| The subject of tracking control as applied to switching power converters is investigated. Unlike in all the previous control strategies in which the output voltage is regulated around a constant reference value, the tracking control objective is to force the output voltage to follow a time-varying reference signal. Because the old control tools can no longer be suitable to satisfy the tracking control objectives, some newer tools borrowed from the nonlinear control field such as variable-structure system, sliding-mode control, tracking control, feedback-feedforward and feedback linearization are introduced and applied extensively.; For buck converters, the variable-structure system theory is utilized to investigate the start-up and transient responses and then its applications are compared with the pulse-width-modulation (PWM) control method equipped with a PID (proportional-integral-derivative) controller. The reaching and sliding conditions are also examined.; For boost- and buck-boost converters, the stability conditions of all methods of cycle-by-cycle integration control are examined. As results, these converters are proven to be just conditionally stable whenever the cycle-by-cycle integration control is strictly enforced. As an alternative, an input current predictor under the form of a nonlinear observer is proposed and its operation is confirmed via simulation. By regulating the input current with either hysteresis or cycle-by-cycle integration, the output current pumped to the RC load can be indirectly controlled. Therefore, the tracking control objective can be achieved using these methods together with a first-order tracking control law.; Tracking control for the SRC (series-resonant converter) is also studied and explored using the same tracking control law together with some specific schemes to provide a unique cycle-by-cycle current control for this specific converter. |
