Point potential modulation strategy for three-level PWM rectifiers in unbalanced grid

In practical application, the phenomenon of power grid imbalance is becoming more and more common, which makes PWM rectifier have abnormal working conditions of low power factor and low harmonic content.In order to solve the problem of mid-point potential fluctuation of three-level PWM rectifier under unbalanced grid, this paper uses the elimination of negative sequence components to give control to find out the desired power and desired current of the rectifier under unbalanced grid, and uses repetitive control to achieve the static-free tracking of the desired current, the harmonic content of current at the grid side is reduced,and proposes the improved VSVPWM modulation strategy, reconstructs the virtual small vector and virtual mid-vector, realizes the active control of mid-point potential by introducing the duty cycle coefficient, and verifies the correctness and stability of the improved VSVPWM by experiment.