Reliant Monotonic Charging Controllers for Parallel-Connected Battery Storage Units to Reduce PV Power Ramp Rate and Battery Aging

The inherited intermittency of solar photovoltaic (PV) systems impacts the power grid by creating power fluctuations, which are mitigated by the integration of battery energy storage systems (BESS) augmented with a smoothing controller. However, the conventional charging and discharging schemes result in a repetitive and chaotic state of charge (SOC) which might degrade the BESS performance. This paper proposes a reliant monotonic charging/discharging controller (RMCC) to reduce battery degradation while maintaining smoothing efficiency. In this configuration, two battery units operate concurrently, one charging, and the other discharging, which helps to reduce battery cycles and extend BESS lifetime. In addition, the paper presents a smart RMCC (S-RMCC) controller to control the operation of a BESS made up of an even number of battery units greater than two. The controller forecasts the short-term irradiance and identifies the existence of power ramps using a ramp event detector. Hence, the forecasted irradiance is then utilized to obtain the PV output power and to compute the forecasted needed charging and discharging energy to compensate for PV power intermittency. These estimates are then compared to the remaining energy of battery units to determine whether to work with the entire BESS system or a subset of units. The proposed controllers were tested for battery degradation, ramp rate reduction, and power smoothing efficiency. The battery degradation is significantly minimal when using RMCC-operated units, accounting for 0.1877% and 0.1918%, as compared to 9.1514% when using a single BESS for smoothing.