This paper describes the development and in-orbit demonstration of an electrical power system (EPS) for the 100 W/50 kg-class micro-satellite TSUBAME. Due to the high power consumption per surface area of the TSUBAME and the high power-to-mass ratio, we encountered several technical issues to be solved before the launch. TSUBAME's power demand varies drastically depending on the operation mode, from 2 W to 90 W. Therefore, we could not use the shunt regulator widely used for satellites. To suppress the exhaust heat from the dump power during low-power mode, we developed a series linear regulator that supplies less than 31 V to the main bus. Using this method, the operation point of the current-voltage curve for solar arrays was optimized automatically. However, this control law possesses a hysteresis which invokes a deadlock mode called battery lockup. In addition, the PWM current controller in the battery charger had 35 VPP spike noises, which resulted in system-wide failure. To resolve the fatal problem, we redeveloped the EPS, specifically the noise charger, taking into account physical mechanisms that emitted noise. After environmental and integration tests, the EPS placed on the satellite, which was launched and worked correctly on orbit.
