Mona Meisami-Azad

Technical communique: Dissipative analysis and control of state-space symmetric systems

The paper addresses the problem of analysis and static output feedback control synthesis for strict quadratic dissipativity of linear time-invariant systems with state-space symmetry. As a particular case of dissipative systems, we consider the mixed Hinfin and positive real performance criterion and we develop an explicit expression for calculating the Hinfin norm of these systems. Subsequently, an explicit parametrization of the static output feedback control gains that solve the mixed Hinfin and positive real performance problem is obtained. Computational examples demonstrate the use and computational advantages of the proposed explicit solutions.

An adaptive control strategy for urea-SCR aftertreatment system

Hydrocarbons, carbon monoxide, and other polluting emissions produced by diesel engines are usually much lower than those from gasoline engines. However, higher combustion temperature in diesel engines cause substantially larger percentage of nitrogen oxides (NOx) emissions. Selective catalyst reduction (SCR) is a well proven technology for reducing NOx emissions from automotive sources and in particular, heavy-duty truck diesel engines. In this paper, we develop a linear parameter varying (LPV) control design method for the urea-SCR aftertreatment system to minimize the NOx emissions and ammonia slippage downstream the catalyst. Performance of the closed-loop system obtained from the interconnection of the SCR system and the output feedback LPV control strategy is then compared with other control design methods including sliding mode, and observer-based static state feedback methods.

LPV gain-scheduled control of SCR aftertreatment systems

Hydrocarbons, carbon monoxide and some of other polluting emissions produced by diesel engines are usually lower than those produced by gasoline engines. While great strides have been made in the exhaust aftertreatment of vehicular pollutants, the elimination of nitrogen oxide (NO x ) from diesel vehicles is still a challenge. The primary reason is that diesel combustion is a fuel-lean process, and hence there is significant unreacted oxygen in the exhaust. Selective catalytic reduction (SCR) is a well-developed technology for power plants and has been recently employed for reducing NO x emissions from automotive sources and in particular, heavy-duty diesel engines. In this article, we develop a linear parameter-varying (LPV) feedforward/feedback control design method for the SCR aftertreatment system to decrease NO x emissions while keeping ammonia slippage to a desired low level downstream the catalyst. The performance of the closed-loop system obtained from the interconnection of the SCR system and the output feedback LPV control strategy is then compared with other control design methods including sliding mode, and observer-based static state-feedback parameter-varying control. To reduce the computational complexity involved in the control design process, the number of LPV parameters in the developed quasi-LPV (qLPV) model is reduced by applying the principal component analysis technique. An LPV feedback/feedforward controller is then designed for the qLPV model with reduced number of scheduling parameters. The designed full-order controller is further simplified to a first-order transfer function with a parameter-varying gain and pole. Finally, simulation results using both a low-order model and a high-fidelity and high-order model of SCR reactions in GT-POWER interfaced with MATLAB/SIMULINK illustrate the high NO x conversion efficiency of the closed-loop SCR system using the proposed parameter-varying control law.

PCA-based linear parameter varying control of SCR aftertreatment systems

Hydrocarbons, carbon monoxide, and other polluting emissions produced by diesel engines are usually much lower than those by gasoline engines. However, higher combustion temperature in diesel engines cause substantially larger percentage of nitrogen oxides (NOχ) emissions. Selective catalytic reduction (SCR) is a well proven technology for reducing NOx emissions from automotive sources and in particular, heavy-duty diesel engines. In this paper, we develop a quasi linear parameter varying (qLPV) model to capture the non-linearities in the dynamics of the ammonia SCR system with varying catalyst surface temperature. To effectively enable the use of LMI-based control design methods, the number of LPV parameters in the qLPV model is then reduced by using the principal component analysis (PCA) technique. An LPV feedback/feedforward controller is designed for the qLPV model with reduced number of scheduling parameters. The designed full-order controller is further simplified to a first-order transfer function with parameter-varying gain and pole. Finally, simulation results illustrate the high conversion efficiency with minimum ammonia slip of the closed-loop SCR system using the parameter-varying control law.

An H2 Upper Bound Approach for Control of Collocated Structural Systems

This paper presents an explicit expression for an upper bound on the H2 norm for structural systems with collocated sensors and actuators. First, we consider an open-loop collocated structural system and obtain an upper bound for the H2 norm using a particular solution for the linear matrix inequality formulation of the H2 norm analysis conditions. Next, we address the problem of static output feedback controller design for such systems. By employing simple algebraic tools, we derive an explicit parametrization of controller gains which guarantee a prescribed H2 norm performance of the closed-loop system. At last, numerical examples are provided to validate the advantages of the proposed techniques. The effectiveness of the proposed bound and control design method becomes apparent, especially in very large scale structural systems where using classical methods of solving Lyapunov and Riccati equations are time-consuming or intractable.

Upper bound mixed H 2 /H ∞ control and integrated design for collocated structural systems

The present paper addresses the mixed H2/H∞ norm analysis and feedback control design problem for structural systems with collocated actuators and sensors. The mixed norm formulation provides a trade-off measure of a system performance and robustness in the presence of uncertainties in the system model. First, we develop an explicit upper bound expression for the mixed H2/H∞ norm of collocated structural systems and an explicit parametrization of output feedback control gains to guarantee such bounds. The results offer computationally efficient solutions for system analysis and multi-objective controller design that are especially suitable for large-scale collocated systems where traditional analysis and design methods fail. The second part of the paper uses the proposed bounds to address the simultaneous design of structural damping parameters and feedback control gains for optimized closed-loop mixed-norm performance. A linear matrix inequality (LMI) formulation is provided for the integrated damping and control gain optimization. Structural control design numerical examples are presented to demonstrate the advantages and computational efficiency of the proposed bounds and the integrated design approach.

Anti-Windup LPV Control of Magneto-Rheological Dampers

In this paper, we develop a linear parameter varying (LPV) model for the structural systems including the Magneto-Rheological (MR) dampers where the LPV parameter is the MR damper velocity. We then propose an LPV anti-windup control design method to prevent the closed-loop system instability and performance degradation due to the MR damper actuator saturation. The proposed control design method accounts for the actuator nonlinearities by representing the status of the saturated actuator as an additional gain-scheduled varying parameter. The resulting controller is scheduled with respect to the system operating parameter and the actuator saturation parameter. Simulation results demonstrate that the anti-windup compensator scheduled based on the MR damper velocity and the saturation parameter is able to keep the voltage within the specified limits and meets the design requirement of rejecting the effect of the external disturbance signals.Copyright

Anti-windup linear parameter varying control of structural systems with magneto-rheological dampers

Magneto-rheological (MR) dampers are a family of semi-active devices widely used for vibration attenuation in space and civil engineering structures. In this paper, we study the use of MR dampers for seismic protection of a model two-story structure in the presence of actuation saturation. A modified Bingham model is considered for linear parameter varying (LPV) modeling and control of the system. The main contribution of the paper is the design and experimental validation of a LPV anti-windup compensator to tackle the effect of actuator saturation on the control design performance. The designed LPV anti-windup control scheme is advantageous from the implementation standpoint because it can be considered as an addition to the existing control system. Experimental results demonstrate the ability of the design method to attenuate the effects of seismic excitation by controlling the MR damper and simultaneously avoid the adverse effects of actuator saturation by taking advantage of the designed anti-windup compensator and leading to savings in power consumption.

A new approach to integrated damping parameter and control design in structural systems

The paper presents a linear matrix inequality (LMI)-based approach for the simultaneous optimal design of output feedback control gains and damping parameters in structural systems with collocated actuators and sensors. The proposed integrated design is based on simplified H 2 and H ¿ norm upper bound calculations for collocated structural systems. Using these upper bound results, the combined design of the damping parameters of the structural system and the output feedback controller to satisfy closed-loop H 2 or H ¿ performance specifications is formulated as an LMI optimization problem with respect to the unknown damping coefficients and feedback gains. Numerical examples motivated from structural and aerospace engineering applications demonstrate the advantages and computational efficiency of the proposed technique for integrated structural and control design. The effectiveness of the proposed integrated design becomes apparent, especially in very large scale structural systems where the use of classical methods for solving Lyapunov and Riccati equations associated with H 2 and H ¿ designs are time-consuming or intractable.

An Efficient Approach for Damping Parameter Design in Collocated Structural Systems Using An H2 Upper Bound

The paper presents an LMI-based approach for optimally designing the damping parameters in structural systems with collocated actuators and sensors. The proposed design methodology is based on a recently developed H2 norm upper bound for collocated structural systems in [1]. Using the proof for this upper bound result, the design problem is formulated as a convex optimization problem with respect to the damping coefficients of the structural system. A numerical example motivated from an engineering application demonstrates the theoretical advantages and computational efficiency of the proposed method.