A PV-Battery System Resilient to Weak Grid Conditions With Regulated Power Injection and Grid Supportive Features

Abstract

This paper presents a weak grid coupled single stage photovoltaic (PV) system. The system incorporates a battery energy storage (BES) via a bi-directional DC-DC converter (BDDC). The system does not allow the grid power quality to be deteriorated at nonlinear loading conditions, as well as when the grid voltages are unbalanced or distorted. Moreover, the control scheme is resilient to DC offset in the acquired grid voltage signals due to sensor circuit anomalies. The flexibility afforded by the BES is utilized for several benefits. The intermittent power injection associated with the PV system, is resolved by sustaining the defined grid power at fluctuating PV generation or local loads. The developed control makes use of the BES to adjust the grid power with the feed-in tariffs, adding the capability to act as a power sink at low tariff periods, thus increasing the economic returns. The control avoids overcurrent tripping at large voltage dips and enables fault ride through, whereas the conventional single stage system frequently trips and ceases operation. The system helps the utility at large voltage rise by stopping power flow to the grid while allowing power import from the grid. The BES is prevented from being excessively charged or discharged by the monitored transfer to a recovery mode. Moreover, the dual mode control of the DC link voltage allows peak power extraction from the PV array, while conserving grid power quality. The claimed benefits are evaluated at different operating scenarios using simulated and test results.