Abstract:
The switched mode DC-DC converters are nonlinear systems that are commonly used in power
electronic circuits due to their high conversion of efficiency and large output voltage range. Gen erally, they are used in all situations where there is a need of stabilizing a given DC voltage to
the desired value. DC-DC buck-boost converter is used in applications for voltage step-up/down.
The output voltage of the DC-DC Buck-Boost converter alone is usually unstable, oscillates, and
has a large overshoot and long settling time. In addition, this converter is unable to give the de sired output voltage for input voltage and load variations. To solve this problem, various control lers are required. PID controller has been usually applied to the converter to obtain the desired
output voltage because of its simplicity. But the application of PID controller is not reliable and
satisfactory in the case of non-linear systems. Therefore, non-linear controllers are required to
improve the system's performance. In this thesis, a second-order sliding mode controller based
on the super-twisting algorithm has been designed to achieve a fast and stable performance of the
buck-boost converter. Using MATLAB/Simulink, the performance of the proposed second-order
sliding mode controller is compared to that of fuzzy PID and sliding mode controllers based on
the system’s dynamic response in terms of overshoot, rise time, settling time, and steady-state
error. In order to test the performance of the proposed controller, the load resistance decreased
and increased by 50% from the operating point while the input voltage decreased by 25% and
increased by 33.4% from the operating point. Also, to test the effectiveness of the second-order
sliding mode controller, the input voltage is varied from the operating point (i.e., 24V) up to
192V. The simulation results shown that using a second-order sliding mode controller, the rise
and settling times are improved by 13% and 28.7% respectively as compared to that obtained
using fuzzy PID controller. Also, as compared to SMC, the rise and settling times are improved
by 50% and 58.3% respectively. The overshoot is removed and the steady state error became ze ro using SOSMC and FPID controllers. But using SMC, the overshoot is 0.76% and the steady
state error is 0.025%. The actual output voltage is not deviated from desired value even for large
input voltage disturbances using second-order sliding mode controller. Generally, it is possible to
conclude that the performance of the buck-boost converter using a second-order sliding mode
controller is better than the fuzzy PID and conventional sliding mode controllers.
