Time-frequency (TF) analysis (TFA) method is an important tool in industrial engineering fields. However, restricted to Heisenberg uncertainty principle or unexpected cross-terms, the classical TFA methods often generate blurry TF representation, which heavily hinder its engineering applications. How to generate the concentrated TF representation for a strongly time-varying signal is a challenging task. In this paper, we propose a new TFA method to study the non-stationary features of strongly time-varying signals. The proposed method is based on synchrosqueezing transform and employs an iterative reassignment procedure to concentrate the blurry TF energy in a step-wise manner, meanwhile retaining the signal reconstruction ability. Two implementations of the discrete algorithm are provided, which show that the proposed method has limited computational burden and has potential in real-time application. Moreover, we introduce an effective algorithm to detect the instantaneous frequency trajectory, which can be used to decompose mono-component modes. Numerical and real-world signals are employed to validate the effectiveness of the proposed method by comparing with some advanced methods. By comparisons, it is shown that, the proposed method has the better performances in addressing strongly time-varying signals and noisy signals.

Based on the LuGre friction model, a sliding mode adaptive controller is presented to compensate for the friction in the servo system. The terminal switching function is selected as the sliding mode surface, which can make the error of the system converge to the equilibrium point in finite time. The main analytical result is a stability theorem for the proposed controller which can achieve asymptotical stability of the closed‐loop system. Furthermore, the transient performance of the system is analytically quantified. To support the theoretical concepts, the authors present dynamic simulations for the proposed control scheme.

This paper proposes a strategy to suppress the torque ripple based on three‐phase four‐switch (TPFS) inverter for the permanent magnet synchronous motor (PMSM) drives system to ensure safe and reliable operation in case of single‐phase open circuit of the three‐phase six‐switch (TPSS) inverter. When a TPFS inverter fault‐tolerant topology is adopted, the voltage fluctuations of the DC‐split capacitors will cause the command voltages and currents to have a second harmonic components in addition to the effective DC components. This also results in the existence of second harmonics in the torque and speed, which causes the torque and speed to generate periodic ripple. Therefore, in order to solve this problem, this paper proposes a proportional‐integral quasi‐resonant (PIQR) control strategy for the current loop. By suppressing the second harmonics in the motor currents, the current waveform can be improved, and the ripple in the torque and speed can be well suppressed. The feasibility and effectiveness of the strategy are verified by simulation results.