Sharif Digital Repository

This paper presents a robust model predictive control algorithm with a time-varying terminal constraint set for systems with model uncertainty and input constraints. In this algorithm, the nonlinear system is approximated by a linear model where the approximation error is considered as an unstructured uncertainty that can be represented by a Lipschitz nonlinear function. A continuum of terminal constraint sets is constructed off-line, and robust stability is achieved on-line by using a variable control horizon. This approach significantly reduces the computational complexity. The proposed robust model predictive controller with a terminal constraint set is used in tracking set-points for... 

The turbine control system is one of the key control loops in the dynamic performance of steam power generation units. In this paper a multivariable PID controller is designed for the governing system of steam turbine power generators. The necessary and sufficient conditions for existence of a strong robust H ∞ dynamic compensator are established in terms of linear matrix inequality (LMI) approach. This controller is designed in succeeding to the existing proportional controller in a power plant. To reach to this goal, the complete dynamic model of an actual turbine-generator including the governor, turbine and generator, are derived. Simulation results show that proposed controller has good... 

This paper deals with the decentralized polynomial trajectory generation for the formation flight of a leader-follower network of quadrotors. The proposed decentralized trajectory planning method guarantees stability of the formation in missions with aggressive trajectories or low information exchange frequencies or data loss. Moreover, designed formation protocol ensures robustness of the formation against variations of the network communication topology. First, quadrotor translational dynamics is represented as a quadruple integrator by linearizing and differentiating its equations of translational motion. Then, a formation control law for a leader-follower network of the quadruple... 

This paper presents some computationally efficient algorithms for online tracking of set points in robust model predictive control context subject to state and input constraints. The nonlinear systems are represented by a linear model along with an additive nonlinear term which is locally Lipschitz. As an unstructured uncertainty, this term is replaced in the robust stability constraint by its Lipschitz coefficient. A scheduled control technique is employed to transfer the system to desired set points, given online, by designing local robust model predictive controllers. This scheme includes estimating the regions of feasibility and stability of the related equilibriums and online switching... 

Renovation and retrofit of gas turbine control systems yield significant economic savings, enhanced reliability, and improved performance. In recent years, the gas turbine industry is increasingly facing the need to well-established procedures for the acceptance tests of renovated control systems. This paper proposes a unified framework to evaluate the performance of renovated gas turbine control systems. Under a set of assumptions on the ambient and fuel conditions, a low-complexity modular model is presented and identified using optimization-oriented identification techniques. The accuracy of the proposed model is validated through experimental studies in full-load, min-load, and no-load... 

This paper presents a new robust control strategy for islanded operation of a microgrid consisting of several distributed generation (DG) units with arbitrary topology. Each DG unit is connected to its local load through a voltage-source converter (VSC), a series RL filter and a step-up transformer. The multi-DG microgrid with arbitrary connectivity graph is modeled as a linear time-invariant (LTI) system subject to a parametric, norm-bounded uncertain block. By utilizing the developed model for multi-DG microgrids, a systematic approach for the design of structured dynamic output feedback control is proposed. A convex optimization problem is developed which yields a low-order dynamic... 

This paper presents a new robust control strategy for islanded operation of a microgrid consisting of several distributed generation (DG) units with arbitrary topology. Each DG unit is connected to its local load through a voltage-source converter, a series RL filter and a step-up transformer. The multi-DG microgrid with arbitrary connectivity graph is modeled as a linear time-invariant system subject to a parametric, norm-bounded uncertain block. By utilizing the developed model for multi-DG microgrids, a systematic approach for the design of structured dynamic output feedback control is proposed. A convex optimization problem is developed which yields a low-order dynamic controller of... 

Renovation and retrofit of gas turbine control systems yield significant economic savings, enhanced reliability, and improved performance. In recent years, the gas turbine industry is increasingly facing the need to well-established procedures for the acceptance tests of renovated control systems. This paper proposes a unified framework to evaluate the performance of renovated gas turbine control systems. Under a set of assumptions on the ambient and fuel conditions, a low-complexity modular model is presented and identified using optimization-oriented identification techniques. The accuracy of the proposed model is validated through experimental studies in full-load, min-load, and no-load... 

Wind turbines are generally controlled for the objectives of the turbine protection and generation of the acceptable power for the utility grid. In this paper, a nonlinear multivariable model of the wind turbine with a DFIG generator is considered. The rotor speed and the d-axis rotor current, as the controlled variables, are controlled via manipulation of the two generator voltages, as the control signals. Two robust control strategies including the sliding mode control and H∞ robust control, designed via μ-synthesis based on DK-iteration algorithm, are presented for switching between various operating modes. Development of an acceptable dynamic model and two innovative control strategies... 

Efficient robust control methods are required to keep the boiler-turbine unit performance appropriately. In this paper, a hybrid multivariable robust control strategy including the regulator and observer is designed to improve the performance of an industrial boiler-turbine unit. In the nonlinear model of the process, output variables including the drum pressure, electric power and water level of the drum are controlled at the desired set-points by manipulation of the fuel, steam, and feed-water flow rates. Due to economic and technical reasons and for the estimation of process states, the full-order observer is designed. For disturbance rejection and process stability, a regulator system is... 

In recent years, unmanned aerial systems have attracted great attention due to the electronic systems technology advancements. Among these vehicles, unmanned helicopters are more important because of their special abilities and superior performance. The complex nonlinear dynamic system (caused by main rotor flapping dynamics coupled with the rigid body rotational motion) and considerable effects of ambient disturbance make their utilization hard in actual missions. Attitude dynamics have the main role in helicopter stabilization, so implementing proper control system for attitude is an important issue for unmanned helicopter hovering and trajectory tracking performance. Besides this,... 

This paper describes the design and implementation of a H∞-based robust controller for a commercial 2MW variable-speed variable-pitch wind turbine. The single controller is able to deliver specification performance for the entire full load region. Various aspects of modeling and design procedures including reduced order model validation, torsional mode damping of drivetrain and uncertainty estimation are explained in detail. To make the design more reliable and industrially attractive, simple routines for the derivation of required weighting functions are introduced. To investigate the benefits of the suggested design, its closed-loop performance is compared with the wind turbine's baseline... 

Fractional order PID controllers are suitable for almost all types of dynamic models. In this paper, a new adaptive fractional order PID controller using neural networks is introduced.The overall performance using the proposed adaptive fractional order PID controller is demonstrated through some examples. It is shown that the new controller scheme can give excellent performance and more robustness in comparison with the conventional controllers like GPC  

The problem of time optimal magnetic attitude control is treated and an open loop solution is first obtained using a variational approach. In order to close the control loop, a neural network with time varying weights is proposed as a feedback optimal controller applicable to the time varying nonlinear system. The good robustness and low real-time computational burden of the proposed neuro-controller makes the controller more useful compared to the other control methods. © 2008 IEEE  

Reducing the renewable energy costs is necessary for the competition with the fossil energies and control strategies have great impact on the efficiency of wind machines. In the wind turbine industry, a practical approach is to maximize the energy capture of a wind machine by optimizing the power coefficient in the under-rated situations. In this paper, with the main objective of maximizing the energy capture in the second region, four different control strategies are compared in the presence of uncertainties. The proposed control methods are compared based on their power capture and robustness against probable uncertainties in the structural and environmental parameters. A two-mass... 

In this study, an auxiliary damping controller based on a robust controller considering the active and reactive power control loops for a doubly-fed induction generator for wind farms is proposed. The presented controller is able to improve the inter-area oscillation damping. In addition, the proposed controller applies only one accessible local signal as the input; however, it can improve the inter-area oscillation damping and, consequently the system stability for the various working conditions and uncertainties. The oscillatory modes of the system are appointed using the linear analysis. Then, the controller’s parameters are determined using the robust control approaches (H∞/ H2) with the... 

Reducing the renewable energy costs is necessary for the competition with the fossil energies and control strategies have great impact on the efficiency of wind machines. In the wind turbine industry, a practical approach is to maximize the energy capture of a wind machine by optimizing the power coefficient in the under-rated situations. In this paper, with the main objective of maximizing the energy capture in the second region, four different control strategies are compared in the presence of uncertainties. The proposed control methods are compared based on their power capture and robustness against probable uncertainties in the structural and environmental parameters. A two-mass...