Steady State Analysis & Small Signal Modeling of Variable Duty Cycle Controlled Three Level LLC Converter = 듀티 제어가 적용된 3레벨 LLC 컨버터의 정상상태 및 소신호 해석

다국어 초록 (Multilingual Abstract)

Recently, in order to reduce fuel consumption and greenhouse gas emissions, research and analysis regarding Electrical Vehicle (EV) Charger are increasing rapidly. Among the dc-dc converter topologies, which is an essential element architecture of an EV charger, LLC converter is among the prevalent choices. The output regulation of the converters is one of the key research areas of LLC converter. This thesis presents a three level variable duty cycle controlled half-bridge LLC converter for EV charger application. The topology and operating regions of the converter are briefly discussed. The state space equations are derived for different operation modes. The steady state analysis of the LLC series resonant converter are conducted in both time and frequency domain. The waveforms and DC gain characteristics are observed through simulation results. A small signal model of the proposed converter is developed by perturbation and linearization of the steady state model about their operating point based on Extended Describing Function. Based on the small-signal model, a duty to output voltage transfer function is derived. A control strategy is proposed and designed for the duty controlled converter. Both analog and digital controllers are designed and the simulation results are compared for reference voltage variation and load resistance variation. Lastly, the findings of this research is discussed.

목차 (Table of Contents)

• 1. Introduction 1
• 1.1. EV Charger 1
• 1.2. DC gain Characteristics 2
• 1.3. 3-Level Half Bridge Converter. 5
• 1.3.1. 3-level LLC Converter with variable frequency 6
• 1. 4. 3-level LLC Converter with variable duty control 11
• 2. Steady State Analysis 12
• 2.1. State-space Equations in Time domain for duty control 12
• 2.2. Steady state analysis 15
• 2.2.1. Mode 1 15
• 2.2.2. Mode 2 16
• 2.2.3. Mode 3 17
• 2.2.4. Power Transfer 19
• 2.3. Frequency Domain Analysis 21
• 2.4. Simulation Verification 23
• 2.5. DC gain Characteristics of duty controlled LLC Converter 26
• 3. Small Signal Modeling 29
• 3.1. Modeling with Extended Describing Function 29
• 3.1.1. Nonlinear State Equations 29
• 3.1.2. Harmonic Approximation 30
• 3.1.3. Extended Describing Function. 31
• 3.1.4. Harmonic Balance 31
• 3.2. Equivalent Circuit Modeling 33
• 4. Controller Design 40
• 4.1. Compensator Design. 40
• 4.2 Simulation Result 42
• 5. Conclusion. 50
• 6. References 51
• Appendix A 55
• Acknowledgement 57