In this article, a double normalization fault diagnosis (DNFD) method is proposed to cope with open-circuit faults of permanent magnet synchronous motor drives. The proposed DNFD method consists of a current normalizer, a time-domain fault variable determinator, a time-domain to angle-domain converter, an angle normalizer, and a fault identification encoder. The affections of the variable torque can be eliminated by the current normalizer, whereas the affections of the variable speed can be eliminated by the angle normalizer, which is the main contribution of this article. To reduce the affections of the following factors, i.e., the calculation error of the time-domain to angle-domain converter, the measurement noises of current sensors, the performance of the analog-to-digital converter, the sampling frequency, and the electromagnetic interference of the system, the hysteresis comparator is employed, in which two fault thresholds are required. Compared with the conventional single normalization fault diagnosis method, the DNFD method has better robustness. The effectiveness of the proposed DNFD method is verified by the experimental results.

Repairing processing is a significant method for damaged high-cost Ti-6Al-4V components to decrease economic loss, which usually utilizes a welding technique. For a large-size structural component, welding processing is commonly completed in air conditioning, which makes it difficult to avoid welding defects. To this end, an appropriate matching technique is important for improving welding performance. In the present research, asynchronized laser shock peening (ALSP) and synchronized laser shock peening (SLSP) techniques were utilized to decrease the influence of macro welding defects on laser-welded Ti-6Al-4V joints. The results show that SLSP has a greater effect on inducing surface plastic deformation on Ti-6Al-4V joints with a pitting depth of more than 25 microns while ALSP can lead to a pitting depth of about 15 microns. Through micro-CT observation a long hot crack exists in the central area of as-welded joints with a length of about 2.24 mm, accompanied by lots of pores in different sizes on double sides. After ALSP processing, some pores are eliminated while others are enlarged, and one-side crack tips present closure morphology. However, some microcracks exist on the side-wall of hot cracks. With the influence of SLSP, significant shrinkage of pores can be observed and both sides of crack tips tend to be closed, which presents a better effect than ALSP processing. Moreover, greater effects of grain refinement and thermal stress release could be achieved by SLSP processing than ALSP, which can be ascribed to dynamic recrystallization. For the as-welded joint, the ultimate tensile strength (UTS) and elongation (EL) values are 418 MPa and 0.73%, respectively. The values of UTS and EL in the ALSP processed joint are increased to 437 MPa and 1.07%, which are 4.55% and 46.48% higher than the as-welded joint, respectively. Such values after SLSP processing are 498 MPa and 1.23%, which are 19.14% and 68.49% higher than the as-welded joint, respectively.

Considering that the degradation of ball screw grease involves fractal characteristics, which exhibit long-term dependency and autocorrelation, a multivariate accelerated degradation modeling and reliability assessment method based on the fractional Brownian motion process model is proposed in this paper. Firstly, a nonlinear accelerated degradation model of grease is established using fractional Brownian motion, considering the heterogeneity of samples as well as the memory effect and long-term dependence in the deterioration process, and realizing parameter estimation. Secondly, a multivariate reliability evaluation model is established by considering multivariate performance indicators in combination with the Frank copula function. Finally, the effectiveness and potential engineering application value of this method are verified through actual degradation data of the grease.

In this paper, a fault tolerant control method is proposed for a permeant magnet synchronous motor (PMSM) servo drive system with four leg inverters to cope with the open phase fault. As one of common faults in the motor drive system, the open phase fault will degrade the control performance and efficiency. Even serious damage is caused in some extreme cases. Hence, it is meaningful to realize the fault tolerance of the drive system with open phase fault. The proposed method includes three parts: a torque-producing current calculator, phase voltage determination and voltage distributor. The torque-producing current calculator is designed by taking the third harmonic flux into consideration to calculate the torque-producing current. In the phase voltage determination, it is proved that the third harmonic flux has no influence on the line voltage equation. For healthy operation and fault operation, the voltage requirements in remaining healthy phases are determined based on the line voltages. Finally, two voltage distributors are designed to distributor the phase voltages into remaining inverter leg. The main difference of two voltage distributors is the polarity of two remaining voltage. Compared to the conventional method, the proposed method can reduce the torque ripple under a postfault condition. In addition, the controller structure will not be changed under a pre-fault and postfault condition. The proposed method has been validated by simulated results and experimental results.

In permanent magnet synchronous machines (PMSMs), the harmonic currents induced by harmonic back electromotive force (BEMF) and the inverter nonlinearity are inevitable. Existing methods typically rely on the design of high-performance controllers for harmonic suppression, which inevitably requires complex parameter tuning. In contrast, parameter identification methods, widely used in machine control, can achieve high-performance control while avoiding complex parameter tuning. However, there is a lack of methods that apply parameter identification for harmonic suppression. Consequently, this article models the harmonic voltages caused by the inverter nonlinearity, dq circuit cross coupling, and harmonic permanent magnet flux linkage as the virtual harmonic BEMF. Furthermore, this article proposes a harmonic current suppression method based on the 2-D identification of virtual harmonic BEMF. The proposed method utilizes only two integral regulators to achieve static-errorless identification of the amplitude and phase of the virtual BEMF while simultaneously ensuring static-errorless suppression of the harmonic currents. Furthermore, this article also considers the impact of system delay and incorporates compensation. Finally, the effectiveness of the proposed method is verified experimentally.

The stator interturn short-circuit fault can cause great harm to the permanent magnet synchronous motor (PMSM), necessitating timely diagnosis to mitigate the damage. Under servo conditions, the variation of the speed, torque, and amplitude and frequency of electrical signals of PMSM present challenges to fault diagnosis. This article proposes a double normalization interturn short-circuit fault diagnosis method. The healthy PMSM current is calculated using a linear extended state observer, subtracted from the faulty PMSM current to generate the residual. Considering the existence of model errors, the second harmonic current residual is converted into a dc component in the negative sequence rotating frame, such that the impact of model parameters is reduced. Since the current residual is directly related to the fault current and short-circuit turns ratio, whose amplitude and frequency will change under the servo conditions, the current residual is first divided by the voltage to normalize the amplitude; then the dc component is extracted by angle integration to normalize the frequency change. The effectiveness of the proposed method is verified by experimental results.