Repetitive Control Research Articles

Active Disturbance Rejection Repetitive Control for Current Harmonic Suppression of PMSM

Active Disturbance Rejection Repetitive Control for Current Harmonic Suppression of PMSM

High-Bandwidth Repetitive Trajectory Tracking Control of Piezoelectric Actuators via Phase-Hysteresis Hybrid Compensation and Feedforward-Feedback Combined Control.

Piezoelectric actuators (PEAs) are widely used in many nano-resolution manipulations. A PEA's hysteresis becomes the main factor limiting its motion accuracy. The distinctive feature of a PEA's hysteresis is the interdependence between the width of the hysteresis loop and the frequency or rate of the control voltage. Generally, the control voltage is first amplified using a voltage amplifier (VA) and then exerted on the PEA. In this VA-PEA module, the linear dynamics of the VA and the nonlinearities of the PEA are coupled. In this paper, it is found that the phase lag of the VA also contributes to the rate dependence of the VA-PEA module. If only the PEA's hysteresis is considered, it will be difficult to achieve high-frequency modeling and control. Consequently, great difficulties arise in high-frequency hysteresis compensation and trajectory tracking, e.g., in the fast scanning of atomic force microscopes. In this paper, the VA-PEA module is modeled to be the series connection of a linear subsystem and a nonlinear subsystem. Subsequently, a feedforward phase-dynamics compensator is proposed to compensate for both the PEA's hysteresis and the phase lag of the VA. Further, an unscented Kalman-filter-based proportional-integral-derivative controller is adopted as the feedback controller. Under this feedforward-feedback combined control scheme, high-bandwidth hysteresis compensation and trajectory tracking are achieved. The trajectory tracking results show that the closed-loop trajectory tracking bandwidth has been increased to the range of 0-1500 Hz, exhibiting excellent performance for fast scanning applications.

Improved sliding mode observer based repetitive control for linear systems with time‐varying input and state delays

SummaryControl systems are frequently subject to the negative effects of time delays and disturbances, which diminish the systems' tracking performance. In response to these challenges, this paper presents a novel approach, that is, the improved sliding mode observer based repetitive control (ISMO‐RC), to enhance the system's periodic signal tracking in the presence of the input and state time delays and the input disturbances. The design takes the advantages of RC and ISMO, in which RC effectively compensates periodic signals, while ISMO compensates both aperiodic disturbances and the time‐varying input and state delays. The stability of the whole system is guaranteed via the linear matrix inequality (LMI) and the Lyapunov–Krasovskii functional analysis. The proposed controller is evaluated through extensive simulations and experiments, which demonstrate its superiority over comparative control methods.

Output tracking control design with anti-disturbance rejection for modified repetitive nonlinear control systems

ABSTRACTThis paper intends to analyse the disturbance rejection and output tracking control for a class of nonlinear control systems with disturbances. In this connection, we present a method that combines a proportional-integral observer and nonlinear-equivalent-input-disturbance estimator for superior disturbance rejection performance. Specifically, the nonlinear-equivalent-input-disturbance estimator comprises of equivalent-input-disturbance estimator and nonlinear feedback term, which is employed to estimate and reject the disturbances from the nonlinear system. Notably, the proportional-integral loop in the proportional-integral observer reduces the estimation inaccuracy of the nonlinear-equivalent-input-disturbance. Then the estimated disturbance is intertwined into the repetitive control input to compensate it efficiently. In order to obtain the required results, the proposed control system is converted into a two-dimensional modified repetitive control system to describe the learning and control actions. In particular, the proposed controller enables to adjust the gains directly to improve the learning and control performance and as a result, the tracking accuracy increases. Using a general Lyapunov–Krasovskii functional, singular value decomposition technique and linear matrix inequalities approach, a design algorithm for establishing proportional-integral observer and feedback gains is developed for the system under consideration. Finally, simulation results are given to illustrate the developed method's validity and superiority.

Disturbance attenuation for neutral Markovian jump systems with multiple delays

The work explores the study of a neutral Markovian jump system that contains multiple delays, external disturbances, and unknown non-linear uncertainties. To overcome the tracking problem, a modified repetitive controller infused with the higher equivalent-input-disturbance approach and the extended Smith predictor approach is suggested. To guarantee the mean-square asymptotic stability of the system, an appropriate mode-dependent loop-based Lyapunov–Krasovskii functional is used. The proposed controller explicitly forces the system output and accurately follows any supplied periodic reference signal. Subsequently, the efficiency of the recommended technique is demonstrated with the simulations that validate the outcomes by comparing them to the existing results.

Research on the control strategy of LCL grid-connected inverters based on improved auto disturbance rejection.

The grid-connected inverter is the key to ensure stable, reliable, safe, and efficient operation of the power generation system; the quality of the grid-connected output current waveform directly affects the performance of the entire power generation system. To improve the anti-interference performance and reduce the output current harmonic content of the grid-connected inverter, an improved control strategy that combined repetitive control (RC) and auto disturbance rejection control (ADRC) is designed in this paper. Firstly, decoupled the ADRC to realize the individual adaptation between tracking performance parameters and anti-interference performance parameters of the controller, through which the difficulty of adjusting parameters is reduced. Secondly, the control approach is devised by adding RC to ADRC. To demonstrate the effectiveness of the proposed method in this paper, detailed experimental studies are conducted using proportional integral control, traditional ADRC, and the proposed method under normal power grids, weak power grids, and periodic disturbances. And dynamic performance simulation experiment is done to verify the dynamic performance of the self-disturbance rejection controller before and after the addition of RC links. The results indicated the effectiveness and feasibility of the proposed method. Finally, after simulation, the steady state and dynamic performance are conducted on a hardware testing platform. The impacts of the obtained results indicate the effectiveness and feasibility of the control algorithm proposed, the ability to suppress intermediate frequency disturbances is improved, the bandwidth of the auto disturbance rejection controller is expanded, and the harmonic content of the output current is depressed.

High-Performance Position Control for Repetitive Tasks of Motor-Driven Servo Systems Based on Periodic Disturbance Observer

Repetitive position control of the motor-driven servo system (MDSS) plays an important role in numerous industrial processing and production. In this article, based on the Euler–Lagrange equation, a dynamics model was established by analyzing the relationship of the energy conversion to describe the motion of an <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> -degree-of-freedom MDSS. For repetitive position control tasks of the considered system, a robust controller was designed to improve the performance of the closed-loop system, where the disturbance observer was employed to approximate the periodic dynamics of the system to improve both the transient and steady-state performances. The stability of the closed-loop system was analyzed based on the Lyapunov method. Moreover, to validate the control effect of the proposed method, the coordinated contouring task was considered for a dual-linear-motor-driven gantry system, where a B-spline wavelet series was employed as the periodic disturbance observer. The results of the comparative experiment show not only the effectiveness of the designed control scheme but also the superiority of the B-spline wavelet series on the approximation of periodic functions.

Robust Predictive Repetitive Current Control for a Grid-Connected Inverter Under Parametric Uncertainty

Robust Predictive Repetitive Current Control for a Grid-Connected Inverter Under Parametric Uncertainty

Artificial neural network–based modelling of pacemaker and its pace tracking using discrete wavelet transform–based finite dimension repetitive controller

Efficient control of cardiac pacing is a very important aspect as it provides lifesaving regulated cardiac rhythm in this dynamic hostile environment. The foremost control objective is set to design a highly reliable and advanced control strategy to ensure the utmost accuracy in the control effort. A modified artificial neural network (ANN)–based modelling and pace tracking using finite dimension repetitive controller (FDRC) design based on internal model principle (IMP) has been presented here. This controller will not only provide accurate tracking but also minimize the control action time due to less amount of data handling through the deployment of discrete wavelet transform (DWT) in the loop of repetitive controller (RC). Finally, a case study has been propounded considering ANN model using available data sets and software to validate the control strategy and justify the control objective for optimizing the pace tracking in a pacemaker. Result of the experiment showed good accuracy as well as very low error in terms of mean-squared error (MSE), integral absolute error (IAE), integral time absolute error (ITAE) and integral time square error (ITSE). Along with that, it is observed that DWT not only benefits the handling of very less memory but also acts as an additional filter while reconstructing the signal, which serves as an added advantage of this model.

Efficient signed-rank based EWMA and HWMA repetitive control charts for monitoring process mean with and without auxiliary information

Control charts are powerful tools to observe the presentation of the manufacturing process. Mostly, when the data in industries come from the process may follow non-normal or unknown distributions. So, the distribution-free control charts are useful in practice when the possibility model of the process productivity is unknown. In such situations, the correct selection of the sampling mechanism is beneficial for process examination. This paper proposes a nonparametric exponentially weighted moving average signed-rank (EWMA-SR) and also proposed a homogeneously weighted moving average Signed-Rank (HWMA-SR) control charts for examining the small shift in process with the help of an auxiliary variable (in the form of a regression estimator) by using an efficient plan, namely, a repetitive sampling plan. The proposal’s presentation is evaluated and matched with its complements for different symmetric distributions by using some famous run length properties including average run length, median run length, and standard deviation of run length.

A Novel Fractional Delay Proportional–Integral Multi-Resonant-Type Repetitive Control Based on a Farrow-Structure Filter for Grid-Tied Inverters

The integer-order delay of proportional–integral multi-resonant-type repetitive control (PIMR-RC) cannot provide excellent control performance for grid-tied inverters when the grid frequency fluctuates. To address this issue and reduce control errors, a fractional delay PIMR-RC (FD-PIMR-RC) scheme is proposed. In addition, to reduce the computational load and memory consumption, a Farrow-structure fractional delay (FFD) filter is adopted. The digital filter with the Farrow structure is flexibly and efficiently used for fractional delay. For each new fractional delay, a large number of calculations and storage for the FFD filter coefficients are avoided, which significantly reduces the computational load and memory consumption. The parameter design of the FD-PIMR-RC scheme is provided in detail, including the implementation of fractional delay based on the Farrow structure. Then, a system stability analysis and parameter optimization are presented. Finally, simulations for the steady-state and dynamic responses are presented, and the validity of the proposed method is demonstrated.

Research on current dual closed-loop scheme for PMSM control system utilizing cascaded PI-RC controller

In the permanent magnet synchronous motor (PMSM) control system used proportional integral (PI) controller, a large resonance in high-frequency band will be generated through the PI controller. Additionally, high amount alternating current harmonics will be introduced to the PMSM caused by the inverter nonlinearity and other factors, which cannot be eliminated by PI controller. To eliminate the current harmonics in the control system, a novel current dual closed-loop scheme used the PI controller on the current inner loop and the repetitive controller on the current outer loop (cascaded PI-RC controller) is proposed in this paper. First of all, the reference current signal is added to the inner current loop, thus, the satisfied dynamic performance to the control system can be guaranteed. And then, the frequency characteristic and the resonance of the control plant are analysed. Furthermore, in order to suppress the periodic current harmonics for this PMSM, the internal model element and the compensator are studied for the current outer loop controller. Consequently, the stability of the proposed cascaded PI-RC controller is actual by Lyapunov theory. Finally, the effectiveness of the proposed current dual closed-loop scheme is verified by simulation results.

Tracking control for a position-dependent periodic signal in a variable-speed rotational system

This paper concerns the problem of tracking a position-related periodic signal for an uncertain nonlinear rotational system. Applying the additive-state-decomposition (ASD) technique decomposes the original uncertain nonlinear system into two subsystems: A primary linear time-invariant system that performs spatial repetitive control, and a secondary nonlinear system that ensures robust stability of the whole system with respect to unknown nonlinear dynamics and exogenous disturbances. This method has four features: (i) The ASD technique provides an effective way to deal with the coupling between the spatial periodicity and other factors (temporal and state-dependent uncertainties and disturbances) in a rotational system. This technique ensures satisfactory tracking and disturbance rejection performance; (ii) A real-time digital implementation of a spatial repetitive controller enables repetitive control with an exact period in the position. This ensures the synchronous execution of repetitive control in the position domain and robust stability in the time domain; (iii) The method of accurate phase compensation in a spatial repetitive controller leads to a significant improvement in steady-state tracking performance; and (iv) An extended-state observer precisely estimates the overall effect of disturbances. Integrating a disturbance estimate into a control input effectively compensates for disturbances. Stability criteria and design algorithms are presented in detail. Finally, experiments of a rotational speed-control system demonstrate the effectiveness of this method.

Current harmonic suppression for PMSM driven system utilizing PI-DFT-RC controller

The permanent magnet synchronous motor (PMSM) driven by the two-level voltage inverters features some drawbacks, such as dead-zone time, nonlinearity and other factors, leading to high amount harmonics in the stator currents. Additionally, the current harmonics amplitude will be decayed with the increasing of the harmonic order, and the main current harmonic components can be illustrated as 6th control signal harmonics. To improve the current harmonics suppression efficiency and maintain the simplicity of the PMSM driven system, the relationships between traditional repetitive controller and bandpass filter are analysed firstly. And then, a proportional–integral​ discrete Fourier transform repetitive control (PI-DFT-RC) scheme is proposed through adopting independent band-pass filters of state frequencies, which can provide infinite gain in stated frequency. Secondly, the discrete periodic signals for RC controller are analysed, and the lead step for DFT-RC controller is also studied, which can increase the signal tracking accuracy of the driven system. Furthermore, the stability of the driven system used PI-DFT-RC controller is analysed through Lyapunov theory. Finally, the effectiveness of the proposed PI-DFT-RC controller is verified by simulation results.

An Improved Dual Second-Order Generalized Integrator Phased-Locked Loop Strategy for an Inverter of Flexible High-Voltage Direct Current Transmission Systems under Nonideal Grid Conditions

High-voltage flexible power systems, with their intrinsic characteristics, play an increasingly important role in electronic power systems. Synchronization between the inverter and the grid needs to be achieved by a phase-locked loop (PLL), the performance of which determines the quality of power transmission. This paper proposes a PLL adapted to extremely harsh grid conditions. Firstly, the traditional synchronous reference frame PLL and the dual second-order generalized integrator (DSOGI-PLL) are analyzed, and the errors in phase-locking and the shortcomings of these two methods in the presence of DC components in the grid are pointed out. Secondly, based on the harmonic grid voltage, a repetitive control internal model is introduced by DSOGI to realize the real-time tracking and regulation of the harmonic signals in order to suppress the harmonic voltage disturbance. In addition, a DC bias elimination and frequency adaptive method is proposed to solve the problems of DC bias and grid voltage frequency fluctuation in order to achieve adaptive tracking of the grid phase. Finally, the superiority of the proposed strategy is verified through simulations and experiments.

High-Precision Suppression of Harmonic Vibration Force by Repetitive Controller With Triple-Loop Structure

The harmonic vibration force generated by multi-source disturbances through the magnetic bearing closed-loop control system seriously affects the improvement of the performance of the magnetically suspended control moment gyroscope (MSCMG). The harmonic noise introduced by the displacement sensor generates harmonic components through a closed-loop control system, and the compensation accuracy of synchronous displacement stiffness force is reduced by the low-pass characteristics of the power amplifier. In this paper, the rotor displacement signal and current signal are used as inputs to the repetitive controller and notch filter, and the power amplifier and repetitive controller are constructed into three closed-loop systems to achieve high-precision suppression of harmonic vibration forces. Finally, the effectiveness of the method is demonstrated by using a 200Nms MSCMG and a micro-vibration test system.

Three-Level Isolated Direct AC–AC Converter and its Closed-Loop Control Strategy

The isolated direct AC-AC converter has the advantages of high power density and long life time, however, suffering from the high cost and relatively low efficiency. In this paper, a three-level isolated direct resonant AC-AC converter is proposed, thus the voltage stress of power switches reduce to half of the input voltage amplitude and as a result, the voltage rating of the power switches is reduced. A hybrid modulation strategy for the proposed converter is proposed to realize the AC-AC conversion and reduce the switching power loss. Furthermore, in order to obtain a good control of the output voltage based on the proposed converter, the closed-loop control strategy of the output voltage combining a linear controller with the repetitive controller is proposed and the detailed parameters design rule is discussed. The proposed control strategy not only realizes the sinusoidal output voltage waveforms and good dynamic performance, but also effectively eliminates the effect of input voltage harmonics. The corresponding proposed topology, modulation and closed-loop control strategy are all verified by the detailed experimental results.

Using IIR Filter in Fractional Order Phase Lead Compensation PIMR-RC for Grid-Tied Inverters

Phase lead compensation precision dramatically affects the performance of repetitive controller (RC). Integer order phase lead compensation of proportional integral multi-resonant type RC (PIMR-RC) with low sampling frequency cannot meet the need of fine phase compensation. In addition, the digital control delay affects the actual modeling of the system, and then influences the precision phase compensation. To finely compensate the phase lag of the PIMR-RC system, this paper proposes a fine fractional order phase lead compensation PIMR-RC (FL-PIMR-RC) scheme based on a novel phase lead infinite impulse response (IIR) filter. Its comprehensive synthesis is systematically detailed, including actual modeling considering 1.5-period digital control delay, IIR fractional lead filter design, stability analysis, and parameter optimization. Finally, experiments on a 2 kW prototype grid-tied inverter are successfully carried out to verify the solution.

Adaptive repetitive control of wrist tremor suppression based on functional electrical stimulation

Tremor is an involuntary and repetitive swinging movement of limb, which can be regarded as a periodic disturbance in tremor suppression system based on functional electrical stimulation (FES). Therefore, using repetitive controller to adjust the level and timing of FES applied to the corresponding muscles, so as to generate the muscle torque opposite to the tremor motion, is a feasible means of tremor suppression. At present, most repetitive control systems based on FES assume that tremor is a fixed single frequency signal, but in fact, tremor may be a multi-frequency signal and the tremor frequency also varies with time. In this paper, the tremor data of intention tremor patients are analyzed from the perspective of frequency, and an adaptive repetitive controller with internal model switching is proposed to suppress tremor signals with different frequencies. Simulation and experimental results show that the proposed adaptive repetitive controller based on parallel multiple internal models and series high-order internal model switching can suppress tremor by up to 84.98% on average, which is a significant improvement compared to the traditional single internal model repetitive controller and filter based feedback controller. Therefore, the adaptive repetitive control method based on FES proposed in this paper can effectively address the issue of wrist intention tremor in patients, and can offer valuable technical support for the rehabilitation of patients with subsequent motor dysfunction.

Effects of repetitive pinprick stimulation on preterm offspring: Alterations in nociceptive responses and inflammatory hypersensitivity in adulthood

IntroductionThis study investigates the effects of repetitive pinprick stimulation on preterm offspring and its impact on nociceptive responses and inflammatory hypersensitivity in adulthood. ObjectivesThe objective is to shed light on the potential long-term consequences of neonatal pain and prematurity on sensory processing. MethodsTerm and preterm rats were subjected to repetitive pinprick (PP) stimulation or control (CC) during the neonatal period. Adult rats received CFA injection to induce inflammatory hypersensitivity, and mechanical hypersensitivity was measured. Gender differences in inflammatory hypersensitivity were also examined. Maternal behavior, litter weight, and offspring growth were monitored to assess any potential influences of the stimulation on these parameters. ResultsIn preterm rats, the PP stimulation did not affect baseline thresholds to mechanical stimuli, but increased mechanical hypersensitivity after CFA injection in adult rats. Females exhibited greater inflammatory hypersensitivity compared to males. Maternal behavior, litter weight, and offspring growth were not influenced by the stimulation. PP stimulation during the neonatal period led to changes in nociceptive responses in adulthood, potentially altering sensory processing. ConclusionPP stimulation in preterm rats during the neonatal period resulted in changes in nociceptive responses in adulthood, leading to increased inflammatory hypersensitivity. The study emphasizes how early development can significantly impact sensory processing and further highlights the potential long-term consequences of prematurity and neonatal pain on this processing.