Resonant Converter Control Circuit Hard Commutation Prevention
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Solution Overview
Problem
Resonant converters experience high losses and potential damage due to hard commutation, particularly when MOSFETs with integrated body diodes are used, as it leads to degradation or damage of the MOSFETs and causes high current or voltage changes.
Innovation Solution
A method and control circuit that alternately operate the switching circuit in on-states and high-impedance states, monitoring a hard commutation parameter to prevent hard commutation by maintaining the high-impedance state until the parameter meets specific conditions, thereby avoiding cross-currents and reducing stress on the switches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching circuit is operated with alternating on-states and high-impedance states without monitoring, then the converter structure is simple, but hard commutation occurs causing high losses and potential damage to MOSFETs
Solution Approach 1:
The control circuit monitors a hard commutation parameter (such as current or voltage) and uses this feedback to dynamically adjust the switching circuit operation. When the parameter indicates imminent hard commutation, the control circuit extends the high-impedance state duration to prevent it, thereby reducing losses while maintaining controlled complexity through intelligent feedback-based decision making
Solution Approach 2:
The control circuit performs preliminary monitoring of the hard commutation parameter before hard commutation actually occurs. By detecting the parameter in advance and proactively extending the high-impedance state, the system prevents hard commutation before it happens, reducing losses without requiring complex real-time intervention circuits
2Reliability
If the switching circuit operates without extended high-impedance state monitoring, then the switching frequency is high improving productivity, but hard commutation causes damage to switching components
Solution Approach 1:
The control circuit dynamically adjusts the high-impedance state duration based on real-time monitoring of the hard commutation parameter. Instead of using fixed timing, the system adapts the switching waveform dynamically to prevent hard commutation while maintaining high switching frequency operation, thereby protecting MOSFETs without sacrificing productivity
Solution Approach 2:
The system changes the timing parameter (high-impedance state duration) based on the monitored hard commutation parameter. When the parameter indicates risk of hard commutation, the high-impedance state is extended, effectively protecting MOSFETs while allowing the switching frequency to remain high for maintaining productivity
3Reliability
If the high-impedance state is extended based on parameter monitoring, then hard commutation is minimized improving reliability, but the control logic becomes more complex
Solution Approach 1:
The control logic uses feedback from the hard commutation parameter to determine when to extend the high-impedance state. This feedback mechanism achieves reliable hard commutation prevention through a relatively simple decision rule: monitor the parameter, and if it indicates imminent hard commutation, extend the high-impedance state. The feedback-based approach keeps control logic complexity manageable while achieving high reliability
Data Source
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AI summary
A method and a control circuit are disclosed. The method includes: in a resonant converter comprising a switching circuit (2) coupled to an input (11, 12), and comprising a resonant circuit (3) coupled to the switching circuit (2), alternatingly operating the switching circuit (2) in an on-state and a high-impedance state; monitoring a hard commutation parameter; if the hard commutation parameter, at an end of at least one of the on-states, meets a certain condition, operating the switching circuit (2) in the high-impedance state for a predefined duration (Td1, Td2); and if the hard commutation parameter, at the end of the least one of the on-states, does not meets the certain condition, operating the switching circuit (2) in the high-impedance state at least until the hard commutation parameter meets the certain condition.