Concepção e análise de um sistema de energia para picosatélites

Abstract

In 1999 the CubeSat project was created to favor and minimize launch costs of picosatellites, mostly didactic. Given the constraints of volume, weight and cost, energy systems must aim for efficiency and simplicity. The CubeSat electric power system can be classified into two types: centralized systems and distributed systems. The distributed systems have numerous advantages compared to concentrated systems, for example: improved thermal distribution, lower noise generation, among others. The objectives of a CubeSat electric power system are: Keep the satellite working in both periods of sun and Eclipse, ensure the necessary power for mantain the subsystems functioning; Keep the batteries charged to supply eclipse periods; meet all the power demand peaks. To achieve these goals and meet the physical constraints imposed by the CubeSat project, the systems must operate with a reduced number of power conversion stages, particularly if they are operating in cascade; should have a stage focused in achieve the photovoltaic generator maximum power point of and control the DC bus voltage supply. This paper proposes a CubeSat power system that contains two converters in stacked topology. A boost converter that performs the regulation of the DC bus to distributed CubeSat loads, and a buck-boost converter which has two functions: to track the PV array maximum power point (MPPT) and control the batteries load current. The combination of the battery charge control and the pursuit of maximum power point in the same drive results in less battery charging time. The connection of the inverters creating the stacked topology provides duty cycle reduction in boost converter and consequently the reduction of losses in driving due to reduction of the current. In addition, the series composition with the battery voltage boost converter provides an increased DC bus voltage distributed to CubeSat loads, which reduces the load current and both converters driving losses. The experimental results show the proposed topology working and EPS efficiency compatible with concentrated commercial architecture.