Control of Multiple SPV Integrated Parallel Inverters for Microgrid Applications

This work presents a hybrid control method (HCM) for inverters in a single-phase AC grid-interactive photovoltaic (PV) microgrid connecting multiple PV inverter (PVI) units. The HCM is incorporated into a single control method employing three cascaded loops -grid current loop, voltage control loop and improved third order adaptive integrator-quadrature signal generator (ITOAI-QSG). The HCM is used for mode transitions between the grid integrated mode (GIM) to islanding mode (IAM) and vice-versa, and this confirms the seamless transfer between the modes without rearranging the control structure. In GIM, the presented controller regulates the grid current and provides dynamic grid support by the reactive power compensation. In IAM, the controller changes from the grid current control to the voltage control to adjust the PV inverter's output voltage. The control method is presented for a parallel-operated single-stage where PV panels are interfaced with the inverters with independent maximum power point tracking (MPPT) to harvest maximum power. The battery energy storage (BES) is interfaced with the main PVI unit to support the load demand in peak demand periods and maintains the power balance in IAM. The charging and discharging profiles of BES are achieved by a DC-DC bidirectional converter (DBC). Test results verify the performance of the developed control.