Research On Nonlinear Composite Control Of Power Electronic Converter Based On Differential Geometry

The power electronic converter is a typital switching nonlinear system. The existing classical PI control technique can not satisfy the demands on the high performance of power electronic converter. With the development of the nonlinear control theory and digital control technique, adopting the nonlinear control theory of power electronic control system can highly improve the control performance of the converter, which is a significant theory with practical values.Currently nonlinear control methods based on differential geometry theory have attracted the attention of scholars. Relevant literature shows that such control better than the PI control with static and dynamic performance. Currently most control method based on feedback linearization adopts the strategy which designs the optimal controller of linear system after feedback linearization. But the state feedback linearization and optimal control theory are needed to establish the accurate mathematical model of controlled object which is often difficult. So current nonlinear control method based on state feedback has a strong dependence on mathematical model of the controlled object and is not easy to promote in engineering applications. Moreover, there is no theory shows that the optimal control of linear systems is optimal in the corresponding diffeomorphism nonlinear system. It is for these reasons that this paper does not rigidly adhere to optinal performance and try to introduce sliding mode control theory to design the controller of linearized system using state feedback linearization. The strategy can enhance the robustness of control system and weaken the dependence of the accurate mathematical model. The control strategy based on feedback linearization is easy to promte in engineering applications.This paper proposes a novel sliding mode control strategy of DC-DC converters (buck, boost and buck-boost) based on state feedback exact linearization. Firstly using state space averging method, affine nonlinear model of DC-DC converter which works on CCM mode is established. It is testified that the model is satisfied the condition of state feedback exact linearization in theory. Secondly according to different topologies, the nonlinear coordinate change matrix and state variable feedback equations are derived. Then the exact feedback linearization model is obtained. Finally using linear system sliding mode control theory, the sliding mode controller is designed by selecting linear sliding surface and exponent reaching law. The research result shows that the exact feedback linearization sliding mode control method is superior to the customer control method in the dynamic response performance and steady-stage error regulating characteristics. At the same time, the method overcomes the inherent disadvantage of dependence on the model accuracy of existing feedback linearization control method and shows the stronger robustness. So it is a generality theory with practical significance.Active power filter as an ideal harmonic suppress device, its control strategy is one of the key factors. Currently active power filter control strategies are based on double-loop structure including current inner loop and voltage outer loop. A unified control method based on exact feedback linearization is presented for single-phase active power filter in this paper. First, the output function which contains compensation current and DC side voltage variables is obtained by solving the partial differential equation. Then, in order to transferring the nonlinear system into diffeomorphisms second-order linear system, the nonlinear state feedback control law is derived. Third, the controller which forces the output function asymptotically track the reference output is designed by selecting appropriate feedback coefficients. So it is come true that unified controlling of compensation current and DC side voltage. Unified control theory of this method has a general sense and can be extended to other power electronic converter topology.For more complex functions and topology power electronic converters, this paper presents a novel nonlinear control method based on state feedback linearization for three-phase active power filter. The method adopts double-loop structure including current inner loop and voltage outer loop. Voltage outer controller is designed using sliding mode control theory. Current inner controller transforms original nonlinear system into diffeomorphism linear system using state feedback exact linearization method and realized decouple control of active and reactive compensation currents. The command voltage can be exactly obtained which should be output from AC side of APF by selecting appropriate feedback coefficients. The command voltage is approached using SVPWM method. The control method combines the advantages of both, realized the decouple control of active compensation current and reactive compensation current, and enhance the robustness of the control system.In order to overcome switching frequency fluctuation shortcoming of traditional direct power control method, this paper presents a predictive direct power control method for three-phase shunt active power filter. The method looks active power filter AC side output voltage as control object. It gathers the votage and current signal from transducer and calculates the voltage that active power AC side should output to make instantaneous power tracking the reference value through a certain prediction algorithm. Then the voltage is output from PWM converter of active power filter using SVPWM method. On the base of theory analysis, the state feedback linearization nonlinear control method is applied to design active power filter industry prototype which connects with production and research projects. Extensive simulation and experiment are carried out to validate correctness and feasibility of presented novel nonlinear control stratege.