Research On Control Strategy Of Three-phase Inverter Under Asymmertrical Load

Nowadays,power electronic technology is developing rapidly,and three-phase inverters are widely used in various fields,for example,new energy,aviation power supply,and on-board UPS.In practical applications,three-phase inverters have a wide variety of loads,and asymmetrical loads and non-linear loads are extremely common.This places higher requirements on the load capacity of three-phase inverters.For various loads,symmetry of the three-phase voltage is the basis for their normal operation.Therefore,in-depth study of its topology and control technology makes it meaningful to output a symmetrical three-phase voltage under various conditions.When the three-phase three-leg inverter has a balance load,it can provide symmetrical voltage.When the load is asymmetrical,voltage will be asymmetric.The inverter with three-phase four-leg topology has the ability to carry unbalanced load.This subject takes the three-phase four-leg inverter as the object of study,designing and improving its control strategy.Firstly,this article established the mathematical models of the three-phase four-leg inverter,and compares the advantages and disadvantages of the mathematical models under different coordinates.In the dq coordinate system,the control strategy of the three-phase four-leg inverter is designed based on the PI controller.Separate the phase sequence of the load voltage to obtain the positive,negative,and zero sequence components,and design control strategies respectively.In this paper,the control strategy of virtual axis re-coordinate transformation is adopted for the zero-sequence component to eliminate the influence of the zero-sequence component on the system.This paper also conducts detailed derivation and analysis of two 3D-SVPWM,and this subject uses 3DSVPWM technology under abc coordinates,and finally completes the simulation verification of the entire control system in the Simulink simulation environment.In the process of designing traditional PI controllers,the use of symmetrical component method,multiple coordinate transformations,and space vector modulation methods that require a lot of calculations increase the complexity of the controller design.This paper proposes and designs a quasi-proportional resonance control strategy under abc coordinates,and conducts detailed derivation and research on carrier-based scalar PWM modulation.The modulation effect is the same as that of 3D-SVPWM and the implementation is simpler.Finally,complete control system simulation,the simulation data diaplay that the three-phase inverter based on the quasi-PR control system has greatly improved various indicators compared with the three-phase inverter based on the PI control strategy,and its output voltage The THD is smaller,the voltage imbalance is smaller,and the dynamic performance is better,thus proving the superiority of the quasi-PR control system.This subject selects TMS320F28335 as the control chip,designs and builds a three-phase four bridge arm hardware experimental platform,completes the program design,simulation and experimental results show the correctness of the control strategy studied in this subject.