Journal of Electrical Engineering & Technology最新文献

In order to study the structural strength change of automotive drive motor rotor under different cyclic conditions, and the fatigue life change after considering the internal damage of rotor material from the microscopic point of view, the strength and life calculation of automotive drive motor rotor is carried out based on the theory related to thermal-mechanical coupling and microscopic damage mechanics. Firstly, uniaxial tensile tests were conducted on the specimens at different temperatures to obtain the mechanical parameters of the silicon steel material at the corresponding temperature; secondly, the damage parameters at the corresponding temperature were fitted by the finite element inverse calibration method, and the temperature distribution law of the motor rotor was obtained by CFD calculation; then, based on the material parameters and temperature data, the damage condition and fatigue life of the rotor under four different cyclic operating conditions were studied by the finite element method. The results show that under the rated cycle condition, the stress does not reach the yield limit of the silicon steel material, and the volume fraction of holes inside the rotor material is still the initial hole volume fraction; under the peak cycle condition and rated-peak cycle condition, although the magnitude of the stress and stress distribution of the rotor are almost the same, the equivalent plastic strain of the latter is larger than that of the former, and the corresponding hole volume fraction is also larger; under the limit cycle condition In the ultimate cycling condition, the stress, equivalent plastic strain and pore volume fraction of the rotor have increased more obviously than the first three; and under the same cycling condition, the fatigue life of the rotor is smaller than that without considering the internal damage of the material.

This paper studies firstly the fault analysis method of valve-side winding single-phase grounding of converter transformer in line-commutated-converter high-voltage direct-current system. One power frequency cycle after fault is divided into 12 time periods according to the valve state, then the 12 time periods of high-voltage bridge faults are classified into 6 types based on the common characteristics, and the 12 time periods of low-voltage (LV) bridge faults are classified into 3 types. For each type of time period, the current flow path is analyzed, the corresponding circuit equation is written. By combining multiple time periods, the expressions of valve-side current and grid-side current are solved. On this basis, the differential current of converter transformer differential protection is derived and the performance of differential protection under valve-side winding single-phase grounding is studied. The research results show that when a single-phase grounding fault occurs in the valve-side winding of the LV bridge converter transformer, the second-harmonic ratio in the differential current is bigger than 15%, so the differential protection refuses to act due to mis-locking. In order to prevent differential protection from failing to act, an improved scheme of converter transformer differential protection is proposed. Through the logic coordination between the zero-sequence current unit and differential protection, the improved scheme can not only reflect various internal faults of converter transformer, but also ensure no action under the inrush current. The effectiveness of the proposed scheme is verified by simulation.

This paper proposes an improved interleaved boost converter with a single zero voltage transition (ZVT) soft switching cell (IBSC) to achieve high power density and efficiency. By applying the single ZVT soft switching cell to the interleaved structure, the volume of the converter can be reduced compared to the multi ZVT soft switching cell that has a soft switching cell for each phase. Furthermore, the efficiency of the converter can also be increased because each phase can achieve soft switching regardless of the number of phases. This paper provides a detailed analysis of the operating principle based on the duty of the main switch (S_m) and the design method for resonant parameters using the equivalent circuit of S_m. To verify the feasibility, a 3 kW prototype IBSC is designed and implemented. Based on the experimental results, the volume of the soft switching converter decreased by 29.84%, while its efficiency increased by 0.4% compared to the conventional hard switching converter. Therefore, it is confirmed that the proposed IBSC has advantages in terms of power density and efficiency.

Describing the networked inverter in an AC microgrid as a multi-intelligent system and considering the voltage restoration problem as a tracking problem, a finite-time quadratic control strategy for microgrid voltages considering cyber-attacks is proposed. Aiming at the false data injection attacks occurring in the microgrid actuators, a fixed-time sliding mode observer is designed, which can quickly and accurately estimate the attack signals without considering the initial conditions of the system. Then the super-twisting sliding mode is improved, and an adaptive super-twisting sliding mode is proposed. It is used to design secondary controller to solve the bias problem arising from the droop control, and realises the finite-time control. Furthermore, through the adaptive adjust of gains, the chattering problem is suppressed in the sliding mode control. The estimation value of the attack signal is introduced into the designed controller, which achieves the fast compensation of the unknown attack signal. Strict stability proofs of the observer and controller are given in this paper. Simulation experiments verify the effectiveness of the proposed scheme.

In a bearingless switched reluctance motor (BSRM), there is a conflict between the output regions of effective radial force and positive torque. So a compromise between radial force and torque is usually applied in a classical control scheme of the BSRM, resulting in under-utilization of its optimal performance of both levitation and motion. For a 12/8-pole BSRM, this paper implements a levitation control in the efficient excitation region to maximize the radial load capacity, performs a torque excitation from the unaligned position to the aligned position and adjusts in real time the instantaneous total torque so as to improve its torque output. In a 12/8-pole BSRM, the efficient levitation excitation region of each phase consists of two equal-width sectors, and a rotor angular position cycle is formed with the six equal-width sectors. Based on the optimal objective within each sector and combined with the derived mathematical models of the radial force and torque, the corresponding current constraint is designed to calculate the five currents in the two-excited phases. Further, the control scheme for a 12/8-pole BSRM under efficient levitation excitation is developed to simultaneously regulate four instantaneous values of two radial forces and two phase torques. Finally, the good performance of the proposed method for the 12/8-pole BSRM under efficient suspension excitation is proved by simulation analysis.

Existing artificial neural network-based methodologies for salient object detection in RGB-depth (RGB-D) images typically require significant memory and computation time. In this paper, we propose ReBiT-Net, an novel and resource-efficient network designed to addresses this issue. ReBiT-Net utilizes a mobile network for feature extraction and incorporates depth map quality to regulate the fusion of multi-modal features, resulting in top-to-bottom refinement of salient objects using salient information. Empirical evaluations conducted on five benchmark datasets demonstrate the superior performance of our model in terms of accuracy (achieving 334 frames per second for an input size of 320 (times) 320) and model parameters (merely 5.1 MB). Moreover, we introduce ReBiT-Net*, a simplified variant of ReBiT-Net, which entails reduced model parameters (4.2 MB) and enhanced processing speed (793 frames per second for a 256 (times) 256 input size). These improvements are achieved through reduced memory requirements and computational demands via the adoption of a smaller input image size.

Placement of μPMUs in active distribution networks (ADNs) can significantly improve the system’s observability. Existing research mostly focused on how to achieve global observability with a minimum number of μPMUs, but ignored the system observability under special cases such as line faults, μPMU failures, and topology changes. To ensure ADN’s observability with a minimum number of μPMUs in both normal and special cases, this paper proposes a μPMU placement method that considers the observability of existing monitoring devices, the distribution of observation redundancy, and the nodal priority of μPMUs placement. Simulation results verify that the proposed method needs fewer μPMUs than existing methods and enhances the stability of observability for achieving the global observability of an AND. Both the economic feasibility and observability performance of the PMU placement are considered.

This paper presents a fault detection approach for doubly-fed induction generators (DFIG) utilizing an improved fractional-order PID sliding mode observer (IFOPID-SMO). The IFOPID-SMO eliminates chattering and demonstrates superior stability effectively and has a faster convergence speed compared to other observers. Firstly, the stator voltage-oriented vector control method is employed to establish the nonlinear space state vector equation of the DFIG. Then, the IFOPID-SMO is constructed based on the DFIG’s mathematical model, and the d-q axis currents of the rotor are estimated. Secondly, the observer parameters are optimized using the adaptive golden eagle optimization algorithm, which enhances the convergence speed and steady-state accurateness of the observer significantly. Furthermore, the asymptotic stability of the IFOPID-SMO is analyzed by Lyapunov’s second law, which guarantees that the system state converges to a steady value rapidly and stably. Finally, three faults of DFIG including stator inter-turn short-circuit fault, rotor inter-turn short-circuit fault, and rotor current sensor faults are detected respectively. The effectiveness of the IFOPID-SMO is demonstrated through the data recorded of a doubly-fed wind power test bench under unfaulty and three faulty operation conditions.

Transformers’ vibration and noise problems are critical to environmental comfort and reliability of equipment. To reduce the vibration and noise of transformers, the vibration and noise of medium and medium-high transformer cores under Maxwell force and magnetostriction were analyzed. A three-dimensional magneto-mechanical-acoustic coupled finite element model was established under sinusoidal and rectangular wave excitation. The deformation, vibration acceleration, and sound pressure distribution were analyzed under the Maxwell force and the magnetostrictive force of medium and medium-high transformers. A vibration noise optimization design architecture for medium and medium-high frequency transformers has been proposed. A transformer core structure with low noise vibration is designed based on the proposed optimization design architecture. The experimental results show that under the sinusoidal excitation, the vibration acceleration in the lamination direction decreases the most, from 18.748 m/s² before optimization to 4.89 m/s² and under rectangular wave excitation, it decreases from 51.08 m/s² before optimization to 13.182 m/s². The proposed method provides a reference for the optimization design of low noise vibration transformers.

To deal with the modeling error, dynamical uncertainties and disturbances caused by actual operating conditions, i.e., total disturbance, a speed composite sensorless controller based on tracking differentiator (TD) for a permanent magnet synchronous motor system (PMSMs) is proposed in the paper. Aiming to obtain precise electric angular velocity and the rotor position without mechanical sensors, a sliding mode observer (SMO) is established, which can estimate above signals from the back electromotive force (EMF). A time-optimal tracking differentiator (TD), attenuating the chattering phenomenon with a low-pass filter, is designed to optimize the performance of SMO. In addition, an extended state observer (ESO) is introduced to obtain the estimation value of the total disturbance, and can achieve satisfactory control performance via a feedforward compensation channel. Simulation and experimental results validate that the proposed speed sensorless composite control algorithm has excellent anti-disturbance ability and satisfactory speed regulation performance.