Session
Pre-Conference: CubeSat Developers' Workshop
Abstract
Most of the electrical power systems for Cubesat use solar arrays as energy source. There are two power regulation techniques for these systems, which are: direct energy transfer (DET) and peak power tracking (PPT). This last one is also known as Maximum Power Point Tracking (MPPT). In DET, the solar array is directly connected to the battery through a diode for protection; however, this technique requires a matching between the solar array and the batteries for having good efficiency. In MPPT, power converters are used as interface between the solar array and the batteries for extracting the maximum power of the solar array; however, this requires more components and therefore MPPT is more complex than DET. Some researchers have claimed that DET should be used in small spacecraft; however, MPPT is the best option when the power converter is efficient since it can compensate the temperature effects over the current – voltage characteristic of the solar array. Furthermore, cubesats should employ MPPT because the solar array and the batteries generally are mismatched, since the solar arrays are usually sized according to size constraints without consider the batteries. Once the designer chooses MPPT as the power regulation architecture, he also has to choose among the different MPPT techniques such as: perturbation and observation, fractional voltage, extremum seeking control, etc. In spite of previous work showed evaluations of MPPT techniques, these studies were based mainly on simulations with few details on the power converter topology. This work compares different MPPT techniques to find which is more efficient in a 3U Cubesat. We employ mathematical models that describe the electrical behavioral of the solar arrays, the batteries and the power converters. By using the space environment characteristics we obtain the efficiencies of each one of the MPPT methods to determine which one is the best technique for the given conditions. In addition, we present experimental results of the MPPT techniques implemented on microcontrollers.
Presentation Slides
Comparison of Maximum Power Point Techniques in Electrical Power Systems of CubeSats
Most of the electrical power systems for Cubesat use solar arrays as energy source. There are two power regulation techniques for these systems, which are: direct energy transfer (DET) and peak power tracking (PPT). This last one is also known as Maximum Power Point Tracking (MPPT). In DET, the solar array is directly connected to the battery through a diode for protection; however, this technique requires a matching between the solar array and the batteries for having good efficiency. In MPPT, power converters are used as interface between the solar array and the batteries for extracting the maximum power of the solar array; however, this requires more components and therefore MPPT is more complex than DET. Some researchers have claimed that DET should be used in small spacecraft; however, MPPT is the best option when the power converter is efficient since it can compensate the temperature effects over the current – voltage characteristic of the solar array. Furthermore, cubesats should employ MPPT because the solar array and the batteries generally are mismatched, since the solar arrays are usually sized according to size constraints without consider the batteries. Once the designer chooses MPPT as the power regulation architecture, he also has to choose among the different MPPT techniques such as: perturbation and observation, fractional voltage, extremum seeking control, etc. In spite of previous work showed evaluations of MPPT techniques, these studies were based mainly on simulations with few details on the power converter topology. This work compares different MPPT techniques to find which is more efficient in a 3U Cubesat. We employ mathematical models that describe the electrical behavioral of the solar arrays, the batteries and the power converters. By using the space environment characteristics we obtain the efficiencies of each one of the MPPT methods to determine which one is the best technique for the given conditions. In addition, we present experimental results of the MPPT techniques implemented on microcontrollers.
