Switching Control Method Of Three Phase Inverter Based On Switching System Theory

The three-phase inverter is widely used as an energy exchange device.It is a high-order,multi input,multi output,multi variable coupling strong nonlinear complex system.The traditional modeling and control method based on linear system theory ignores the discrete switching state,and the established model can not accurately describe the dynamic process of the system.The controller is only effective near the working point.In the face of large signal disturbance and system parameter mutation,the control performance will be degraded or even out of control.With the development of nonlinear system theory,the emergence of switching system theory provides a new idea for power electronic converter modeling and control.The description of the inverter based on the switched system theory can reflect the essential characteristics of the system.According to the switched system theory,the design of the switching control law can make the system adapt to the requirements of large changes in the working range.At the same time,the calculation of the control process is simplified,and the parameter robustness is strong.It is of great significance to improve the control performance of the inverter.In this paper,based on the switching system theory,two kinds of three-phase inverters with different topologies are studied from two aspects:the establishment of system switching model and the design of switching law.The main contributions of this paper are as follows:(1)Firstly,the typical control methods of inverter are divided into PWM based control strategy and model predictive control strategy,which are discussed and analyzed respectively.The double closed-loop controller and model predictive controller of L句pe three-phase grid connected inverter are designed and simulated.(2)For L-type three-phase grid connected inverter,a switching strategy based on stability analysis of common Lyapunov function is designed.The switching eηor model of the system is established,which can accurately describe the system and reflect the nonlinear nature of the system including both discrete switching variables and continuous dynamic process.At the same time,the parasitic resistance of DC voltage,grid side inductance and line additional resistance are considered.Based on the established switching error model and the stability theory of common Lyapunov function,the switching control law is obtained by finding the subsystem which minimizes the derivative of Lyapunov function.The switching control law does not need complex coordinate transformation and PWM modulation,and has no control parameters.The output directly acts on the power device of the inverter to control its on-off to complete the inverter process.Simulation results verify the feasibility and effectiveness of the designed CLF switching control law.Compared with the traditional double closed-loop controller and model predictive controller,it has stronger robustness to system parameters and better dynamic performance.(3)A robust H_∞ switching control law is proposed for LC inverter with three-phase balanced load.The switching error model of the system is established;By using the common Lyapunov function,the conditions of H_∞ robust switchable stabilization are proved,and the switching laws satisfying the conditions of switched stabilization are given.The simulation results verify the feasibility and effectiveness of the designed H_∞ switching control law.When the system parameters change dramatically,it can still track the expectation stably,showing competitive control effect and strong robustness.