Faryar Jabbari

Brief Output feedback controllers for disturbance attenuation with actuator amplitude and rate saturation

Output feedback controllers for disturbance attenuation of linear systems with constraints on inputs are studied. The constraints are limited actuator capacity as well as limits on the actuator rates. The main features include guaranteed performance levels that depend on both actuator magnitude and rate limits, and controllers that operate at, or close to, maximum actuator capacity. The controllers have a structure similar to those used in the linear parameter varying (LPV) approach. Sufficient conditions for finding appropriate nonlinear control laws are expressed in terms of a convex search.

Disturbance attenuation for systems with input saturation: An LMI approach

A new design technique is proposed to improve disturbance attenuation for systems with input saturation. The main results rely on a multiobjective approach which combines the quadratic stabilization technique with constraints on inputs. For the full-state feedback problem, the sufficient conditions for the feasibility of a high-gain controller are expressed in terms of linear matrix inequalities (LMI). For output feedback design, the controllers are assumed to have an observer-based structure. The sufficient conditions for the output feedback controller to recover the full-state properties are also given in terms of LMI.

Accurate Sliding-Mode Control of Pneumatic Systems Using Low-Cost Solenoid Valves

A control law is developed for an inexpensive pneumatic motion control system using four solenoid on/off valves and a position feedback sensor. A sliding-mode approach is used, which is well known for its tolerance for system uncertainties. In contrast to previous control laws, our approach does not use pulsewidth modulation. The control law has an energy-saving mode that saves electrical power, reduces chattering, and prolongs the valves life. Our simulation and experimental results show that the proposed tracking control law performs very well with good tracking and relatively low steady-state position errors

Dynamic Simulation of an Integrated Solid Oxide Fuel Cell System Including Current-Based Fuel Flow Control

A two-dimensional dynamic model was created for a Siemens Westinghouse type tubular solid oxide fuel cell (SOFC). This SOFC model was integrated with simulation modules for other system components (e.g., reformer, combustion chamber, and dissipater) to comprise a system model that can simulate an integrated 25 kilowatt SOFC system located at the University of California, Irvine. A comparison of steady-state model results to data suggests that the integrated model can well predict actual system power performance to within 3 percent, and temperature to within 5 percent. In addition, the model predictions well characterize observed voltage and temperature transients that are representative of tubular SOFC system performance. The characteristic voltage transient due to changes in SOFC hydrogen concentration has a time scale that is shown to be on the order of seconds while the characteristic temperature transient is on the order of hours. Voltage transients due to hydrogen concentration change are investigated in detail. Particularly, the results reinforce the importance of maintaining fuel utilization during transient operation. The model is shown to be a useful tool for investigating the impacts of component response characteristics on overall system dynamic performance. Current-based flow control (CBFC), a control strategy of changing the fuel flow rate in proportion to the fuel cell current is tested and shown to be highly effective. The results further demonstrate the impact of fuel flow delay that may result from slow dynamic responses of control valves, and that such flow delays impose major limitations on the system transient response capability.Copyright

Modified Anti-Windup Compensators for Stable Plants

We investigate the effects of deferring the activation of anti-windup by allowing actuators to remain in the saturated regime longer, without any assistance. The basic idea is to apply anti-windup when the performance of the saturated system faces substantial degradation. For this, we present a modified anti-windup scheme along with the appropriate LMIs to obtain the gains. For two examples, we show that the modified anti-windup scheme renders better performance than the immediate application of anti-windup.

Scheduled controllers for linear systems with bounded actuators

For linear systems under bounded actuators, a new scheduling scheme is used to improve the performance of the closed-loop system, in disturbance attenuation problems. The approach selects the controller, among a continuous family of controllers, that provides the best performance while avoiding saturation, based on the closed-loop behavior (i.e., the closed-loop state vector). As a result, the controller has a quasi linear parameter varying structure. Graphically, the resulting scheduling scheme relies on slab regions of the phase plain. Numerically, the family of the controllers are based on linear splines, and can be obtained by standard LMI software. Benefits of the proposed scheduling scheme is demonstrated through a numerical example.

Effects of using observers on stabilization of uncertain linear systems

The effects of observers on robust linear feedback controllers are studied. Sufficient conditions are obtained that guarantee full recovery of the allowable uncertainty bounds attainable by full state feedback. The effects of the resulting high gain observers on the disturbance rejection bounds are also studied. It is shown that full recovery of the uncertainty bound leads to possible large degradation in disturbance rejection. However, if there is only additive plant disturbance and no measurement disturbance, this degradation can be prevented. >

A noniterative method for the design of linear robust controllers

A procedure for determining a linear control law which guarantees asymptotic stability for an uncertain system is derived. Using an elementary matrix identity, an alternative proof of the existence of stabilizing control law for the matched case is provided. Bounds for the rates of decay are established, and by using these bounds it is shown that every trajectory of the closed-loop system can be made to decay at a prespecified exponential rate. The technique is simpler to use than existing techniques since it does not require a numerical procedure, but allows the control law to be obtained from some simple formulas. >

Control of LPV systems with partly measured parameters

The control of linear parameter-varying (LPV) systems with time-varying real uncertain parameters, where only some of the parameters are measured and available for feedback, is considered. The control objectives are internal stability and disturbance attenuation in the sense of a bounded induced L/sub 2/-norm from the disturbance to the controlled output. Using parametric Lyapunov functions, the solvability conditions for dynamic output feedback controllers that depend on the measured parameters are expressed in terms of a set of linear matrix inequalities (LMIs) and an additional coupling constraint which destroys the convexity of the overall problem. By transforming the coupling constraint into a rank condition, the problem is recast into a rank-minimization problem with LMI constraints. An example is included that demonstrates the application of the results.

A New Approach to Shock Isolation and Vibration Suppression Using a Resetable Actuator

A novel low power control technique along with a new class of actuators is developed for shock isolation and control of structural vibrations. In contrast to other techniques, including conventional viscous or rate damping, the force produced by the actuator has no velocity dependence. Several experimental, analytical, and simulation results are presented in support of this new, semi-active technique for structural control. The basic approach is to manipulate the system stiffness through the use of resetable actuators. With the proposed control approach, the actuator behaves like a linear spring. However, at appropriate times, the effective unstretched length of the actuator is changed—or reset—to extract energy from the vibrating structure. Experimental validation of the actuator model, analytical results on stability and actuator-placement, and simulation results for earthquake applications are presented.@S0022-0434~00!01603-8#