Input Shaping enhanced Active Disturbance Rejection Control for a twin rotor multi-input multi-output system (TRMS)

Switched step integral backstepping control for nonlinear motion systems with application to a laboratory helicopter

In this paper, the energy efficiency of the widespread application of backstepping control to a class of nonlinear motion systems is investigated. A Switched Step Integral Backstepping Control (SSIBC) scheme is introduced to improve immunity to measurement noise and to increase the energy efficiency of conventional backstepping in practice. The SSIBC is realized by switching between two candidate controllers obtained at different steps of the iterative backstepping design process. A bi-state dependent hysteresis rule is developed to supervise stable switching between the different regimes in the presence of noise. The proposed method is experimentally verified on a MIMO twin rotor laboratory helicopter involving coupled nonlinear dynamics, inaccessible states and uncertainties. Experimental results show that in addition to a reduction in power consumption, the SSIBC reduces saturation of the control signal and visible motor jerking in contrast with conventional backstepping. Additional comparisons with a previously proposed optimized decoupling PID controller also show significant improvement in precision achieved with higher energy efficiency. Experimental results obtained with the introduction of an external disturbance into the system also show the robustness of the proposed SSIBC.

Cascaded adaptive integral backstepping sliding mode and super-twisting controller for twin rotor system using bond graph model

This work presents a bond graph (BG) model and a robust cascaded controller for a twin-rotor system (TRS). The BG model accounts for all the energetic and dynamical couplings. An adaptive integral backstepping sliding mode (AIBSM) controller is used in the outer loop to control the slow yaw and pitch dynamics of the mechanical sub-system whereas a higher-order sliding mode (HOSM) observer-based super-twisting algorithm (STA) controller is used in the inner loop to control the fast electromechanical actuator dynamics. The gain of the discontinuous control term of the integral backstepping sliding mode (IBSM) controller is adjusted by using an adaptive switching gain law, where the adaptive gain decreases or increases as the system state variables move closer to or away from a sliding surface; thereby reducing chatter and discontinuities near the sliding manifold, and ensuring a nearly smooth reference signal to the inner-loop controller. The unavailable states are estimated by using an unscented Kalman filter. All the used controllers are shown to be Lyapunov stable. The performance of the developed controller is validated through simulation and experiment, and it is further compared with other existing robust controllers. The proposed controller is robust against un-modeled dynamics and external disturbances, and it performs better, in terms of trajectory tracking error and disturbance rejection, than presently existing controllers for the TRS.

Design of a multivariable stimulus for Emotional-Learning based control of a 2-DOF laboratory helicopter

Emotional-Learning based controllers are becoming increasingly popular due to their non-parametric and flexible design approach. However, most of the existing Emotional-Learning based control strategies are designed specifically for individual loops and are not suitable for superior performance in a strongly coupled MIMO system. In this technical note, a multi-variable Emotional-Learning based strategy for trajectory tracking in a strongly coupled MIMO system is proposed. This strategy incorporates an improved stimulus design that deals with tracking, regulation, disturbance-rejection and coupling effects in a systematic way. The strategy also addresses the deleterious effects of mechanical resonance associated with flexible structures from the perspective of stimulus design. The proposed strategy is validated through simulations and hardware based experiments on a 2-DOF laboratory helicopter. Effectiveness of the proposed strategy is illustrated through comparisons with an optimized multi-variable LQG controller.

Particle swarm-based and neuro-based FOPID controllers for a Twin Rotor System with improved tracking performance and energy reduction

This paper examines two approaches in tuning fractional order proportional-integral-differential (FOPID) control named as neuro-based FOPID (NNFOPID) and particle swarm-based FOPID (PSOFOPID) for pitch control of a Twin Rotor Aerodynamic System (TRAS). For the neuro-based FOPID control, the innovations are the modification of output equation in the artificial neural network and the implementation of the Rectified Linear Unit (ReLU) activation function. The advantages of the proposed approach are a lighter network and the ability to tune more practical controller parameters without a deep knowledge of the system to achieve a satisfying pitch tracking response. As for the particle swarm-based FOPID control, the application of PSO with spreading factor algorithm is extended for tuning the FOPID controller gains and the innovation here is a new procedure in setting the initial search range. The important advantages of this proposed swarm-based algorithm are the avoidance of being trapped in local optima and reduction of the search area respectively. The performances of the proposed controllers are proven by extensive simulations and experimental verifications based on five standard criteria: square-wave characteristics, reference to disturbance ratio, evaluation time, energy consumption of the control signal and tracking performance. The performances of the proposed controllers are compared against an optimised PID control in three system conditions, namely Case I) without coupling effect and wind disturbance, Case II) with coupling effect only and Case III) with wind disturbance only. Together, this study finds that NNFOPID control offers an accurate system positioning by a 34% reduction in steady-state error with the lowest energy consumption and minimum evaluation time in Case II. In terms of the tracking performance and robustness for Case II, the superiority of PSOFOPID control is confirmed by a 27% reduction in the tracking error and the lowest oscillation value. The experimental results also validate the robustness and energy consumption of both controllers in Case III. It is envisaged that the proposed control designs can be very useful in tuning FOPID controller gains for high performance, low energy, and robust aerodynamics systems.

Improved integral backstepping control of variable speed motion systems with application to a laboratory helicopter

This paper proposes an improved method of integral backstepping for real time control of a laboratory helicopter with variable speed rotors known as the Two-Rotor Aero-dynamic System (TRAS). The coupled system is decomposed into the horizontal subsystem (HS) and the vertical subsystem (VS) and traditional backstepping, augmented with direct integral action is designed for each subsystem. The transient response to both constant and time varying references is then simultaneously improved by modifying an already proposed method called dual boundary conditional integration. A switching technique is also employed to enhance the tracking response of the undamped HS for its bi-directional motor which exhibits jerking effects. Experimental results show that the proposed approach yields improved transient and tracking performance when compared to previously proposed methods exploiting conditional integration earlier proposed for improving the transient response of controlled nonlinear systems with integral action. The results also show the robustness of the proposed method in the presence of the coupling effects and additional external disturbance applied to the system in the form of a wind gust.

Fractional Order (FO) Two Degree of Freedom (2-DOF) control of Linear Time Invariant (LTI) plants

The dynamics of Fractional Order (FO) System have recently attracted substantial attention in the field of control. Taking note of this, the Fractional Order (FO) controllers provides additional flexibility in the design by virtue of its non-integer orders. However, all the available control schemes in this domain are mostly featured in 1-DOF (Degree of Freedom) formation which compromises between response and loop goals. Differently, a 2-DOF (Degree of Freedom) topology allows one to shape the transient response ensuring at the same time satisfactory loop margins. It is thus anticipated here that the integration of 2-DOF (Degree of Freedom) control scheme with FO Compensator may accelerate successful attainment of system response and loop robustness. Hence, this paper addresses the development of 2-DOF (Degree of Freedom) FO control system design methodology for integer as well as non-integer order plants. The additional degree of freedom and the non-integer order of the controller together ensure desired output response as well as adequate loop robustness. Novel design procedures for the 2-DOF (Degree of Freedom) control scheme are presented in meticulous manner depending upon the nature of the plant under consideration. A unique approach for FO pre-filter is presented depending upon the nature of the loop compensators in case of non-commensurate order plants. It is observed here that the proposed 2-DOF (Degree of Freedom) scheme bestows an added DOF in addition to the auxiliary design parameter by the virtue of its non-integer orders. The closed loop system response manifests that the proposed approach show cases exclusively surpassing system response and robustness compared to its 1-DOF (Degree of Freedom) as well as integer order 2-DOF (Degree of Freedom) counterparts. The potency of the method put forward is established with MATLAB simulation as well as real-time experimentation. The proposed control schemes are implemented to two highly non-linear real time systems of TRMS system and Cart-Inverted Pendulum System. The experimental outcomes are demonstrated to endorse the benefits of the control scheme advocated.

Modified reduced order observer based linear active disturbance rejection control for TITO systems

This paper proposes an observer based control approach for two input and two output (TITO) plant affected by the lumped disturbance which includes the undesirable effect of cross couplings, parametric uncertainties, and external disturbances. A modified reduced order extended state observer (ESO) based active disturbance rejection control (ADRC) is designed to estimate the lumped disturbance actively as an extended state and compensate its effect by adding it to the control. The decoupled mechanism has been used to determine the controller parameters, while the proposed control technique is applied to the TITO coupled plant without using decoupler to show its efficacy. Simulation results show that the proposed design is efficiently able to nullify the interactions within the loops in the multivariable process with better transient performance as compared to the existing proportional-integral-derivative (PID) control methods. An experimental application of two tanks multivariable level control system is investigated to present the validity of proposed scheme.

Optimal feedback control of twin rotor MIMO system with a prescribed degree of stability

Purpose

The purpose of this paper is to investigate an optimal control solution with prescribed degree of stability for the position and tracking control problem of the twin rotor multiple input-multiple output (MIMO) system (TRMS). The twin rotor MIMO system is a benchmark aerodynamical laboratory model having strongly non-linear characteristics and unstable coupling dynamics which make the control of such system for either posture stabilization or trajectory tracking a challenging task.

Design/methodology/approach

This paper first describes the dynamical model of twin rotor MIMO system (TRMS) and then it adopts linear-quadratic regulator (LQR)-based optimal control technique with prescribed degree of stability to achieve the desired trajectory or posture stabilization of TRMS.

Findings

The simulation results show that the investigated controller has both static and dynamic performance; therefore, the stability and the quick control effect can be obtained simultaneously for the twin rotor MIMO system.

Originality/value

The articles on LQR optimal controllers for TRMS can also be found in many literatures, but the prescribed degree of stability concept was not discussed in any of the paper. In this work, new LQR with the prescribed degree of stability concept is applied to provide an optimal control solution for the position and tracking control problem of TRMS.