Disturbance Observer-based Control Scheme Research Articles

Disturbance Observer-Based Model Predictive Control for an Unmanned Underwater Vehicle

This work addresses the motion control problem for a 4-degree-of-freedom unmanned underwater vehicle (UUV) in the presence of nonlinear dynamics, parametric uncertainties, system constraints, and time-varying external disturbances. A disturbance observer-based control scheme is proposed, which is structured around the model predictive control (MPC) method integrated with an extended active observer (EAOB). Compared to the conventional disturbance observer, the developed EAOB has the ability to handle both external disturbances and system/measurement noises simultaneously. The EAOB leverages a combination of sensor measurements and a system dynamic model to estimate disturbances in real-time, which allows continuous estimation and compensation of time-varying disturbances back to the controller. The proposed disturbance observer-based MPC is implemented by feeding the estimated disturbances back into the MPC’s prediction model, which forms an effective adaptive controller with a parameter-varying model. The proposed control strategy is validated through simulations in a Gazebo and robot operating system environment. The results show that the proposed method can effectively reject unpredictable disturbances and improve the UUV’s control performance.

Active control for system with multiple microchannel heat exchangers using disturbance observer

To prevent flow maldistribution and imbalanced temperature, a disturbance observer-based control strategy is presented for microchannel cooling systems with multiple heat exchangers. A disturbance observer is designed using the extended Kalman filter for estimating the states and disturbance. The performance of the observer is validated using experimental data from a pumped liquid cycle testbed. Disturbance observer-based control is applied to systems with two and three heat exchangers. The findings demonstrate that the wall temperatures and the temperature differences for the heat exchangers could be maintained at the desired values. When the heat exchangers are subjected to heat loads in the form of square, sinusoidal, and sawtooth functions, the temperature fluctuation could be suppressed by 60%-80% and the temperatures could be maintained at the same values. Our research demonstrates that the proposed control strategy has acceptable accuracy and robustness for the system with multiple heat exchangers undergoing various operating situations.

Fault Tolerant Control for Remotely Operated Vehicles with Thruster Faults using Nonlinear Disturbance Observers

In this paper, a disturbance observer based control strategy is developed to provide fault tolerance to thruster faults for a remotely operated vehicle. The scheme relies on the vehicle's position, orientation and velocity information only, without the need for additional measurements from the thrusters such as voltage, current, and rotation speed. Because the system is over-actuated, a bank of observers is designed for purposes of fault detection and isolation. A nonlinear disturbance observer is designed to restructure itself, according to the fault isolation outcome, to estimate the fault magnitude. The fault estimation is finally exploited by the control law using an active fault tolerant control strategy. The solution is designed for the cases where at most one faulty thruster is expected. The fault tolerant control strategy is tested in simulation, where a severe thruster fault is injected.

Attitude Exponential Stabilization Control of Rigid Bodies via Disturbance Observer

The attitude stabilization problem of rigid bodies with external disturbance is studied. A novel disturbance observer-based control scheme is presented. Comparing with the existing observers for external disturbance, the proposed observer releases the assumption that the external disturbance should be constant or with the minor rate of change. The closed-loop attitude stabilization system is governed by the controller to be exponentially stable with disturbance rejected. The observer error of disturbance, the attitude, and the angular velocity are exponentially stabilized to be zero or within a small set with an arbitrary radius. The key feature of this scheme is that it ensures the control performance to be more robust to any external disturbance. The controller has a simple structure and does not involve complicated computation. The effectiveness of the presented solution is validated by a rigid satellite example.

Disturbance-observer-based attitude control under input nonlinearity

A disturbance observer-based control scheme is proposed in this paper to deal with the attitude stabilization problems of spacecraft subjected to external disturbances, parameter uncertainties, and input nonlinearities. Particularly, the proposed approach addresses the dead-zone issue, a non-smooth nonlinearity affiliated with control input that significantly increases controller design difficulties. A novel nonlinear disturbance observer (NDO) is developed, which relaxes the strong assumption in conventional NDO design that disturbances should be constants or varying with slow rates. After that, a special integral sliding mode controller (ISMC) is combined with the NDO to achieve asymptotic convergence of system states. Simulations are performed in the presence of time-varying disturbances, parameter uncertainties, and dead-zone nonlinearity to justify the effectiveness of the proposed control scheme.

Advanced Control Strategies for DC–DC Buck Converters With Parametric Uncertainties via Experimental Evaluation

In this paper, four control strategies for DC-DC buck converters are proposed, compared and analyzed: a single-loop adaptive control strategy (SA), a double-loop adaptive control strategy (DA), a single-loop disturbance observer-based control strategy (SDOB) and a double-loop disturbance observer-based control strategy (DDOB). First, the nominal system without considering the parametric uncertainties of the DC-DC buck converter is built to help develop the SA and DA. The SA is built by adaptive and backstepping control approaches, and the DA is set up by adaptive and sliding mode control approaches. Additionally, a model considering parametric uncertainties is introduced, giving the opportunity to develop the SDOB and DDOB. The SDOB is developed using a designed disturbance observer and backstepping control technique, and the DDOB is synthesized using a designed disturbance observer and sliding mode control method. Finally, the advantages and disadvantages of the four proposed control strategies are compared and analyzed through experiments.

Robust Voltage Control in Inverter-Interfaced Microgrids Under Plug-and-Play Functionalities

In this article, a new scheme of designing decentralized extended proportional derivative (DEPD) controllers with combining novel disturbance observers is proposed for the issue of voltage control in islanded inverter-interfaced microgrids. A microgrid system under plug-and-play (PnP) functionality is described by an uncertain linear time-invariant system, and then, the stability of microgrid system is studied for voltage regulation based on the robust control theory and linear matrix inequality. The DEPD controller and the proposed disturbance observers are capable of minimizing undesirable oscillations in PnP operation of distributed generators and topology changes. To attenuate the effects of disturbances and uncertainties, a new nonlinear disturbance observer-based control strategy is provided in this article. The new disturbance observers proposed in this article can estimate any disturbances such as constant, harmonic, random walk, and any time-varying disturbances with slow varying rate. Some case studies and numerical simulations are investigated for evaluating the new control scheme via the MATLAB software. Simulations effectively validate the performance of the proposed approach.

Multirate iterative learning disturbance observer with robustness to frequency deviation for high precision attitude stabilization of flexible spacecraft subject to complex disturbances

High precision attitude stabilization of spacecraft is essential for the operation of precision instruments onboard. However, attitude vibrations of spacecraft are inevitably induced by complex disturbances. Disturbance observer based control scheme (DOBC) is a promising anti-disturbance technique, while it is restricted by the inadequate estimation performance of conventional disturbance observers for complex disturbances when taking structural complexity and noise sensitivity into account. To achieve high performance attitude stabilization of spacecraft subject to complex disturbances, a multirate iterative learning disturbance observer (MILDO) based controller is designed in this paper. Firstly, an augmented disturbance model is constructed in view of the periodicities of disturbances with known fundamental frequencies. Then, a generic proportional-derivative type MILDO (PD-MILDO) is designed by using previous disturbance estimates to update current estimates. The gain tuning method and the disturbance estimation performance of PD-MILDO are also presented. It is demonstrated that accurate disturbance estimation for low-frequency disturbance and multiple periodic disturbances can be achieved by PD-MILDO. Besides, the robustness of PD-MILDO to undesired frequency deviation can be significantly improved by introducing the proportional-derivative correction terms. Based on MILDO, a feedback controller is then designed to stabilize the spacecraft attitude. In the concept of DOBC, the controller and observer can be tuned independently. Finally, the effectiveness of the proposed control scheme is verified by simulations.

Zynq Implemented Luenberger Disturbance Observer Based Predictive Control Scheme for PMSM Drives

A Luenberger disturbance observer based control scheme for surface mounted permanent magnet synchronous motor (SPMSM) is proposed in this paper. First, an extended SPMSM model is given by considering the external disturbances and parameter mismatches. Second, a Luenberger observer is introduced to estimate the lumped disturbances in the speed and current loops, respectively. Third, based on the observed disturbances, a speed controller is designed, which is proved to be stable. Finally, an improved deadbeat-based predictive current control (DPCC) based on the estimated disturbances and the new SPMSM model is designed to control the current loop. The proposed method is implemented on a Xilinx Zynq SoC XC7Z020-CLG484-1 and field programmable gate array (FPGA) implementations of the improved DPCC and conventional DPCC are compared and analyzed in detail in terms of area utilization and time consumption. Although the execution time of both methods is very short, the improved DPCC takes less time than the conventional DPCC due to the parallel processing capabilities of FPGAs. The experimental results verify that the proposed method has good dynamic performance, load disturbance suppression performance, and parameter robustness.

Disturbance observer based control for four wheel steering vehicles with model reference

This paper presents a disturbance observer based control strategy for four wheel steering systems in order to improve vehicle handling stability. By combination of feedforward control and feedback control, the front and rear wheel steering angles are controlled simultaneously to follow both the desired sideslip angle and the yaw rate of the reference vehicle model. A nonlinear three degree-of-freedom four wheel steering vehicle model containing lateral, yaw and roll motions is built up, which also takes the dynamic effects of crosswind into consideration. The disturbance observer based control method is provided to cope with ignored nonlinear dynamics and to handle exogenous disturbances. Finally, a simulation experiment is carried out, which shows that the proposed four wheel steering vehicle can guarantee handling stability and present strong robustness against external disturbances.

Optimal control of non-minimum phase integrating processes with time delay using disturbance observer-based control scheme

ABSTRACTA systematical design method of optimal control for non-minimum phase integrating processes with time delay using disturbance observer-based (DOB) control scheme is presented. All stabilising controllers and the filter of DOBs for integrating plants are developed. Then the optimal set-point tracking controller and the optimal filter of DOB are systematically derived by minimising the H2 norm performance specifications. The proposed design method has three main advantages. First, the design procedure is systematical and simple. Specified weight functions are chosen for step inputs and inputs similar to steps. The designed set-point tracking controller and the filter of DOB are given in analytical forms. Second, the designed set-point tracking controller and the filter of the DOB are optimal. They are derived from minimising the performance indexes of set-point tracking and input load disturbance rejection (ILDR). Finally, the set-point tracking performance specification and ILDR specification can be quantitatively achieved by conveniently tuning the adjustable parameters. Numerical simulations are given to illustrate the effectiveness of the proposed method.

Extended state observer based control for generic hypersonic vehicles with nonaffine-in-control character

This paper investigates the flight control problem of generic hypersonic vehicles subject to nonaffine-in-control character. Considering the large uncertainties and external disturbance, the disturbance observer based control strategy is incorporated in the control scheme. Firstly, an extended state observer is used to estimate the system states and the total disturbance. Then, based on the output of the extended state observer, we follow the backstepping design procedure. The dynamic inversion method is involved in the last step of backstepping to solve the nonaffine-in-control problem. The proposed control scheme ensures that the hypersonic vehicle tracks the command signal with almost no aerodynamic knowledge. Rigorous stability proof is given based on the separated time-scale structure of the extended state observer and the dynamic inversion method. At last, numerical simulations are presented in different conditions to demonstrate the effectiveness and good tracking performance of the proposed control scheme.

Consensus disturbance rejection of network-connected dynamic systems with input delay and unknown network connectivity

In this paper, we consider the distributed consensus problem for multi-agent systems with input delay and unknown disturbances. To deal with the input delay and disturbances, a predictor- and disturbance observer-based control strategy is developed for each follower. Then, a distributed robust adaptive consensus protocol with dynamic coupling gains is proposed based on the relative state of the neighbouring agents, guaranteeing that all signals in the closed-loop dynamics are uniformly ultimately bounded and the consensus tracking error converges to an arbitrarily small residual set. The controllers are proposed in a fully distributed way such that the global information related to the eigenvalues of the Laplacian matrix is not needed. Finally, the validity of the proposed controller is demonstrated through a numerical example.

Formation control with disturbance rejection for a class of Lipschitz nonlinear systems

In this paper, we consider the leader-follower formation control problem for general multi-agent systems with Lipschitz nonlinearity and unknown disturbances. To deal with the disturbances, a disturbance observer-based control strategy is developed for each follower. Then, a time-varying formation protocol is proposed based on the relative state of the neighbouring agents and sufficient conditions for global stability of the formation control are identified using Lyapunov method in the time domain. The proposed strategy and analysis guarantee that all signals in the closed-loop dynamics are uniformly ultimately bounded and the formation tracking errors converge to an arbitrarily small residual set. Finally, the validity of the proposed controller is demonstrated through a numerical example.

Active disturbance attenuation control for permanent magnet synchronous motor via feedback domination and disturbance observer

In this study, a novel active disturbance attenuation controller is investigated for the permanent magnet synchronous motor servo system by integrating a feedback domination technique and disturbance observer-based control strategy. A disturbance observer is first constructed to enable an active estimation process of the mismatched disturbances. Second, the authors adopt a feedback domination technique, rather than popularly used feedback linearisation methods, to handle the system non-linearities. A Lyapunov function-based recursive design is then carried out to derive the composite controllers in an explicit way, while a semi-global input-to-state stability can be guaranteed. The proposed methodology not only performs an improved closed-loop control performance comparing to several existing results, but also renders a simple control law which will ease its practical implementations. Abundant comparison simulation results are provided to demonstrate the effectiveness of the proposed scheme.

High-acceleration and high-precision point-to-point motion control based on disturbance observer with improved Q-filter

Under conditions of high acceleration, high-precision and fast positioning of point-to-point motions with short strokes is restricted by the internal and external disturbances occurring in the motion process. To address this issue, a disturbance observer-based control scheme is employed here to suppress the disturbances, which combines a feedforward controller and a feedback controller. Since the low-pass filter of disturbance observer (Q-filter) determines the disturbance suppression ability after the nominal model has been identified, the Q-filter design becomes the most important consideration in practical control. In this article, an improved Q-filter is proposed to further suppress the disturbances by canceling the resonance peak of the binomial filter. High-acceleration point-to-point motions are conducted on a linear-driving stage and the experimental results demonstrate that the proposed control scheme is capable of achieving high-precision and fast positioning control. Since the improved Q-filter exhibits superior disturbance suppression ability, the positioning time with positioning error of 2 µm has been shortened from 13.1 to 11.4 ms.

Disturbance Observer-Based Control of a Dual-Output LLC Converter for Solid-State Lighting Applications

Feedback sensor isolation is often an expensive necessity in power converters, for reasons of safety and electromagnetic compatibility. A disturbance observer-based control strategy for a dual-output resonant converter is proposed to overcome this problem. Current control of two LED loads is achieved through estimation rather than measurement. Robustness against temperature changes, which have significant impact on the behavior of the LEDs, is achieved through estimation of offsets in the forward voltages of the LED strings. The power converter and LEDs are modeled accurately to obtain a good estimation accuracy. The whole implementation is steered toward a low-cost solution.

Disturbance Observer-Based Robust Control of Free-Floating Space Manipulators

A disturbance observer-based control scheme is proposed for free-floating space manipulator with nonlinear dynamics derived using the virtual manipulator approach. The derived dynamic equation uses only link angles as generalized coordinates, which is suitable for the controller design in joint space. Since joint coupling, model uncertainties in robot dynamics are treated as lumped disturbances, a disturbance observer is developed at each joint of degree-of-freedom space manipulator to decouple and simplify the controller design. Simulation results of a six-link space manipulator show that the proposed scheme achieves superior performance, especially when large external disturbances are present.

Control of integral processes with dead-time. Part 1: Disturbance observer-based 2DOF control scheme

A disturbance observer-based control scheme (a version of 2DOF internal model control) which is very effective in controlling integral processes with dead time is presented. The controller can be designed to reject ramp disturbances as well as step disturbances and even arbitrary disturbances. When the plant model is available only two parameters are left to tune. One is the time constant of the set-point response and the other is the time constant of the disturbance response. The latter is tuned according to the compromise between disturbance response and robustness. This control scheme has a simple, clear, easy-to-design, easy-to-implement structure and good performance. It is compared to the best results (so far) using some simulation examples.

Robust force control based on compensation for parameter variations of dynamic environment

Force control strategies that are robust against disturbance and parameter variations are proposed. These strategies are expansions of disturbance observer-based control strategy, and require little computation. Observers are proposed that estimate parameter variations of the dynamic environment on which the force is imposed are introduced. Since the observer-based control represents a nominal system, a second derivative of force can be controlled. A force control strategy for controlling the second derivative of force is also proposed. The force response similar to the force command is realized by these strategies in spite of the disturbance and the parameter variations of the control object. The effectiveness of the proposed methods is confirmed by simulation and experimental results. >