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.