# State-of-the-Art DC-DC Converters for Satellite Applications: A Comprehensive Review
## 1 Introduction
However, achieving high power without increasing the overall mass or cost is another challenge [25]. Figure 1: Classification of satellites based on their mass and approximate power levels. Power electronic converters are critical for generating, transmitting, and storing power in satellites. The power harnessed from solar panels is transformed using a DC-DC converter, stored, and converted for satellite onboard electronics. The power distribution module uses DC-DC converters to regulate the main bus voltage to meet the demands of individual subsystems in the satellite. The battery storage module also needs a DC-DC converter for charge and discharge regulation. Furthermore, isolation may be required at various power conversion phases, depending on the application. Figure 3 shows the various applications of DC-DC converters in satellites. Satellite power designs are driven by increasing power levels while keeping the power system mass and cost within reasonable limits [32]. These demands necessitate power electronic designs capable of managing high distribution currents, thus eventually requiring an increase in the bus voltage (typical voltages are 28 V DC for low-power satellites and 70 V and 100 V DC for larger satellites) to minimize the current and mass of the satellite's EPS [33; 34]. Additionally, owing to its benefits, the EP is expected to be a major contributor to propel future deep space and interplanetary missions. This again demands high-power Power Processing Units (PPUs) consisting of highly efficient DC-DC converters for satellite EP systems. Space-level power electronic designs have complex design constraints compared to other commercial applications, as they are exposed to extreme temperatures and radiations. Even though high efficiency and power density are required, reliability is crucial for satellite EPS designs. Moreover, the choice of a DC-DC topology for a given space application is determined by the type of satellite, the orbit, the mission duration, and the power requirements for the mission while adhering to the strict design constraints in space. In this regard, identifying the practical design constraints in space and reviewing the existing literature to compare topologies for various applications based on these constraints becomes essential. A few notable studies in the literature are either limited to a particular type of satellite or mission, or they do not provide comparisons based on practical design constraints in space. For example, Ref. [35] compared boost-based non-isolated DC-DC converter topologies for satellite MPPT applications. However, the study did not consider other non-isolated or isolated topologies or other applications. Ref. [36] provided a detailed study on small satellite microgrids, where the authors reviewed DC-DC converter topologies, solar arrays, and satellite battery technologies. However, the scope of the study was limited to small satellites, particularly nano-satellites, and did not discuss EP for satellites. This review paper provides an in-depth review of DC-DC topologies for various satellite applications. The scope of this review is not limited to small satellites or Earth-orbiting satellites; it also considers large satellites, interplanetary missions, and deep space missions. This paper spans a wide range of applications of DC-DC converters for satellites. Unlike the existing literature, the topologies are compared using various practical parameters and applications. Figure 2: Types of missions and their distances from Earth. The important contributions of this paper are as follows, with a graphical abstract provided in Figure 4:  
* We identify the design requirements for DC-DC converters and provide an up-to-date review of various isolated and non-isolated topologies for satellite applications. * We analyze the scope of EP for future manned and deep space missions and review DC-DC converters for EP in satellites.