Bidirectional Resonant DC Converter Timing for Reverse Current Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing bidirectional direct-current converters face issues of low-frequency oscillation and high conduction loss due to the use of silicon MOSFETs with poor reverse recovery characteristics and increased reverse current duration in synchronous rectification, especially with SiC and GaN devices, leading to efficiency decreases.
Innovation Solution
A control method and circuit for bidirectional resonant direct-current converters that determine a zero-crossing point of the secondary resonant current and implement a preset delay duration before turning off switching transistors, followed by a dead time before turning on complementary transistors, reducing reverse current duration and avoiding low-frequency oscillation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If anti-parallel diodes are used in switching transistors, then reverse current protection is provided, but low-frequency oscillation occurs due to poor reverse recovery characteristics
Solution Approach 1:
The patent extracts the reverse current protection function from the anti-parallel diode by using the controlled turn-off timing of the switching transistor itself. By turning off the transistor at the zero-crossing point with preset delay, the patent eliminates the need for anti-parallel diode reverse recovery, thereby removing the source of low-frequency oscillation while maintaining protection functionality
Solution Approach 2:
The patent introduces a control circuit with zero-crossing detection and preset delay timing as an intermediary between the resonant current and the switching transistor gate drive. This intermediary control mechanism precisely times the transistor turn-off to coincide with current zero-crossing, avoiding the oscillation problems associated with diode reverse recovery while maintaining reliable reverse current protection
2Reliability
If dead time is extended to prevent shoot-through, then switching safety is improved, but reverse current duration increases and conduction loss increases
Solution Approach 1:
The patent changes the timing parameter from a fixed extended dead time to a dynamic timing based on zero-crossing detection plus preset delay. This parameter change allows the transistor to remain on longer (reducing dead time) while still preventing shoot-through, because the turn-off is precisely synchronized with the current zero-crossing point, thereby reducing reverse current duration and conduction loss
Data Source
AI summary
A control method and a control circuit for a bidirectional resonant direct-current converter are provided. The control method includes determining a zero-crossing point of a secondary resonant current of the bidirectional resonant direct-current converter, determining, for a switching transistor to be turned off in the secondary circuit within each half cycle of the secondary resonant current, a turn-off start time instant of the switching transistor as an end time instant of a preset delay duration starting from the zero-crossing point; and determining, for a switching transistor to be turned on in the secondary circuit within each half cycle of the secondary resonant current, a turn-on start time instant of the switching transistor as an end time instant of a dead time starting from the turn-off start time instant of the switching transistor complementary to the switching transistor to be turned on.