## 1 Introduction  
Unmanned aerial vehicles (UAVs) are nowadays experiencing unprecedented technological progress, which promoted them as a significantly cost-effective solution for many applications such as geographical survey, communications support, agriculture, and remote sensing [1; 2; 3; 4]. Alternative propulsion based on environmentally friendly energy sources is rapidly growing to minimize carbon dioxide emissions. Accordingly, the applications of electric UAVs powered by electric power sources are expected to have more expansions, especially for the photovoltaic (PV)-powered UAVs that became widely popular due to their increased flight endurance [5; 6; 7]. Advanced applications of electric UAVs in advanced remote sensing techniques using synthetic aperture radar (SAR) as a payload [8; 9] introduce more challenges for the design of UAVs power system, which is required to supply the high-power pulses consumed by these payloads whilst being restricted by the weight/volume limits imposed on UAVs' subsystems. For instance, the limited surfaces and weight available for installing the PV cells on UAVs' structure limit its power and energy harvesting capabilities; hence the power system should rely on an energy storage system (ESS) to supply the high load power peaks. This, in return, introduces more challenges in the design of the ESS, which due to the relatively large amount of energy required, is likely to require a Lithium-ion type of battery, and therefore may result in a contradictory relationship between the specific energy and the specific power that a battery struggles to fulfill. In this context, hybrid energy storage systems (HESS) based on high specific energy Li-ion batteries and high-power dense supercapacitors (SCs) have become more popular in UAVs applications [10; 11]. Integration of the HESS and the PVs to the DC-bus typically utilizes separate converters that control the charge/discharge operations of the battery/SC and the maximum power point tracking of the PVs as shown in Figure 0(a) [10; 11; 12; 13]. In this architecture, the range of the SC voltage, which defines the utilization level of the SC rated energy capacity, allowed by the interfaced converter playing an important role in the sizing of SC, is analyzed in Section 2. Allowing discharge of SC to lower voltage levels increases the energy extraction from the cells but, for given power demand, results in higher currents ratings for the power semiconductors and the heavier magnetic components [14; 15]. Many converter topologies can be utilized for extending the range of the voltage swing for the SC either by increasing the voltage boosting ratio [16; 17; 18; 19] or enabling buck-boost operations [20; 21; 22; 23] but at the cost of a significant increase in the number of power switches and/or passive components. Recently, the multiport converter (MPC) was introduced as a better option to interface and integrate the HESS and power sources to the DC-bus (as illustrated in Figure 1b) with higher system efficiency, lower cost, compact and simpler control compared to the distributed converter architectures [24; 25]. In [26; 27; 28; 29; 30; 31; 32], MPCs were proposed with two bidirectional ports that suit the interfacing of the HESS to the power bus, but with increased components count and only allowing voltage boosting at the input ports, which limits the allowed voltage range for the SC. The MPCs proposed in [33; 34] provided buck/boost operation for the SC port to extend its voltage range, but at the cost of increased components count. This paper proposes a new MPC topology with multiple input ports for PV, battery, and supercapacitor strings that are suitable for UAV applications and investigates the potential design improvements of the power system by achieving the following benefits:  
1. Fully controlled voltage step-down and step-up capability for the battery and SC was obtained at no extra cost/component size;
2.