DESIGN CONSIDERATIONS AND CONTROL CHALLENGES OF DC-DC CONVERTERS IN SOLAR UAV ENERGY SYSTEMS

SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 4 DESIGN CONSIDERATIONS AND CONTROL CHALLENGES OF DC-DC CONVERTERS IN SOLAR UAV ENERGY SYSTEMS J. Narimanov1, R. Koňarik2 Tashkent state transport university, Tashkent, Uzbekistan1 University of Žilina, Žilina, The Slovak Republic2 https://doi.org/10.5281/zenodo.17833258 Abstract. The integration of solar energy systems into unmanned aerial vehicles (UAVs) presents a promising solution for extending flight endurance and enhancing operational autonomy. A critical component of such systems is the DC-DC converter, which regulates power flow between solar panels, energy storage units, and propulsion systems. This paper presents a theoretical overview of the design considerations and control challenges associated with DC-DC converters used in solar-powered UAVs. Key converter topologies–including buck, boost, buckboost, interleaved, and flyback converters–are reviewed and compared based on efficiency, complexity, size, weight, and control requirements. The paper discusses the inherent trade-offs in selecting an optimal topology, emphasizing the importance of robust control strategies to maintain stable and efficient operation amid rapidly changing environmental conditions typical of UAV flight. This analysis aims to guide researchers and engineers in designing efficient and reliable power management systems tailored to the unique constraints and demands of solar UAV applications. Keywords: DC-DC converters, power electronics, maximum power point tracking, converter topologies, buck-boost converters, energy management systems. 1. INTRODUCTION Unmanned aerial vehicles (UAVs) have become increasingly prevalent in applications requiring extended operational endurance, including surveillance, environmental monitoring, and communication relay. A critical limitation in traditional UAV designs is the reliance on battery storage with limited energy density, which restricts flight duration and operational range. To overcome these constraints, solar energy harvesting has been integrated into UAV designs, leveraging lightweight photovoltaic (PV) panels mounted on wings and fuselage surfaces [1]. These PV systems continuously convert incident solar irradiance into electrical power, enabling sustained flight over extended periods. However, efficient integration of solar energy sources requires sophisticated power electronics to manage the varying voltage and current levels produced by the solar panels under fluctuating environmental conditions. Figure 1. Solar UAV energy system block diagram. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 5 Central to this energy management system is the DC-DC converter, which conditions the variable voltage and current outputs of PV arrays to match the voltage requirements of onboard batteries and propulsion systems. Due to the nonlinear and time-varying characteristics of PV cells, along with dynamic flight conditions, the DC-DC converter must maintain efficient power transfer, ensure system stability, and minimize losses. Recent studies also propose advanced converter architectures like multiport converters for hybrid energy systems in UAVs [2] and comprehensive reviews on converter topologies and control strategies in power systems [3]. These works underscore the importance of integrating converter design with system-level energy management. This paper presents a theoretical exploration of the key design considerations and control challenges associated with DC-DC converters in solar UAVs. Focusing on fundamental principles and topology selection, this work intends to aid designers in optimizing converter performance and reliability within the stringent constraints of UAV platforms. 2. DC-DC CONVERTER FUNDAMENTALS AND TOPOLOGIES DC-DC converters are switching-mode power supplies designed to efficiently convert one DC voltage level to another. The principle of operation is based on energy storage and transfer through inductive and capacitive elements regulated by semiconductor switches. 2.1 Basic Operating Principles. The switching converter alternates between states in which energy is stored in magnetic fields (inductors) or electric fields (capacitors), and states in which this energy is released to the load. The switch duty cycle-the ratio of on-time to total switching period-controls the average output voltage. Key theoretical concepts include: • Inductor Voltage-Second Balance: For steady-state operation, the volt‑seconds applied across the inductor in the on and off states must be equal to prevent inductor saturation. • Capacitor Charge Balance: Output capacitors smooth the output voltage by balancing charge flow to the load and input. • Continuous vs. Discontinuous Conduction Mode: Depending on load and switching frequency, converters operate either with continuous inductor current (CCM) or with current dropping to zero between switching intervals (DCM). These modes affect control design and efficiency [4]. 2.2 Topologies in Solar UAV Systems. Solar UAV systems impose stringent constraints on weight, efficiency, and size, guiding topology selection. Buck Converter Operation: The switch connects the inductor to the input during on-time, storing energy, and the inductor supplies energy to the load during off-time. Voltage relationship: Vout = D×Vin where D is duty cycle (0 < D < 1). Characteristics: High efficiency, simple design, suitable when Vin >Vout. Many designers adopt buck converters for aerial systems due to low complexity and reliable performance. Boost Converter Operation: The switch grounds the inductor during on-time, storing energy, which is transferred to the output during off-time via a diode [5]. Voltage relationship: Vout = with D typically less than 1. Characteristics: Increases voltage, but increased voltage stress on components and diode losses can reduce efficiency. Especially useful under low irradiance when panel voltage drops. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 6 Figure 2. Simple circuit diagrams of Buck Converter Figure 3. Simple circuit diagrams of Boost Converter Buck‑Boost Converter Operation: Allows output voltage to be above or below input voltage, inverting polarity in the traditional form; non-inverting variants exist. Voltage relationship: Vout = =×Vin (ideal) Characteristics: Versatile but more complex control and potentially lower efficiency due to higher switching losses. Figure 4. Simple circuit diagrams of Buck‑Boost Converter Interleaved Converters Operation: Multiple converter phases operate in parallel with phase‑shifted switching signals, dividing current and smoothing output. Advantages: Reduced input/output current ripple, improved thermal distribution, and higher overall power handling. Trade-offs: Increased component count and control complexity. Interleaved operation is often proposed in higher-power UAV systems or hybrid energy architectures [2]. Flyback Converter Operation: Utilizes transformer isolation and stores energy in a magnetic field during switch on-time, transferring energy to output during off-time. SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 7 Voltage relationship: Depends on transformer turns ratio, enabling voltage step-up or stepdown with isolation. Considerations: Heavier and bulkier due to transformer; less suitable for weightconstrained UAVs. A growing body of literature reviews non-isolated converter topologies and their control methods in renewable energy systems, which also apply to UAV contexts [6]. 3. DESIGN CONSIDERATIONS IN SOLAR UAV APPLICATIONS Designing DC-DC converters for solar UAVs requires optimization across multiple competing objectives. Efficiency Efficiency (η) is defined as: η = = Losses arise from conduction in switches and diodes, switching transitions, inductor core and copper losses, and capacitors’ ESR. Switching losses increase with higher switching frequency; soft-switching techniques (ZVS, ZCS) can mitigate them [6]. Conduction losses are reduced with low-R_(DS(on)). MOSFETs and synchronous rectification. A trade-off arises: higher switching frequencies reduce passive component sizes but increase switching losses, requiring careful balance. Size and Weight Minimal weight and compact form factor are critical. Inductors, capacitors, and circuit boards must be designed for minimal footprint. Cooling solutions (heatsinks, airflow) add weight; design must strike trade-offs. Voltage and Current Handling Converters must accommodate input voltage swings (for example, from ~10 V under low irradiance to ~40 V or more at peak). Components must have sufficient voltage ratings plus safety margins. Inductor and capacitor selection aims to limit current ripple and maintain stable output. Thermal Management Thermal modeling uses formulas such as: ) where is the junction temperature, ambient temperature, hermal resistance, and power loss. Preventing thermal runaway requires component derating, adequate heat sinking, and layout optimization. Reliability and Environmental Considerations UAVs are subject to vibration, humidity, temperature cycling, and possible shock. Components must be rugged. EMI must be minimized through layout, filtering, and shielding. Protection circuits (overcurrent, reverse polarity) safeguard against system faults. 4. CONTROL CHALLENGES OF DC-DC CONVERTERS IN SOLAR UAVS 4.1 Maximum Power Point Tracking (MPPT) MPPT algorithms dynamically adjust the converter duty cycle to extract maximum power from the PV panels. Common methods include: • Perturb & Observe (P&O) • Incremental Conductance • Fuzzy Logic / Neural Networks SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 8 Hybrid or adaptive fuzzy‑MRAC schemes have shown promising performance improvements in tracking accuracy and response under dynamic conditions [7, 8]. Also, metaheuristic-augmented fuzzy control (e.g., fuzzy-PSO) helps in faster adaptation and tuning [1]. 4.2 Dynamic and Nonlinear System Characteristics PV panels and converter systems are inherently nonlinear. The I–V characteristic is often modeled as: Controllers must manage these nonlinearities and uncertainties. Reviews of control methods in renewable systems emphasize hybrid and intelligent control to handle such complexities. 4.3 Fast Transient Response Flight maneuvers or rapid irradiance changes require control loops with sufficient bandwidth to respond without excessive overshoot or instability. Controller design must balance speed and stability. 4.4 Computational Constraints Onboard UAV controllers often have limited processing power, memory, and energy budget. Control algorithms must be efficient enough to run real-time on embedded hardware. 4.5 Stability and Robustness Stability must be ensured using techniques such as frequency-domain methods (Bode, Nyquist) or state-space control. Robust or adaptive control techniques (e.g., sliding mode, adaptive control) may help manage parameter variations and environmental disturbances [3, 9]. 5. COMPARISON OF DC-DC CONVERTER TOPOLOGIES FOR SOLAR UAV APPLICATIONS Table 1. Comparison of DC-DC converter topologies Topology Voltage Conversion Efficiency Complexity Size & Weight Control Difficulty Suitability Buck Step-down High (90– 98%) Low Small, Light Moderate When PV voltage > battery voltage Boost Step-up High (85– 95%) Low Small, Light Moderate When PV voltage < battery voltage BuckBoost Step-up & Step-down Moderate (80– 90%) Moderate Moderate Moderate to High Handles wide input voltage variations Interleaved Buck/ Boost Step-up or Step-down High (90– 95%) High Moderate to Large High High power; reduces ripple and improves thermal management SCIENCE AND INNOVATION INTERNATIONAL SCIENTIFIC JOURNAL VOLUME 4 ISSUE 11 NOVEMBER 2025 ISSN: 2181-3337 | SCIENTISTS.UZ 9 Flyback Isolated Moderate (75–85%) Moderate Larger, Heavier Moderate Isolation required; less common in UAVs Buck and boost converters are often preferred in UAV systems due to their efficiency and simplicity. Versatile architectures such as multiport or interleaved converters may offer enhanced flexibility, particularly when integrated with hybrid energy storage systems [3]. Nonisolated converter topologies and control techniques are reviewed more broadly in renewable energy literature [6]. 6. CONCLUSION The design and control of DC-DC converters for solar UAVs are multifaceted challenges combining power electronics, control theory, and aerospace constraints. Efficient and reliable converter operation directly impacts UAV endurance and mission capability. Selecting a converter topology involves trade-offs among efficiency, weight, size, complexity, and control demands. Buck and boost converters offer relative simplicity and high efficiency, while buck-boost and interleaved topologies support broader operating conditions and higher power, especially when integrated with hybrid systems. Control systems must handle nonlinear PV behavior, dynamic variability, and computational constraints to maximize power extraction and maintain system stability. Hybrid and intelligent control schemes, informed by renewable energy research, provide promising path forward. This theoretical analysis supplies a reference framework to guide future converter design and control in solar UAV energy systems. REFERENCES 1. P Oettershagen, A Melzer, T Mantel, K Rudin, R Lotz, D Siebenmann, S Leutenegger, K Alexis, R Siegwart. (2015). A Solar-Powered Hand-Launchable UAV for Low-Altitude Multi-Day Continuous Flight. ETH Zurich. 2. Ahmed M. Fares, Christian Klumpner, Mark Sumner. (2022). “A Novel Multiport DC‑DC Converter for Enhancing the Design and Performance of Battery–Supercapacitor Hybrid Energy Storage Systems for Unmanned Aerial Vehicles,” Applied Sciences, 12(6), 2767. 3. Mohammad Sarvi. 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