Differential flatness control strategy of modular multilevel matrix converter based on double dq coordinate transformation under unbalanced grid conditions
Aiming at the problems of incomplete decoupling of double αβ coordinate transformation com-monly used in modular multilevel matrix converter(M3C)research,on the basis of the analysis of topol-ogical structure and mathematical model,poor effect of traditional PID control method,and little research on unbalanced working conditions,etc.,double dq coordinate transformation was adopted to decouple the electrical quantity.The mathematical model of M3C's input and output side was established,the voltage and current were separated in positive and negative order,and the differential flatness control(DFC)of the input side and the output side was derived by combining the differential flatness theory.Finally,the operation under two unbalanced conditions was simulated.Compared with linear PID control,the simula-tion results show that nonlinear differential flat control improves the tracking speed and accuracy of inner loop current,and is more suitable for nonlinear M3C system.When the power grid balance or asymmetric fault occurs,M3C system under differential flat control has better dynamic stability and rapidity,higher power quality,and can suppress negative sequence current more effectively.The current THD can be re-duced by up to 1.42%.