Weak Grid Integrated Improved Power Quality PV-Battery System With Controlled Power Flow and Grid Assistive Capabilities

The presented work demonstrates a battery energy storage (BES) equipped photovoltaic array (PVA) generation unit, with the capability to operate reliably in weak grid conditions, while maintaining distortion-free and balanced grid currents. The grid voltages are treated using a pair of presented multiple second order generalized integrator with DC offset rejection (MSOGI-DCR) filters. A frequency locked loop (FLL) is also incorporated to lend flexibility at frequency deviations. The PVA is coupled via a boost converter for improved flexibility over DC link voltage, making it adaptive with grid voltages. The BES integrated via a DC-DC bi-directional converter (BDC), is employed to get multiple operational advances. The power exchanged with the grid is made independent of fluctuations in PV array power, and local load demand. The controlled power flow is adjusted based on real time feed-in tariffs, thereby helping to flatten distribution load demand, and yielding economic benefits. The system also suppresses grid neutral current. The control tackles severe undervoltage conditions by rapidly reducing injected grid power to avoid tripping, and continued grid support is provided, even at lack of PVA power. At overvoltage scenarios, control prohibits power delivery to the grid, whereas power import is permitted depending on tariff. At these deviations, PVA de-rating is not required, in contrast to conventional systems. The benefits of BES are temporarily suspended if in danger of over-discharge or over-charge, and the system works in a separate recovery mode. The system behavior at various adverse conditions, is analyzed using simulation and experimental results, to confirm claimed benefits.