Traditional open-switch fault diagnosis methods suffer from poor rapidity or robustness. To solve this issue, a new differential current observer-based fault diagnosis method is proposed in this paper. With the designed differential observer, fault symptoms (residuals) can be generated and adopted for fault diagnosis easily. Considering that the residuals are sensitive to motor operating condition in the conventional model-based method due to model error, an adaptive fault detection threshold is designed. As a result, the false detection and missed detection caused by the change of working condition can be avoided, and stronger robustness against speed, load and parameter variations can be achieved with superior rapidity compared with existing methods. Finally, the rapidity and robustness of the proposed fault diagnosis method are verified sufficiently through experimental results.

Active-passive magnetically suspended control moment gyro is a novel attitude control actuator for superquiet satellite. Harmonic current in its active magnetic bearing will be caused by mass unbalance of the rotor and sensor runout. It can generate multifrequency vibration and then degrade the pointing accuracy of the superquiet satellite. In this paper, an improved repetitive controller (RC) is proposed to suppress harmonic current validly. The low-pass filter in improved RC is put from internal loop to outside for reducing the tracking error of harmonic current. Phase compensators are designed to compensate the phase lag in high, middle, and low frequencies for enhancing the stability of magnetically suspended rotor system, respectively. Simulation and experimental results are given to show the validity and superiority of improved RC in harmonic current suppression.

This paper investigates a hybrid fractional repetitive control (HFRC) scheme for magnetically suspended rotor systems to suppress harmonic current caused by mass imbalance and sensor runout. With parallel structure, HFRC consists of a frequency-adaptive dual-mode repetitive controller (DMRC) and a phase-shift notch filter. By introducing fractional delay filters, the proposed DMRC provides frequency adaptability to eliminate odd and even harmonics independently at fixed sampling rate. Its delay time is halved compared with the conventional repetitive control scheme, and the control gains can be weighted to ameliorate system dynamic response according to harmonics distribution. Moreover, as the domination of control current, fundamental frequency current is additionally rejected by the notch filter; thus, achieving smaller overshoot and faster suppression performance. An improved phase compensator is designed in HFRC to expedite current convergence rate while stabilizing the overall system. Experimental results on a magnetically suspended flywheel demonstrate the advantages of the proposed method.

The suppression of harmonic vibration of active magnetic bearing (AMB) rotor system depends on the speed signal. Aiming at the problem of harmonic vibration suppression when the speed measurement sensor fails, a dynamic model of the AMB-rotor system, including mass unbalance and sensor runout, is established. This article analyzes the main sources of harmonic vibration force, and proposes a double-input filter based on adaptive frequency estimation. The characteristic that the displacement output signals of the radial X- channel and Y-channel of the rotor are orthogonal to each other can be used to quickly and accurately estimate the actual speed of the rotor adaptively. At the same time, the harmonic components of the control current are also compensated. Finally, the effectiveness of the proposed harmonic vibration suppression method with adaptive frequency estimator is verified by the simulation and experiments.

In response to the higher requirements of pulsar navigation performance for deep space exploration and remote sensing missions (such as Earth-Moon navigation and space observation), this paper proposes a time-delay estimation for pulsar navigation based on Peak-trough Amplitude and Rayleigh Entropy (PARE) to further improve the estimation accuracy and calculation speed. Firstly, the Fast Folding Algorithm (FFA) is used to perform parallel profile folding. According to the convergence and significance characteristics of the folded profiles, the FFA 3-D peak-valley map is threshold screened to narrow the search range, achieve the preliminary positioning of the subsequent profile test range, and improve the efficiency of pulsar frequency calculation. Secondly, according to the high sensitive response characteristics of the peak-valley difference of the folded profiles to the test frequency, ‘peak-trough amplitude’ is introduced to perform weighted operation on Rayleigh entropy of the folded profiles, and the significance of the folded profiles are jointly tested from the amplitude and structural characteristics to improve the accuracy and stability of pulsar frequency estimation. Finally, the cross-correlation operation is used to estimate the time-delay of the folded profiles. We also conducted simulations, influencing factor analysis, and NICER satellite actual observation data verification for the PARE method and the $\chi ^{2}$ test method. NICER satellite data verification shows that compared with the $\chi ^{2}$ test method, the PARE method has a 77.83% increase in time-delay estimation speed and a 57.93% increase in time-delay estimation accuracy. In addition, this method is insensitive to changes in observation duration and has better estimation stability.

Imbalanced vibration generated during the operation of a high-speed rotor inside a gyro is transmitted to the magnetically suspended control moment gyro through a magnetic bearing stator, resulting in micro-jitter. This greatly affects the control accuracy of the spacecraft attitude. In order to effectively suppress micro-jitter, the dynamic model of the magnetically suspended rotor with imbalanced mass is established in this article, and the imbalanced characteristics of the high-speed rotor are analyzed. Finally, a double-channel adaptive least mean square error algorithm is proposed. By utilizing that the radial X- and Y- displacement signals from the rotor displacement sensor are orthogonal to each other, a feedforward correction is applied to adaptively compensate the residual displacement stiffness of the magnetically suspended rotor system due to mass imbalance. While eliminating this synchronous current, the proposed algorithm also offsets the adverse effects of the low-pass characteristics of the power amplifier. Simulation and experimental results show that the method compensates the synchronous displacement stiffness force generated by the system with high precision, and realizes the micro-jitter control of the magnetically suspendedcontrol moment gyro.