Homopolar harmonic injection and grid synchronization in distributed control systems for grid-tied intelligent power electronic blocks in 4-wire 3-phase converters

This paper studies two issues related with the use of distributed control for modular power converters based on the use of single-phase power units, namely intelligent Power Electronics Building Block (iPEBB) for power conversion in hybrid DC/AC microgrids. Some issues related to the distributed control are studied in this paper. Homopolar injection for PWM generation becomes more difficult, since each distributed controller calculates (and knows) only its control action. A possible solution is provided, based on the calculation of this homopolar injection by the central controller at 1 kHz. Synchronization with the grid becomes more difficult too, because each controller acts independently, without communication with the other ones (only with the central controller). Two alternatives are studied for this synchronization angle calculation: calculation in the central controller at central control frequency (1 kHz) or in each module at distributed control frequency (10 kHz).