Nonlinear Control Strategy Application In DC-DC Power Electronic Converters

DC-DC converter is applied widely in switch power supply and special power supply, which are used in the field of aviation, spaceflight, industry and home electrical appliances. So far, the research to DC-DC converter is limited to the wave analytical method. It can't be denied that this method is used to guide the design and regulation in engineering practice. But the physical variables, which affect the performance of DC-DC converter, can't be analyzed more deeply by this method, Moreover, for ensuring the performance of DC-DC converter linear controllers are designed around the working point by the small signal model in traditional DC-DC converter. These controllers only can ensure the local stability around the working point, which can obtain the requirements of system when the DC-DC converter needs fixed voltage (or current) and small range of load change (or power supply voltage). In the special field of aviation, spaceflight, in which the working points change in a large range, linear methods can't gain the global stability. Therefore, these methods are all noneffective.In order to solve these problems, this paper discusses the average state-space model of DC-DC converter which deals with both continuous and discrete variables (namely the hybrid system). On the basis of this analyse, DC-DC converter controllers are designed by some popular nonlinear control method in the field of control. Three targets can be realized: global stability, stability in the range of the working point changing, performance of dynamic and static state.In this paper, the main kinds of nonlinear control methods which are applied in the DC-DC converter system are Passivity-based control and Sliding-mode control. The basic idea of Passivity-based control is to configure the dissipation part in energy equation and make the system to satisfy the passivity condition. But the traditional Passivity-based method shows a weak robustness. In order to improve the system performance the integral factor is introduced to the Passivity-based control method. The simulation results indicate that the improved method can enhance the robustness and accelerate the respond speed at the same time.Sliding-mode control has the strongpoint of fast response and strong robustness of system parameters and disturbs. And the disadvantage is the chattering problems in practical Sliding-mode. The paper provides a combining method, which includes Passivity-base control and Sliding-mode control. Simulation results indicate that this method can eliminate the Sliding-mode chattering to some extent and the system respond time is longer than the Sliding-mode only.In order to prove the validity of nonlinear controllers in practice, Boost converter sample circuit is designed in this paper, which is controlled by nonlinear control method. The experiment results show that the improved Passivity-based controller makes the system reach the given value smoothly and obtain much better robustness compared with PI controller; Sliding-mode controller achieves good robustness under the disturbance of load and power supply voltage but there exists acute chattering in voltage and current.