Comparative performance evaluation between the S4R and the S3R regulated bus topologies

摘要

The S3R and S4R topologies have shown to be suitable for regulated bus power systems. The S3R topology is currently used in space applications for several decades, mainly in GEO projects. However the power involved in actual spacecraft reaching the tens of kW as well as the increasing demands of LEO applications requiring fast recharges of the batteries show the limits of the capability of the S3R topology. They concern mainly the mass, and consequently the cost of the PCU, this essential unit of the power system which may reaches more than 80kg for the next generation of spacecrafts dealing with power around 25kW. These important mass figures are essentially caused by the high number of battery charger and discharger modules operating in a PWM mode. Another direct consequence of this technology is the dissipated power of these modules which require, with 1250 W losses for 95% efficiency, the support of an active cooling system including heat pipes and radiators. The S4R topology is a preliminary approach to cope with these constraints as it allows the replacement of the bulky BCR modules by efficient and low mass switching series regulators. The fact that these regulators are associated with the shunt modules and operate on the same solar array sections contributes to increase the flexibility and the reliability of this new power cell. It results a direct mass saving of the PCU around 30% which in turn penalizes the mass contribution of the solar array by around 5%. However part of this unused power is recovered directly by a better efficiency of the switching series regulators compared to the buck cell, in the order of 3 to 4%. This advantage gives another advantage to the S4R system by reducing the mass of the active cooling and its required associated power and reliability. The only constraint imposed by this topology is its restriction to contribute only to regulated bus systems with the battery voltage below the bus voltage. The S4R power cell has shown to be a promising approach in the design of large platforms as well for GEO as for LEO applications not only by the improvements available in the electrical and mechanical performances of the PCU but also in the improvement of the dynamic performances of the power system due the transfer of the 3 domain control into a simpler 2 domain control. The obligation to reduce more the power losses in the PCU already indicates the next step for future large power platforms which will concern the evolution of the battery discharger modules.