| In recent years,with the rapid development and utilization of smart grid and new energy in modern society,new energy DC distributed power supply systems have attracted more and more attention.Among them,the DC-DC converter regarded as the main power processing unit have been widely applied in many applications,such as aerospace,ships,aircraft,electric vehicles,micro-grid and other fields.The converters generally adopts closed-loop regulation.Therefore,when it used as a load converter,it exhibits constant power load(CPL)characteristics at the input port.The DC-DC converter system feeding constant power load is a strong coupling nonlinear system,which is frequently suffer from the input voltage change,load disturbance and unmodeled dynamics.Therefore,in order to satisfied the requirements of high control performance in practical conditions,the linear control methods based on traditional control theory is no longer applicable,In recent years,the application of nonlinear control algorithm based on nonlinear theory in DC-DC converter system has been attracted more and more attention.The nonlinear control method is applied to the modeling and control design of DC-DC converter,and then the nonlinear control strategy is obtained,which ensure the stability of DC-DC converter system feeding CPL.This thesis takes the Boost converter feeding CPL and resistive load system as an example,in order to enhance the output of the system dynamic performance and anti-disturbance ability,eliminate the influence of CPL negative impedance characteristics and employ the system stable and reliable operation,the thesis put forward a non-singular Terminal sliding mode control(NTSMC)strategy and proposes a composite control strategy based on the nonlinear disturbance observer(NDO)combines Backstepping algorithm respectively.The main research contents of this thesis are summarized as follows.(1)The thesis analyzed the negative impedance characteristics of CPL,and large-signal,small-signal models.Then,expounded the unstable influence mechanism of CPL on the system in detail and established the system model for the DC-DC Boost converter feeding CPL.(2)The SISO affine nonlinear model of the system is established based on differential geometry theory.so as to complete the precise linearization of the system on the basis of the exact feedback linearization technique.(3)In order to further improve the robustness of DC-DC Boost converter system feeding CPL,considering that sliding mode control has excellent ability to suppress external disturbances and actual uncertainties,The sliding mode control idea is introduced into the stability control of Boost converter system feeding CPL.Then combined the compound sliding mode switching surface with stepwise exponential reaching law,a NTSMC control strategy based on composite sliding mode surface is proposed to effectively make the system has excellent steady state characteristics and strong robustness.(4)Considering the control difficulties of the system nonlinear characteristics parameter perturbation and load disturbance,aiming at the stability control of DC-DC Boost converter system with CPL,the thesis designed NDO to estimate the uncertainty disturbance and uses it as a feed forward compensation for tracking reference,and then a Backstepping control strategy based on NDO is synthesized so that the output voltage of converter and current of inductance is capable of tracking its reference value rapidly and accurately under the influence of CPL fluctuations.The proposed NDO-Backstepping controller can effectively improves dynamic performance and stability of the system. |
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