Foundations and Trends® in Electric Energy Systems > Vol 5 > Issue 2–4

LLC Resonant Converters: An Overview of Modeling, Control and Design Methods and Challenges

By Claudio Adragna, STMicroelectronics, Italy, claudio.adragna@st.com

 
Suggested Citation
Claudio Adragna (2022), "LLC Resonant Converters: An Overview of Modeling, Control and Design Methods and Challenges", Foundations and Trends® in Electric Energy Systems: Vol. 5: No. 2–4, pp 75-491. http://dx.doi.org/10.1561/3100000029

Publication Date: 10 Nov 2022
© 2022 C. Adragna
 
Subjects
Power Management Circuits,  Analog Circuits and Systems,  Control of Nonlinear Systems
 

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In this article:
1. Background
2. Historical Outline
3. Definition and Classification of Resonant Converters
4. Introduction
5. The Switching Mechanism
6. ZVS Conditions Analysis
7. Hard Switching in the LLC Resonant Converter
8. Design-Oriented ZVS Conditions
9. Magnetic Integration in the LLC Resonant Converter
10. Fundamental Steady-State Operating Modes
11. Abnormal Operating Conditions and Protection Functions
12. Start-Up of the LLC Resonant Converter
13. Modeling Approaches
14. FHA Approach: Input Impedance Analysis
15. FHA Approach: Voltage Gain M(fsw) Analysis
16. FHA Approach: Output Impedance Analysis
17. FHA Approach: Modeling Feedback Reversal at Light Load
18. FHA Approach: ZVS Conditions
19. FHA Approach: LLC Tank Design Considerations and Procedure
20. LLC Tank Design Improvements Based on a Simplified TDA
21. Power Stage Design
22. Introduction
23. Direct Frequency Control (DFC)
24. Time-Shift Control (TSC)
25. Charge-Mode Control (CMC)
26. Average Input Current Control (AICC)
27. Synchronous Rectification
28. Interleaving of LLC Resonant Converters
29. Topology Variants
30. Single-Stage LLC PFC
Acknowledgements
References

Abstract

The LLC resonant converter is perhaps today’s most popular resonant conversion topology. Yet, though in existence for many years, only relatively recently has it gained the popularity it certainly deserves. Since its first appearance in the literature in 1988, it has been confined for a long time to niche applications: high-voltage power supplies or high-end audio systems, to name a few.

Its significant industrial usage started in the mid-2000s with the boom of flat screen TVs, whose power supply requirements found in the LLC resonant converter their best answer, and was fueled by the introduction of new regulations, both voluntary and mandatory, concerning an efficient use of energy. This combination of events pushed power designers to find more and more efficient ac-dc conversion systems.

Since then, several other mass-produced electronic devices, such as All-In-One and small form factor PCs, high-power ac-dc adapters and LED drivers, have made a massive usage of this topology, especially in its half-bridge version. Higher power systems, such as server and telecom power supplies and, more recently, charging stations for electric vehicles, have mainly adopted the full-bridge version.

Over these last three decades, there has been a lot of progress on both theoretical and practical aspects related to the LLC resonant converter. Lots of papers and application notes deal with it, and many IC manufacturers have dedicated driver ICs in their portfolio. Despite that, its design is still considered a challenging task in Power Conversion. Thus, a guided tour through its intricacies may be beneficial to both the neophyte and the experienced engineer.

The monograph will cover the basics (operating modes, soft switching mechanism, first-harmonic approximation, etc.), as well as some advanced topics (design optimization, control methods, synchronous rectification, interleaving, etc.) using a hands-on, design-oriented approach.

DOI:10.1561/3100000029
ISBN: 978-1-63828-066-8
452 pp. $99.00
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ISBN: 978-1-63828-067-5
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Table of contents:
1. Background
2. Historical Outline
3. Definition and Classification of Resonant Converters
4. Introduction
5. The Switching Mechanism
6. ZVS Conditions Analysis
7. Hard Switching in the LLC Resonant Converter
8. Design-Oriented ZVS Conditions
9. Magnetic Integration in the LLC Resonant Converter
10. Fundamental Steady-State Operating Modes
11. Abnormal Operating Conditions and Protection Functions
12. Start-Up of the LLC Resonant Converter
13. Modeling Approaches
14. FHA Approach: Input Impedance Analysis
15. FHA Approach: Voltage Gain M(fsw) Analysis
16. FHA Approach: Output Impedance Analysis
17. FHA Approach: Modeling Feedback Reversal at Light Load
18. FHA Approach: ZVS Conditions
19. FHA Approach: LLC Tank Design Considerations and Procedure
20. LLC Tank Design Improvements Based on a Simplified TDA
21. Power Stage Design
22. Introduction
23. Direct Frequency Control (DFC)
24. Time-Shift Control (TSC)
25. Charge-Mode Control (CMC)
26. Average Input Current Control (AICC)
27. Synchronous Rectification
28. Interleaving of LLC Resonant Converters
29. Topology Variants
30. Single-Stage LLC PFC
Acknowledgements
References

LLC Resonant Converters: An Overview of Modeling, Control and Design Methods and Challenges

A resonant converter is a type of electric power converter that contains a network of inductors and capacitors called a "resonant tank", tuned to resonate at a specific frequency. They find applications in electronics and integrated circuits. The LLC resonant converter is perhaps today’s most popular resonant conversion topology. Though in existence for many years, only relatively recently has the LLC resonant converter gained in popularity. Since its first appearance in the literature in 1988, for a long time it was confined to niche applications such as high-voltage power supplies or high-end audio systems.

Its significant industrial usage started in mid 2000s with the boom of flat screen TVs, whose power supply requirements found in the LLC resonant converter their best answer, and was fueled by the introduction of new regulations, both voluntary and mandatory, concerning an efficient use of energy. This combination of events pushed power designers to find more and more efficient AC-DC conversion systems.

Since then, several other mass-produced electronic devices, such as All-In-One and small form factor PCs, high-power AC-DC adapters and LED drivers, have made a massive usage of this topology, especially in its half-bridge version. Higher power systems, such as server and telecom power supplies and, more recently, charging stations for electric vehicles, have adopted mainly the full-bridge version.

Much progress has been made on both the theoretical and practical aspects related to the LLC resonant converter. Numerous publications and application notes deal with it, and many IC manufacturers have dedicated driver ICs in their portfolio. Despite that, its design is still considered a challenging task in Power Conversion. Thus, a guided tour through its intricacies may be beneficial to both the neophyte and the experienced engineer, as well as students active in this field.

This monograph covers the basics (operating modes, soft switching mechanism, first-harmonic approximation, etc.) and advanced topics (design optimization, control methods, synchronous rectification, interleaving, etc.) of power conversion using the LLC resonant converter, using a hands-on, design-oriented approach.

 
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