Research On Control Strategy Of Bi-directional Z-source Three-level Inverter

The development of microgrids and the development of distributed generation have put forward higher requirements for energy storage systems.The energy storage system is connected to the grid through a bidirectional converter to complete the energy input and output control of the energy storage system.The bi-directional converter affects the performance and efficiency of the microgrid.The Z-source inverter realizes the controllable boost of the single-stage circuit through the Z-source network,and the output waveform of the three-level inverter has low harmonic content.Therefore,the Z-source inverter is combined with a three-level inverter to form a bidirectional device.The Z-sourced three-level inverter is applied to a single-stage energy storage system and is of great significance to the development of the microgrid.This paper introduces the research status and development trend of Z-sourced three-level inverters at home and abroad,and analyzes the working principle of Z-source inverters.According to the principle of volt-second balance and Kirchhoff's law,the relationship between the physical quantities in the Z-source networks and the non-through state is determined.The state-averaging method and small-signal perturbation method are used to mathematically model the Z-source three-level inverter,and the transfer function between the on-duty ratio,the DC input voltage,the Z-source network output voltage,and the Z-source network capacitor voltage is derived.Clear Z source network control objectives.Based on the Space Vector Pulse Width Modulation(SVPWM)and the unified voltage modulation algorithm,the traditional SVPWM three-level algorithm is simplified.It only needs to determine the position of the sector where the vector is located.It does not involve trigonometric functions.It is simple to implement and has fast calculation speed.For the DC link voltage control of bi-directional Z-source three-level inverter,the PI controller is used to directly control the DC link voltage.Based on this,the PID algorithm based on BP neural network is proposed to directly control the DC link voltage,and the external DC is designed.The chain voltage reference value,after the BP neural network outputs the dynamic through-duty ratio,controls the output DC link voltage of the Z-source inverter,does not require a mathematical model of the system,and has a simple design.Matlab simulation software was used to build a system simulation platform based on a bi-directional Z-sourced three-level inverter.Simulation experiments were conducted under various working modes to verify the validity of the proposed algorithm and control strategy.