Study On The Batteries Management In Stand-alone Photovoltaic System

Nowadays, with the increasing of energy exhaustion and environment pollution, the application of photovoltaic technology has become a hotspot of the whole world. So the grid-connected photovoltaic system and the stand-alone photovoltaic system develop quickly. Especially, it has become the national emphasis of investment to develop the stand-alone photovoltaic systems. It can supply residents which live in remote and/or far from utility grid area with power .This paper focuses on the stand-alone photovoltaic system using valve regulated lead-acid battery(VRLA). In order to improve the performance and reduce cost of the system, we pay our emphases on the implementation about the charging, discharging, capacity prediction, maintenance of storage batteries, and so on. The main contents are listed as follows:1. An overview on developing actuality of management of storage batteries in the stand-alone photovoltaic system at home and abroad is discussed.2. The charging and discharging electrochemistry mechanism of the storage battery is analyzed. The equipment of measuring capacity of storage batteries is developed.3. Various charging models of lead-acid storage battery are analyzed. More discussions about their feasibility of application are taken. Simultaneously, the charging control technology (including the MPPT technology for photovoltaic array ) in photovoltaic system is studied.4. The factors affecting the capacity of the storage battery are detailed and various methods or models predicting the capacity of the storage battery are presented.5. The paper proposes a method that combines "Mass law"--acceptable charging current with technology of solar photovoltaic array's maximum power point tracking in stand-alone photovoltaic system. It realizes a efficient charging management of VRLA storage battery. And fuzzy hierarchical control technology is applied to the depolarization control. It achieves the maximal energy utilization of the system. With the technology, too much rules of the more fuzzy input parameters can be decreased effectively, but the control effect doesn't decrease.6. A simple test method for array MPPT control is proposed and is verified.7. The paper describes a capacity predicting method: Combining the Open Circuit voltage prediction with the fuzzy prediction of the "storage batteries health". And the method does not only increase the prediction speed but also improve the prediction precision, so it can offer credible data to charging management.8. Integrated the characteristic of storage battery in the stand-alone photovoltaic system, thepaper produces a valid method for the charging and discharging management:1) The storage batteries are grouped in order to achieve the average-charging > the average-discharging and the quick-charging.2) When the energy of photovoltaic array is full, capacity maintenance to the "illness" storage battery is taken.3) Under the current system condition, the time(hours) that the batteries continue to work is displayed.4) It's necessary to maintenance charging in order to prolong the life of the storage battery.9. A charging (discharging) circuit for storage battery and a DC/DC circuit for MPPT of array are designed.10. An energy management system based on a MSP430F147 in stand-alone photovoltaic system is designed. It achieves array's MPPT control, the storage batteries' capacity prediction, charging and discharging control.11. A program is designed, which can accomplish the strategy for array's MPPT control, the storage batteries' capacity prediction, the storage batteries' charging and discharging control.Finally, the results of experiments have proved that the proposed control methods have some advantages.