Study and Implementation on Batteries Charging Method of Micro-Grid Photovoltaic Systems

Abstract

In the micro-grid photovoltaic systems, the random changes of solar radiation enable lead-acid batteries to experience low SOC (State of Charge) or overcharged for periods of time if directly charged with such traditional methods as decreased charging current, which will reduce lifetime of batteries. What’s more, it’s difficult to find a proper reduction coefficient in decreasing charging current. To adapt to the random changes of circumstance and avoid selecting the reduction coefficient, a new fast charging method named decreased charging current based on SOC is proposed to apply into micro-grid photovoltaic systems. It combines batteries’ SOC with the maximum charging voltage to determine the charging rate without strictly selecting reduction coefficient. By close-loop current control strategy and related scheme, the experiment proves the new method is feasible and verifies that, comparing with decreased charging current, the improved method make batteries’ SOC reach 100% in shorter time as well as the temperature of batteries raise more slowly

Optimal Battery Charger Fed by Photovoltaic System based on Decreased Charging Current Method

“…9 [15] [16]. It is observed that the maximum charging voltage or overcharging voltage set to V g is about 2.4 V/cell.…”

Power Balancing Control for Grid Energy Storage System in Photovoltaic Applications—Real Time Digital Simulation Implementation

“…In this case, the charger needs to be rated only for the rating of the battery. In the configuration presented in [3,4], independent DC-DC converters are required to connect the battery and PV array to the DC link as shown in Figure 2c.…”

Power Balancing Control for Grid Energy Storage System in PV Applications—Real Time Digital Simulation Implementation

“…In this case, charger needs to be rated only for the rating of the battery. In the configuration presented in [2] and [3], Independent DC-DC converters are required to connect battery and PV array to DC link as shown in Figure 2 An optimized operation of a Dual Active bridge (DAB) converter feeding a PV inverter connected to the grid is presented in [4] and [5]. Isolation between Grid and DC side is provided through high-frequency transformer used in DAB as shown in Figure 2(d).…”