Research On Low Power Three-Phase Four-Leg Inverter

With the rapid development of various fields of industrial production,inverter with load capacity continues to expand,and increasing the types of load,three-phase inverter has been widely used and rapid development.In the banks,military,hospitals,aviation and other institutions with higher power quality requirements,due to load nonlinear and imbalance and other issues,resulting in the load of the neutral point potential drift.In the application of traditional three-leg inverter power supply for the load,the three-phase output voltage asymmetry,and in the traditional three-leg topology by adding the fourth leg,it can provide zero sequence current path to solve the load Imbalance problem.This paper is the application of three-phase four-leg main circuit structure,its control strategy to carry out technical research.First of all,this paper briefly introduces the background and significance of the research,and gives an overview of the development of three-phase four-leg inverter.After comparing several common topologies,it is concluded that the three-phase four-leg inverter is small in size,simple in structure and high in voltage utilization rate.Secondly,the paper makes mathematical modeling of the inverter system in a-b-c stationary coordinate system,d-q-0 rotating coordinate system and ?-?-0 coordinate system,and compares the three coordinate systems.The 3D-SVPWM in ?-?-? coordinate system and a-b-c coordinate system are described in detail after a brief description of the modulation strategy of the system,thus laying a solid theoretical foundation for the following simulation analysis.In the control strategy,this paper applies PI double closed-loop sequential control based on d-q-0 coordinate system.After introducing the concept of symmetrical component method,the formula is deduced and the PI of current loop and voltage loop regulators were designed.Finally,MATLAB software is used to simulate and analyze the inverter system under the condition of three-phase balanced load and unbalanced load,respectively,and the reliability of the system control strategy is verified.In order to further verify the validity of the simulation results,this paper takes the STM32F407 control chip as the core,builds the hardware experimental platform of 3kW three-phase four-leg inverter and designs the parameters of the main circuit and the control circuit.It is proved that the inverter system with positive,negative and zero sequence PI double closed-loop control strategy has the advantages of fast dynamic response,less harmonic content and strong anti-interference ability,especially for solving the load imbalance problem.Strategy is more superior.