Abstract:In order to accurately predict the springback of high-strength steel， it is necessary to use the material model parameters that accurately and comprehensively describe the material mechanical properties. Therefore， an inverse calculationmethod of the parameters of the Barlat89 and Yoshida-Uemori （Y-U） combined model was proposed based on the modified Levenberg Marquardt （LM） optimization algorithm. Using high-strength steelDP780 as an example， the mechanical property curve of the material was obtained through unidirectional tensile and tensile compression tests. LS-DYNA software was used to simulate and analyze the object of the test. The modified LM algorithm was used for continuously optimizing the material model parameters preset by simulation. Finally， the simulation output equals the material property curve obtained from the experiment in the sense of least squares， and the optimal material combination model parameters are obtained. The results show that the correlation coefficient of the LM algorithm is 0.951 4， and the convergence of the LM algorithm is good. The inverse Barlat89 and Y-U model parameters can accurately describe the uniaxial tensile and tensile compression mechanical properties of DP780 materials at the same time. The simulation curve fits well with the test curve， and the average relative error of the two curves is 4.65%. The material model parameters obtained by this method reflect the mechanical properties of materials under forward and reverse loading and can markedly improve the prediction accuracy of springback.

Abstract:To achieve an accurate measure of the strain value of the measured structures， a metallic packaged fiber Bragg grating （FBG） strain sensor is designed. A six-layer strain transfer model of the FBG sensor is established， and its strain transfer mechanism from the measured substrate layer， substrate adhesive layer， packaging substrate layer， adhesive layer of FBG， protective layer， and FBG layer is analyzed and derived. Through theoretical analysis and finite element simulation， the effects of the FBG length， the thickness of the FBG layer and substrate bonded layer， the elastic modulus， and Poisson's ratio of middle layers on the average strain transfer rate are comparatively analyzed. According to the simulation results， the packaging material， size， and adhesive layer thickness of the designed FBG sensor are determined. Finally， an equal-intensity cantilever beam that provides the load on FBG is designed， and a correction coefficient of the strain transfer error is proposed. A comparison test of strain transfer is carried out on the bare FBG and metallic packaged FBG sensors. The results show that their average strain transfer rates are 98.25% and 98.15%， respectively， and the error between the simulation results is within 0.15%~0.25%.

Abstract:In order to solve the uncertainty of azimuth in the ultrasonic sensor measurement process， a target distance and azimuth measurement method based on time of arrival （TOA） is proposed， and an environment sensing method based on ultrasonic detection is developed. The echo signal is processed based on the mixed Gaussian fitting， which eliminates the problem of signal crosstalk and improves the measurement accuracy of target distance and azimuth information. Based on the characteristics of the sensor beam angle， the simultaneous measurement of targets at different distances is achieved. By introducing “uncertainty”， a set of belief assignment functions is defined， and the DSmT（Dezert-Smarandache Theory） method is used for data fusion to realize map updates. Finally， the experimental device and environment are constructed for verification， and the result shows that the basic contour of the environment can be built through 135 measurements， and the mapping error is less than 3 cm.

Abstract:In order to explore the influence of coaxial cable shielding influencing factors on its shielding effectiveness （SE）， a test set was built based on the shielding attenuation triaxial method to evaluate the SE of coaxial cables and connectors for in-vehicle communication. The effect of the shielding layer， end connector， and segmentation on the SE of coaxial cable was investigated， and the SE test data in the range of 0.1 MHz to 3 GHz was obtained. The analysis results show that for the vehicle communication coaxial cable RG174 series， the double shielding layer is 10~15 dB higher than the SE of the single shielding layer.The cable segmentation and end connector can all reduce their SE. The SE of the cable with the end connector and segmentation is more obvious， and the drop can reach 10 dB.Moreover， the end connector changes the cutoff frequency of the cable. The research results can be used to guide the selection and segment layout design of coaxial cables for in-vehicle communication and solve electromagnetic compatibility problems such as electromagnetic emission and interference of in-vehicle communication equipment in the coaxial cable and their connection parts.

Abstract:Aiming at the low-speed climbing condition of a commercial vehicle， a three-dimensional hydrodynamics simulation method is used to study heat management in some commercial vehicle cabins. The mechanism of the heat dissipation influencing the coolant system is focused on. The ventilation rate of the radiator and the outlet temperature of the radiator are taken as the experimental targets. By introducing the orthogonal design and Box-Behnken experiment design method， combined with the establishment and analysis of the regression equation， the relationship between the moving distance of the condenser， the moving distance of the cooling fan， and the extension of the windshield are constructed and optimized. A set of experimental design and optimization processes suitable for engine room thermal management is put forward， which provides a reference for the layout of heat dissipation components in the engine room. The results show that the change in the position of the coolant systems in the commercial vehicle cabin affects the airflow state and temperature field， thus affecting the heat dissipation performance of the engine room. After optimization， the ventilation capacity of the commercial vehicle radiator is improved by 5.26%，the outlet temperature of the radiator is reduced by 3.44%， and the heat dissipation efficiency of the engine room is significantly improved.

Abstract:Based on GB/T 18655—2018 standard， an experimental system was built for fuel cell vehicles’ DC/DC converter in an anechoic chamber. Conduction emission and radiation emission experiments were carried out. The interference current of each cable port and electric field intensity of the reference point was obtained during the normal operating state of fuel cell vehicles’ DC/DC converter. Then， an electromagnetic simulation model of fuel cell vehicles’ DC/DC converter was established based on the measured geometric parameters of each component in the experimental system. The obtained interference current from the conduction emission experiment was used as the excitation signal of the electromagnetic simulation model. The electric field intensity of the reference point position obtained by simulations was compared with the experimental results. The comparisons show that the overall change trend of simulation results is consistent with the overall change trend of the experimental results. The average error is about 5 dB in the high-frequency band， while the accuracy is relatively poor in the low-frequency band. Overall， the electromagnetic simulation model of the fuel cell vehicles’ DC/DC converter is reliable. Finally， the electromagnetic simulation model was used to analyze the radiation immunity characteristics of fuel cell vehicles’ DC/DC converters. The results show that the normal operating state of DC/DC converters will not be affected in the case of plane wave interference with the electric field strength of 30~100 V/m. Thus， the radiation immunity characteristics of fuel cell vehicles’ DC/DC converters meet the electromagnetic compatibility requirements.

Abstract:To handle the complex cases that the uncertain parameters of the Powertrain Mounting Systems （PMSs） of electric vehicles are of imprecise information and correlation， a reliability analysis method of electric vehicle PMS is proposed by considering the imprecise information and correlation of PMS parameters. Firstly， evidence variables were employed to describe the parametrical imprecise information， and the correlation between evidence variables was described by the correlation coefficient matrix. Then， based on the affine transformation and standardization techniques， the relevant evidence variables were transformed into standard irrelevant evidence variables. Finally， by calculating the inherent characteristic response of the PMS as well as the belief function and plausibility function that meets design requirements， the reliable probability intervals of PMS responses were evaluated. The reliability analysis results of the numerical example of an electric vehicle PMS show that the parametrical imprecise information and correlation can be effectively handled by the correlated evidence variables； the parametrical imprecise information has a great influence on the system reliability， especially on the reliability related to the natural frequency in Roll direction； the system reliability changes obviously as the parametrical correlation increases， and ignoring the parametrical correlation may lead to large errors of reliability analysis.

Abstract:In the envieronmntal vehicle trajectory prediction link of intelligent driving， to obtain the trajectory timing characteristics of the surrounding vehicles more accurately， the dropout layer is embedded into the long short-term memory （LSTM） neural networks model to enhance network generalization， and the attention mechanism is introduced into LSTM to distribute larger weight to the time series data with a marked influence on the prediction effect， so as to improve the reliability of the prediction results. Subsequently， the improved LSTM model is combined with the GRU model （LSTM-GRU） to further improve the prediction accuracy of the surrounding vehicle trajectory. On this basis， the LSTM-GRU model is trained， verified， and tested using the NGSIM public dataset. The results show that， compared with the standard LSTM and GRU model， the LSTM-GRU model integrating dropout and attention mechanism has advantages in predicting the surrounding vehicle trajectory with a longer time sequence， which improves the accuracy of trajectory prediction and reduces the root mean square error and mean absolute error between the actual and the predicted trajectory.

Abstract:To resolve the difficulties of mesh generation existing in the preprocessing module of numerical simulation， an adaptive unstructured mesh generation method for the implementation of the dual interpolation boundary face method is presented.The binary tree adaptive refinement generation is carried out according to the mesh size， surface curvatures， thickness distribution， and other geometry features. This method avoids using any coordinating transitional template to deal with the hanging points and reduces the difficulties of mesh generation. In addition， a fast intersection algorithm between the volume elements and solid boundaries is proposed.The algorithm improves the computational efficiency and reduces the complexity of algorithm implementation. Experimental results show that the final mesh generation is mainly composed of hexahedral element mesh as a whole and a few pentahedral， tetrahedral， and pyramid element mesh for auxiliary， which verified the validity， accuracy， and robustness of the proposed method.

Abstract:Elastic deformation has always been a key factor restricting the machining quality in thin walled machining. In order to solve this problem， a method for the prediction and compensation of elastic deformation is investigated in this study. Firstly， based on the finite element method， a layered milling model is built for the straight micro-thin wall with different thicknesses. The deformation law of the thin wall along the direction of height and length is studied. A thin wall deformation model with the cantilever beam method is establishedby considering the effect of material removal on the stiffness of the thinwall. Secondly， a single degree of freedom cutting force measurement and real-time cutting parameter compensation device is developed. The thin wall deformation is estimated based on the cutting force and deformation model measured in real-time during the thin wall cutting process. The deformation prediction is used for the compensation value to compensate for the radial cutting parameters in real-time. At last， a comparative experiment is conducted. The results show that the average relative error of the thin wall decreases from 6.86% to 2.19% after the radial cutting parameter compensation， which verifies the model reliability and the effectiveness of the compensation device.

Abstract:To solve the difficulty that the Dirichlet constraint condition cannot be imposed directly for the extended isogeometric analysis （XIGA） on the boundaries of 3-D laminates with the holes， an enhanced XIGA was proposed. The enhanced XIGA is the combination of the XIGA and the B++ splines method to deal with the 3-D laminate holes. The control points related to the holes trimmed elements are converted into the collocation points on the hole’s boundaries. The Kronecker delta property is satisfied for these collocation points， which facilitates the direct imposition of constraints on the trimmed boundaries with holes. The proposed method is adopted to analyze the examples of the sandwich plate and hat beam laminate plate， and the result shows that the displacement and stress results calculated by the enhanced XIGA are consistent with those obtained by the FEM.The results coincide with the results obtained by the experimental method. With the above numerical examples， the accuracy and effectiveness of the enhanced XIGA to deal with the problems of 3-D laminates with holes are illustrated.

Abstract:In order to meet the promotion and application of the domain-specific innovation methods， facing the puzzle of enterprises’ optimization of numerous innovation methods， a decision-making model for optimization of the domain-specific innovation methods is proposed by analyzing and evaluating the applicability of different methods in practical application situations. Taking the field of rail transit equipment as an example， through the analysis of the practical application situation of enterprises， a five-dimensional application situation space including product type， innovation object， innovation chain link， innovation category， and innovation process is established. According to the spatial dimension and its hierarchical relationship， the evaluation index system of application situation applicability is constructed. At the same time， in order to reduce the subjective influence of man-made evaluation， a combination weighting method combining FAHP （Fuzzy Analytic Hierarchy Process） and EM （ Entropy Method ） is proposed. Combining with TOPSIS （Technique for Order Preference by Similarity to Ideal Solution）， the FE-T optimization decision model of various field characteristic innovation methods is established. The total applicability score of each method is solved by the model， and the multi-method optimization sequence is determined based on rule sorting. The decision model is used to guide the selection of a method in the bogie innovation project of an enterprise， and the optimization sequence of domain characteristic innovation methods suitable for the application situation of the project is obtained， which provides a reference for the optimization of domain characteristic innovation methods.

Abstract:In this paper， an intelligent inversion optimization design method for generators running in the transmission chain system is proposed， and a 15 kW permanent magnet synchronous generator running in the transmission chain system is taken as an example to verify the method by optimizing the design parameters of it for increasing its operating efficiency. Firstly， under full consideration of the influence of the converter side on the transmission chain system， a co-simulation modeling platform for the transmission chain system is established， and the correctness of the electromagnetic design parameters of the transmission chain and the accuracy of co-simulation computing platform are verified.Secondly， six sensitive parameters are selected from the eight design parameters of the generator by variance analysis and a Latin hypercube sampling scheme based on genetic algorithm optimization is proposed after selecting the optimization variables.This sampling plan can balance the uniform distribution of the sample space and the uniformity of the projection of each variable dimension.Then， through the intelligent inversion optimization design model based on the Gaussian stochastic process combined with the PESA-Ⅱ multi-objective optimization algorithm， the Pareto frontier of generator efficiency and maximum rated output torque is obtained， and winding design according to the optimized cogging variable is carried out.The results show that the optimized efficiency is 96.2%， which is increased by 0.6% compared with its original design， and the electromagnetic loss of the generator is reduced by 16.8%. Finally， the accuracy of the simulation platform is verified by experiments， which further illustrates the effectiveness of the sample data and the optimal design.The design method proposed in this paper can be optimized for large-scale transmission chain systems of different specifications. The optimization method has certain universality and can be used for integrating accurate simulation calculation and process optimization design of large-scale offshore transmission chain systems in our country.

Abstract:To improve the transmission reliability of multi-terminal systems， this paper proposes a hybrid three-terminal DC trans-mission line pilot protection method based on the Mann-Kendall test method. The method uses the T-connected bus three terminal current fault component to determine the fault area， then uses the Mann-Kendall test method to analyze the changing trend of the current at both ends of the line in the fault area， and realizes the fault type identification and the fault pole selection. Finally， the model is built in PSCAD/EMTDC and different fault conditions are simulated， and the proposed protection method is verified with MATLAB. Simulation results show that the proposed method can operate reliably within 2.5 ms under various fault conditions， with good quick-action， and has strong resistance to noise interference and transition resistance.

Abstract:A V2G energy interaction strategyconsidering the cost of response and EV owners’ willingness is proposed， to address the issues of insufficient consideration of user willingnesswhen electric vehicles （EV） participate in demand response and the unfair distribution of benefits between the power grid and EVs in demand response. The strategy quantifies and analyzes the charging time delay and battery degradation costs incurred by EV users in the interaction.And allows EV owners to express their interactive willingness by specifying their cost coefficients to obtain reasonable compensation. Subsequently， a two-level Stackelberg game model between the distribution system operator （DSO） and EVs clusters is established and converted into a single-level mixed-integer second-order cone programming （MISOCP） problem based on Karush-Kuhn-Tucker conditions. The effectiveness of the model is verified on the IEEE 33-node system， and a win-win situation between EV owners and DSO is achieved.

Abstract:To solve the problem that the traditional transponder systems are susceptible to strong-noise interference and the transmission delay accuracy is not high when simulating underwater targets at different distances， a coarse-fine two-stage arrival time estimation method is proposed， and a reliable transponder system with high precision delay is developed. The system is mainly composed of the upper system， which collects and processes signals， and the lower system， which amplifies and transducers. The upper system uses multistage spectrum analysis， and its peak ratio is greater than the set threshold for rough estimation，and the signal wave headis preliminarily obtained. Then， the double threshold detection algorithm based on the energy entropy ratio is used toacquire a more accurate arrival time by fine estimation.The problem of inaccurate delay is solved. Finally， the lower system receives the response signal transmitted by the upper computer through TCP and responds to the echo signal at a predetermined time. Lake trails show that the delay error of the system is less than 40 ms， and the system has the advantage of high-precision forwarding delay and has good robustness under strong-noiseinterference.

Abstract:Aiming at grid-connected speed control of a hydraulic wind turbine with bladder accumulator under the conditions of wind and synchronous generator load changes， a new grid-connected speed control method is proposed—decoupled generalized predictive optimization control （DGPOC）. Firstly， the feedforward decoupling method and generalized prediction are used in DGPOC to remove the coupling relationship between the variable motor swing angle and the accumulator proportional valve lift. The accumulator proportional valve and the variable motor swing angle are adjusted synchronously to achieve constant speed control. Secondly， as a performance constraint， the energy loss of the accumulator proportional valve is introduced into the optimization objective function to improve the wind energy utilization rate. Finally， the simulation results conducted on the MATLAB-AMESim platform validate that the DGPOC can not only improve the speed and robustness of variable motor speed control， but also reduce the energy loss of the system.

Abstract:Aiming at the problems of serious distortion and excessive peak value of grid-side current waveform in power conversion systems（PCS）under unbalanced voltage， this paper proposes an energy optimal control strategy for PCS under unbalanced grid voltage. The control strategy deeply analyzes the influence of parameter k and grid voltage imbalance on the energy operation of the system through the relationship between the control target parameter k， the grid voltage imbalance and the instantaneous power fluctuation， the grid-side current imbalance， and the grid-side current peak. On this basis， to focus on the two control objectives of suppressing the current amplitude and power fluctuations， the optimization algorithm is added， and the energy optimization control strategy of the current limiting PCS with the parameter k selected only within ［-1，0］ is proposed. The simulation results show that the control strategy can more quickly and effectively limit the current peak value to the maximum allowable peak value through the k parameter and current limiting control strategy， and further reduce the power fluctuation and improve the active power output capacity of PCS， which reflects the energy optimization of PCS operation.

Abstract:In order to solve the problems of flow out-of-limit and load loss of distribution network caused by planned maintenance， this paper proposed a quantitative analysis method of operation risk classification of intelligent distribution network considering maintenance plan. Firstly， the influence of the maintenance plan on the safe operation of the distribution network was analyzed， and the risk assessment index system of the intelligent distribution network was established from three aspects： operation and maintenance factors， external factors， equipment factors， and so on； secondly， the interval algorithm was introduced， the subjective and objective mixed evaluation method was used to weight the indicators， and the combined weights were obtained by combining the weight factors； thirdly， based on the risk assessment index and its weight， the operation risk level was divided， so as to realize the comprehensive risk quantitative evaluation of the failure probability and impact consequences； finally， combined with the annual operation data of Tianjin power grid， the Ada-DT algorithm was used to predict the risk level， and the operational risk assessment index system and classification method constructed in this paper were effectively verified. The case analysis results showed that the proposed method can effectively classify the operational risk level， identify the weak links of the distribution network and give targeted prevention and control measures， which could provide a reference for the maintenance personnel.

Abstract:The state of health （SOH） of a lithium-ion battery reflects the aging degree of Lithium-ion the battery. When the battery is charged in constant current-constant voltage mode， the charging curves with different aging degrees are also different. Based on this fact， this paper proposes a data-driven model based on a temporal convolutional network （TCN） to establish the mapping relationship between the charging curve and SOH. TCN is a novel neural network composed of multi-layer causal convolution， which can encode the sequence of sampling points on the charging curve. The experiment proves that the encoding vector is easier to establish the mapping relationship with SOH. The experimental results show that the proposed SOH estimation model has high estimation accuracy andgood adaptability to different types of batteries.

Abstract:Aiming at the problem that the traditional protection gap can not extinguish the electric arc quickly and the trip rate of the line is high， this paper studies and designs the electromagnetic arc extinguishing air cannon. The device uses the electromagnetic piston theory to eject high-speed air masses. The high-speed air mass can impact the arc， take away the heat of the arc and draw the arc fine， enhancing the removing-free effect of the arc and forcing it to be extinguished quickly. And the spring mechanism installed at the piston end of theelectromagnetic arc extinguishing air cannon can automatically reset the piston after the electric arc extinguishing and be ready for the next time. According to the finite element method simulation， the arc can be drawn to 1/8 of its original thickness and the electric arc center temperature can be reduced to 1/3 within 16 msdue to the installation of the protection gap of electromagnetic arcing air cannon， which significantly enhances the removing free effect and forces the arc to be extinguished quickly. Therefore， the electromagnetic arc extinguishing air cannon has a stronger extinguishing ability and certain self-reliance， which can effectively reduce the lightning trip-out rate and improve power quality.

Abstract:An improved sliding mode control method based on an extended state observer is proposed to address the problem of control performance degradation of the permanent electric magnetic suspension system caused by unknown perturbations. Firstly， the control experimental platform and theoretical model of the system are analyzed and built for the permanent electric magnetic suspension type magnetic floating ball. Secondly， an extended state observer is introduced to estimate and compensate the system disturbances， and an improved sliding mode control method is designed using an integral sliding mode surface and an improved exponential convergence law to weaken the sliding mode control output jitter and improve the dynamic and static performance of the magnetic floating ball， and to analyze the stability of the system and the approximate range of error convergence with and without the extended state observer to estimate and compensate the disturbances. Finally， the proposed improved sliding mode control method based on the extended state observer， the improved sliding mode control method， the traditional sliding mode control method and the proportional-integral-derivative control method are compared and experimented by the semi-physical joint simulation technique. The theoretical analysis and experimental results show that the proposed improved sliding mode control method based on extended state observer has stronger stability and immunity， more robustness to external magnetic field uptake， and more adaptability to changes and sudden changes in the given signal range. The proposed control method further improves the control performance of the permanent electric magnetic suspension system， and is also a good reference for the control of such nonlinear systems as permanent electric magnetic suspension type magnetic floating ball.

Abstract:Interturn short circuit fault is one of the most common incipient faults in transformers. To improve the diagnosis accuracy of the mild faults， a multi-feature fusion diagnosis method for transformer winding short-circuit faults is proposed considering winding short-circuit current， winding temperature， current density， and magnetic flux characteristics. A COMSOL space model of a transformer with winding short faults is established. And the comparison of simulation results with the theoretical calculations is performed， which proves the correctness of the represented model. Then， the fault simulation and characteristics of transformers with mild faults are analyzed， and the characteristic parameters from current， temperature characteristics， current density， and magnetic deviation are extracted as fault features. BP network is used to identify the fault types. The effectiveness of this method is verified by an engineering diagnosis example of a transformer.