Synchronous Rectifier Commutation Current Steering for ZVS Power Converters
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Solution Overview
Problem
Soft switched power converters, particularly those using zero voltage switching (ZVS), face efficiency losses due to commutation current, which also reduces reliability and can cause output voltage dips, requiring complex control solutions and current sensing.
Innovation Solution
The method involves inducing a boosting resonance by controlling synchronous rectifier switches to turn off earlier than ZVS switches, sharing commutation current between primary and secondary switches, and maintaining constant dead time and phase shift, reducing reactive energy circulation and power losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If commutation current is minimized to reduce power losses, then efficiency is improved, but ZVS reliability deteriorates
Solution Approach 1:
The synchronous rectifier switches are turned off in advance (before the corresponding ZVS switches turn off) to proactively shape the commutation current waveform. This preliminary action ensures that the commutation current maintains sufficient amplitude for reliable ZVS while reducing the overall circulating reactive energy, thus resolving the contradiction between efficiency and reliability.
Solution Approach 2:
The control method dynamically adjusts the turn-off timing of synchronous rectifier switches relative to ZVS switches, creating a variable phase shift that adapts to different operating conditions. This dynamic control optimizes commutation current characteristics across varying loads and input voltages, maintaining both efficiency and ZVS reliability.
2Reliability
If variable dead time and variable phase shift are implemented to ensure ZVS reliability, then ZVS reliability is improved, but device complexity increases
Solution Approach 1:
The invention changes the control parameter from variable dead time to constant dead time with variable phase shift of synchronous rectifier switches. This parameter transformation simplifies the control logic while maintaining ZVS reliability, as the phase shift can be implemented through fixed timing relationships rather than continuous adjustment of dead time intervals.
3Loss of energy
If synchronous rectifier switches are enabled/disabled based on load current to improve efficiency, then efficiency is improved, but output voltage stability deteriorates
Solution Approach 1:
The synchronous rectifier switches operate continuously across the entire output current range rather than being enabled/disabled based on load conditions. This continuous operation eliminates output voltage dips that would occur during switching transitions, maintaining stable output voltage while still achieving efficiency improvements through optimized commutation current control.
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
This approach enhances ZVS reliability and efficiency by minimizing commutation current, reducing power losses, and maintaining stable output voltage across varying load and input conditions.
Implementation Method 1
A boosting resonance is induced by controlling each of the synchronous rectifier switches to turn off at a time prior to a turn-off time for a corresponding one of the switches operating under ZVS conditions. The boosting resonance derives a commutation current boosting effect
Data Source
AI summary
A commutation current steering method is provided for a power converter having an isolation transformer, a plurality of primary ZVS switches, a plurality of secondary switches for synchronous rectification, and a boosting resonant circuit. A commutation current is shared between all of the switches, and a resonance is induced in the boosting resonant circuit by controlling each of the synchronous rectifier switches to turn off at a time prior to a turn-off time for a corresponding one of the switches operating under ZVS conditions, wherein the primary current is boosted above a minimum commutation value during ZVS periods. The ZVS switches are further driven with a constant dead time, and the synchronous rectifier switches are driven to provide a fixed time relation with respect to all of the switches.