Single phase synchronous reference frame power control of grid connected multi string inverters

The objective of this paper is to study the active and reactive power control of multi string nine-level inverters with LCL output filters connected to grid. With the qd synchronous model of the system obtained using the harmonic balance technique, a novel active and reactive power control method with an all pass filter suitable for digital implementation is introduced. A single phase locked loop (PLL) control scheme to synchronize the grid voltage and frequency to the filtered output voltage and frequency is also provided. Computer simulation results of both output filter types verify the effectiveness and utility of the proposed control schemes.