Chunjiang Qian

Finite-Time Attitude Tracking Control of Spacecraft With Application to Attitude Synchronization

This note investigates the finite-time attitude control problems for a single spacecraft and multiple spacecraft. First of all, a finite-time controller is designed to solve finite-time attitude tracking problem for a single spacecraft. Rigorous proof shows that the desired attitude can be tracked in finite time in the absence of disturbances. In the presence of disturbances, the tracking errors can reach a region around the origin in finite time. Then, based on the neighbor rule, a distributed finite-time attitude control law is proposed for a group of spacecraft with a leader-follower architecture. Under the finite-time control law, the attitude synchronization can be achieved in finite time.

Global finite-time stabilization by output feedback for planar systems without observable linearization

This note considers the problem of global finite-time stabilization by output feedback for a class of planar systems without controllable/observable linearization. A sufficient condition for the solvability of the problem is established. By developing a nonsmooth observer and modifying the adding a power integrator technique, we show that an output feedback controller can be explicitly constructed to globally stabilize the systems in finite time. As a direct application of the main result, global output feedback finite-time stabilization is achieved for the double linear integrator systems perturbed by some nonlinear functions which are not necessarily homogeneous.

Global finite-time stabilization by dynamic output feedback for a class of continuous nonlinear systems

This note studies the problem of global finite-time stabilization by dynamic output feedback for a class of continuous but nonsmooth nonlinear systems. By extending the adding-a-power-integrator technique and a special continuous observer design, a dynamic output feedback controller is explicitly constructed to render the systems globally finite-time stable. The novelty of the note is the development of a recursive design procedure, which takes full advantage of the continuous structure of the systems in constructing the state feedback stabilizer and the continuous observer with rigorously selected gains.

Robust Control for PWM-Based DC–DC Buck Power Converters With Uncertainty Via Sampled-Data Output Feedback

This paper investigates the sampled-data output feedback control problem for dc-dc buck power converters taking consideration of components uncertainties. A reduced-order observer and a robust output feedback controller, both in the sampled-data form, have been explicitly constructed with strong robustness in the presence of uncertain parameters. A delicate stability analysis process is presented to show that, by carefully selecting the design gains and the tunable sampling period, the output voltage of the hybrid closed-loop dc-dc buck converter system will globally asymptotically tend to the desired value even though the separation principle is out of reach and the controller is only switched at the sampling points. The proposed controller consists of a set of linear difference equations which will lead to direct and easier digital implementation. Numerical simulations and experimental results are shown to illustrate the performance of the proposed control scheme.

Recursive design of finite-time convergent observers for a class of time-varying nonlinear systems

This paper considers the problem of designing globally finite-time convergent observers for a class of nonlinear systems with time-varying and output-dependent coefficients, which make the existing design approaches inapplicable. To solve this problem, a bottom-up design approach is first employed to recursively construct a finite-time convergent observer with time-varying coefficients for the nominal system. Then, using the homogeneous domination approach, we scale the finite-time convergent observer with an appropriate choice of gain for the original nonlinear system satisfying a Holder condition. In addition, we show that the Holder condition imposed on the nonlinearities can be removed for nonlinear systems with bounded trajectories.

Global finite-time stabilisation by output feedback for a class of uncertain nonlinear systems

This article considers the problem of global finite-time stabilisation by output feedback for a class of nonlinear systems comprised of a chain of power integrators perturbed by an uncertain vector field. To solve the problem, we first construct a homogeneous observer and controller in a recursive way for the nominal system without the perturbing nonlinearities. Then, using the homogeneous domination approach, we scale the homogeneous observer and controller with an appropriate choice of gain to render the uncertain nonlinear system globally finite-time stable. Due to the use of a reduced-order observer, the proposed output feedback controller is applicable to those systems with unknown gains associated with the power integrators.

Global Output Feedback Stabilization of a Class of Nonlinear Systems via Linear Sampled-Data Control

In the literature, it has been proved that under a lower-triangular linear growth condition, a class of uncertain nonlinear systems can be globally stabilized by a linear state feedback controller (Tsinias) and later by a linear output feedback controller (Qian and Lin), both in the continuous-time form. This technical note shows that the same continuous-time system under the same assumption can be globally stabilized by a sampled-data output feedback controller whose observer and control law are discrete-time and linear, and hence can be easily implemented by computers.

Global Stabilization of a Class of Feedforward Systems with Lower-Order Nonlinearities

This note considers the problem of global stabilization for a class of feedforward systems whose nonlinearities are allowed to be lower-order growing, instead of higher-order or linear growing as required by many existing results. To solve the problem, a domination approach is developed to design the stabilizer with a new structure, which is also integrated with the adding a power integrator and nested saturation methods. The use of a locally homogeneous stabilizer enables us to relax the growth condition imposed on the nonlinearities and hence enlarges the class of feedforward systems which are globally stabilizable.

Technical communique: Global practical tracking of a class of nonlinear systems by output feedback

In this paper we address the practical tracking problem for a class of nonlinear systems by dynamic output feedback control. Unlike most of the existing results where the unmeasurable states in the nonlinear vector field can only grow linearly, we allow higher-order growth of unmeasurable states. The proposed controller makes the tracking error arbitrarily small and demonstrates nice properties such as robustness to disturbances and universal property to reference signals.

Smooth output feedback stabilization of planar systems without controllable/observable linearization

This note considers the problem of global stabilization by output feedback for a family of planar systems whose Jacobian linearization is neither controllable nor observable. The problem cannot be dealt with by existing output feedback design methods-most of them are based on the separation principle. Under appropriate growth conditions, we propose an output feedback control scheme that does not rely on the separation principle and achieves global asymptotic stabilization. The novelty of our control scheme lies in the explicit design of a dynamic output compensator, which combines a nonlinear-gain observer design and the technique of adding a power integrator. As a consequence, an interesting global stabilization result by output feedback can be obtained for feedback linearizable systems in a triangular form, which turns out to be new even in the two-dimensional case.