M.Tech (Department of Electronic Engineering, Faculty of Engineering and Technology), Vaal University of Technology. / Due to the fickle nature of weather upon which renewable energy sources mostly depend, a shift towards a sustainable renewable energy system should be accompanied with a good intermediate energy storage system, such as a battery bank, set up to store the excess supply from renewable sources during their peak periods. The stored energy can later be utilised to supply a regulated and steady power supply for use during the off-peak periods of these renewable energy sources. Battery banks, however, are often faced with the challenge of charge imbalance due to the disparities that occur in the operating characteristics of the batteries that constitute a bank. When a battery bank with charge imbalance is repeatedly used in applications without an effective battery management system (BMS) through active charge equalisation, there could be an early degradation, loss of efficiency and reduction of service life of the entire batteries in the bank. In this research, a universal battery management system (BMS) in stand-alone photovoltaic application was proposed and designed. The BMS consists majorly of a switched capacitor (SC) active charge equaliser, designed with a unique configuration of high capacitance and relatively low switching frequency, which can be applicable to common battery types used in stand-alone photovoltaic application. The circuit was mathematically optimised to minimise losses attributed to impulsive charging and tested with lead acid, silver calcium, lead calcium and lithium ion batteries being commonly used in stand-alone photovoltaic application. The SC design was verified by comparing its simulation results to the digital oscilloscope results, and with both results showing similar values and graphs, the design configuration was validated. The design introduced a simple control strategy and less complicated circuit configuration process, which can allow an easy setup for local usage. The benefit of its multiple usage with different stand-alone photovoltaic battery types saves the cost of purchasing a different charger and balancer for different battery types. More so, the design is solar energy dependent. This could provide an additional benefit for usage in areas where energy dependence is off-grid.

Este trabalho propÃe o desenvolvimento de uma fonte de alimentaÃÃo portÃtil para notebooks e outros equipamentos eletrÃnicos usando energia fotovoltaica. O sistema completo à composto por dois mÃdulos fotovoltaicos poli-cristalinos de 54W conectados em paralelo; um conversor boost clÃssico usado para controlar a carga das baterias de chumbo-Ãcido reguladas a vÃlvula (VRLA-Valve Regulated Lead Acid) de 40 Ah associadas em sÃrie formando um barramento de 24Vcc e um conversor boost-flyback que tem a funÃÃo de elevar a tensÃo do banco de baterias de 24Vcc a uma tensÃo de saÃda de 250Vcc. O conversor boost utiliza o algoritmo perturba e observa (P&O) para conseguir o ponto de mÃxima potÃncia dos mÃdulos fotovoltaicos. Por outro lado, no conversor boost-flyback que opera em modo de conduÃÃo contÃnua (MCC) à usada a tÃcnica de controle por corrente de pico. Para verificar o princÃpio de funcionamento da fonte de alimentaÃÃo de dois estÃgios, o primeiro estÃgio foi desenvolvido com potÃncia de saÃda de 120W e o segundo estÃgio com potÃncia de saÃda de 200W. / This study proposes the development of a portable power supply to feed notebook computers and other electronic equipment using photovoltaic energy. The complete system is composed by two polycrystalline photovoltaic modules of 54W in parallel, a classic boost converter that allows to work the photovoltaic modules in the maximum power point (MPP) and to charge two lead-acid valve regulated batteries (VRLA Valve-Regulated Lead Acid) of 40Ah associates in series to form a bus of 24Vcc, and a boost-flyback converter that has as function to raise the battery bank voltage of 24Vcc to output voltage of 250Vcc. The boost converter uses the algorithm perturb and observe (P&O) to track the maximum power point of the photovoltaic modules. On the other hand, in the boost-flyback converter operates in continuous conduction mode (CCM) using peak current mode control technique to regulate the output voltage. To verify the feasibility of the two stage power supply, was developed a prototype with first stage of 120W output power, and the second stage of 200W output power.