| Power electronic converters have been widely used in the transmission and conversion of electric power. In essence, the power electronic converter is a typical non-linear switching system. Traditional control scheme usually designs controller based on the small-signal linearized model near the work point. This kind of controller can only ensure the performance near the work point and can only meet the basic requirements of the system for the applications of the fixed output voltage (or current). For some special applications with large range of work point, it is difficult to guarantee the performance of the system. In order to achieve a wide range stability of system and assure better performance, this paper, considering the nonlinearity of the power electronic converter, designs the nonlinear controller with popular nonlinear control strategy based on their nonlinear mathematical models.Input-output feedback linearization method is global linearization sense based on the differential geometric theory, which can transform the complex nonlinear system into simple linear system under appropriate conditions. It is difficult to design the controller for traditional BOOST converter because of its non-minimum phase characteristic. For non-minimum phase system, the traditional approach is to design the system's closed-loop bandwidth that is much smaller than turning frequency at right half plane in order to avoid the influence of the non-minimum phase on stability. However, the expense is that it sacrifices the system's rapid dynamic response.In order to solve the problem of non-minimum phase of traditional single-phase BOOST DC / DC converter, Viswanathan K has proposed a new topology of the tri-state BOOST DC / DC converter. Whereas his controller is to be further enhanced, this paper originally applies the differential geometric theory for designing controller. Having established the nonlinear model of this converter, this paper utilizes the input-output feedback linearization to transform it into controllable linear system. Then by mature linear control theory, control strategy is designed. The simulation results show that this nonlinear control strategy not only ensures the system's good dynamic characteristics but also can serve to achieve the constant voltage output within a large scope. Moreover, even if the disturbance (input voltage and load changes) is large, this nonlinear controller can also ensure the stability of the system.For three-phase voltage source PWM rectifier, this paper, based on its topological structure, establishes its affine nonlinear model in synchronous rotation coordinates. The differential geometrics theory is used to transform the nonlinear system into its standard from in order to obtain its zero dynamic expression. Then by judging the zero dynamic's stability, this paper comes to a conclusion that the system is non-minimum phase system as the capacitor voltage is taken as the output of the systems, whereas it is minimum phase system as the inductor current is taken as the output of the system. Hence, the inductor current is chosen as the output of system in this paper. Hereafter, based on the input-output feedback linearization, in order to obtain stable external dynamic characteristics and realize the complete decoupling of active current and reactive current, a controller is then designed according to the existing linear control strategy. In addition, to control the DC voltage which appears as the internal dynamic after input-output feedback linearization, this paper introduces the fuzzy PI strategy as voltage controller to improve the robustness of the system and dynamic response speed. Simulation result shows that this nonlinear control strategy can ensure better performance compared with linear controller. |
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