This paper considers actuator redundancy management for a class of overactuated nonlinear systems. Two tools for distributing the control effort among a redundant set of actuators are optimal control design and control allocation. In this paper, we investigate the relationship between these two design tools when the performance indexes are quadratic in the control input. We show that for a particular class of nonlinear systems, they give exactly the same design freedom in distributing the control effort among the actuators. Linear quadratic optimal control is contained as a special case. A benefit of using a separate control allocator is that actuator constraints can be considered, which is illustrated with a flight control example.

Resolving actuator redundancy: optimal control vs. control allocation

The normal approach to digital control is to sample periodically in time. Using an analog of integration theory we can call this Riemann sampling. Lebesgue sampling or event based sampling is an alternative to Riemann sampling. It means that signals are sampled only when measurements pass certain limits. In this paper it is shown that Lebesgue sampling gives better performance for some simple systems.

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Comparison of Riemann and Lebesque sampling for first order stochastic systems

The human immunodeficiency virus (HIV), as one of the most hazardous viruses, causes destructive effects on the human bodies’ immune system. Hence, an immense body of research has focused on developing antiretroviral therapies for HIV infection. In the current study, we propose a new control technique for a fractional-order HIV infection model. Firstly, a fractional model of the HIV model is investigated, and the importance of the fractional-order derivative in the modeling of the system is shown. Afterward, a type-2 fuzzy logic controller is proposed for antiretroviral therapy of HIV infection. The developed control scheme consists of two individual controllers and an aggregator. The optimal aggregator modifies the output of each individual controller. Simulations for two different strategies are conducted. In the first strategy, only reverse transcriptase inhibitor (RTI) is used, and the superiority of the proposed controller over a conventional fuzzy controller is demonstrated. Lastly, in the second strategy, both RTI and protease inhibitors (PI) are used simultaneously. In this case, an optimal type-2 fuzzy aggregator is also proposed to modify the output of the individual controllers based on optimal rules. Simulations results demonstrate the appropriate performance of the designed control scheme for the uncertain system.

Antiretroviral therapy of HIV infection using a novel optimal type-2 fuzzy control strategy

Event-triggered controllers are well known for guaranteeing the desired stability for a sampled-data system with minimum resource utilization. Over the past decade, the study has revealed that the overall performance improvement for a sampled-data system can be achieved by replacing the time-based sampling with an event-triggered one. The design of sliding mode control (SMC) in the event-triggering framework has also shown similar outcomes, especially for uncertain systems. There are different design strategies for event-triggered SMC available in the literature for networked dynamical systems that are potentially affected by uncertainties and transmission delays. The purpose of this survey article is to present the state of the art on event-triggered SMC and familiarize the readers with the design techniques with their pros and cons, since this will be very helpful to the researchers and engineers for implementing SMC using event-based feedback strategies.

A Survey on Event-Triggered Sliding Mode Control

Decentralized formation flight via PID and integral sliding mode control

Design of event-triggered sliding mode controller based on reaching law with time varying event generation approach

This article presents an event-triggered implementation of sliding-mode control (SMC) to track the desired trajectory by a two-wheeled differential drive mobile robot. Here, a situation is considered where the communication between the remote controller and mobile robot is established via a wireless network and the objective is to achieve a satisfactory tracking performance while reducing the usages of network bandwidth and control computation. The continuous-time SMC law is redesigned in the context of event-based framework and an event condition is proposed, which has a switching structure to avoid the singularity of the control law. The convergence of the tracking error in the sense of practical stability has been guaranteed by the Lyapunov method. To ensure the Zeno-free behavior of the system, the minimum interevent execution time has been proved to be bounded by a positive value. Also, the time delay associated with the communication network is considered while designing the triggering parameter. Finally, the proposed event-triggered sliding-mode controller has been implemented on a benchmark. The performance of the proposed strategy is compared with the classical time-triggered set up in terms of tracking performance, communication burden, and computational load.

Event-Triggered Sliding-Mode Control of Two Wheeled Mobile Robot: An Experimental Validation

This paper concerns with the robust stabilization of a perturbed linear time-invariant (LTI) single-input single-output (SISO) system based on event-based/ event-triggered sliding mode control (SMC) with logarithmic quantized state measurement. This technique is expected to reduce communication traffic in control networks with the assurance of robust stability against the quantization error and external perturbations. In practice, delay is inevitable in the control computation during the implementation of the control law. The proposed event-triggering mechanism is analysed for the two scenarios: with delay and without delay in control computation. The robust stability of the uncertain system is ensured with the external disturbances, the error introduced by the quantization process and delay encountered in control computation with the proposed event-based SMC. The lower bound of minimum inter event execution time is derived to ensure the Zeno free behaviour. To show the effect of delay on the triggering mechanism, the maximum bound of the delay is obtained to guarantee the Zeno free behaviour with the robust stability of the closed loop system. An example of a mechanical system is simulated and results are shown to validate the effectiveness of the proposed methodology.

Design of event-based sliding mode controller with logarithmic quantized state measurement and delayed control update.

Dynamic event-triggering based design of sliding mode control

This paper proposes an aperiodic sampled-data implementation of integral sliding mode control (ISMC) for linear-time-invariant (LTI) perturbed systems. The proposed control scheme involves a new triggering scheme which is derived based on stability condition. This proposed methodology can reduce the number of control computation in comparison to the periodic implementation of ISMC. The closed loop stability is derived and it has been shown that the practical sliding mode is achieved with the proposed triggering control scheme. To guarantee the Zeno free behavior of the system the existence of a positive lower bound of the inter event execution time has been shown. Finally, the simulation result is provided with a mechanical system to illustrate the benefits of the proposed approach.

Manas Kumar Bera

Papers

Design of event-triggered sliding mode controller based on reaching law with time varying event generation approach

Event-Triggered Sliding-Mode Control of Two Wheeled Mobile Robot: An Experimental Validation

Design of event-based sliding mode controller with logarithmic quantized state measurement and delayed control update.

Dynamic event-triggering based design of sliding mode control

Event-triggered Integral Sliding Mode Control