Ouassima Akhrif

Application of a multivariable feedback linearization scheme for rotor angle stability and voltage regulation of power systems

This paper investigates the application of a nonlinear controller to the multi-input multi-output model of a system consisting of a hydraulic turbine and a synchronous generator. The controller proposed is based on a feedback linearization scheme. Its main goal is to control the rotor angle as well as the terminal voltage, to improve the systems stability and damping properties under large disturbances and to obtain good post-fault voltage regulation. The response of the system is simulated in the presence of a short-circuit at the terminal of the machine in two different configurations and compared to the performance of a standard IEEE type 1 voltage regulator, PSS and a PID speed regulator.

Speed tracking control of a permanent-magnet synchronous motor with state and load torque observer

This paper is concerned with the speed tracking control problem for a permanent-magnet synchronous motor (PMSM) in the presence of an unknown load torque disturbance. After a brief review of the mathematical model of the PMSM, a speed tracking control law using the exact linearization methodology is introduced. The tracking control algorithm is completed by adding an extended observer which provides, on the one hand, the motor speed and acceleration and, on the other hand, estimates the unknown load torque. The stability of the closed-loop system composed of a nonlinear speed tracking controller and an observer is studied by the way of Lyapunov theory. Furthermore, the decoupling of the state observer and the load torque observer is discussed. Finally, a real-time implementation and the experimental results of the proposed control strategy are presented.

A nonlinear state observer for the sensorless control of a permanent-magnet AC machine

This paper presents a sensorless speed regulation scheme for a permanent-magnet synchronous motor (PMSM) based solely on the motor line currents measurements. The proposed scheme combines an exact linearization-based controller with a nonlinear state observer which estimates the rotor position and speed. Moreover, the stability of the closed-loop system, including the observer, is demonstrated through Lyapunov stability theory. The proposed observer has the advantage of being insensitive to rotation direction. It is shown how a singularity at zero velocity appears in the scheme and how it can be avoided by switching smoothly from the observer-based closed-loop control to an open-loop control at low velocity. The system performance is tested with an experimental setup consisting of a PMSM servo drive and a digital-signal-processor-based controller for both unidirectional and bidirectional speed regulation.

Experimental nonlinear torque control of a permanent-magnet synchronous motor using saliency

In this paper, a new nonlinear control strategy is proposed for a permanent-magnet salient-pole synchronous motor. This control strategy simultaneously achieves accurate torque control and copper losses minimization without recurring to an internal current loop nor to any feedforward compensation. It takes advantage of the rotor saliency by allowing the current (i/sub d/) to have nonzero values. This, in turn, allows us to increase the power factor of the machine and to raise the maximum admissible torque. We apply input-output linearization techniques where the inputs are the stator voltages and the outputs are the torque and a judiciously chosen new output. This new output insures a well-defined relative degree and is linked to the copper losses in such a way that, when forced to zero, it leads to maximum machine efficiency. The performance of our nonlinear controller is demonstrated by a real-time implementation using a digital signal processor (DSP) chip on a permanent-magnet salient-pole synchronous motor with sinusoidal flux distribution. The results are compared to the ones obtained with a scheme which forces the i/sub d/ current to zero.

Stabilisation and control synthesis of switching systems subject to actuator saturation

This article presents sufficient conditions for the stabilisation of switching discrete-time linear systems subject to actuator saturations. These conditions are obtained by using successively state and output feedback control laws. The obtained results are formulated in terms of linear matrix inequalities (LMIs). The saturating and non-saturating controllers are synthesised for both cases in this work. Three sets of LMIs are presented for output feedback case. Numerical examples are used to illustrate these techniques by using a linear optimisation problem subject to LMI constraints.

Gain scheduling with guardian maps for longitudinal flight control

A new approach to gain scheduling of linear controllers is proposed and applied to a longitudinal flight control pro-blem. Traditionally, gain scheduling is done a posteriori by the interpolation of controller gains designed for several operating points or conditions. The method proposed here is based on guardian maps and does not require as many linear controller syntheses as there are design points. Rather, it extends the performance of an initial single controller carried out on an arbitrary operating point to the entire domain while ensuring generalized stability all along the process. The method, which uses a given fixed architecture controller, is successfully applied on the longitudinal flight control of a business jet aircraft.

Robust stabilization of feedback linearizable systems

An examination is made of the robust stabilization of a class of uncertain nonlinear systems for which the uncertainties are not required to satisfy the so-called structure matching conditions. Sufficient conditions for two systems belonging to this class to be both feedback linearizable are obtained. In the case of models with unknown parameters entering linearly, an adaptive control law is synthesized based on the exact linearization of the model system.<<ETX>>

Stabilization of Switched Systems Subject to Actuator Saturation by Output Feedback

This paper presents sufficient conditions for asymptotic stabilizability of switched discrete-time linear systems subject to actuator saturations using output feedback. The results are obtained by using a composite Lyapunov function and are given in the form of LMI conditions. It is shown that the union of all the associated level sets is a set of asymptotic stability of the switched system. A numerical example is used to illustrate the technique

Adaptive nonlinear control of a permanent magnet synchronous motor

In this work an adaptive nonlinear control method is applied to a permanent magnet synchronous motor. Quadratic and direct currents decoupling and control are achieved through feedback linearization. Direct current is controlled to zero and torque becomes only proportional to the quadratic current. Also a near unity power factor is achieved. Parameters variation is compensated by using an adaptive scheme and no a priori knowledge of real parameters is required. The performance of the proposed adaptive nonlinear control scheme is demonstrated by simulation results. These results show that the proposed method achieves the same high dynamic performance as vector control.<<ETX>>

Longitudinal flight control design with handling quality requirements

This work presents a method for selecting the gain parameters of a C* control law for an aircraft’s longitudinal motion. The design incorporates various handling quality requirements involving modal, time- and frequency-domain criteria that were fixed by the aircraft manufacturer. After necessary model order- reductions, the design proceeds in essentially two-step s: Stability Augmentation System (SAS) loop design and Control Augmentation System (CAS) loop design. The approach partly relies on the use of guardian maps to characterize, in each case, the set of gain parameters for which desired handling quality requirements are satisfied. The approach is applied throughout the full flight envelope of a business jet aircraft and yields satisfactory results.