Second-order Sliding Mode Control Of Fixed Frequency Buck Converter

There are many researches on renewable energy sources,such as wind energy,solar energy,geothermal energy which lead to many applications.However,the management of power systems of renewable energy always have problems in the disturbances of load switching,unstable power supply and difficulty in accurate modeling,etc.Smaller and higher-quality stable power supply is required in the design of electronic products.The DC-DC converter can reduce the volume of the energy storage element in the circuit by increasing the operating frequency.DC-DC converters are widely used in various fields because of their smaller size and lighter weight.When the traditional sliding mode control system is stable,the traj ectory of the system will be switched at high speed near the sliding mode surface.Not only is it difficult to determine the operating frequency of the circuit,but it also introduces a lot of electromagnetic noise to the DC-DC converter circuit.The introduction of hysteresis parameters usually used to limit the excessively high switching frequency of traditional sliding mode control.However,the problem that uncertain switching frequency of sliding mode control has not been solved.The switching frequency cannot be kept constant when the converter circuit parameters change or the load is disturbed,which makes the design of the filter circuit very difficult.Therefore,it is necessary to perform fixed-frequency sliding mode control on the DC-DC converter.In the DC-DC converter control,the parasitic parameters will have an uncertain effect on the control effect of the controller.For better control effect,this paper makes a detailed analysis of the influence of the parasitic parameters of the output capacitance of the synchronous buck converter in the second-order sliding mode controller.A second-order sliding mode fixed frequency control method is proposed base on the relationship between the switching frequency f and the hysteresis parameter δ of the switching frequency in the second-order sliding mode controller.By controlling the hysteresis parameters,the switching frequency of the buck converter is fixed near the expected value.Not only the adjustment speed is fast,but also the influence of parasitic parameters on the output capacitance of the synchronous buck converter can be overcome.The main research content and work of the paper are as follows:(1) For the second-order sliding mode controller,analyze the relationship between the switching frequency f and the hysteresis parameter δ in the buck converter without considering the parasitic parameters.(2)Analyze the influence of the parasitic parameters on the second-order sliding mode controller,which is exist on the output capacitance of the buck converter.In order to eliminate the possible overshoot caused by parasitic inductance,an improved secondorder sliding mode controller is proposed in this paper,which suppresses the overshoot of the output voltage effectively.(3)Considering the influence of parasitic parameters.This paper proposes a method to achieve the fixed frequency control of the buck converter based on the correspondence between the switching frequency f of the buck converter and the hysteresis parameter δ.The simulation results show that the proposed method could achieve the fixed frequency control of the converter with good robustness.