Resonant Converter Control Device for Hard Switching Prevention
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Solution Overview
Problem
Resonant converters face hard switching issues during start-up, leading to potential transistor destruction due to rapid voltage changes and shoot-through conditions, which existing solutions attempt to mitigate through additional mechanisms like synchronizing the oscillator with current zero crossing.
Innovation Solution
A control device for a resonant apparatus that detects the sign of current flowing through the resonant load and extends the operation time period of transistors using a correction circuit, preventing hard switching without requiring additional mechanisms specific to the start-up step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the high-side transistor is switched on during start-up when the low-side transistor's body diode is still conducting, then the converter can initiate operation, but hard switching conditions occur causing rapid voltage changes and potential transistor destruction
Solution Approach 1:
The control device extends the dead time period before switching on the high-side transistor during start-up, ensuring the low-side body diode has fully recovered before applying voltage to the primary winding. This preliminary action prevents hard switching conditions and potential transistor destruction while maintaining start-up capability.
Solution Approach 2:
The control device dynamically adjusts the dead time period based on operating conditions. During start-up, the dead time is extended beyond the normal value to accommodate the body diode recovery time, while under normal operation the dead time returns to its standard value. This dynamic adjustment resolves the contradiction between start-up reliability and normal operation efficiency.
2Reliability
If the dead time period is extended to prevent hard switching during start-up, then transistor reliability improves, but switching frequency and conversion efficiency may deteriorate
Solution Approach 1:
The control device implements dynamic dead time adjustment where the dead time period is extended only during the critical start-up phase when body diode recovery is needed, and returns to normal values during steady-state operation. This dynamic approach maintains transistor reliability while minimizing impact on switching frequency and conversion efficiency.
Solution Approach 2:
The control device applies extended dead time periodically only during start-up sequences rather than continuously. This periodic application of extended dead time ensures transistor protection during vulnerable start-up conditions while maintaining optimal switching performance during normal operation, thus resolving the productivity-reliability contradiction.
3Reliability
If additional mechanisms like oscillator synchronization with current zero crossing are added to prevent hard switching, then transistor reliability improves, but device complexity increases
Solution Approach 1:
The control device extracts and eliminates the need for complex additional mechanisms like oscillator synchronization by implementing a simplified approach: extending the dead time period during start-up. This extraction of the essential protective function from complex mechanisms reduces device complexity while maintaining transistor reliability.
Solution Approach 2:
The control device uses its existing dead time generation capability to provide the protective function during start-up, rather than requiring separate dedicated protection circuits. The existing control logic self-adjusts the dead time period to prevent hard switching, eliminating the need for additional protection mechanisms and reducing overall device complexity.
Data Source
AI summary
A control device of a switching circuit of a resonant apparatus is described. The switching circuit comprises at least one half-bridge having a high-side transistor and a low-side transistor connected between an input voltage and a reference voltage; the resonant apparatus comprises a resonant load. The control device is configured to determine the on time period and the off time period of the transistors alternatively and a dead time of both the transistors so that a periodic square-wave voltage is applied to the resonant load. The control device comprises a detector adapted to detect the current sign flowing through the resonant load and a correction circuit configured to extend the current operating time period of said two transistors in response to at least the current sign detected from the detection means.