Modular and Decentralized PCU

Abstract

This paper presents the studies made on the definition and design of a decentralized and modular electrical architecture of Power Conditioning Unit (PCU). The modular PCU is able to cover a large range of mission demands by adapting the number of power modules (PM) while the electrical interfaces remain the same. A decentralized architecture is proposed where each module is able to control the solar arrays and to manage the batteries. It appears that this kind of architecture becomes feasible thanks to digital circuits and using a communication bus [1]. Breadboards are being tested in order to validate the concept. Reliability and robustness aspects are studied and a redundant architecture is tested. CONTEXTStudies made by CNES and TAS from 2008 to 2014, focused on a modular PCU based on BUCK solar array regulator with MPPT control [2]. This architecture is composed by N+1 power modules which control the solar array, manage the battery and use a reliable digital bus for communication. This solution is compatible with unregulated or regulated busses, and the MPPT can address very large needs in spacecraft power supplies. CNES decided to go on a second way by considering DET (Direct Energy Transfer) topologies for solar array regulator, unregulated bus and the possibility to implement remote power modules. For these reasons, this architecture is called Ultra Modular PCU. The trade-offs made for the architecture and the electronic design are more adapted for low cost applications or micro-satellites. ARCHITECTURE Architecture general considerationsThe architecture is based on remote power modules connected on the same primary Unregulated Power Bus (UPB). Each module controls one or several Solar Array sections and is connected to one or several battery modules (Figure 1 and 2). A digital bus interconnects all the modules via control circuits, and is directly connected to the On-board Computer (OBC). Lots of possibilities exist for the PM topology. In our objective to build a modular PCU, the elementary PM is sized for 8A to 10A which allows supplying a microsatellite and with 10 PM in parallel a big LEO spacecraft can be supplied. For example the figure 3 shows different topologies studied. The first one is composed of 8 SA sections with the possibilities to connect in parallel some or all of them for modularity and adaptability aspects. Each section is sized for the total PM current divided by 8. Second topology uses 3 SA sections, 2 DETs and one PWM. The third one is a DCDC converter which can operate at MPPT. We want to keep the possibility to have remote PMs and then solutions with PWM DCDC converters (second and third examples) were not chosen because of EMC

Space Power Topology Selection and its System Level Modeling and Control

“…Topology with bidirectional DC/DC converters appears again in Schirone and Macellari (2014) as a solution for a lunar rover with a topology that makes use of four switches. A fully regulated solution with a block diagram showing a BCDR equipment was presented by Bonnet et al (2017). Nevertheless, the BCR and BDR functions are separated and not performed by bidirectional DC/DC converter, with discussions focused on modular and decentralized architectures of the PCU.…”