Power Electronics in Modular Solar Home Systems

Abstract

Access to electricity is a key actuator in order to tackle poverty in areas of limited resources. While the population without access to electricity has a decreasing tendency, still almost 1 billion people continue to live without this basic amenity. This thesis has been carried out at the company DC Opportunities as part of the rural electrification project. On this field, the main activity focuses on developing cost-effective DC solutions in the form of a solar home system which consists of a total of 4 devices including low-power LED lights, a solar charging station, a high-power rate power bank and a power hub. The report analyses various existing electrification projects identifying the characteristics of their approaches in order to recognize the shortcomings of market available products and to build a design criterion. Given that the main target application is aimed at rural areas, a modular approach has been the base of the design criterion with the purpose of tailoring the SHS to developing countries with limited resources. The project analyses each step within this modular process together with the power electronics involved in every stage. The main objective of the project is to perform direct charging between the charging station and the power bank, which consists in feeding power directly from the bus voltage of the charging station into the battery cells with only one active converter. This feature is implemented as a result of the introduction of the power delivery protocol released together with the USB type C connector . This offers a wide variety of possibilities which includes negotiable voltage levels ranging from 5 to 20V. The first element taking part in the direct charging is the charging station .This thesis addresses the challenge of designing and building a circuit with dynamic adjustment of voltage and current in a cost-effective and reliable manner. By adding a digital to analogue converter and 2 operational amplifiers, it is possible to add this feature to a wide range of standard voltage converters available in the market. The report analyses this circuit in 3 steps: first with circuit theory, secondly by simulation and eventually by including the results obtained in an empirical test implemented in one of the prototypes. The power delivery protocol is also beneficial for a power-bank application, which is the second element of the direct charging. It is one of the purposes of the thesis to evaluate the performance of direct charging. Eventually, the report presents the main conclusions derived from the analysis of the aforementioned elements and also covers future lines which include improvements to be implemented within the components of the solar home systems.