Modeling and Control of PV – Battery Hybrid System

Abstract

The Electrical Power Subsystem (EPS) is significantly essential element for satellite. It gives the required power to the spacecraft to achieve its role. After the spacecraft demands have been found out, the EPS will be picked out. The satellites in Low Earth Orbit (LEO) are very fast and able to revolve Earth in about 100 minutes, these intervals are divided into two parts; two-third in light and one-third in dark. In other words, about 66 minutes in sunlight period and 34 minutes in eclipse period. Since the Sun is the only renewable energy source available in space and it has immense amount of solar energy, therefore, the photovoltaic (PV) has considerably the most widespread usage for space application. However, PV system needs another secondary storage system to be relied on it when PV system cannot generate adequate power. The Chemical Battery (CB) is considered the most realistic choice for energy storage because its mechanism is well-known. In the last decade, Lithium-Ion Battery proved its performance and efficiency in space application and that led to be massively popular usage as rechargeable secondary power supply. It has long charge and discharge cycles, bulk energy density, high cell voltage, besides that, it has miscellaneous types. Recently, Ultracapacitor (UC) is used for space application and it has got space qualified license. It seems like being promising in spacecraft application especially in deep space exploratory / interplanetary application as it has extremely long number of cycles, speedy charging, and huge specific power. This thesis focuses on designing, simulating the satellite power sources just after distinguishing the loads for each subsystem. Using primary source with auxiliary source as a complementary source so that the EPS can electrify the satellite’s subsystems under any circumstances during the entire lifetime interval. PV is selected to be the primary source and it should carry out two duties; it supplies the subsystems with electric power during sunlight intervals and charges the auxiliary power source when it has extra power after supplying the loads. Lithium-Ion Battery (LIB) and / or Lithium-Ion Capacitor (LIC) are / is selected to be rechargeable secondary storage source and they have / it has to supply the loads during off light (eclipse) intervals. Software programs like Matlab and Satellite Tool Kit (STK) are used to establishing the mathematical model of satellite power sources. Then, after each design phase, there are a set of tests are executed to ensure power subsystem performance and capability. At first, the power system will implement PV – LIB hybrid power source. Then PV – LIC hybrid power system is implemented. Then, the system PV – LIB besides LIC hybrid secondary sources is executed. finally, a comparison between them including the pros and cons for each designed system is presented. Keywords: Satellite, Photovoltaic, storage system, Lithium-ion battery, Ultracapacitor, Lithium-ion capacitor