Disturbance observer (DOB) has been one of the most widely used robust control tools since it was proposed by Ohnishi in 1983. This paper introduces the origins of DOB and presents a survey of the ...major results on DOB-based robust control in the last 35 years. Furthermore, it explains DOB's analysis and synthesis techniques for linear and nonlinear systems by using a unified framework. In final section, this paper presents concluding remarks on DOB-based robust control and its engineering applications.
A nonlinear position tracking controller with a disturbance observer (DOB) is proposed to track the desired position in the presence of the disturbance for electrohydraulic actuators (EHAs). The DOB ...is designed in the form of a second-order high-pass filter in order to estimate the disturbance. The nonlinear controller is designed for position tracking as a near input-output linearizing inner-loop load pressure controller and a backstepping outer-loop position controller. Variable structure control is implemented in order to compensate for the error in disturbance estimation. The desired load pressure is designed to generate the pressure using the differential flatness property of the EHA's mechanical subsystem. The disturbance within the bandwidth of the DOB can be cancelled by the proposed method. The performance of the proposed method is validated via simulations and experiments.
A new approach to the design of nonlinear disturbance observers (DOBs) for a class of nonlinear systems described by input-output differential equations is presented in this paper. In contrast with ...established forms of nonlinear DOBs, the most important feature of this new type of DOB is that only measurement of the output variable is required, rather than the state variables. An inverse simulation model is first constructed based on knowledge of the structure and parameters of a conventional model of the system. The disturbance can then be estimated by comparing the output of the inverse model and the input of the original nonlinear system. Mathematical analysis demonstrates the convergence of this new form of nonlinear DOB. The approach has been applied to disturbance estimation for a linear system and a new form of linear DOB has been developed. The differences between the proposed linear DOB and the conventional form of frequency-domain DOB are discussed through a numerical example. Finally, the nonlinear DOB design method is illustrated through an application involving a simulation of a jacketed continuous stirred tank reactor system.
Redovna fizička aktivnost može da donese značajne zdravstvene benefite kod ljudi svih godina, te se potreba za fizičkom aktivnošću ne smanjuje sa brojem godina već je dokazano da ona može produžiti ...zdraviji i samostalniji život, spriječiti invaliditet i značajno doprinijeti poboljšanju života kod starijih osoba. Pored toga što svaka vrsta fizičke aktivnosti u određenoj mjeri pobošljava motoričke sposobnosti (snagu, koordinaciju, ravnotežu, agilnost, ...), mentalno zdravlje (samopoštovanje, kvalitet života) i umanjuje rizik od kardiovaskularnih i svih drugih uzroka smrti, redovno učestvovanje u vježbanju pospješuje mobilnost i funkcionalnu nezavisnost kod odraslih osoba. Pad je događaj u kojem učesnik bez sopstvene namjere dolazi u ležeći položaj na zemlji ili na nižem nivou. Bez obzira na zdravstveno stanje pojedinca, padovi su povezani sa nedovoljnim kretanjem, smanjenim mogućnostima za izvođenje svakodnevnih aktivnosti (oblačenje, kupanje, kućni poslovi, ...) i rizikom za prijem u ustanove u kojima se vodi briga o nesamostalnim osobama. Artritis, depresija, kognitivna oštećenja, vid, problemi s ravnotežom i neuravnoteženim hodom, smanjenje mišićne mase, kao i prekomjerna upotreba medikamenata povećavaju rizik od pada. Ukupan obim i vrsta fizičke aktinosti potrebna za starije osobe nije baš najbolje definisana. Međutim, može se zaključiti da spoj fizičke aktivnosti (treninzi snage, izdržljivosti, vježbe za razvoj ravnoteže i mobilnosti, ...) i adekvatne ishrane (dovoljan unos esencijalnih amino kiselina/izvora proteina) je od krucijalnog značaja za očuvanje fizičkog stanja, motoričkih sposobnosti i zdravstvenog statusa osoba treće dobi, a samim tim i u prevenciji padova. Cilj ovog rada se ogleda u opisu i pronalaženju najboljih trenažnih programa za prevenciju padova kod starih osoba.
This paper proposes a new hybrid disturbance observer (DOB) to help suppress disturbance to the control systems. The proposed hybrid DOB consists of three main parts: (1) an actual system, (2) a ...simulated system, and (3) a learning filter that connects the actual and simulated systems. The simulated system aims to replicate the actual system response, where it leverages a neural network model to predict the input disturbance and generate the predicted system response. Such system response is used to generate a learning signal through a learning filter; this learning signal is then added to the feedforward loop of the estimation framework to enhance the disturbance estimate and its suppression performance for the actual system. The proposed hybrid DOB is designed to advance the standard DOB structure with a learning-based feedforward compensation. While the proposed method does not modify the baseline controller, it is well suited to systems whose baseline controllers are difficult or impossible to be changed. Considering the delivery drones are subject to oscillations when dropping payloads, experimental tests with multiple payload dropping scenarios have been conducted using both the hybrid and standard DOB, where the compared results validate the effectiveness and advantages of the proposed hybrid DOB.
•A new hybrid learning-based disturbance observer (DOB) is proposed to suppress drone’s oscillation.•The learning filter design problem has been systematically formulated into an optimization problem.•Performance improvement is theoretically guaranteed and experimental verified.
The ball-ramp dual-clutch transmission (BR-DCT) was proposed to overcome the disadvantages of conventional DCT. Specifically, BR-DCT is designed to reduce the amount of clutch actuator energy ...consumption and reverse torque during tie-up, in which two clutches are engaged simultaneously. In addition, since the self-energizing principle is used, the actuator model can be used without the friction coefficient, which is the main uncertainty of the clutch actuator. These features can greatly contribute to enhancing the shift control performance of the BR-DCT. However, the measurement error due to friction between actuator parts causes a small amount of uncertainty. In this article, a method using extended high-order disturbance observer (EH-DOB) is proposed to estimate this uncertainty. The EH-DOB used in the proposed method guarantees convergence even in a system in which the gain of the disturbance is time-varying. The convergence of the estimation error was verified through proof of the proposed algorithm. Experimental verification of the proposed algorithm was performed using a test bench that simulates a powertrain equipped with BR-DCT. As a result, it was confirmed that the uncertainty estimation result using EH-DOB showed high accuracy. As a result, it was verified that the uncertainty estimation method using the proposed algorithm has high accuracy and stability enough to perform disturbance rejection control.
This paper develops a sliding-mode control (SMC) approach for systems with mismatched uncertainties via a nonlinear disturbance observer (DOB). By designing a novel sliding surface based on the ...disturbance estimation, a DOB-based SMC method is developed in this paper to counteract the mismatched disturbance. The newly proposed method exhibits the following two attractive features. First, the switching gain is only required to be designed greater than the bound of the disturbance estimation error rather than that of the disturbance; thus, the chattering problem is substantially alleviated. Second, the proposed method retains its nominal performance, which means the proposed method acts the same as the baseline sliding-mode controller in the absence of uncertainties. Simulation results of both the numerical and application examples show that the proposed method exhibits much better control performance than the baseline SMC and the integral SMC (I-SMC) methods, such as reduced chattering and nominal performance recovery.
The speed regulation problem of permanent magnet synchronous motor system is investigated under a noncascade structure. Despite its superiority in straightforward control design, simple parameter ...adjustment, and satisfying system dynamic performance, the structure brings two problems: the overcurrent protection and unmatched disturbance rejection. Under this structure, the current cannot any more be restricted by a reference value, and ought to be constrained within a certain range to ensure the circuit safety. Besides, unmatched disturbances, mainly caused by external load torques, may result in undesired interference and violate the constraint requirement, since they affect the current directly via the same channel. Toward that end, a novel current-constrained control algorithm is designed to tackle the current constraint and unmatched disturbances simultaneously. A disturbance observer (DOB) is utilized for unmatched disturbance estimation. A constraint coping mechanism is constructed to restrict the current. Then, a key nonlinear item is proposed by augmenting the disturbance estimation and the constrained current. Finally, a composite controller is proposed with concise structure and rigorous closed-loop stability analysis. Numerical and experimental tests further validate that the proposed control approach achieves promising speed tracking performance and guarantees the current constraint in the presence of unmatched disturbances.
This paper investigates the disturbance observer (DOB)-based neural adaptive control on the longitudinal dynamics of a flexible hypersonic flight vehicle (HFV) in the presence of wind effects. The ...coupling effect between flexible states and rigid body, and the accessional angle of attack (AOA) due to wind, is modeled as unknown disturbance, where the nonlinear DOB is constructed using the neural approximation. For the weight update in neural networks (NNs), a novel algorithm is proposed with the additional prediction error derived from the serial-parallel estimation model (SPEM) using both neural approximation and disturbance estimation. Different from previous work, the wind effect is taken into the hypersonic flight dynamics for realistic analysis, and the novel controller is designed using compound estimation, where the NN and the DOB are constructed to deal with aerodynamic uncertainty and unknown disturbance. Simulation studies of a flexible HFV with wind effects show that the proposed controller can achieve high tracking accuracy, while the compound estimation can closely follow the system uncertainty with fast convergence.
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