Abstract:Because of the problem of wind power grid connection， and comprehensively considering the grid-connected power error， period power fluctuation， and battery state of charge， this paper proposes a multi-objective optimal control strategy for the battery energy storage to compensate for the generation plan curve error and stabilize the wind power fluctuation. Firstly， by analyzing the characteristics of the wind storage combined system， an evaluation system with multiple evaluation indexes is established， and a multi-objective optimal control model of the output of the battery energy storage is constructed. Then， combined with the NSGA-Ⅱ algorithm and fuzzy comprehensive evaluation， the multi-objective optimal control model is solved and decided， and the output power command of the battery energy storage system is optimized in real-time. Finally， based on the measured power generation data of a wind power station， the comparative simulation verifies that the proposed multi-objective optimal control strategy can effectively improve the ability to track the power generation plan curve and reduce the frequent fluctuation of wind power and improve the service life of the energy storage battery by optimizing the active output and charge state of the battery energy storage system.

Abstract:To solve the lighting energy consumption monitoring problem caused by the increasingly complex electrical equipment of modern urban smart lighting lines， the system of urban road lighting energy consumption and power theft monitoring is designed based on LoRa Internet of Things technology. The system consists of a LoRa wireless communication network of centralized controllers， LED lighting fixtures， and other electrical equipment with LoRa wireless communication capabilities. The central controller is the system host. And LED lighting and other electrical equipment are the monitoring nodes. A real-time lighting energy consumption and power theft monitoring strategy of two-step wireless communication， time-sharing， and synchronous collection of power data of all monitoring nodes are proposed， where the lighting power and energy consumption of lighting lines are calculated by the centralized controller. The hardware module design of the centralized controller is introduced， and the software realization methods of the strategy are given in detail， including the program design of the centralized controller and the modification of the power program of the LED lamp driver. The experimental results of the lighting energy consumption and power theft monitoring system test platform verify that the system can effectively achieve wireless lighting energy consumption synchronous collection and power theft monitoring functions， which can better meet the requirements of intelligent control of urban street lights.

Abstract:To restrain the strong galloping and the discharge of transmission line for the overhead contact system （OCS ） positive feeder of the Lanzhou-Urumqi high-speed railway under strong wind environment， a new type of insulation and anti-galloping device is proposed based on the OCS structure and the galloping characteristic of the positive feeder， its insulation layer thickness can improve the insulation margin between the line， and the spoiler can change the overall aerodynamic characteristics of the line. The aerodynamic characteristic and galloping response of the positive feeder before and after installation of the anti-galloping device at different wind speed is analyzed by simulation， and the anti-galloping effect of the device under the influence of different coverage rate， spoiler heights， and insulation layer thicknesses parameters is studied， finally， the electric field characteristic of the new insulation and the anti-galloping device is analyzed. The results show that the installation of new insulate anti-galloping devices has an anti-galloping effect， and the higher the coverage rates， the more significant of anti-galloping effect. After the installation of the four sections， the maximum vertical and horizontal galloping amplitude declined by 57.76% and 54.68%， respectively. The device with a higher spoiler section of 75% outer diameter and 3 mm insulation layer thickness has a more obvious anti-galloping effect. The maximum field intensity on the surface of the positive feeder is reduced by 52.96%， and the average field intensity around the 4 mm circle from the positive feeder is reduced by 36.71% after the installation of the device. The research results can provide a reasonable and effective anti-galloping design for the galloping of the OCS positive feeder and other overhead transmission lines in the strong wind section of the Lanzhou-Urumqi high-speed railway.

Abstract:To better obtain the current operating state of the battery energy storage system， a state of charge （SOC） evaluation method of the battery energy storage system based on neural network fusion is proposed. First， the advantages and disadvantages of back-propagation （BP）， gated recurrent unit （GRU）， and long and short-term memory （LSTM） neural network algorithms are compared. The calculation time of BP is usually short， while the estimation accuracy of LSTM for temporal data is high. Then the correlation degree between different input parameters and SOC is analyzed by KL divergence， Pearson correlation coefficient， and grey correlation degree. Compared with the LSTM estimation results， the characteristic parameters that have a greater impact on the SOC of the battery energy storage system are selected. Finally， the empirical mode decomposition algorithm is applied to decompose the SOC data into multiple components， and the sample entropy is used to aggregate the components into high and low-frequency bands. BP and LSTM neural network algorithms are used to estimate SOC in different frequency bands. Compared with a single strategy， the proposed method not only improves the estimation accuracy of SOC， but also reduces the calculation time.

Abstract:Aiming at the problems of cross-influence between the two output branches va and vb of the single-inductor dual-output Buck-Boost converter and poor transient performance， an active disturbance rejection control （ADRC） strategy based on cascaded extended state observer （CESO） is proposed. First， according to the ADRC theory， the main road and the branch roads are fitted as independent systems to reduce the cross-influence between the branches. Secondly， CESO is designed to estimate the total disturbance of the system to eliminate the observation residual error caused by the incomplete estimation of the traditional extended state observer， CESO is also used to suppress the high-frequency noise of the circuit sensor to further improve the estimation accuracy of the observed value， and then the observed value acts on the state error feedback control rate of ADRC to improve the transient performance of the system. Finally， the closed-loop stability of the control system is proved by the Lyapunov theory. The simulation results show that the control strategy proposed in this paper effectively reduces the cross-influence between the two output branches va and vb， and improves the transient performance of the system at the same time.

Abstract:To improve the State of Charge （SOC） estimation accuracy， an improved Cubature Kalman Filter （CKF） algorithm is proposed， in which an error compensation module based on Kernel Extreme Learning Machine （KELM） algorithm is integrated into CKF properly. The Recursive Least-Square method （RLS） is used to online estimate the parameters of the equivalent circuit model of the battery， and the preliminary SOC value is estimated using the CKF algorithm accordingly. Then， taking the operation voltage and current of the battery， and residuals mean and variance of the preliminary SOC estimation values as the input， and the corresponding SOC estimation error as the output， the SOC estimation error prediction model based on the KELM algorithm is obtained， and trained by using the Federal Urban Driving Schedule （FUDS） condition data. The regression prediction ability of the KELM model is utilized to perform error compensation on preliminary estimation， so as to reduce the error of SOC estimation. To verify the effectiveness and advancement of the proposed method， the experimental data of the Arbin battery test platform are used for simulation analysis. The results show that the proposed method has higher estimation accuracy， stronger generalization， and robustness under various operating conditions.

Abstract:A zero phase shift synchronous rotary frame filter-based single-phase locked loop is proposed to overcome the harmonic ripple in the rotor position estimation of sliding mode observer and the phase lag caused by the first stage low-pass filter. Firstly， the sliding mode observer is established based on the mathematical model of the motor， and the reason for the phase lag of the traditional synchronous rotary frame filter is analyzed； Secondly， the first stage low-pass filter is omitted， and the high-order harmonics and chattering in back electromotive force are filtered by dq transformation； Finally， the Matlab/Simulink simulation model and the sensorless vector control experimental platform of permanent magnet synchronous motor are built to compare the performance of the traditional synchronous rotary filter and the zero phase shift synchronous rotary frame filter based on single-phase locked loop. Simulation and experimental results show that the proposed method has better tracking performance and higher observation accuracy than the traditional synchronous rotary frame filter structure.

Abstract:The occurrence of asymmetric faults in the grid can cause adverse effects such as a drop in the point of common coupling （PCC） and an increase in the output current amplitude of the power conversion system （PCS）， which may cause the PCS to cut out in severe cases. To address the above problems， this paper proposes a PCC voltage dynamic support strategy under asymmetric faults. First， the operating characteristics of PCS under asymmetric faults are analyzed， and the voltage support equation is obtained. Then the fault-ride-through operation area is divided according to the grid connection criteria， and the PCC voltage dynamic support scheme is designed based on the voltage support equation and the fault ride-through operation area， while the PCS output current amplitude is limited to further suppress the negative sequence voltage， ensuring the voltage support effect and sufficient capacity. Finally， the effectiveness of the proposed strategy is verified in Matlab/Simulink.

Abstract:To meet the high linearity requirement of high-performance RF front-end receivers， a high linearity low noise amplifier （LNA） operating at 2.4 GHz based on SiGe BiCMOS technology is proposed. The amplifier adopts the cascade structure to achieve a balance between gain and noise， and the feedback capacitor is connected in parallel between the input and output of the Cascode structure to achieve simultaneous noise and power match. An improved dynamic bias active current mirror is designed to improve the linearity parameters of the input 1 dB compression point and the input-referred third-order intercept point. To meet the requirements in application， LNA is integrated with an RF switch and power module to form an RF receiver front-end chip for processing and testing. The test results show that： within the operating frequency range of 2.4 ~ 2.5 GHz， the gain of the whole receiver chip is 14.6 ~ 15.2 dB. Return loss < -9.8 dB， and NF < 2.1 dB. At 2.45 GHz， the input 1 dB compression point is -2.7 dBm， and the input-referred third-order intercept point is +12 dBm. The chip area is 1.23 mm×0.91 mm. The test results are consistent with the simulation results， and the designed LNA exhibits good linearity performance.

Abstract:To address the current of avalanche photodiodes （APD） with large differences in orders of magnitude before and after the avalanche and drastic changes in I-V characteristic curves， a shallow neural network is used to complete the I-V function fitting based on logarithmic and normalized pre-processing of I-V characteristic data， and the neural network structure is further optimized to improve the model accuracy. On this basis， the SPICE model of APD is implemented in Verilog-A hardware description language， the validity and accuracy of the model are verified by designing the circuit in Cadence， and the relative error is introduced to evaluate the model accuracy. The results show that the mean square error loss of the I-V characteristic function learned by the optimized neural network and the TCAD simulation data is 2.544×10-7， the maximum relative error of the SPICE model verification circuit and the TCAD simulation data is 3.448%， the average relative error is 0.630%， and the time spent to construct the SPICE model is about 50 hours. High-precision and high-efficiency device SPICE model construction are realized， which has important guiding significance for the design and application of new APDs.

Abstract:A finite time backstepping control strategy is proposed for a class of uncertain nonlinear systems with asymmetric time-varying output constraints and input delay. Firstly， a new nonlinear transformation function that transforms the constrained system into an unconstrained system is proposed to solve the asymmetric time-varying output constraint. Secondly， To deal with the “explosion of complexity” problem of backstepping control， a new finite-time filter is constructed， where the filter error is eliminated by an error compensation mechanism. Then the Pade approximation method and intermediate variable are applied to compensate for the influence of input delay on the control system. According to the Lyapunov theory， the finite-time stability of the closed-loop system is proved， and the output does not violate the constraint. Finally， the effectiveness of the new filter and finite-time control strategy is verified by the comparative simulation of the filter and the simulation of a manipulator system.

Abstract:The three-level neutral point clamped （3L-NPC） converters with conventional virtual space vector pulse width modulation （VSVPWM） scheme have some inherent disadvantages. For example， its reference voltage frequently passes through small triangle regions and it has a high total harmonic distortion （THD） of ac voltage which cannot be tuned by the amplitude of the virtual space vector. Aiming to solve the above issues， a modulation ratio tracking-based VSVPWM is proposed in this paper to reduce THD. First， the disadvantages of the division method of small triangle regions in the convention VSVPWM strategy are analyzed in detail. It is found that the THD of the line voltage in the 3L-NPC converter is very high when the conventional VSVPWM strategy is adopted. Second， the proposed VSVPWM strategy based on modulation ratio tracking is proposed in detail. It can be concluded that in the 3L-NPC converter with the proposed VSVPWM strategy when the modulation ratio is equal to the ratio of the virtual medium vector amplitude to medium vector amplitude， the minimum harmonic of the line voltage is achieved. At last， a 3L-NPC converter model in Matlab/Simulink is built to verify the proposed VSVPWM strategy， and the simulation results demonstrate that the proposed VSVPWM strategy is very simple， correct， and effective.

Abstract:Using unmanned aerial vehicles （UAV） is an effective means to solve firefighting problems in urban high-rise buildings. This paper proposes a control strategy based on constraint following theory for the pan/tilt water-jet nozzle tracking to solve the problem of UAV pan/tilt movement control. First， according to the actual firefighting demand in high-rise buildings， the two-degree-of-freedom driving structure of the pan/tilt water-jet nozzle is designed. Second， Denavit-Hartenberg （D-H） method is used to model the pan/tilt system， and the pan/tilt kinematics equation is established. Then the dynamic model of pan/tilt without constraints is constructed according to the Lagrangian equation. The expected trajectory of the pan/tilt water-jet nozzle is regarded as the constraint. Without introducing any variables or pseudo-variables such as the Lagrange multiplier， the analytical formula of driving torque which can meet the requirement of constraints following is obtained based on the Udwadia-Kalaba equation， and continuous state feedback control is realized， which achieves the purpose of water-jet nozzle trajectory tracking. What’s more， to reduce the tracking error， the Baumgarte method is used for stability processing， and the trajectory tracking control is simulated in Matlab/Simulink environment. Finally， an experiment platform with the digital signal processor （DSP） as a control core is built to conduct the trajectory tracking control. The results show that the control algorithm based on constraint following theory could effectively complete the tracking task and achieve high-precision tracking of the desired trajectory.

Abstract:The current nonlinear models of bolted joints ignore the influence of the effective contact area of bolts and deviate significantly from the actual assembly features of joints. In this regard， a dynamic modeling method of bolted joints considering local contact features is proposed. An orthogonal and nonlinear virtual material model with a cylindrical shape is introduced to express the flexible characteristics of joint interfaces under external load. Through establishing a stress-strain analysis model of micro-virtual material， the equations of calculating physical parameters of virtual materials are derived based on the principle of minimum potential energy and the Takashi Yoshimura method. A geometric parameter prediction model of the contact area of bolted joints is established based on the deep neural network （DNN） so that the nonlinear relationship mapping between the contact state of bolted joints and the diameter of the contact characteristic area is realized. Finally， a dynamic model of bolted joints with actual assembly characteristics is developed. Taking steel plates connected with bolts under a free boundary state as an experimental object， the effectiveness and accuracy of the proposed method are proved by comparing the result from the finite element simulation model established by the abovementioned method and experiments. The model developed by the proposed method shows a significant improvement in the comprehensive evaluation index of root mean square error （RMSE） compared with the virtual material modeling method without considering local contact features.

Abstract:This paper presents a mathematical model for the topological optimization of multi-material structures under inertial load based on the guide-weight method， which aims to minimize structural compliance while adhering to volume constraints. The topological optimization problem of multi-material structures is decomposed into topological optimization problems of single-material structures. Rational approximation of material properties （RAMP） was used to express the nonlinear relationship between density and elastic modulus. The guide-weight method was employed to develop iterative expressions for design variables under inertial loads. Numerical examples demonstrate the effectiveness of this approach in optimizing multi-material structures under inertial loads. The results show that the RAMP interpolation method produces clearer topology configurations with fewer gray units and reduces structural compliance （up to 35.2% in example 1） compared with other general interpolation models. The greater the influence of inertial load on the design area， the higher the elastic modulus of distributed material. A high ratio of modulus to density can significantly increase the stiffness of a structure.

Abstract:To address the difficulty in controlling groove depth and roughness during micron-level groove machining of dry gas seals， a theoretical evaluation method was proposed， and a model was constructed to investigate the machining depth and roughness. Using this numerical simulation， the relationships between the laser fill spacing S and spot diameter ds， and the resulting groove depth ha and roughness Ras were systematically investigated. The results demonstrate that the groove depth and roughness decrease with the increasing filling spacing， and the influence on groove depth and roughness is significant when S < 7 μm. The effect of spot diameter on the groove depth is insignificant， the roughness initially increased slowly and then rapidly with the increase in spot diameter， and the critical value of ds was approximately 7 μm. The experimental results well supported those of the numerical analysis of groove depth， which was slightly different from the results of roughness analysis. In this study， the TOPSIS comprehensive evaluation method was used to optimize the optimal range of the processing parameters： considering the processing efficiency， the optimal parameter ranges are 8 μm ≤ S ≤ 15 μm and 9 μm ≤ ds ≤ 15 μm； however， when the processing efficiency is not considered， the optimal parameter ranges are 5 μm ≤ S ≤ 10 μm and 5 μm ≤ ds ≤ 15 μm. The research results have certain guiding significance for further improving the high efficiency and precision machining of micron-level groove depth of dry gas seal.

Abstract:To improve the bottom flow field structure and further reduce the aerodynamic drag of the high-speed train， based on the idea of bottom flow control， a triangular cross-sectional deflector located before and after the bogie cabins on the train bottom is designed， and its aerodynamic drag reduction characteristics are studied. Taking the open line running high-speed train with three coach formation CRH380B at the speed of 300 km/h as the research subject， and using the Realizable k-ε turbulence model， four typical deflector installation positions are explored， and the deflector installation position with the best drag reduction effect is selected to investigate the differences of deflector drag reduction characteristics under different combinations of five angles and five heights. The drag changes on the train bodies， bogies， and bogie cabins before and after the installation of the deflectors， the pressure distribution changes， and the flow field structure changes in the bogie area are also compared. The results show that the best drag reduction effect is achieved only when the deflectors are installed in the direction of incoming flow in front of each bogie cabin in both directions. After the installation of the deflectors， the aerodynamic drag on the train bodies and bogie cabins increases， but the drag on the bogies is significantly reduced， the flow velocity and the pressure difference in the bogie areas decreases， and the bottom flow field is significantly improved. At the same time， it is found that the 15° and 100 mm combination of the deflector has the best drag reduction effect， and the drag reduction rate of the three cars reaches 7.08%. The numerical simulation proves that the bottom deflectors can effectively reduce the train running resistance.

Abstract:The difficulty of high-precision and high-efficiency dressing of multi-grooved and small-arc- shaped grinding wheels seriously limits its application in precision grinding. The principle of electrode Electrical Discharge Machining （EDM） concave small circular arc-forming grinding wheel is expounded in this paper. The optimal combination of processing parameters is designed through single-factor experimental research. And the V-groove contour shape corresponding to the copper electrode turning grinding wheel is trimmed by a high-precision turning tool device. The EDM multi-groove small circular arc forming grinding wheel research is carried out step by step to reduce energy， the 2 500# and 1 000# particle size diamond grinding wheel forming and dressing verification is completed， and the graphite sheet specimen is ground for testing. The experimental results show that the proposed method controls the surface quality and contour accuracy of the grinding wheel under high efficiency， which has a guiding effect.

Abstract:The data fusion between onboard Light Detection and Ranging（LiDAR）and GNSS/IMU can improve the accuracy of the localization system in intelligent driving， and the calibration of external parameters between two sensors is the premise of data fusion. It is hard to measure external parameters between onboard sensors manually and the the calibration of automation degree is lower. In this paper， an automatic calibration method that does not rely on markers is proposed. First， the line feature map and surface feature map are constructed， respectively， and closed-loop constraints are used to reduce the accumulated error. The laser points in each frame are matched with surface feature voxels and line feature clusters extracted from two feature maps. The matching errors are integrated with the constraints based on motion calibration. Then a least squares problem is built to optimize the external parameters. Finally， we evaluate the efficiency and robustness of the proposed algorithm by conducting experiments with real vehicles.

Abstract:With the increase in the complexity and reliability of mechanical systems， electromagnetic wear particle detection sensors have been widely studied and gradually applied in the field of wear-state monitoring for mechanical devices. Aiming at the problem that the velocity-randomness of metal wear particles in lubricating oil leads to poor consistency of detection results of electromagnetic wear particle detectors， the magnetic model of a spherical wear particle in an alternating magnetic field was established， and the distribution law of magnetic flux density and the method for calculating magnetic energy perturbation was studied. Meanwhile， the loss coefficient of magnetic energy for non-ferromagnetic wear particles was proposed and measured by experiments， and the characteristic signals of wear particles exported from the sensor are then compensated. The experimental results show that the method can eliminate the influence on the output signal amplitude by the speed of wear particles， which markedly improves the consistency of wear particle detection results.

Abstract:Based on the first-order shear deformation theory， the free vibration characteristics of a circular plate of porous Functionally Gradient Material （FGM） on an elastic foundation in a thermal environment are studied. First， Voigt modified mixed power law model with pores is considered， and a unified temperature field is given to describe the temperature dependence of materials. Using Hamilton’s principle， the governing differential equation of free vibration of porous FGM circular plate on elastic foundation under thermal environment is derived and dimensionless. Then the dimensionless governing differential equation and boundary conditions are transformed by using the differential transformation method， and the algebraic characteristic equations for dimensionless natural frequencies and critical temperature rise are obtained. The problem is degenerated and compared with the existing literature results to verify its effectiveness. Finally， the influence of gradient index， porosity， boundary conditions， thickness radius ratio， temperature rise， and Winkler elastic foundation coefficient on the dimensionless natural frequency of porous FGM circular plate as well as the influence of relevant parameters on the critical temperature rise is calculated and analyzed. The results show that the gradient index affects the frequency， reflecting the characteristics of the transition of materials from ceramics to metals. Porosity weakens the stiffness and then affects the natural frequency. Winkler foundation has a role in strengthening the stiffness， and the increase in temperature causes thermal buckling and instability of the structure.

Abstract:Based on the traditional concave hexagonal honeycomb structure， a new type of honeycomb structure with a negative Poisson’s ratio is proposed in combination with the beetle’s sheath wing structure. The impact resistance and energy absorption capacity of the new types of honeycomb structures with negative Poisson’s ratio and the concave hexagonal structure are compared based on the simulation calculation of the finite element software Abaqus/Explicit. The initial impact peak force and energy absorption per unit mass are taken as evaluation indexes. The results show that the initial peak force of the new structure with negative Poisson’s ratio is 28% lower than that of the concave hexagonal structure， and the energy absorption capacity of the structure is increased by 35% before compression enters the densification stage. The cell angle is used as the gradient transformation parameter to construct a new type of negative Poisson’s ratio structure with different gradient arrangements. The cushioning performance of different gradient structures and new uniform types of negative Poisson’s ratio structures are calculated， analyzed， and compared， together with the deformation modes of each structure in the impact process. The results show that the four gradient structures can enhance the impact resistance of the structure， but in terms of energy absorption performance， the layered progressive positive gradient structure （C3） has a strong energy absorption capacity. The experimental samples of the C3 structure and uniform new negative Poisson’s ratio structure are made using 3D printing technology， and the quasi-static impact test is carried out. The correctness of the simulation results is verified through comparative analysis. The research results in this paper show that the reasonable gradient distribution arrangement is of great significance to improve the impact resistance and energy absorption capacity of the structure， and provides a reference for the subsequent exploration of structural buffer design.

Abstract:To solve the orientation disorder of flexible biomass particles in food processing and bioenergy production， a triangular groove channel was designed. Based on the computational fluid dynamics-discrete element method （CFD-DEM）， a gas-solid coupling model for flexible particle movement in a triangular grooved channel was established. Among them， the double-chain bonded sphere model was used to characterize the flexible biomass particles. Orthogonal experiments were designed to study the influence of gas velocity， particle length， channel inclination， and groove angle on the orientation of flexible particles. The results show that the proportion of flexible particles with an orientation angle of 0 to 10° is as high as 0.9； the channel inclination angle β has the greatest impact on the orderliness of particle orientation， and as the particle length increases， the channel inclination angle and groove angle decrease， but the orientation orderliness increases. In the optimized model， the proportion of particle orientation angles from 0 to 10° is 0.96， the orientation order parameter S is -1.911， and the particle orientation is generally consistent with the direction of the groove； the average velocity of particle movement is 2.467 m·s-1. This achievement provides a theoretical basis for the study of particle orientation.