Multilevel PWM VSIs

The coordinated control strategy between the grid and load controllers for a regenerative AC converter consisting of backto-back, three-level, neutral-point-clamped PWM VSIs was studied in this article. The focus here is on the coordinated DC link voltage control through the coordinated power flow control and the coordinated DC link neutral point control. Various neutral point control methods, including a new linear control scheme, were also discussed. The simulation and experiment results showed that the coordinated approach can significantly improve system response, reduce system stress, and help eliminating nuisance trips.