The reliability of a process machine can be significantly enhanced by introducing a fault-tolerant control system in it. Hardware redundancy is an important aspect to enhance fault tolerance capability and is studied in this paper. A novel modified triple modular redundancy (MTMR) approach is proposed for the sensors to avoid a shutdown in the case of simultaneous faults in more than one sensor, and dual redundancy is proposed for the actuators to avoid a single point of failure due to the single actuator fault. The performance of the control system is verified by simulation in MATLAB Simulink environment. The proposed MTMR fulfills the gap in conventional TMR by maintaining stability even in the case of simultaneous faults in two channels. Cost and benefit analysis (CBA) is carried out to determine the financial feasibility of the implementation of the proposed system. The results of the CBA demonstrate that the proposed system is financially feasible due to the positive net present value and small breakeven period. INDEX TERMS Air-fuel ratio control, fault tolerant control, hardware redundancy, IC gas engine, triple modular redundancy.
In this paper, a hybrid fault tolerant control system is proposed for air–fuel ratio control of internal combustion gasoline engines based on Kalman filters and triple modular redundancy. Hybrid fault tolerant control system possesses properties of both active fault tolerant control system and passive fault tolerant control system. As part of active fault tolerant control system, fault detection and isolation unit is designed using Kalman filters to provide estimated values of the sensors to the engine controller in case of faults in the sensors. As part of passive fault tolerant control system, a dedicated proportional–integral feedback controller is incorporated to maintain air–fuel ratio by adjusting the throttle actuator in the fuel supply line in faulty and noisy conditions for robustness to faults and sensors’ noise. Redundancy is proposed in the sensors and actuators as a simultaneous failure of more than one sensor, and failure of the single actuator will cause the engine shutdown. Advanced redundancy protocol triple modular redundancy is proposed for the sensors and dual redundancy is proposed for actuators. Simulation results in the MATLAB Simulink environment show that the proposed system remains stable during faults in the sensors and actuators. It also maintains air–fuel ratio without any degradation in the faulty conditions and is robust to noise. Finally, the probabilistic reliability analysis of the proposed model is carried out. The study shows that the proposed hybrid fault tolerant control system with redundant components presents a novel and highly reliable solution for the air–fuel ratio control in internal combustion engines to prevent engine shutdown and production loss for greater profits.
This paper presents the development of an indirect adaptive state-feedback controller to improve the disturbance-rejection capability of under-actuated multivariable systems. The ubiquitous Linear-Quadratic-Regulator (LQR) is employed as the baseline state-feedback controller. Despite its optimality, the LQR lacks robustness against parametric uncertainties. Hence, the main contribution of this paper is to devise and retrofit the LQR with a stable online gain-adjustment mechanism that dynamically adjusts the state weighting-coefficients of LQR's quadratic cost-function via state-error dependent nonlinear-scaling functions. An original self-mutating phase-based adaptive modulation scheme is systematically formulated in this paper to self-adjust the state weighting-coefficients. The scheme employs pre-calibrated secanthyperbolic-functions whose waveforms are dynamically reconfigured online based on the variations in magnitude and polarity of state-error variables. This augmentation dynamically alters the solution of the Riccati-Equation which modifies the state-feedback gains online. The proposed adaptation flexibly manipulates the system's control effort as the response converges to or diverges from the reference. The efficacy of proposed adaptive controller is validated by conducting hardware-in-the-loop experiments to vertically stabilize the QNET 2.0 Rotary Pendulum system. As compared to the standard LQR, the proposed adaptive controller renders rapid transits in system's response with improved damping against oscillations, while maintaining its asymptotic-stability, under bounded exogenous disturbances. INDEX TERMS Hyperbolic functions, linear quadratic regulator, cost-function, rotary inverted pendulum, self-tuning control, state weighting-coefficients.
Fault-tolerant control systems are utilized in safety and critical applications to achieve greater reliability and availability for continued operation despite faults in the system components. These systems can be utilized in the process plants to avoid costly production loss due to abnormal and unscheduled tripping of the machines. In this paper, advanced fault-tolerant control systems of active type are proposed for air–fuel ratio control of internal combustion gas engine in a process plant to achieve greater reliability and availability to avoid a shutdown of the gas engine. Gas engines are extensively used equipment in the process industry and proper air–fuel ratio control in the fuel system of these engines is quite important to achieve greater engine efficiency, fuel energy savings and environmental protection. Active fault-tolerant control system is proposed in this paper in which linear regression–based observer model is used in the fault detection and isolation unit for fault detection, isolation and reconfiguration. Fuel actuator is introduced in the fuel supply line and proportional feedback controller is implemented to maintain the air–fuel ratio in faulty conditions. Redundancy in the sensors and fuel actuator is proposed to avoid engine shutdown in case of simultaneous faults in more than one sensor and to avoid a single point of failure due to fault in the single actuator. Noise is introduced in the sensor measurements to determine the robustness of proposed active fault-tolerant control system in noisy and faulty conditions. Results show that the proposed system remains stable, maintaining air–fuel ratio well in faulty conditions and is robust to noise.
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