저궤도 위성용 전기추진 시스템의 고효율화를 위한 주파수 제어 기법 = High-Efficiency Frequency Control Scheme for Electric Propulsion Systems in Low Earth Orbit Satellites

다국어 초록 (Multilingual Abstract)

With the growing complexity of satellite missions, research on electric propulsion (EP) systems is becoming more important due to its high energy efficiency and longer operational lifespans. In addition, as satellite bus voltages rise from 50 V to 300-400 V to support high-power EP systems, the development of high-power and high-efficiency power systems has become essential. Among the various power processing units in EP systems, heater power converters play a crucial role in regulating temperature for propellant vaporization and plasma ignition processes. The half-bridge type topologies are generally being considered to handle the high input bus voltage of the heater power system. However, the half-bridge LLC converter has drawbacks related to performance degradation under large temperature fluctuations and reduced efficiency under wide input voltage variations in space environments, and the asymmetrical half-bridge (AHB) converter suffers from insufficient ZVS energy under light load conditions, resulting in low efficiency. Therefore, this paper proposes a frequency control scheme for the AHB converter to enhance efficiency under light load conditions in EP heater power applications. By decreasing the switching frequency under light load conditions, the proposed control scheme secures sufficient ZVS energy, resulting in high efficiency without requiring additional components or redesign of magnetic components. A prototype with the proposed control scheme is implemented to validate its effectiveness and feasibility under 250-400 V input and 12 V/20 A output specifications.

목차 (Table of Contents)

• List of Figuresⅲ
• List of Tables ⅳ
• 국 문 요 약ⅴ
• Ⅰ. Introduction 1
• 1.1 Research Background 1
• 1.2 Conventional Converter Limitations 6
• 1.3 Research Objectives 8
• Ⅱ. Analysis of Conventional Asymmetrical Half-Bridge Converter 9
• 2.1 Converter Structure and Operational Principle 9
• 2.2 Transformer DC Offset Current 11
• 2.3 Transformer Utilization Problem 12
• Ⅲ. Proposed Frequency Control Scheme 14
• 3.1 Concept of the Proposed Scheme 14
• 3.2 Load-Adaptive Frequency Design 17
• 3.3 Zero Voltage Switching Condition Analysis 19
• 3.4 Zero Voltage Switching Energy Comparison 21
• Ⅳ. Experimental Verification 23
• 4.1 LEO Satellite Power Profile 23
• 4.2 Experimental Setup 25
• 4.3 Waveform Analysis 28
• 4.4 Zero Voltage Switching Verification Analysis 32
• 4.5 Loss and Efficiency Analysis 36
• Ⅴ. Conclusion 39
• References 40
• ABSTRACT 45