LLC DC/DC Converter Control for Bidirectional Power Flow
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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, which is crucial for 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 terminals of the resonant tank 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
1Loss of energy
If a center-tapped transformer with synchronous rectifiers is used in an LLC resonant converter, then rectification efficiency is improved and transformer utilization is enhanced, but control capability for bidirectional power flow is lost
Solution Approach 1:
The patent inverts the conventional control approach by using the body diode conduction detection (typically used for forward power flow triggering) to control reverse power flow. The control circuit detects when the body diode conducts during reverse power flow and uses this signal to trigger the synchronous rectifier switches, enabling bidirectional operation with the same center-tapped transformer topology that was previously limited to unidirectional control.
Solution Approach 2:
The patent makes the synchronous rectifier circuit universal by enabling it to operate in both forward and reverse power flow directions. The same center-tapped transformer and synchronous rectifier switches can handle power flow in either direction by adjusting the control circuit's detection and triggering logic, eliminating the need for separate control circuits for each direction.
2Ease of operation
If body diode conduction detection is used to trigger synchronous rectifiers, then control is straightforward for unidirectional power flow, but bidirectional power flow control becomes impossible
Solution Approach 1:
The patent employs self-service by using the body diode's natural conduction during reverse power flow as the trigger signal for the synchronous rectifier switches. The body diode automatically conducts when reverse power flow occurs, and this conduction event is detected by the control circuit to initiate switch operation, eliminating the need for complex external triggering mechanisms while maintaining ease of operation.
Solution Approach 2:
The control circuit implements feedback by continuously monitoring the body diode conduction status and using this information to control the synchronous rectifier switches. The detection circuit senses the voltage drop across the body diode during reverse power flow and feeds this signal back to the control logic, which then triggers the appropriate switches to maintain efficient synchronous rectification in both directions.
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 controlled power transfer, suitable for vehicles with high-voltage and low-voltage systems.
Implementation Method 1
LLC resonant 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
Implementation Method 2
The converter power flow may be controlled by modulating the square wave frequency with respect to the tank circuit's resonance. In an LLC resonant converter, semiconductor switches may be soft-switching, or zero-voltage switching (ZVS), at turn-on for the primary MOSFETs
Data Source
AI summary
A circuit comprises a primary port for providing a primary voltage and a secondary port for providing a secondary voltage. The circuit comprises a primary side comprising at least one rectifier circuit coupled to the primary port. The rectifier circuit comprises a first primary winding coupled to a first terminal of the primary port via a first switch and coupled to a second terminal of the primary port via a tap. The rectifier circuit comprises a second primary winding coupled to the first terminal of the primary port via a second switch and coupled to the second terminal of the primary port via the tap between the first and the second winding. The circuit comprises a secondary side comprising a bridge circuit of switches and a resonant tank circuit coupled to the secondary port via the bridge circuit.