Improved Direct Current Control for Grid-Connected Multilevel Inverters

This article presents a sensorless voltage detection method for direct current control in grid-connected multilevel inverters. The direct current control is based on scalar hysteresis controller (SHC). The SHC is a simplified, and parametric direct current controller with the ability to work with an arbitrary level count on multilevel inverters. In combination with the sensorless voltage detection method, it is able to improve the switching behavior, and minimize the current error compared to existing direct current controllers. The proposed control concept is validated with experimental measurements using a three-, and five-level diode clamped inverter under steady-state conditions, and various grid disturbances. In comparison to the standard SHC method, it is verified that the proposed concept shows an improved switching behavior, and a reduced error current.