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The current-loop control of a permanent magnet synchronous motor (PMSM) system suffers from periodic and aperiodic disturbances, which result in current ripples and degrade control performance. This paper presents an enhanced equivalent-input-disturbance (EID) approach to reject periodic and aperiodic disturbances in the current loop of a PMSM. Two additional quasi-resonant compensators (QRCs) are integrated into a conventional EID estimator with a low-pass filter (LPF) to handle the disturbances. The configuration of an enhanced EID (EEID)-based control system for PMSM current loop is explained. An analysis in the frequency domain shows the mechanism of the presented method for rejecting periodic and aperiodic disturbances simultaneously. It reveals that the sensitivity reduction of the system for aperiodic disturbances is mainly determined by the bandwidth of the LPF and that for periodic disturbances is determined by the parameters of the QRCs. The stability of the system is analyzed using the Nyquist stability criterion. The design algorithm for system parameters is provided. Compared to the conventional EID approach, the proposed method provides an additional degree of freedom to deal with periodic disturbances. The design of the QRCs is independent of each other, which makes the proposed method flexible and easy to implement. The effectiveness and the superiority of the EEID approach are validated by simulation results of a PMSM system. [ABSTRACT FROM AUTHOR]

The current-loop control of a permanent magnet synchronous motor (PMSM) system suffers from periodic and aperiodic disturbances, which result in current ripples and degrade control performance. This paper presents an enhanced equivalent-input-disturbance (EID) approach to reject periodic and aperiodic disturbances in the current loop of a PMSM. Two additional quasi-resonant compensators (QRCs) are integrated into a conventional EID estimator with a low-pass filter (LPF) to handle the disturbances. The configuration of an enhanced EID (EEID)-based control system for PMSM current loop is explained. An analysis in the frequency domain shows the mechanism of the presented method for rejecting periodic and aperiodic disturbances simultaneously. It reveals that the sensitivity reduction of the system for aperiodic disturbances is mainly determined by the bandwidth of the LPF and that for periodic disturbances is determined by the parameters of the QRCs. The stability of the system is analyzed using the Nyquist stability criterion. The design algorithm for system parameters is provided. Compared to the conventional EID approach, the proposed method provides an additional degree of freedom to deal with periodic disturbances. The design of the QRCs is independent of each other, which makes the proposed method flexible and easy to implement. The effectiveness and the superiority of the EEID approach are validated by simulation results of a PMSM system. [ABSTRACT FROM AUTHOR]

Rotate vector (RV) reducers have widely been used in high-performance precision drives for industrial robots. However, the current nonlinear dynamic studies on RV reducers are not extensive and require a deeper focus. To bridge this gap, a translational–torsional nonlinear dynamic model for an RV reducer transmission system is proposed. The gear backlash, time-varying mesh stiffness, and comprehensive meshing errors are taken into account in the model. The dimensionless vibration differential equations of the system were derived and solved numerically. By means of bifurcation diagrams, phase trajectories, Poincaré sections, and the power spectrum, the motion state of the system was studied with the bifurcation parameters' variation, including excitation frequency and meshing damping. The results demonstrate that this system presents enriched nonlinear dynamic characteristics under different parameter combinations. The motion state of the system is more susceptible to change at lower frequencies. Increasing the meshing damping coefficient proves effective in suppressing the occurrence of chaos and reducing vibration amplitudes, significantly enhancing the stability of the transmission system. [ABSTRACT FROM AUTHOR]

This paper aims to realize multi-objective optimization of cycloid-pin gears to improve the positioning accuracy and load-carrying capacity of the rotary vector (RV) reducer, via the consideration of backlash, transmission error, and torsional stiffness. Initially, the analytical models of the RV transmission backlash and transmission error are developed by using both purely geometrical and equivalent model methods individually. Based on the generalized Hooke's law, a torsion angle model is established to characterize the torsional stiffness of the system, utilizing methods such as Hertzian contact theory and bearing stiffness models. Subsequently, employing the Monte Carlo method, extremum method, and quality loss function, mapping objective functions for dimensional accuracy (tolerance) and transmission performance (backlash, transmission error, and torsional stiffness) are constructed. The geometry dimensions, dimensional accuracy, and modification of the cycloid-pin gear are considered as design variables to create a multi-objective optimization model. The improved Parallel Adaptive Genetic Algorithm using Deferential Evolution (PAGA-DE) is used for multi-objective solutions. Through example calculations, the impact of cycloid-pin gear parameters on transmission performance before and after optimization is determined. The reliability of backlash after optimization within 1.5′ reaches 99.99%, showing an increase of 8.24%. The reliability of transmission error within 1′ reaches 98.52%, demonstrating an increase of 1.35%. The torsional angle is reduced by 8.9% before optimization. The results indicate that the proposed multi-objective optimization design method for cycloid-pin gears can achieve the goal of improving the transmission performance of the RV reducer. [ABSTRACT FROM AUTHOR]

This article presents a new method that employs the active disturbance rejection control (ADRC) paradigm to handle the control problem for a class of nonlinear systems with unknown disturbances and measurement noise. An improved extended state observer (ESO) is devised to separate disturbance estimation from state reconstruction and a new parameter is used to adjust disturbance-rejection performance independently. This increases the flexibility of system design and makes the gain of the improved ESO (IESO) small compared to that of a conventional ESO in the ADRC. A low-pass filter is added to the IESO. This changes the slope of the magnitude curve of the Bode diagram from $-20$ dB/dec to $-40$ dB/dec at high frequencies for measurement noise, which improves the noise-suppression performance. Comparison with a conventional ESO reveals the superiority of the IESO in disturbance rejection and noise suppression. The presented method is validated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a method of altitude control of the powered parafoil with uncertainties and disturbances based on sliding-mode backstepping control combined with a linear extended state observer (LESO). First, the dynamics of a powered parafoil is derived in the longitudinal plane using its inclination angle. The problem of altitude control is converted to the issue of angle control. Next, uncertainties and disturbances are considered as a total disturbance. An LESO is used to estimate the total disturbance and form an inner-loop compensation. Backstepping control is employed to regulate the inclination angle to follow the desired value. A fractional sliding surface is introduced to the backstepping control. This ensures the transient performance of altitude control of the powered parafoil. Then, stability analysis shows that the observation errors of the LESO are bounded and the control system is uniformly ultimately bounded. Simulation results of an 8 degree-of-freedom powered parafoil illustrate that the LESO can effectively estimate the states of the system and demonstrate the validity and the superiority of the presented method. [ABSTRACT FROM AUTHOR]

This article presents an improved equivalent-input-disturbance (EID) approach to handle unknown disturbances and plant uncertainties. The disturbances and uncertainties are treated as a lumped disturbance in an EID-based control system. The effect of the lumped disturbance is compensated by an EID estimator. A constraint between design parameters and uncertainties is imposed on the design of the estimator. In addition, there are insufficient analyses of the influence of uncertainties on the control performance and the stability of the system. A new filter is devised for an improved EID estimator in this article to remove the constraint. This ensures that the sensitivity of the system to disturbances at low frequencies can be freely decreased. An analysis of the system reveals that uncertainties not only influence disturbance-rejection and reference-tracking performance but also affect system stability. A sufficient stability criterion is derived with consideration of uncertainties. The validity of the presented method is demonstrated by simulation and experimental results. [ABSTRACT FROM AUTHOR]

Disturbance rejection and time-delay compensation are important for control systems in practice. This article presents an observer-and-predictor-based method to reject an unknown exogenous disturbance for an input-delay system in which only delayed output is available. First, the equivalent-input-disturbance method is employed to reconstruct the system state and to estimate the disturbance. A prediction of the disturbance is calculated to reduce the effect of a phase lag caused by the delays. A new predictive scheme is designed for feedback control. Next, the system is divided into two subsystems for analysis and design: one for reference tracking and the other for disturbance rejection. Sufficient conditions are derived to guarantee the system’s stability. An analysis of the method reveals that the disturbance rejection can be viewed as a patch to the predictor-based feedback control. Finally, two case studies are used to show the validity and superiority of the method. [ABSTRACT FROM AUTHOR]

This article addresses the control problem of an open-loop unstable linear time-invariant system with an input delay and an unknown disturbance. An observer-predictor-based control method is presented for such a system in which only output information is available. First, the system state is reconstructed and the disturbance is estimated using the equivalent-input-disturbance approach. Next, the future information on the state and the disturbance is predicted to reduce the effect of the input delay. Then, a new predictive control scheme is developed. The closed-loop system is simplified into two subsystems for analysis. Stability conditions are derived for each subsystem separately. Finally, a comparison with previous approaches through simulations shows the superiority of the presented method over others for disturbance rejection. [ABSTRACT FROM AUTHOR]

This paper presents an improved equivalent input disturbance (EID) approach to deal with exogenous disturbances and system nonlinearities. The disturbances and nonlinearities are regarded as a lumped disturbance on the control input channel. The EID approach, which has a state observer and an EID estimator, is used to estimate the lumped disturbance. There is a constraint between the observer and the estimator on the design of the control system for the conventional EID approach. A stable zero was added to the estimator to remove the constraint and to improve the stability of the system in this paper. This ensures that the observer and the estimator can be designed independently. An analysis of the improved EID approach explains the mechanism of disturbance rejection. The simulation and experimental results of position control of a ball-and-beam system demonstrate the validity of the method. [ABSTRACT FROM AUTHOR]