A Study Of Control Methods For DC-DC Converters Based On Hybrid Automata Model

DC DC converters essentially are typical hybrid dynamic systems which include bothcontinuous and discrete subsystems. Hybrid automaton model is a simple formalized modelwhich can describe continuous and discrete characteristic of hybrid systems intuitively andsuccinctly. This article mainly has carried on the research of following several aspects:Firstly, this paper introduced the definition, characteristics and research of hybridsystems and focused on the hybrid automata model. Then, in view of the three kinds of basicDC DC converters which are Buck, Boost and Buck boost converter, their hybrid automatamodels are established respectively.Secondly, base on the hybrid automaton model, the basic control methods of DC DCconverters, which are peak current control, average current control, current hysteresis controland predict duty cycle control, are designed. According to the circuit theory, the controlproblem of these basic control methods is simplified to boundary selection problem. Thereinto,the peak inductor current and constant switching cycles are selected as boundary conditions inpeak current control method. And, the appropriate sawtooth wave compared with inductorcurrent is selected as boundary conditions in average current control method. And, throughsetting certain ring width, the upper and lower inductor currents are selected as boundaryconditions in current hysteresis control method. And last, based on the predicted duty ratio,the conducting time of switch and constant switching cycles are selected as boundaryconditions in predict duty cycle control method.Thirdly, taking the advantages and disadvantages of the basic control methodsabove-mentioned into consideration, a new control method based on hybrid automata modelwhich can control CCM and DCM mode uniformly is proposed. According to the law ofconservation of energy, peak inductor current and off time of switch are calculatedrespectively in CCM and DCM mode, as well as the critical resistance. First of all, the workmode of DC DC converter is judged by the critical resistance. Then the peak inductor currentand off time of switch in the corresponding mode are selected as boundary conditions. Thismethod can make DC DC converter working in both CCM and DCM mode with constantswitching frequency in wide load range and the duty cycle is unrestricted. Then, using theMATLAB/stateflow simulation software, the simulation results show that this new methodhas a simple algorithm, fast dynamic response, high steady precision.Hybrid automata model is a model which contains continuous time and discrete eventdynamic systems and does not make any approximate of discrete event dynamic characteristic. So, it can describe the dynamic process of DC DC converter accurately. What is more, thecontrol methods based on hybrid automata model can control continuous process and discreteswitching process of DC DC converter uniformly. Therefore, this method has importanttheoretical and realistic significance and can be further extended to other power electronicconverters.