Indirect implementations of sliding-mode control law in buck-type converters

Some practical methods for implementing the sliding-mode control law to control the buck-type converters are introduced. The control equations are derived from the basic sliding-mode control law to accommodate the conventional fixed-frequency PWM control method. As a result, the overall feedback control systems can be expressed under a form similar to state-feedback control where the voltage and current of the output capacitor are sensed and controlled. With the switching frequency maintained to be constant (not varied over a wide range as in the original law), these control techniques are insensitive to power circuit parameter changes. The output voltage errors in these implementations are proven to converge to zero exponentially similarly to the cases implementing the basic sliding-mode control equation. These control implementations can be applied to both constant output voltage regulation (as in popular DC-DC converters) and to time-varying output voltage tracking (as in switching power amplifiers)