Study On The Control Algorithm For Two-stage DC-DC Converter Based On Sliding Mode Control

After more than a century development, automobile industry has become a pillarindustry in the world, which has a great influence on economy, culture, science andtechnology, etc. However, as the increase of car ownership, the problems ofenvironment and energy become more and more intractable. It is imperative for us totake action. Electric vehicles (EVs), as an environmentally friendly car, rise in responseto the proper time and conditions. DC-DC converter is an indispensable component forEVs and its quality of output voltage is a direct factor to EVs`safety and reliability. Asto how to effectively improve the quality of output voltage processed by converter, it isknown that controller is the key which has been a research focus in this field. Althoughconventional linear control methods have many merits such as low cost, high reliabilityand simple structure, they are not the most suitable methods for DC-DC converterswhich have the characteristics of nonlinearity, time varying and high order. Because ofthese, it is meaningful to design a suitable controller based on nonlinear controlmethods to ensure the quality of converter`s output voltage. Also, this is important andmeaningful for EVs to guarantee the safety.In this thesis, we firstly investigate and survey the overview on present researchsituation. Based on this, the advantages and disadvantages of some control methods areobtained. Combining the characters of Buck+half bridge two-stage DC-DC converter,we finally adopt sliding mode theory to design the controller. Secondly, the topologystructure of two-stage DC-DC converter is analyzed and simplified. Using circuitaveraging method and state-space averaging method, system`s models are established.Furthermore, converter`s transfer function are analyzed by using S-domain andfrequency domain analyses as well. For the problems of slow response and steady-stateerror, a Lag controller and a sliding mode controller are designed respectively. Finally,by using Matlab/Simulink, the simulation models of two-stage DC-DC converter withLag controller, sliding mode controller and double integral sliding mode controller areestablished, and some simulations are achieved. In order to verify the validity andfeasibility, a series of experiments based on Lag controller and sliding mode controllerare accomplished as well as some comparisons with relevant standards and products. Through simulations, it is shown that the converter with sliding mode controllerand double integral sliding mode controller has better dynamic specifications than Lagcontroller, and the double integral sliding mode controller is able to eliminate thesteady-state error of output voltage. According to experiment results, we get theconclusion that the control capability of sliding mode controller is better than that ofLag controller, which agrees with simulation results. Also, comparison results withsome relevant standards and products are obtained, it is shown that the control precisionand response time of output voltage are satisfactory, which is a strong confirmation ofthe designed controller`s validity and feasibility.