TABLE OF CONTENTS Control techniques for switching converters were reviewed. Linear controllers based on state-space averaged models or circuits are well established and suitable for the application of linear systems control theory. Obtained linear controllers are useful, if the converter operating point is almost constant and the disturbances are not relevant. For changing operating points and strong disturbances, linear controllers can be enhanced with nonlinear, antiwindup, soft-start, or saturation techniques. Current-mode control will also help to overcome the main drawbacks of linear controllers.
Sliding mode is a nonlinear approach well adapted for the variable structure of the switching converters. The critical problem of obtaining the correct sliding surface was highlighted, and examples were given. The sliding-mode control law allows the implementation of the switching converter controller, and the switching law gives the PWM modulator. The system variables to be measured and fed back are identified. The obtained reduced-order dynamics is not dependent on system parameters or power supply (as long as it is high enough), presents no steady-state errors, and has a faster response speed (compared with linear controllers), as the system order is reduced and non-idealities are eliminated. Should the measure of the state variables be difficult, state observers may be used, with steady-state errors easily corrected. Sliding-mode controllers provide robustness against bounded disturbances and an elegant way to obtain the controller and modulator, using just the same theoretical approach. Fixed-frequency operation was addressed and solved, together with the short-circuit-proof operation.
Presently, fixed-frequency techniques were applied to converters that can...
