A generalized and flexible control scheme for photovoltaic grid-tie microinverters

In this paper, the design and implementation of a dsPIC microcontroller-based photovoltaic (PV) microinverter control scheme using Direct Digital Synthesis (DDS) technique has been presented. The proposed scheme has the inherent voltage phase detection with phase-locked loop in a DQ reference frame and all control features implemented via the DDS technique adopted. The advantages of DDS technique applied on a dsPIC microcontroller as compared to other digital signal processing techniques based on sine wave generation by using a look-up table are that the output voltage magnitude and phase angle can be adjusted at a much higher resolution, thus inherently locking to the grid voltage with a high precision. DDS technique is also at the core of the maximum power point tracking and anti-islanding feature, which are satisfactorily integrated within the software of the same microcontroller, thus resulting in a low-cost, easy to implement, and compact system. The computer simulation results have been compared with the experimental ones obtained on a 120-W, 220-V/50-Hz protoype flyback converter to verify the satisfactory implementation of the DDS technique on a low-cost dsPIC. This scheme is quite suitable for use in a PV AC module integrated converter application where all the required functions of a PV microinverter are met.