PROJECT TITLE :

Photovoltaic Fly back Micro inverter with tertiary winding current sensing

ABSTRACT:

This work describes a new grid-tied photovoltaic (PV) flyback microinverter current monitoring approach that is low-cost, non-invasive, and isolated. This is accomplished by employing the flyback transformer as a current sensor, which is accomplished by adding a tertiary winding to the transformer. The magnetising current is sensed via mathematical integration of the tertiary winding's open circuit voltage through a ground-clamped-integrator. Because the magnetising current is a mix of main and secondary currents, sensing simply the magnetising current allows control of both grid current and maximum power point tracking (MPPT). This eliminates the need for invasive current sensors in the PV, main, secondary, and grid current loops. Furthermore, adjusting the magnetising current provides an alternative solution to the control complexity problem that comes with continuous conduction mode (CCM). The magnetising current can be linearly ramped and de-ramped, allowing for set-reset hysteresis control, similar to the boundary and discontinuous conduction modes. For verification, a grid-tied microinverter prototype is shown, with the following experimental result: THD of 1.9 percent grid current, power factor of 0.9988, static MPPT efficiency of above 99 percent, and dynamic efficiency of 98.50 percent.