Modeling And Controling Based On Differential Flatness Of Boost Converter With Constant Power Load

With the development of power electronic power converter which topological structure is becoming more and more complex, the stability problem of multistage cascade DC/DC converter system is paid more and more attention. DC/DC converter which can output stabilized voltage amounts to constant power load. It has a negative impedance characteristic which makes the cascade linearizing system is non minimum phase system, the closed-loop system of using the conventional PI controller is difficult to ensure good dynamic and static performance. Nonlinear control method based on Differential Flatness theory can completely depict system state transition trajectory and control laws and can convert DC/DC converter system with strong nonlinear characteristics to linear system on the basis of selecting appropriate flatness output, convenient to design the corresponding controller based on Lyapunov theorem. The results show that the control law based on the nonlinear theory can make the AC-DC or DC-DC converter with constant power load is stable, reliable and the performance is better.Two level DC/DC converter were acted as the research object, front level for source converter is Boost circuit with single switch transistor, rear stage circuit acts as a constant power load by BUCK converter which can output stabilized voltage. On the basis of selecting the input power for flatness output, the state space equation of source converter can be converted to a mathematical model with Differential Flatness characteristics. Afterwards, this paper introduces in detail the process of using the Lyapunov function to design the controller and the method to ascertain and search the unknown parameters in the controller by the improved ant colony algorithm. And then, the stability of the system was proved through the Barbara’s lemma. Finally, the closed-loop controlling system based on differential flatness theory of Boost converter with constant load is simulated by MATLAB/SIMULINK, the simulation results show that the control law is feasible and effective.The third、fourth chapter focuse on the hardware and software design process of the experimental platform which can verify the control scheme. Finally, a cascade prototype which can output constant 100W-150W was developed in the laboratory. Through testing the experimental prototype, the relevant experimental waveform and datas were obtained finally, besides, the experimental results are consistent with the expected index. So, the correctness and feasibility of the control scheme adopted in the paper were verified.