The objective of this research is to analyze and simulate the pulse-width-modulated (PWM) dc-dc buck-boost converter and design a controller to gain stability for the buck-boost converter. The PWM dc-dc buck-boost converter reduces and/or increases dc voltage from one level to a another level in devices that need to, at different times or states, increase or decrease the output voltage.
In this thesis, equations for transfer funtions for a PWM dc-dc open-loop buck-boost converter operating in continuous-conduction-mode (CCM) are derived. For the pre-chosen design, the open-loop characterics and the step responses are studied. The converter is simulated in PSpice to validate the theoretical analysis. AC analysis of the buck-boost converter is performed using theoretical values in MatLab and a discrete point method in PSpice. Three disturbances, change in load current, input voltage, and duty cycle are examined using step responses of the system. The step responses of the output voltage are obtained using MatLab Simulink and validated using PSpice simulation.
Design and simulation of an integral-lead (type III) controller is chosen to reduce dc error and gain stability. Equations for the integral-lead controller are given based on steady-state and AC analysis of the open-loop circuit, with a design method illustrated. The designed controller is implemented in the circuit, and the ac behavior of the system is presented.
Closed loop transfer fuctions are derived for the buck-boost converter. AC analysis of the buck-boost converter is studied using both theoretical values and a discrete point method in PSpice. The step responses of the output voltage due to step change in reference voltage, input voltage and load current are presented. The design and the obtained transfer functions of the PWM dc-dc closed-loop buck-boost converter are validated using PSpice.