<p dir="ltr">Batteries have become essential for a wide range of applications in the field of energy storage and electrification, from portable gadgets to electric cars and renewable energy systems. But effectiveness, performance, and lifespan of a battery pack are closely related to each of the individual cells of which it is composed. The phenomenon of cell voltage imbalance, which can result in a variety of problems ranging from decreased capacity and efficiency to safety concerns and premature failure, poses a significant challenge in managing battery systems.</p><p dir="ltr">Therefore, battery cell balancing plays a crucial role in improving the overall performance of battery packs. To guarantee uniform charge and discharge characteristics, balancing is the process of equalizing the charge of individual cells inside a battery pack. Battery cell balancing seeks to prolong the operational life of packs, improve the efficiency of its energy use, and ensure the safety of the overall system.</p><p dir="ltr">The methods used for battery cell balancing encompass a wide range of approaches, from passive methods that release extra energy as heat, to active methods that move energy across cells. The particular battery chemistry, application requirements, and required level of balancing precision are only a few examples of the variables that influence the choice of balancing technique.</p><p dir="ltr">Lithium Iron Phosphate (LiFePO4) rechargeable batteries are widely used by electric utility companies in battery storage applications. Battery cells are combined to form a battery module. Each module is constantly monitored with sensors and controlled by a Battery Management System (BMS). The BMS performs balancing of the cells. Each cell in the battery stack is monitored to maintain a healthy battery state of charge (SoC). The motivation for this work is to develop an active balancing system to replace a passive system currently being performed manually on an existing battery storage system consisting of LiFePO4 cells. An active cell balancer was designed using the LT8584 active cell balancer, which is based on a flyback DC-DC converter design. An LTspice simulation of the design was created for a single cell. It demonstrates critical parameters of the flyback converter cycle time. A PCB board, designed using KiCAD, was implemented. It is anticipated that the proposed design could be used to restore the health of SoC of faulty modules in lieu of removing and replacing them with a new module, resulting in potential cost savings. The proposed design is scalable in that it could be used for <i>n</i> number of cells in a battery module consisting of LiFePO4 battery cells.</p>

Batteries account for 50% of the overall cost of solar home systems (SHS). The battery packs degrade over time and when they reach 70% state of health (SOH), the whole SHS is discarded. In the predominantly rural off-grid context, battery replacements are expensive and impractical. The customers are often dozens of km away from any sales point. Furthermore, recycling schemes are often limited in the developing world, meaning that old batteries are sometimes discarded in unsafe ways. As the market grows, the environmental impact of this will only get larger. Solaris Offgrid, a premier name in the Solar Offgrid industry, is innovating two solutions designed to tackle this issue; a smart multi-battery packmanager and an easy to recycle battery pack design with cell by cell management. The current study is based on a lossless cell balancing design, where in the charge and discharge cycles of each cell in the string are monitored and to efficiently avoid overcharge and over-discharge. Implementing this strategy reduces the degradation of these batteries which extends the battery life of SHS. A sensitivity analysis is performed to analyze the environmental benefit gained by implementing lossless cell balancing. The thesis provides a literature study on the different battery terminologies, types of batteries used in SHS and, various cell-balancing techniques used today. This is followed by the design of a lossless cell balancing technique with minimal losses. / Batterierna står för 50 % av den totala kostnaden för solcellsanläggningar (SHS). Batteripaketen försämras med tiden och när de når 70 % av sitt hälsotillstånd kasseras hela solcellssystemet. På den övervägande landsbygden utanför elnätet är det dyrt och opraktiskt att byta ut batterierna. Kunderna befinner sig ofta tiotals kilometer från varje försäljningsställe. Dessutom är återvinningssystemen ofta begränsade i utvecklingsländerna, vilket innebär att gamla batterier ibland kasseras på ett osäkert sätt. I takt med att marknaden växer kommer miljöeffekterna av detta att bli allt större. Solaris Offgrid, som är ett ledande företag inom industrin för solcellsanläggningar, utvecklar två lösningar för att lösa detta problem: en smart batteripackförvaltare för flera batterier och en lätt återvinningsbar batteripackkonstruktion med cellvis hantering. Den aktuella studien bygger på en “förlustfri” cellbalanseringskonstruktion, där laddnings- och urladdningscyklerna för varje cell i strängen övervakas och effektivt undviker överladdning och överladdning. Genom att tillämpa denna strategi minskas degraderingen av dessa batterier, vilket förlänger batteritiden för SHS. En känslighetsanalys utförs för att analysera den miljöfördel som uppnås genom att införa förlustfri cellbalansering. Avhandlingen innehåller en litteraturstudie om olika batteriterminologier, typer av batterier som används i SHS och olika tekniker för cellbalansering som används idag. Detta följs av utformningen av en teknik för förlustfricellbalansering med minimala förluster.