Phd in ENERGY AND ENVIRONMENT

Thesis title: Power Electronics Solutions for BESS Integration and Management

The increasing demand for digitalization, data transfer, electric propulsion, habitat modules, and advanced payloads in spaceborne applications is driving the space industry to develop more powerful spacecraft solutions that require higher power output. As a result, spacecraft power systems must evolve to become more efficient and flexible while maintaining competitiveness and reliability. It has become evident that increasing the onboard bus voltage is necessary. In recent years, the 28V regulated aeronautical bus has been supplemented by 100V buses for higher power satellites, such as those on the International Space Station (ISS). The 100V limitation was primarily driven by the availability of space-qualified components. However, a 300V bus has recently been proposed, enabled by new technologies on the market and the growing adoption of Commercial Off-The-Shelf (COTS) components. A comparative analysis between 100 V and 300 V configurations for a 25 kW satellite indicates a potential reduction in Bus current by nearly 67% and a corresponding decrease in Bus capacitance size by approximately 89%. However, currently, there is lack of DC/DC converters available that support input voltages up to 300 V, as highlighted in ESA’s recent Tender Action (1-11712), "DC/DC CONVERTER WITH HIGH VOLTAGE INPUT FOR HIGH POWER TELECOM SATELLITES". While adopting the conventional architectural approach of interconnecting high voltage solar strings with regulators to the bus appears to be the most logical solution, the development of high voltage solar arrays is not without its technical challenges, including electrical arcing, sealed slip rings, voltage equalization among solar cells within the string, and parasitic capacitance in solar array sections. Additionally, there are economic considerations, such as qualification and manufacturing costs. Therefore, transitioning to a 300 V system involves substantial implications. In terms of existing technologies, GaN switches rated up to 650 V, have been successfully tested for operation in the space environment, demonstrating their capability for higher voltage applications. Additionally, in terrestrial settings, 300 V applications are common, as they align with the rectified mains voltage of 325 V. Such applications share architectural similarities with satellite systems, exemplified by the interconnection of solar Photovoltaics (PV) systems with single-phase grids and the interfacing of Battery Energy Storage System (BESS) for Electric Vehicles (EV) charging stations. This indicates that developing a high-voltage DC/DC converter for space applications is technically feasible. Moreover, the space industry recently is shifting towards cost efficiency and rapid development by integrating COTS components, commonly used in terrestrial circuit and component solutions, into spacecraft systems. This approach, along with shorter mission lifespans, enables the exploration of terrestrial circuit and topological solutions beyond conventional designs, which can be tested and refined for future compliance and qualification in space applications. Conventional power converter architectures process the entire power between the two stages they interconnect. As the system’s efficiency is directly related to the converter’s efficiency, significant effort is directed toward minimizing power losses. An alternative approach that accommodates higher bus voltages without altering the solar arrays and load voltages in conventional power architectures is Partial Power Processing (PPP). It is a concept applied to power converters where only a fraction of the total power between the two stages is processed. In PPP converters, most of the power flows directly from the input to the output, bypassing the conversion stage. By implementing PPP, a system can benefit in several ways. Since only part of the power is processed, the efficiency of the PPP converter applies only to the fraction it handles, meaning conversion losses affect only this portion. As a result, the system’s efficiency is not entirely dependent on the converter’s efficiency, allowing for a higher overall system efficiency. This improvement can lead to more efficient power systems, supporting the increasing power capabilities in space systems by providing a viable approach to meeting the space industry’s demand for efficient and cost-effective power conversion, particularly for high voltage and high power systems where lower voltage sources, like solar arrays and batteries, must interface with higher voltage buses and loads. Nevertheless, PPP may not be suitable for every application, as the efficiency of a system utilizing a PPP converter is a non-linear function of the converter’s efficiency, imposing constraints on the converter’s voltage gain. Accordingly, these converters are generally more efficient than full power processing systems when low input-output voltage differences are applied. Additionally, PPP architectures do not offer galvanic isolation, making them unsuitable for applications with strict isolation requirements. In such cases, alternative solutions or additional interconnection stages may be needed, potentially diminishing the advantages of PPP.