Research Of Three-phase Four-leg Inverter Based On Resonant Control

The imbalance of three-phase voltage is one of the important characteristics of powerquality, especially in the instance where unbalanced load such as single-phase load isneeded to supply. The loads are varied, either balanced loads or non-linear unbalancedloads of the mid-frequency inverter in the aviation application. Research of how to outputthree phase voltage which are symmetrical and have small distortion at various loadconditions is significant.Research on the three-phase inverter supplying unbalanced load is mainly focused onthe topology and control strategy of the inverter. we choose the most advantage topology-three-phase four-leg topology as the main circuit structure in our research issue. Themathematic models of three-phase four-leg inverter in three-phase stationary and rotatingcoordinate frame systems have been established. Due to the special structure of three-phasefour-leg inverter, its PWM scheme is also a major research point. The three-dimensionalspace vector modulation (3D-SVPWM) which is commonly used is complex andcomputationally intensive, an carrier-based scalar PWM modulation is adopted, detailedanalysis of its principle and implementation process have been given out. Itsimplementation is simple and has many advantages of space vector modulation.Resonant controller has the capability of tracking AC signals with no static error, Inthe0coordinate frame system, this paper proposed a novel control strategy based onthe voltage and current dual loop control structure. This control system can achieveindependently control of the zero-sequence component, it also can ensure the positivesequence and negative sequence components of accurate tracking, in addition, the harmonicresonant controller can reduce the harmonic content of the output voltage. Analyze thestability of the system with resonant controller using Nyquist stability criterion.Finally, establish a simulation model of the system in Matlab/Simulink environment,the dynamic and steady-state performance of the designed system were analyzed, thesimulation results verify the effectiveness of the proposed control strategy.