The power electronic interface between a satellite electrical power system (EPS) with a photovoltaic main source and battery storage as the secondary power source is modelled based on the state space averaging method. Subsequently, sliding mode controller is designed for maximum power point tracking of the PV array and load voltage regulation. Asymptotic stability is ensured as well. Simulation of the EPS is accomplished using MATLAB. The results show that the outputs of the EPS have good tracking response, low overshoot, short settling time, and zero steady-state error. The proposed controller is robust to environment changes and load variations. Afterwards, passivity based controller is provided to compare the results with those of sliding mode controller responses. This comparison demonstrates that the proposed system has better transient response, and unlike passivity based controller, the proposed controller does not require reference PV current for control law synthesis. 1. Introduction As space missions are getting more involved, satellites systems are getting more complex in parallel. Even the size of satellites are getting smaller due to budgetary constraints, the amount of power required to run the complete system is getting bigger resulting in larger PV arrays, higher battery capacity, and a much more sophisticated electrical power system (EPS). The primary function of EPS is to supply and manage uninterrupted power to its subsystems and payloads. These subsystems include power generation subsystems such as PV arrays, power storage subsystems which are batteries with different chemical structures, power control and distribution subsystems like power converters, power distribution units, power conditioning units, and battery charging units [1]. In the present space power domain, most of the satellite power systems use PV arrays as their power core. Despite all the advantages presented by the generation of energy through PV cells, the efficiency of energy conversion is currently low; thus, it becomes necessary to use techniques to extract the maximum power from these panels, in order to achieve maximum efficiency in operation. The requirement for maximum power point tracking (MPPT) is raised by the fact that the MPP of the PV array continuously varies with temperature and illumination changes. Due to the nonlinear characteristic of the PV array and drastic changes in irradiance and temperature, design of the MPPT unit is important. Several studies have been carried out, such as sliding mode control [2], adaptive control [3], neural networks
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