Chattering Suppression Research Articles

Robust Finite-Time Control for Autonomous Operation of an Inverter-Based Microgrid

Recently, more and more small-scale renewable generation sources based distributed generators are integrated to the existing power network through power electronic-based converters. Microgrid has been proposed as a solution to meet the challenges posed by highly intermittent renewable generations. To address the fast response and complex operating conditions of various inverters in an autonomous microgrid, this paper proposes a robust finite-time control algorithm for frequency/voltage regulation and active/reactive power control. The major advantages of the proposed control algorithm include, being robust and stable against various load disturbances, unmodeled dynamics and system parameter perturbations; enabling flexible convergence time according to user preferences and different operating conditions' requirements. The finite-time convergence of the robust control algorithm is guaranteed through rigorous analysis and the balance between control accuracy and chattering suppression is investigated. Simulation results demonstrate the effectiveness of the proposed robust finite-time control algorithm.

Switched sliding mode approach for motion control systems with friction

The chattering and offset phenomena, which may lead to acceleration disturbances and deteriorate control performance, are the main deficiencies caused by switching signal and mismatched uncertainties when the sliding mode control method is used for motion control systems with friction. The need is highlighted for simultaneous chattering suppression and mismatched uncertainties attenuation of sliding mode control. In this article, a switched sliding mode control method is proposed which uses three sliding surfaces to divide the error state space into three subspaces. Using different sliding mode controllers when error system state is located in different subspaces, the asymptotically stable of motion control system is guaranteed under friction and uncertainties (including matched and mismatched). In addition, through designing proper switching gain for each sliding mode controller, the control law of switched sliding mode control can be continuous. This means that the chattering phenomenon caused by switch...

Dual terminal sliding mode control design for rigid robotic manipulator

This paper proposes a dual terminal sliding mode control scheme for tracking tasks of rigid robotic manipulators. As a significant novelty, the presented design technique integrates the individual sliding mode surfaces to achieve the finite time convergence of tracking errors utilizing specially designed construct, and accordingly the convergence time is easily obtained due to the integral design. The underactuated issue and input limitation are specially considered in this paper, i.e., the underactuated issue is solved by introducing the hierarchical methodology into the basic dual sliding mode controller. The proposed method can easily combine with the adaptive technique to eliminate the negative effect caused by the input limitation in the rigorous stability analysis. These newly proposed methods also have the characteristics of nonsingularity and chattering suppression, and the effectiveness and high efficiency are verified by stabilizing the motions of the overhead crane and the tracking tasks of the rigid robotic manipulator. Simulation results validate the theoretical analyses about the proposed method.

Impact arresting process mechanical modeling and sliding model buffer control based on magneto-rheological fluid

The research on the form and control method of impact load arresting buffer has been an active topic in the field of buffer arresting system (BAS). It becomes significant on reducing the weight of arresting system, improving the hindered efficiency, and guaranteeing the security of BAS. The hydraulic hindered device of impact load is currently used in BAS. There are some problems. For example, the system needs large power sources. However, once the power of active hydraulic control system is turned off, there arise unpredictable security risks. An arresting form of semi-active control based on magneto-rheological damper (MRD) is proposed, and the mechanical model of the BAS is established. Meanwhile, the state equation of impact load BAS is established according to the characteristics of impact load buffer arresting, and its sliding model buffer control is achieved. Due to the chattering characteristic of the output signal of sliding mode controller, the method to prevent chattering is designed based on short-term energy and zero-crossing rate detection. For the model and chattering suppression of sliding model buffer control algorithms, simulation results show that the proposed state equation and the arresting model are reasonable, and the design of semi-active control algorithm is effective. On the condition of the buffer control system requirement and the accuracy, the proposed algorithms effectively control the chattering of sliding mode control algorithms, and improve the security of the BAS.

Robust fault diagnosis of an electro-hydrostatic actuator using the Novel dynamic second-order SVSF and IMM strategy

This paper introduces a new robust fault detection and identification (FDI) structure applied to an electro-hydrostatic actuator (EHA) experimental setup. This FDI structure consists of the dynamic second-order smooth variable structure filter (Dynamic second-SVSF) and the interacting multiple model (IMM) strategy. The dynamic second-order smooth variable structure filter (SVSF) is a new robust-state estimation method that benefits from the robustness and chattering suppression properties of second-order sliding mode systems. It produces robust-state estimation by preserving the first and second-order sliding conditions such that the measurement error and its first difference are pushed towards zero. Moreover, the EHA prototype works under two different operational regimes that are the normal EHA mode and the faulty EHA mode. The faulty EHA setup contains two types of faults, namely friction and internal leakage. The FDI structure contains a bank of dynamic second-order SVSFs estimating state variables ba...

Sliding Mode Control of Three-Phase Four-Leg Inverters via State Feedback

To optimize controller design and improve static and dynamic performances of three-phase four-leg inverter systems, a compound control method that combines state feedback and quasi-sliding mode variable structure control is proposed. The linear coordinate change matrix and the state variable feedback equations are derived based on the mathematical model of three-phase four-leg inverters. Based on system relative degrees, sliding surfaces and quasi-sliding mode controllers are designed for converted linear systems. This control method exhibits the advantages of both state feedback and sliding mode control. The proposed controllers provide flexible dynamic control response and excellent stable control performance with chattering suppression. The feasibility of the proposed strategy is verified by conducting simulations and experiments.

A New State-Dependent of Sliding Mode Control for Three-Phase Induction Motor Drives

Chattering is known as a main obstacle in realizing sliding mode control. In this study, new robust and chattering suppression of sliding mode control method is investigated. First, an integral sliding mode control is developed. Then, a simple smooth function and switching gain with state-dependent based on fast sigmoid function is introduced. This method allows chattering reduction, as well as maintaining the robust characteristics of sliding mode control. The effectiveness of the proposed algorithm is demonstrated using simulation speed control of indirect field-oriented three-phase induction motor drives with regard to external load disturbances

Chattering Problem

AbstractIn many sliding mode implementation, control engineers may experience undesirable phenomenon of oscillations having finite frequency, which is known as ‘chattering'. Chattering is a harmful phenomenon because it leads to low control accuracy, high wear of moving mechanical parts, and high heat losses in electrical power circuits. Thus it can be one of main obstacles in implementation of sliding mode control. The paper surveys the methods of chattering suppression. Application of state observers as a bypass for high frequency component is the traditional approach to the problem. Another design idea implies control of discontinuity magnitude depending on the system state or so-called equivalent control. “Harmonic cancelation” is the core idea for the systems with multiphase actuators. Finally, minimization of frequency (and as a result, of switching heat losses) for given accuracy is demonstrated for three-phase power converters.

Sliding mode controller gain adaptation and chattering reduction techniques for DSP-based PM DC motor drives

In order to achieve and maintain the prospective benefits of sliding mode control (SMC) methodology, the phenomenon known as ``chattering'', the main obstacle encountered in real-time applications, has to be suppressed. In this study, two promising switching control gain adaptation and chattering reduction techniques are investigated, and the effectiveness of chattering suppression for current regulation of PM DC drives is tested. The sampling rate was also examined to determine how it affects the amplitude of chattering. This paper concentrates on various combinations of observer-based methods in order to find the best solution for chattering reduction. To find a practical solution a tunable low-pass filter (LPF) was used to average the discontinuous control term. The validity of the existing conditions for the gain adaptation methods are examined and observer gain value was determined through simulations. To demonstrate the effectiveness of each method, several experiments were performed on a DSP-based PM DC motor drive system. Then, the newly proposed combinations of these methods were implemented. The hardware implementation results are comparatively presented and discussed.

Fuzzy discontinuous term for a second order asymptotic DSMC: An experimental validation on a chemical reactor

In this work, a second order asymptotic discrete sliding mode control with a fuzzy supervised discontinuous term is proposed. The on line variation of the discontinuous term amplitude enhances the convergence rapidity of the sliding function and reduces the chattering phenomenon. These improvements are shown by a numerical simulation and by a real time temperature control of a chemical reactor. Good performances in terms of chattering suppression and reaching phase duration's reduction are noted. Copyright © 2010 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society

Chattering reduction using multiphase sliding mode control

For the system with sliding mode controllers operated by on/off switches, ‘chattering’ appears in the output of the system when its switching frequency is restricted. In power systems, the switching frequency is commonly limited to prevent power losses, and chattering or ‘ripple’ appears especially in the system current. Common methods to decrease such ripple are based on ‘harmonic cancellation’ using the multiple number of phase channels having the desired phase shift that brings cancellation in the sum of outputs from the individual channels. In this article, a design principle of sliding mode control for a multiphase controller is proposed. The methodology is originated from the concept of multidimensional sliding mode and provides desired phase shifts between phases with the help of adaptive width for the hysteresis loops in switching elements. The chattering suppression effect is demonstrated by simulations for the DC–DC converter systems in various situations.

CHATTERING PROBLEM IN SLIDING MODE CONTROL SYSTEMS

In practical applications of sliding mode control, engineers may experience undesirable phenomenon of oscillations having finite frequency and amplitude, which is known as ‘chattering'. At the first stage of sliding mode control theory development the chattering was the main obstacle for its implementation. Chattering is a harmful phenomenon because it leads to low control accuracy, high wear of moving mechanical parts, and high heat losses in power circuits. There are two reasons which can lead to chattering.The chattering can be caused by fast dynamics which were neglected in the ideal model. These ‘unmodeled’ dynamics with small time constants are usually disregarded in models of servomechanisms, sensors and data processors.The second reason of chattering is utilization of digital controllers with finite sampling rate, which causes so called ‘discretization chatter'. Theoretically the ideal sliding mode implies infinite switching frequency. Since the control is constant within a sampling interval, switching frequency can not exceed that of sampling, which lead to chattering as well.Mechanism of chattering generating is demonstrated for control of inverted an pendulum with unmodeled actuator dynamics.The efficient recipe for chattering suppression is use of asymptotic observers. The main idea of using an asymptotic observer to prevent chattering is to generate ideal sliding mode in the auxiliary loop including the observer. In the observer loop, sliding mode is generated in the control software; therefore, any unmodeled dynamics which cause chattering can be excluded.As follows from analysis, based on the describing function method, the amplitude of chattering is proportional to magnitude of discontinuous control. Therefore the methods of chattering suppression can be developed such that the magnitude is decreased properly holding the establishment of sliding mode. First option is to decrease the magnitude along with the system states. The second one implies that the magnitude is the function of an equivalent control derived by a low-pass filter ueq. The method can be applied for the plants subjected to unknown disturbances.“Discretization chattering” in discrete-time systems is caused by discontinuities in control. Increasing a sampling frequency to decrease the chattering amplitude seems unjustified, since using a computer is adequate to control system dynamics if a sampling frequency corresponds to average, slow system motion rather than to a high frequency component.First the definition of sliding mode is introduced embracing both discrete- and continuous-time systems. Then free of chattering design methodology is proposed for discrete-time systems. The fundamental difference is that the control should be a continuous function of the state.Experimental results for sliding mode control of inductions motors with observers are discussed.

A Simple Stator Flux Oriented Induction Motor Control

This paper presents a novel stator flux oriented induction motor control scheme. It utilises a sliding-mode controller in the stator flux control loop. The existence condition of sliding mode control is derived, and chattering suppression at steady-state is also considered. A proportional controller is used in the torque control loop to simplify the control scheme without compromising performance. Design formulas are given for the controller parameters. They are not based on the mathematical motor model but only need rated parameters. Experimental results are shown to prove the effectiveness of the control strategy in transient and steady state operations.

A VSS speed controller with model reference response for induction motor drive

This paper is mainly concerned with the development of a variable-structure system (VSS) controller with model reference speed response for an induction motor drive. An indirect-field-oriented (IFO) induction motor drive is first implemented, and its dynamic model at a nominal operating condition is estimated from measured data. Then, a two-degrees-of-freedom linear model-following controller (2DOFLMFC) is designed to meet the prescribed tracking and load regulation speed responses at the nominal case. As the variations of system parameters and operating condition occur, the prescribed control specifications may not be satisfied further. To improve this, a VSS controller is developed to generate a compensation control signal to reduce the control performance degradation. The proposed VSS controller is easy to implement, since only the output variable is sensed. The existence condition of sliding-mode control is derived, and the chattering suppression during the static period is also considered. Good model-following tracking and load regulation speed responses are obtained by the designed VSS controller. Effectiveness of the proposed controller and the performance of the resulting drive system are confirmed by some simulation and measured results.

Basic Study on Magnetic-Field Assisted Cutting. Improvement of Machinability in Cutting Austenitic Stainless Steel.

Some effects of magnetic field on metal cutting have been revealed. 3-20 wt% cobalt (Co) is used as cement in a common cemented carbide tool. However, Co cement may be washed away from the subsurface of the tool in the cutting area where both high temperature and high pressure are applied. This is one of the main reasons for tool wear. Considering that Co is a ferromagnetic substance, there is a possibility that tool wear can be reduced by applying magnetic power near the cutting area. Thus many cutting tests with various combinations of materials and tools were performed under a magnetic field. Consequently, long life of carbide tools was obtained in the Magnetic-Field Assisted Cutting (MFAC). Improvement of surface roughness and suppression of chattering during the turning of austenitic stainless steel and invar alloy were acomplished by a magnetic-field-induced martensitic transformation.

The slippery road to sliding control: conventional versus dynamical sliding mode control

Theory and design of a conventional sliding mode controller (CSMC) and a dynamical sliding mode controller (DSMC) are discussed and compared. The controllers are applicable to uncertain nonlinear MIMO systems. Emphasis is put on handling of unmodelled dynamics, tuning of controller parameters, suppression of chattering, and robust tracking performance. Experiments are performed with a mechanical manipulator. Errors in the model of this manipulator are due to, amongst other things, neglected flexibilities. It is concluded that for this set-up the robustness to these model-reality differences is approximately the same for both controllers, while nominal performance is best for the CSMC. © 1998 John Wiley & Sons, Ltd.

The slippery road to sliding control: conventional versus dynamical sliding mode control

Theory and design of a conventional sliding mode controller (CSMC) and a dynamical sliding mode controller (DSMC) are discussed and compared. The controllers are applicable to uncertain nonlinear MIMO systems. Emphasis is put on handling of unmodelled dynamics, tuning of controller parameters, suppression of chattering, and robust tracking performance. Experiments are performed with a mechanical manipulator. Errors in the model of this manipulator are due to, amongst other things, neglected flexibilities. It is concluded that for this set-up the robustness to these model-reality differences is approximately the same for both controllers, while nominal performance is best for the CSMC.

Two Adaptive Robust Sliding Mode Controllers for Robot Manipulators

Sliding mode controllers are known to be capable of achieving robustness against modeling errors, plant disturbances and plant parameter variations. They, however, require upper-bounds of uncertainties in plant parameters to specify feedback gains that realize robustness. These upper-bounds are often chosen conservatively and, as a result, high feedback gains and oscillations, refered to as chattering, occur. Recently, on-line identification of the upper-bounds of uncertainties have been successfully incorporated into sliding mode regulators to alleviate the chattering. Here, we propose to extend this on-line identification technique to two types of controllers, called adaptive robust sliding mode controllers, for trajectory control of robot manipulators. The stability properties of the proposed controllers are demonstrated using Lyapunov functions and are implemented using a PUMA-type manipulator. The performance of these controllers is compared with that of regular sliding mode controllers. The result of comparison reveals excellent robustness and chattering suppression of the proposed controllers.

Suppression of morphine abstinence syndrome by body electroacupuncture of different frequencies in rats

The effectiveness of electroacupuncture (EA) stimulation in suppressing the morphine abstinence syndrome was studied. Male Wistar rats were made dependent on morphine either by multiple injections or pellet implantation. EA of 2 Hz or 100 Hz was administered for 30 min followed by naloxone challenge (0.5 mg/kg, i.p.) and the withdrawal syndrome was scored for a period of 45 min. In rats receiving multiple injection regime, 100-Hz EA produced a statistically significant suppression of wet shakes (−61%), teeth chattering (−59%), escape attempts (−48%), weight loss (−3.3%) and penile licking (−28%) ( P < 0.05). EA of 2 Hz produced only a mild but significant suppression in escape attempts (−42%) and wet shakes (−31%). Similar results were obtained in rats receiving pellet implantation. Since 100-Hz EA has been shown to accelerate the release of dynorphins in the CNS, the results seem to be compatible with the notion that dynorphin may play an important role in suppressing the opioid withdrawal syndrome.