Active fault tolerant control for multirotor UAVs: Controllability, design and experiment

This paper presents an integrated structure for a passive and active fault tolerant control (FTC) design approach in the framework of a robust nonlinear control technique called Dynamic Surface Control (DSC). As motivated by the automated vehicle application, we consider two categories of possible faults: pre-specified (a priori) and non-specified faults. It is first shown that DSC can be considered as a passive FTC approach in the sense that it gives simultaneous robust stability to a set of nonlinear systems even in the presence of model uncertainties and the pre-specified faults. Then, the non-specified fault is classified depending on the fault’s impact on the closed-loop system and isolatability from a fault detection and diagnosis (FDD) system. If a fault is both intolerable and isolatable, an active FTC approach is taken which includes FDD and controller reconfiguration. More specifically, trajectory reconfiguration is considered to accommodate the actuator fault, i.e., to compensate for the performance loss due to the fault within the framework of a switched hierarchical structure. Finally, the integrated structure for the longitudinal control of an automated transit bus is designed through the proposed method. Simulation results of the fault tolerant controller are shown for both single and multiple multiplicative faults. This controller was implemented on the California PATH transit buses in a demonstration of automated public transportation technology in San Diego, California in August of 2003.

This paper discusses the design of an active fault-tolerant flight control strategy for improvement of the operational control capability of the aircraft system. The research work draws expertise from actions undertaken within the European Flight Mechanics Action Group [FM-AG(16)] on fault-tolerant control, which develops a collaborative effort in Europe to create new fault-tolerant control technologies that significantly advance the goals of the aviation safety. The methodology is applied to a trimmable horizontal stabilizer runaway fault occurring in a large transport aircraft. The goal is to provide a self-repairing capability to enable the pilot to land the aircraft safely. The fault-tolerant control strategy works in such a way that once the fault is detected by the fault detection and isolation unit, a compensation loop is activated for safe recovery. A key feature of the proposed strategy is that the design of the fault-tolerant control loop is done independently of the nominal autopilot and the nominal flight control system in place. Nonlinear simulation results demonstrate the effectiveness of the proposed fault-tolerant control scheme.

Chapters 2 – 4 all study the problems of active fault-tolerant control. Active fault-tolerant control greatly improves the performance of the control system, which has attracted extensive attention from scholars (Gao and Ding 2007). However, active fault-tolerant control requires adjusting the controller parameters after a fault occurs, and may also change this controller structure. Therefore, more control algorithms need to be designed. In addition, the characteristic of passive fault-tolerant control is that an invariant controller is adopted to ensure the robustness of the closed-loop system to specific faults regardless of whether the fault occurs or not. Therefore, a fault diagnosis unit is not required, that is, it does not need any real-time fault message. At the same time, the research on passive fault-tolerant control is not deep enough (Cao and Wang 2018), which is instructive for us to carry out this work. Meanwhile, passive fault-tolerant control of intermittent faults deserves further development.

Differential geometry based active fault tolerant control for aircraft

In this paper, an active fault tolerant controller is proposed for the unmanned aerial vehicle (UAV) attitude control system using nonsingular fast terminal sliding mode control technique. Firstly, the nonlinear attitude dynamics model of UAV with actuator faults and external disturbance is described. Next, a neural network-based fault estimation observer is designed to obtain the estimated value of unknown actuator faults and external disturbance, and the stability of the designed observer is also proved. Then, an active fault tolerant controller is designed based on the fault estimation observer and nonsingular fast terminal sliding mode control technique. The Lyapunov stability analysis shows that the proposed fault tolerant controller can guarantee the finite time asymptotic stability for nonlinear closed-loop attitude control systems of UAV with actuator faults and external disturbances. Finally, numerical simulation results are presented to illustrate the benefit of the proposed scheme.

New fault diagnosis and active fault tolerant control (FTC) algorithms are proposed for a class of nonlinear singular stochastic distribution control (SDC) systems in this paper. Different from general SDC systems, in singular SDC systems, the relationship between the weights and the control input is expressed by a singular state space model, which increases the difficulty in design of fault diagnosis and fault tolerant control. A non-singular state transformation is made to transform the singular dynamic system into a differential-algebraic system. An adaptive nonlinear observer is designed to estimate the size of the fault occurring in the system. Furthermore, the linear matrix inequality (LMI) approach is applied to establish sufficient conditions for the existence of the observer. Based on the estimated fault information, the active fault tolerant controller is designed to make the post-fault probability density function (PDF) still track the given distribution. At last, an illustrated example is given to demonstrate the effectiveness of the proposed algorithm, and satisfactory results have been obtained.

Handling fault in ambient temperature measurements in a cooling system - A fault tolerant control approach

Active FTC for Non-linear Aircraft based on Feedback Linearization and Robust Estimation

In this paper, an active fault-tolerant control for a robot manipulator based on synchronous sliding mode is proposed. As the synchronization errors approach zero, the joint errors tend to become equal and also approach zero. Therefore, the synchronization technique is inherently effective for a fault-tolerant controller. To demonstrate such a system, the following implementation is presented. First, an estimator was designed with an extended state observer to estimate uncertainties/disturbances along with faults/failures. The estimator signal was used for an online compensator in the controller. A fault-tolerant controller with a combination of synchronous sliding mode technique and estimator was proposed. The stability of the system was established using Lyapunov theory. Finally, fault tolerant control was implemented in a three degree-of-freedom robot manipulator and compared to the conventional sliding mode control. This comparison shows the effectiveness of the proposed active fault-tolerant control with synchronous sliding mode technique.

In this paper, the trajectory tracking control of a quadrotor UAV under external disturbances is considered. Hierarchical inner-outer loop control scheme is adopted which consists of two parts: the inner loop for attitude control which implements linear active disturbance rejection control strategy and the outer loop for position control which applies sliding mode control method. The stability prove of the closed loop system is given in the paper. Setting desired trajectory, the quadrotor can track it accurately. Simulation results show the good performance of the proposed control scheme under different disturbance conditions.

On interval observer design for active Fault Tolerant Control of Linear Parameter-Varying systems

Design of an active fault tolerant control system for a simulated industrial steam turbine

The design and implementation of a multi-stage PID (MS-PID) controller for non-inertial referenced UAVs are highly complex. Symmetrical multirotor UAVs are unstable systems, and it is thought that the kinematics of the symmetrical UAV rotor, such as the quadrotor and hexacopter resembles the kinematics of an inverted pendulum. Several researchers have investigated the structure and design of PID controllers for high-order systems during the last decade. The designs were always concerned with the enhanced response, robustness, model reduction and performance of PID controllers. An accurate tuning process of such a controller depends on the engineer’s experience level. This is due to the number of variables and hyperparameters tuned during the process. An adaptive genetic algorithm (AGA) is utilized to optimize the MS-PID controllers for controlling the quadrotor in this study. The proposed method optimizes the offline-planned approach, providing several possibilities for adapting the controllers with various paths and or varying weather conditions. The MS-PID parameters are optimized in parallel, as every PID controller affects the other controller’s behavior and performance. Furthermore, the proposed AGA generates new chromosomes for “new solutions” by randomly developing new solutions close to the previous best values, which will prevent any local minima solution. This study intends to investigate the design and development of a highly tuned robust multi-stage PID controller for a symmetrical multirotor UAV. The work presents a model for a non-referenced inertial frame multirotor UAV (quadcopter). Once the model is defined, a robust multi-stage PID controller for the non-inertial referenced frame symmetrical multirotor UAV is designed, tuned, and tested. A genetic algorithm (GA) will be used to tune the MS-PID controller. Finally, the performance comparison between the proposed and conventional methods is presented. The results show that the proposed method provides stability improvement, better transient response, and power consumption.

In this paper, an active fault-tolerant control (FTC) scheme for turbofan engines subject to simultaneous multiplicative and additive actuator faults under disturbances is proposed. First, a state error feedback controller is designed based on interval observer as the nominal controller in order to achieve the model reference rotary speed tracking control for the fault-free turbofan engine under disturbances. Subsequently, a virtual actuator based reconfiguration block is developed aiming at preserving the consistent performance in spite of the occurrence of the simultaneous multiplicative and additive actuator faults. Moreover, to improve the performance of the FTC system, the interval observer is slightly modified without reconstruction of the state error feedback controller. And a theoretical sufficiency criterion is provided to ensure the stability of the proposed active FTC system. Simulation results on a turbofan engine indicate that the proposed active FCT scheme is effective despite of the existence of actuator faults and disturbances.

This paper studies the problem of fault estimation (FE) and the active fault tolerant control (FTC) for a class of Takagi-Sugeno (T-S) fuzzy systems with time-varying delay and simultaneous actuator and sensor faults. Based on the fault estimation algorithm, an adaptive observer-based controller is designed to guarantee the dynamic error system to be asymptotically stable and satisfy the H ∞ performance index. Then, based on the information of online fault-estimation information, a dynamic output feedback fault tolerant controller is designed to compensate the fault effects on the closed-loop fuzzy system. Finally, simulation results are given to verify the effectiveness of the proposed method.