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The International Space Station (ISS) electrical power system consists of power generation, energy storage, power management, and distribution (PMAD) equipment. Electricity is generated in a system of solar arrays. Besides the solar arrays on the Russian element, the station currently has two photovoltaic modules on orbit, with two more scheduled to be delivered.
The Electric Power System (EPS) provides all user loads and housekeeping electrical power and is capable of expansion as the station is assembled and grows. Eight independent power channels for high overall reliability supply the electric power.
A photovoltaic (PV) electric power generation subsystem was selected for the space station. A PV system has solar arrays for power generation and chemical energy storage (Nickel-hydrogen) batteries to store excess solar array energy during periods of sunlight and provide power during periods when the station is in Earth’s shadow (eclipse). The station orbits the earth every 90 minutes and for about 35 minutes, the station must run on batteries while the station is in eclipse.
Flexible, deployable solar array wings that are covered with solar cells provide power for the ISS. Each PV module contains two wings and each wing consists of two blanket assemblies. The solar array wings are tightly folded inside a blanket for launch and they are deployed when on orbit and supported by an extendable mast.
Nominal electrical output of each power channel is about 11 kilowatts (kW), or 20.9 kW per PV module. Four PV modules will supply approximately 83.6 kW.
The primary purpose of the Energy Storage Subsystem (ESS) is to provide electrical power during periods when power from the solar arrays is not enough to support channel loads. The ESS stores energy during periods when solar arrays can generate more power than necessary to support loads. The ESS consists of three nickel-hydrogen (Ni-H2) batteries per power channel and each battery consists of two battery Orbital Replacement Units (ORUs). A battery charge/discharge unit (BCDU) controls the charge and discharge of each battery. The Ni/H2 battery design was chosen because of its high energy density (lightweight) and proven heritage in space applications since the late 1970's to early 1980’s.
The entire EPS may be divided into two power subsystems. The primary power subsystem operates at a voltage range of 137 to 173 volts direct current (Vdc) and consists of power generation, storage and primary power distribution. The secondary power subsystem operates at a voltage range of 123 to 126 Vdc and is used to supply power to user loads. Direct Current-to-Direct Current Converter Units (DDCUs) are used to convert primary power to secondary power.
The U.S. power system is also integrated with Russian power sources, so that power from the American power bus can be transferred to the Russian power bus and vice versa. The Russian power system operates at a nominal voltage of 28 Vdc. American to Russian Converter Units (ARCUs) and Russian to American Converter Units (RACUs) are used to convert power from the American secondary power bus to the Russian power bus and vice versa.
If you are looking for Boeing ISS Electric Power System (EPS), please download it from their official website that the link is below.
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