Indirect-Modulated MMC Current Control with Voltage Disturbance Estimation and Compensation

Due to the Modular Mutilevel Converter (MMC) submodule capacitor voltage ripple and sampling delay, a non-negligible error between MMC arm voltage references and synthesized output voltages occurs. Also, the dead-time effect of each submodule is not negligible. These errors act as voltage disturbances to MMC current controllers and deteriorate the performance of current controllers. To tackle with this problem, this paper proposes a voltage disturbance estimation and compensation method for an indirect-modulated MMC. Voltage disturbances can be simply calculated using the proposed estimation method. Furthermore, the proposed compensation method can be flexibly applied to the current controller of choice. The performance of proposed methods is validated through experimental results with a downscaled MMC set.