Bidirectional LLC DC/DC Converter With Resonant Tank Short-Circuit Control
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Solution Overview
Problem
Existing LLC resonant converters struggle with controlling bidirectional power flow, particularly from low-voltage to high-voltage systems, as conventional control concepts are not suitable for reverse power flow applications like DC/DC converters in vehicles.
Innovation Solution
A DC/DC converter circuit with a primary side rectifier circuit and a secondary side resonant tank circuit, controlled by a circuit that periodically short-circuits the resonant tank terminals for adjustable times, allowing power transfer from the primary to the secondary side, and uses phase shifts and zero-current detection for efficient switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional control concepts are used for forward power flow, then unidirectional power transfer is achieved, but bidirectional power flow capability is lost
Solution Approach 1:
The control circuit is designed to perform multiple functions: it can detect body diode conduction for forward power flow control and simultaneously detect current direction and magnitude for reverse power flow control. The same bridge circuit switches are used for both power transfer directions, making the system universal and adaptable to bidirectional operation without requiring separate control circuits for each direction.
2Ease of operation
If body diode conduction detection is used for rectifier control, then forward power flow control is straightforward, but reverse power flow control becomes impossible
Solution Approach 1:
The control method dynamically adapts based on the operating condition. In forward power flow, the control relies on body diode conduction detection which is simple and straightforward. In reverse power flow, the control dynamically switches to using current direction and magnitude detection. This dynamic adaptation allows the system to maintain ease of operation in each specific mode while achieving versatility across both power flow directions.
3Productivity
If high switching frequencies are used with GaN HEMTs, then power density and efficiency are improved, but soft-switching requirements become more stringent
Solution Approach 1:
The control circuit incorporates feedback mechanisms that monitor the actual switching conditions and adjust the gating signals accordingly. By detecting the resonant tank current and voltage conditions, the control system ensures that switches are turned on and off at the optimal moments to maintain zero-voltage switching even at high frequencies. This feedback-based control adapts to varying load and line conditions, ensuring reliable soft-switching operation across the full operating range.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient bidirectional power flow with reduced losses and increased efficiency by ensuring zero-voltage switching and controlling the power transfer through adjustable short-circuiting and phase shifts, suitable for vehicles with high-voltage and low-voltage systems.
Implementation Method 1
An LLC resonant converter is a type of DC/DC converter that uses a resonant tank circuit with an inductor-capacitor-inductor (LLC) configuration to convert a DC input voltage to a DC output voltage at a different level
Implementation Method 2
This in turn may feed a transformer that provides voltage scaling and primary-secondary isolation
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
It is proposed a circuit (100), comprising a primary port (112) for providing a primary voltage and a secondary port (122) for providing a secondary voltage. The circuit (100) comprises a primary side (110) comprising at least one rectifier circuit (114-a) coupled to the primary port (112). The rectifier circuit (114-a) comprises a first primary winding (116-a,1) coupled to a first terminal of the primary port (112) via a first switch (S6a) and coupled to a second terminal of the primary port (112) via a tap (118-a). The rectifier circuit (114-a) comprises a second primary winding (116-a,2) coupled to the first terminal of the primary port (112) via a second switch (S5a) and coupled to the second terminal of the primary port (112) via the tap (118-a) between the first and the second winding. The circuit (100) comprises a secondary side (120) comprising a bridge circuit (124) of switches and a resonant tank circuit (126) coupled to the secondary port (122) via the bridge circuit (124). The resonant tank circuit (126) comprising a series connection of a capacitor and at least one secondary winding (128-a), wherein the primary windings (116-a,1; 116-a.2) and the secondary winding (128-a) form a transformer. The circuit (100) further comprises a control circuit (130) configured to control switches of the primary side (110) and the secondary side (120). The control circuit (130) is configured to control the switches (S2; S4) of the bridge circuit (124) to cause a first and a second terminal (A, B) of the resonant tank circuit (126) being shortcircuited for a time.