Engineering topics

Patil, A. R.

Publications and source records attributed to Patil, A. R..

3 records

NASA NTRS1992

Design and test hardware for a solar array switching unit

This paper describes the control of a pulse width modulated (PWM) type sequential shunt switching unit (SSU) for spacecraft applications. It is found that the solar cell output capacitance has a significant impact on SSU design. Shorting of this cell capacitance by the PWM switch causes input current surges. These surges are minimized by the use of a series filter inductor. The system with a filter is analyzed for ripple and the control to output-voltage transfer function. Stable closed loop design considerations are discussed. The results are supported by modeling and measurements of loop gain and of closed-loop bus impedance on test hardware for NASA's 120 V Earth Observation System (EOS). The analysis and modeling are also applicable to NASA's 160 V Space Station power system.

Patil, A. R.↗

NASA NTRS1990

Design considerations for a solar array switching unit

An analysis of the sequential switching shunt regulator unit (SSU) proposed for the space station and space platform is presented. The solar array and shunt regulator system is analyzed for ripple, output impedance, and stability. The performances of proportional gain and proportional integrator (PI) controllers are compared. A design example is provided, and an EASY5 simulation is presented for the regulation of the bus voltage by the SSU. It is shown that the bus ripple may be limited by the equivalent series resistor, in which case it cannot be reduced by increasing the capacitance or switching frequency. The proportional controller is shown to offer a faster response than the PI controller, but has a load-current-dependent steady state error. This error can be removed by the PI controller, but the bus impedance has a low-frequency pole which slows the response.

Patil, A. R.↗

NASA NTRS1990

Modeling and simulation of the space platform power system

A comprehensive computer-aided modeling and simulation technique for the space platform power system is described. Large-signal and small-signal modeling is presented for the system components. The component models have been integrated to form the complete power system model. The system model is shown to be a powerful tool in simulating the behavior of the system with variation of illumination level and load. It can be used to study the bus regulation in each mode and to observe mode changes as the solar array is subjected to transitions from sunlight to eclipse and back to sunlight. System simulations show how the bus regulation is maintained by activating the shunt switching unit, the charger, or the discharger, depending on the available illumination level. The system model is suitable for verifying hardware results of for analyzing the performance of a proposed system where hardware testing is not feasible. The EASY5 dynamic analysis program is used as the host software for the modeling and simulation.

Patil, A. R.↗