoming increasingly difficult as renewable energy is integrated into the grid on a large scale. In order to more accurately predict the electricity price in the new energy power market, a short-term electricity price forecasting model based on discrete wavelet transform (DWT), bi-directional long short-term memory network (Bi-LSTM) and temporal convolution network (TCN) was proposed. Firstly, the time-frequency diagram of the data was extracted by DWT, and the correlation analysis was performed on the reconstructed subsequences. Then, different models were established to predict the subsequences affected by different factors. Finally, the predicted results were superimposed to obtain the final predicted value. Experiments are performed on the dataset of the Nordic Danish DK1 power market, the root mean square error (RMSE) and mean absolute error (MAE) of this method are 3.081% and 2.588% respectively. Compared with some benchmark models and existing prediction models, the method has higher prediction accuracy.

In the new power system with new energy as the main body, considering the strong regularity of new energy output in medium and long-term time scales, a method for determining the real-time reserve rate of new energy in medium and long-term time scales is proposed. According to the real-time reserve ratio, the credible output of new energy power is included in the reserve, and the multi-power power production model is established. The model establishes the objective function with the minimum production cost, and considers the constraints such as power operation cost, new energy abandonment cost, load shedding penalty cost, unit output, power balance and logical variables. The time iteration is used to simplify the medium- and long-term production simulation into a short-term optimization problem, which is solved by CPLEX. Taking the improved IEEE-24 node system as an example, the optimization results show that the total cost of power system production and operation is lower when the new energy is included in the reserve by using the real-time reserve rate method. The higher the permeability of new energy is, the more obvious the economic benefits of reserve is. When the spare wind power and the photovoltaics are inde-pendently induce in the reserve rate, the production and operation costs will be lower.

The new power system with renewable energy generation as the main body has brought new challenges to the system dispatching. A stochastic unit commitment model considering wind power as the operating reserve is proposed to alleviate the reserve pressure brought by the integration of large-scale renewable energy. Firstly, the probability density estimation of wind power prediction error is obtained based on the kernel density method, and the wind power reserve model is established according to the best confidence level. Secondly, we propose an all-scenario-feasible dispatching model based on the vertex scenarios with variable uncertainty sets and introduce strong nonanticipative constraints to meet the nonanticipativity of economic dispatching. Finally, in the improved IEEE-24 bus system, the effectiveness of the proposed stochastic unit commitment model is verified by the actual data and is compared with the scenario-based two-stage stochastic optimization. The experimental results show that the proposed model has satisfactory performance, can overcome the defects of numerical scenarios and large computing scale in stochastic optimization, and effectively reduces calculating time.

Brushless doubly-fed induction generator (BDFIG) has the potential in stand-alone applications due to its high reliability. However, the special structure leads to difficulty of control parameter design. Even with the help of powerful computer software, the analysis results of commonly used closed-loop function method still contain a lot of interference information, making stability analysis difficult. In view of this, by referring to the impedance analysis commonly used in DFIG grid-connected system, this paper proposes a control parameter design method for BDFIG stand-alone generation system. Impedance models of machine-side and load-side subsystems are built respectively, reducing transfer function complexity caused by information coupling. Then by taking system stability under various operation conditions as the core index, the critical current-loop parameters are designed and evaluated based on generalized Nyquist stability criterion. Since the key phenomena of stability analysis, i.e., the relative relation among Nyquist curves and (-1,j0), are not affected by the complexity of impedance models, the proposed control parameter design method does not need to be artificially simplified, and can give full play to the intelligence of the computer software. Finally, the effectiveness of designed control parameters is verified by BDFIG stand-alone simulation and experimental systems under typical conditions such as sub/super synchronous full-load conditions.

A TOPSIS-based optimal cost function preference order method is proposed to enhance the selection of weight factors to address the computationally intensive problem of selecting appropriate weight factors for the cost function in the predictive control algorithm of a permanent magnet synchronous motor (PMSM) under multi-objective constraints. In order to choose the best control measure for each sampling duration, the TOPSIS method is firstly used to choose a positive solution that is closest to the ideal control action and a negative solution that is farthest from the ideal control action. Secondly, the anticipated state of the following switching instant is utilized to optimize the cost function based on the optimum control state of the preceding moment, shortening the time required for the predictive control method to complete its calculation. According to simulation and experiment results, TOPSIS-based predictive control outperforms conventional control methods in terms of operational performance by effectively suppressing current pulsation, reducing algorithm complexity and computational effort, and reducing electromagnetic torque and magnetic chain ripple during stable operation with lower switching frequency.

The coupling operation of dual-motor system needs to be considered in the optimal design of dual-motor. In the traditional optimization methods, the method of estimating efficiency Map is often used to obtain the optimal torque distribution coefficient of the dual-motor system. However, the error caused by the estimation method cannot be ignored in the optimal design of high-efficiency motor. In addition, the control strategies of the motor are also different under different working conditions. In order to improve the operating efficiency of dual-motor drive system under all operating conditions, based on two kinds of driving cycles, a collaborative optimization design method of dual-motor for electric vehicle is systematically proposed in this paper. Firstly, the parameters of the primary motor are obtained by parameter matching, and then the Map calculation method of motor efficiency based on semi-analytical model is proposed. Based on this method, the optimal torque distribution and control strategy of dual-motor system under different working conditions are studied. Then based on the particle swarm optimization algorithm, considering the control strategy of the motor under different operating conditions, the parameters of the dual motor are optimized under all working conditions. Finally, a hardware-in-the-loop experimental platform is built. Simulation and experimental results show that the proposed optimization method can improve the operation efficiency of the dual-motor drive system.

Traditional active clamp flyback converters rely on the resonance between the transformer leakage inductance and the primary side clamp capacitor to achieve soft switching, eliminating switching losses, but the conduction loss is large, and the output rectifier has current oscillation. In order to solve the above problems, the best working mode of the converter is selected, the equivalent circuit model under different resonance modes is established, the influence of the resonance mode on the working state of the converter is analyzed in depth, and the experimental prototype is made based on the secondary side resonance mode. The experimental results show that the secondary side resonant active clamp flyback converter can realize the soft switching of power devices, reduce the rms value of the primary current, eliminate the phenomenon of secondary side current oscillation, and the maximum full load efficiency of the designed converter reaches 94.06%, and the efficiency of the whole machine is higher than that of the primary side resonance mode.

When the virtual synchronous generator (VSG) is connected to the grid, there is coupling between the steady-state performance and dynamic performance of the output power, which cannot meet the demand of suppressing active oscillation and primary frequency modulation of the grid at the same time. A control strategy based on angular frequency transient feedforward was proposed. This control strategy reduces Δω by compensating the output power, which in turn reduces the oscillation process. This control strategy can effectively suppress the generation of active oscillations, and realize the decoupling between steady state performance and dynamic performance, which does not affect the characteristics of primary frequency modulation, and improves the response speed. First, VSG active closed-loop small signal model is established, the contradiction between steady state and dynamic performance of output power is analyzed, and the active power oscillation mechanism is analyzed according to the power angle characteristics of synchronous generator. On this basis, a control strategy based on angular frequency transient feed-forward is proposed, and the influence of the proposed control strategy on the system is analyzed by using closed-loop zero-pole and Bode diagrams. Finally, the feasibility and superiority of the proposed control strategy are verified by simulation and RT-LAB HIL platform.

In this paper, the torque model of reluctance spherical motor is developed based on the virtual power method for the problem that the finite element method takes a lot of computation time to calculate the torque of reluctance spherical motor. First, the inductance variation law of a single stator coil is simulated using electromagnetic analysis software, and the inductance model is obtained by bilinear interpolation. The obtained inductance are differentiated along the longitudinal and latitudinal directions respectively, to obtain two-dimensional torque values. The two-degree-of-freedom torque is then converted to three-degree-of-freedom torque by coordinate transformation. Finally, a torque measurement platform based on the dynamic torque sensor is built, and the experimental torque is measured and compared with the analytical results to verify the validity of the torque model.

The AC impedance of a lithium-ion battery can provide internal information of the battery and is a powerful tool for online monitoring of battery state. The design of an impedance online measurement device is the key to implementing impedance-based online estimation of battery state and fault warning technology. This study designed an online measurement device for AC impedance of lithium-ion batteries based on an embedded microcontroller. It uses an all-phase fast Fourier transform algorithm to convert time-domain data to the frequency domain, and performs interpolation on the conversion results, achieving online measurement of AC impedance in the frequency range of 0.01 Hz to 10 kHz. This effectively solves the problems of spectrum leakage, fence effect, and inaccurate phase calculation caused by the traditional fast Fourier transform algorithm used in current impedance online measurement devices. By performing static and dynamic impedance measurements on batteries with different capacities and positive electrode materials, the reliability and speed of the device were verified. The sharp change in dynamic impedance at the end of discharge was found to have certain indicative ability for battery state. This design can be easily integrated into a battery management system and has certain application value in lithium-ion battery state estimation and fault warning.

In order to cope with the increasingly severe climate change problem, China has put forward the “double carbon” target, and energy low-carbon transformation has become a global consensus. While the distribution system plays an important role in promoting accommodation of renewable energy and reduction of users' carbon emission, it will also face new challenges. As the center of energy consumption, cities have significant carbon emission effect, so the low-carbon transformation of urban distribution network is in urgent need. Firstly, the framework of urban distribution network side energy storage system considering the cooperative operation of source network load storage is proposed. Secondly, the capacity optimization configuration model of energy storage system is established, considering the cost of energy storage system in the whole life cycle. Thirdly, a system optimization scheduling model is established considering the constraints such as energy storage and power flow in the distribution network, and aiming at the lowest comprehensive operation cost of the system. Finally, a dual-layer optimization model of planning-operation is constructed, considering the capacity optimization of the energy storage system and the optimal scheduling of the load-storage cooperative operation system of the source network, and the effectiveness of the proposed optimal configuration scheme is verified by a numerical example.

ISOP-DAB converters are mostly used in high-power and high-voltage applications. To reduce the current stress of ISOP-DAB converters and improve the dynamic performance of the system, this paper proposes a hybrid optimal control method based on extended phase shift modulation. Firstly, the operating mode and power model of the converter under the extended phase shift are analyzed. The optimal phase shift combination of current stress is obtained through the Lagrangian optimization algorithm, and the virtual voltage balance control scheme is combined to deal with the sudden load change or input voltage disturbance state. At the same time, the average value of input voltage is used to complete the dynamic power balance between modules in combination with the structural characteristics of the converter. Finally, the hybrid optimal control method, the virtual power control based on single phase shifting and the traditional extended phase shifting optimal control are compared. The experimental results show that the hybrid optimal control can achieve current stress optimization at power sharing, improve the energy transmission efficiency, and significantly improve the dynamic characteristics of the converter under disturbance.

In electric vehicle wireless power transfer systems, realizing efficient transmission while reducing magnetic leakage has been a technical challenge. To address this issue, the paper proposes a sunken shielding coil structure applied to a multi-radio wireless power transfer system, which reduces the magnetic leakage from the target surface without affecting the transmission efficiency of the system. Firstly, a method of calculating the magnetic field of a rectangular coil based on the vector magnetic potential is submitted, by which the magnetic leakage from the target surface of the system is analyzed, providing a theoretical basis for the subsequent magnetic leakage optimization; secondly, a method of magnetic leakage optimization is introduced, and each coil parameter meeting the requirements is obtained by applying the method, which provides a key support for the realization of high-efficiency wireless power transfer; lastly, a set of dual-sunken shielded coil structures with magnetic shielding structure is developed based on the coil parameters obtained; and lastly, a set of dual-sunken shielding coil structures with magnetic shielding structure applied to multiple wireless power transfer systems is developed based on the coil parameters obtained, which will not impact the system transmission efficiency. Finally, based on the obtained coil parameters, a dual-position electric vehicle wireless charging system with magnetic shielding structure is developed, and the effectiveness of the proposed shielding structure and method is fully confirmed through simulation and experiment. The results show that the proposed shielding structure not only reduces the maximum leakage magnetic field in the target area by 25% but also achieves a transmission efficiency of up to 95% when the output power of the system is constant at 4 kW.

Accurate parameter identification of synchronous generators is an important foundation for ensuring transient stability analysis of power systems. Firstly, based on the equivalent mathematical model, sequence network diagram and equivalent circuit of synchronous generator, the expression of transient current under the condition of phase to phase short circuit fault through external impedance is derived. Then, using short-circuit tests and identification to obtain the minimum objective function of the square sum of standardized errors between short-circuit currents, an improved whale optimization algorithm with increased weight coefficients is adopted to propose a parameter identification method for synchronous generators based on phase to phase short-circuit fault currents. Finally, a short-circuit test was conducted on an actual synchronous generator to verify the correctness and effectiveness of the proposed method. The method in this paper improves the accuracy of identification by increasing the excitation energy of synchronous generator and using the fault current in the process of large disturbance as the original data. At the same time, combining the nonlinear characteristics of the short-circuit current model, the whale optimization algorithm is improved to better adapt to nonlinear parameter identification.

Vibration signals of an operating transformer has becoming one of the parameters for the evaluation of the working condition of the transformer. To further investigate the variations of vibration signals of a power transformer, a method based on generalized regression neural network (GRNN) and Markov chain correction is proposed in this paper to predict the vibration signals of transformer. The input and output of the established GRNN are the operating voltage, load current and the normalized feature frequency of vibration signals. Then the Markov chain is used to correct the relative error between the calculation results of vibration signal model and the measured vibration signals. The prediction results of vibration signal of transformer are finally obtained. The calculated results of the on-line monitoring vibration signals of a 500 kV transformer show that the vibration signal prediction model of transformer by the generalized regression neural network model and the Markov chain correction is capable of predicting the vibration signals of transformer with higher accuracy. The results can provide an important reference for vibration monitoring technology of power transformer.

In recent years, high voltage direct current (HVDC) transmission system has been an effective scheme for the development of wind power in the deep sea. With the continuous operation of a large number of HVDC transmission systems for the grid connection of wind power in the deep sea, high-frequency oscillation phenomenon frequently occurs in practical projects. However, most of the existing research focuses on the high-frequency oscillation phenomenon generated by the interaction of new energy AC grid-connected system or asynchronous zonal power grid, and the research on the high-frequency oscillation of offshore wind power through flexible direct transmission system is not sufficient. Moreover, the existing modular multilevel converter (MMC) high-band impedance model usually ignores the characteristics of the low frequency band of the converter, so that the influence of the high-frequency oscillation suppression strategy on the low-frequency impedance characteristics cannot be accurately revealed. Therefore, this paper first considers the influence of system time delay, and establishes the impedance model of MMC based on the harmonic state space. On this basis, the high-frequency oscillation mechanism of offshore wind power through HVDC transmission system is analyzed, and the control parameter optimization strategy is designed. Finally, based on Matlab/Simulink, the electromagnetic transient simulation model of the offshore wind power through HVDC transmission system is built to verify the accuracy of the impedance model and the effectiveness of high-frequency oscillation suppression strategy.

At present, the technology of using multi-source fault remote signaling data to diagnose the fault of distribution network is becoming increasingly popular, but the diagnosis results are often unsatisfactory due to the false alarm and missing report of data. Aiming at the problem of imperfect multi-source fault information, this paper presents a fault diagnosis method for distribution network with high fault tolerance, which combines the data check operation with graph convolution neural network. It aims to use the imperfect fault information to diagnose the fault in distribution network. Firstly, and the data after normalization of multi-source fault data are checked, so as to improve the soundness of the data from the source; then, transform multi-source fault data into fault diagram data are transformed according to distribution network diagram model; and finally, the fault diagram data are sent to the graph convolutional neural network for learning and training, and the trained model can realize fault diagnosis for distribution network with high fault tolerance after deployment. The simulation experiment on Python 3.7 platform shows that the proposed method can effectively improve the fault tolerance of distribution network fault diagnosis.

The rapid phase selection and disconnection of short circuit faults in the first half wave is of great significance for improving the stability of power systems. Due to the randomness of the fault starting phase, the short-circuit current often contains decaying DC components with uncertain amplitude, which increases the difficulty of selecting the phase and breaking the short-circuit current. Therefore, a self-learning based method for predicting the zero point of short circuit current in LSTM networks is studied and proposed. The LSTM short circuit current prediction model based on self-learning optimization training is constructed, and the cyclic iteration method is used to predict the short circuit current waveform and zero crossing point. The impact of factors such as the initial phase angle, harmonic content, signal-to-noise ratio, and decaying DC component time constant of different short-circuit fault currents on the prediction accuracy of self-learning LSTM is discussed. The simulation and experimental results show that the self-learning LSTM network has good predictive ability for short-circuit current zero points. When the sampling time is 3 ms, the prediction accuracy of the self-learning LSTM first and zero points is equivalent to that of the RLS algorithm when the sampling time is 5 ms, providing a basis for achieving phase controlled disconnection in the first half wave.

Enhancing the rotational inertia level of the wind power grid-connected system through the coordinated control of the wind-storage combined system (WSCS) is an important means to enhance the frequency stability of the system. The coupling degree of WSCS is low, and it is difficult to give full play to the response and adjustment capabilities of wind power and energy storage to frequency disturbances. In this regard, this paper proposes a coordinated control strategy for the WSCS based on the Linear Quadratic Regulator (LQR). This strategy takes the output frequency of the DFIG and the total output power of the WSCS as the control input of the energy storage to improve the damping and stability of the system and enhance the frequency response adjustment capability of the system. Firstly, according to the state equation of the system, the small-signal stability model of the DFIG and the WSCS is established, and the effect of coordinated control on the damping ratio of WSCS is analyzed. On this basis, the energy storage power capacity is determined according to the maximum rotor kinetic energy released by the synchronous generator. Finally, the grid-connected model of the WSCS is built in Matlab/Simulink, which verifies the effectiveness and superiority of the strategy.

Distribution network fault recovery depends on the looping operation, but the impulse current generated during the looping process may cause the line current to exceed the limit, which may not only damage the equipment, but also endanger personal safety. Currently, the suppression of closing current is mostly focused on the overall optimization, but not on the impact current generated by the closing transient process. In particular, there is a delay between the issuance of the closing command and the actual closing of the loop in the distribution center, which will directly affect the size of the closing ring impulse current. The existing methods assume that the closing operation is completed immediately, ignoring the delay of the closing ring, and that may further cause the suppression of the closing ring impulse current to fail to achieve the expected goal. For this reason, a method considering the synergistic suppression of the closing loop impulse current by the closing loop delay and DG control is presented. By analyzing the generation process and principle of closed-loop impulse current in distribution network, the influence of DG output and closing delay on closed-loop impulse current is depicted, and a control optimization model of DG active control and closing-loop cooperation is established. A collaborative control method for closed-loop impulse current in distribution network with distributed power supply considering closing delay is presented. The example shows that this method can minimize the closing impulse current during the recovery process of distribution network and improve the safety of distribution system by optimizing DG output and the expected closing time.

In order to realize the refined design of the electric locomotive traction transformer, reduce the redundancy in the product design, and improve the efficiency of the product and reduce its volume, it is necessary to accurately calculate its loss characteristics in actual work during the design. Traction transformer is a key component of electric locomotive, how to reduce its size and improve its efficiency has always been the research focus of transformer designers. Therefore, this article first simulates the actual working state of the traction transformer, and starts the simulation research work on the electromagnetic characteristics of the electrical materials used in the traction transformer under the harmonic alternating magnetization. By measuring the electromagnetic characteristic curve of the traction transformer in actual work, the electromagnetic characteristic of the core material is analyzed. Then, considering the non-linear problems of the magnetization angle and the harmonic loss model under harmonic alternating magnetization, the traditional loss model is improved. The variable coefficient equation of the loss model coefficients changing with the magnetization angle and the correction coefficient considering the nonlinearity of the harmonic loss are given. Thereby improving the calculation accuracy of the loss model. It also lays the foundation for the energy-saving optimization design of electric locomotive electrical products.

With the rapid development of the world’s industrialization process, the continuous improvement and development of new energy represented by photovoltaic power generation can alleviate the energy crisis and environmental pollution problems. To ensure the safe, efficient and stable operation of off-grid users’ power supply, this paper analyzes the characteristics of energy storage batteries, fuel cells and supercapacitors, and proposes a hybrid renewable energy power and energy management that combines short-term energy storage of supercapacitors and long-term energy storage of fuel cells for the long-term inability to connect to the grid in remote areas. The electrical energy in the system mainly comes from the photovoltaic power generation system, and the fuel cell system (fuel cell/ electrolysis equipment /hydrogen storage tank) is used as the backup system, and the battery/supercapacitor is used as the energy storage system. In addition, the energy management system (EMS) proposed in this paper can control the behavior patterns among the components of the power system through optimization algorithms on the power supply side to ensure the stability of the user’s voltage and power. On the demand side, through the demand response algorithm, according to the power system time and energy supply capacity under different operating conditions, and the operating strategies are formulated for home appliances including adjustable constant temperature, uninterrupted on/off, and cut-off. Finally, the relevant simulation experiments of the off-grid user energy storage power and energy management system studied in this paper are carried out, and the proposed off-grid system is simulated and verified by Matlab using different lighting conditions and variable load data. The simulation results show that the system can achieve carbon emission reduction while ensuring electricity demand, and improve the economic and environmental benefits of the system, which has certain practical significance.

In recent years, serious accidents have occurred in many DC converter stations inland. It is found that the causes of the accidents are mostly the aging of the converter valve thyristor or even the loss of insulation. To master the law of thyristor parameter degradation is the basis to carry out the operation and maintenance monitoring of thyristor and prevent such accidents from happening again. Therefore, in order to deeply understand the degradation law and aging mechanism of the characteristic parameters of the valve thyristor in the aging process, it is necessary to build the thyristor aging test device required by the test to simulate the operation process of the valve. This paper first analyzes the converter valve thyristor’s actual operating conditions, and based on this the united thyristor electric heating aging main circuit is designed, then the circuit involved in the control unit, as well as the drive circuit of IGBT and thyristor trigger circuit are designed and build, and based on the actual operation condition of thyristor thyristor junction temperature a control system is designed. In order to obtain the degradation law of characteristic parameters during the thyristor aging process, the online monitoring system and the reverse recovery offline measuring system of thyristor leakage current are designed. After testing, each module and the main circuit can maintain long-term stable operation, which lays a good foundation for the aging test of the converter valve thyristor.

Photovoltaic power generation system has different fault response characteristics from synchronous machine, which brings severe challenges to power grid fault protection and control. The output of the phase-locked loop of the photovoltaic power generation system directly affects the fault response characteristics of the photovoltaic system, especially the non-periodic transient response deviation of the output of the phase-locked loop caused by the voltage phase jump after the grid fault, which has a great impact on the short-circuit current. The existing studies ignore the phase-locked transient process or assume that the phase-locked deviation is constant, which may cause large errors in the analytical calculation of photovoltaic short-circuit current. For this reason, in the present paper the expression of the deviation between the output phase of the photovoltaic phase-locked loop and the voltage phase of the grid-connected point is derived, the time-domain variation characteristics of the phase-locked deviation and its influencing factors are analyzed, and the influence of the phase-locked deviation on the three-phase short-circuit current of the photovoltaic power generation system is analyzed, thus the analytical calculation method of the three-phase short-circuit current of the photovoltaic power generation system considering the transient response of the phase-locked loop is proposed, and the characteristics of the short-circuit current are analyzed, Finally, the simulation model of photovoltaic grid-connected system is built to verify the correctness of the theoretical analysis.

Frequent startup and shutdown of metro trains will cause a large impact on the traction load in a short time, which will easily lead to accelerated aging of transformer insulation and overload risk of main transformer. To solve this problem, a coordinated network storage optimization strategy for subway load impact is proposed. Firstly, based on the time-series characteristics of subway load, the formation mechanism of impact load is analyzed, and a two-dimensional fluctuation index considering the characteristics of power curve is established to quantitatively describe the impact degree. Secondly, taking the optimal system economy and the minimum load impact as the upper and lower objectives respectively, a double-layer optimization model for the coordinated control of grid topology and energy storage devices is established to solve the optimal switching change and energy storage scheduling strategy. Finally, the actual power supply load of a subway line in Shanghai is taken as an example, and the results show that the proposed method can effectively suppress the impact load and improve the reliability and economy of power supply.

There is lots of rotational magnetic flux in transformer cores or motor cores. The hysteresis and magnetostrictive properties of silicon steels of core under rotational magnetization will increase the core loss and vibration deformation. In order to model the coupled hysteresis and magnetostrictive properties in the core silicon steel effectively, based on experimental data, this paper proposes that the eddy current loss and abnormal loss of electrical steel sheet under rotational magnetization are introduced into the energy balance formula of traditional Jiles-Atherton hysteresis model to characterize the rotational hysteresis characteristics of electrical steel sheet. At the same time, based on the nonlinear loop curve relationship between magnetostriction and magnetization, the first-order inertial magnetostrictive model under rotational magnetization is established. The magnetization intensity characterized by the hysteresis model is mapped to the magnetostrictive model, and the coupling relationship between hysteresis and magnetostrictive characteristics is established. Finally, the effectiveness of the proposed model is verified by experiment. The results show that the proposed coupling model can effectively characterize the rotational magnetic properties of electrical steel sheets, and provide a reference for the optimization design of high-quality electrical products.

In recent years, the distribution network resilience enhancement technology developed in response to extreme events has developed rapidly. However, in practical applications, the high economic cost of technical solutions is one of the important factors restricting its implementation. Based on the above problems, this paper proposes an economic post-disaster restoration decision-making method for resilient distribution network with MESS and electric vehicle V2G, which reduces the economic cost of restoration while ensuring the restoration effect. In the pre-disaster stage, a pre-disaster electric vehicle scheduling model is established to obtain the distribution of electric vehicles and the maximum output of each V2G station. According to the actual line layout and load information, the MESS temporary warehouse deployment location is determined. In the post-disaster stage, the comprehensive economic cost of post-disaster restoration is taken as the objective function to optimize the V2G station output and MESS scheduling in the restoration process. The proposed method is verified by multiple sets of examples. The simulation results show that the proposed collaborative restoration scheme can effectively improve the economy of the resilient strategy while reducing the post-disaster power loss of the system.

In extreme weather conditions, network reconfiguration and island partition are important means for fault recovery of distribution networks with distributed generations. According to the development process of meteorological disasters, the multi-period fault recovery strategy is conducive to improving the resilience of distribution network. The existing fault recovery strategies do not consider the operation cost of multiple network reconfigurations and island partitions, as well as the fluctuation of distributed power supply in the island, resulting in poor security and economic results of the optimization results. Therefore, this paper proposed a multi-period recovery strategy for improving distribution network resilience during extreme weather conditions. By constructing a unified model of active distribution network reconfiguration and island partition, considering the recovery time scale under different fault causes, and subdividing the time section, the strategy can realize the dynamic adjustment of distribution network structure during the fault duration, and improve the resilience of the power grid. Finally, the proposed strategy is verified in the IEEE 33-bus system. The case shows that the proposed strategy has fewer switching operations and higher load recovery rate; and it can resist power disturbances within a certain range, which can improve the resilience of the distribution network in extreme weather conditions.

To overcome the influence of the auxiliary effect on the end terminal and to realize the accurate fault location of DC distribution line, a fault location method based on active detection principle is proposed. After the fault occurs, a current limiting strategy is designed to limit the fault current, and then switched to the active detection control strategy to inject the characteristic frequency detection signal to the DC line. According to the excitation and response characteristics of the fault equivalent circuit under the characteristic frequency, a fault location equation is constructed, and the single-terminal fault location based on fault analysis method is realized. The corresponding model is built in the PSCAD simulation software, and the performance of the fault location method under different fault areas and fault transition resistances is verified by simulations. The method of using the characteristic frequency detection signal to construct the fault location equation to overcome the influence of the auxiliary effect on the end terminal is verified, and the relative error of the fault location results is within 0.5%.

To address the uncertainty of wind and light output, we combine the wind and light output scenarios simulated by Monte Carlo sampling, and compare the wind and light output data of three scenario reduction techniques, namely synchronous backgeneration, K-Means clustering, and Fuzzy C-Means (FCM) clustering, and find that the synchronous backgeneration scenario reduction technique can better characterize the volatility and randomness of wind and light output. An economic dispatch model with the objective of minimizing the total operating cost of the system is also established for the microgrid system consisting of wind power, photovoltaic, micro gas turbine, proton exchange membrane fuel cell and battery. In the case analysis, the Particle Swarm Optimization (PSO) is used to optimize the power output of each microsource under typical scenarios, and the effectiveness and rationality of the synchronous backgeneration algorithm combined with Monte Carlo sampling to deal with the uncertainty of wind and light power output are verified.

This paper analyzes the topology, parameter design and control strategy of the distributed DC chopper and improves its control strategy. By comparing the response curves of the traditional DC chopper, the distributed DC chopper and the distributed DC chopper with the improved control strategy, it is shown that the distributed DC chopper with the improved control strategy has a smooth energy consumption curve and better fault ride-through (FRT) performance. On this basis, to address the problem of high cost of DC chopper with traditional FRT strategy, the AC-voltage magnitude reduction method is designed based on the permanent magnet direct-drive wind turbine to actively reduce the output power of the wind farm when a fault occurs, and the FRT coordination control strategy is designed in combination with the distributed DC chopper using the improved control strategy, which can significantly reduce the capacity of DC chopper and the cost of system while ensuring FRT performance of system. Based on the actual parameters of the Rudong offshore wind via VSC-HVDC project, the effectiveness of the proposed coordinated control strategy is verified by establishing the system model in the PSCAD/EMTDC.