Resonant Converter Startup Sequence for Soft Switching
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Solution Overview
Problem
Conventional resonant converters experience hard switching during startup, leading to high current events that can damage switching devices and require larger components, especially in applications with frequent startup events.
Innovation Solution
A semiconductor device with a dedicated startup sequence control circuit that initially pulses the lower switch and then the upper switch, iteratively adjusting the upper switch on-time based on measured dead time to avoid hard switching, allowing for soft switching and reducing component size requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resonant converters use symmetric switching at startup, then the converter can start up, but hard switching occurs causing high current events that can damage switching devices and require larger components
Solution Approach 1:
The patent applies preliminary action by implementing a dedicated startup sequence that performs preparatory steps before normal symmetric switching begins. The startup sequence includes: (1) initializing the resonant capacitor voltage to zero, (2) gradually ramping up the switching frequency from a low value to the resonant frequency, and (3) progressively increasing the duty cycle. This preliminary preparation ensures that when normal operation begins, the converter is already in a soft-switching state, avoiding hard switching events and protecting switching devices from damage.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting key operating parameters during startup. Specifically, the switching frequency is ramped from a low initial value up to the resonant frequency, and the duty cycle is progressively increased from a small initial value. These parameter transitions are controlled to ensure that the converter operates in a soft-switching region throughout startup, eliminating hard switching conditions while maintaining reliable operation.
2Reliability
If robust switching components are used to handle hard switching events, then device reliability improves, but component size increases
Solution Approach 1:
By implementing preliminary startup preparation that establishes soft-switching conditions before normal operation, the patent eliminates the need for oversized robust components. The startup sequence pre-charges the resonant capacitor and ramps frequency and duty cycle, ensuring that switching devices only encounter gentle switching conditions, thereby allowing the use of smaller, more efficient components.
Solution Approach 2:
The patent uses parameter changes during startup (frequency ramping and duty cycle progression) to keep switching devices operating in their linear region during transitions, avoiding the high-stress conditions that would require robust, large-sized components. This enables the use of smaller switching devices that are optimized for efficiency rather than ruggedness.
3Adaptability or versatility
If frequent startup events occur, then the converter can adapt to varying load conditions, but the cumulative effect of hard switching events increases component stress and reduces reliability
Solution Approach 1:
The dedicated startup sequence performs preliminary preparation each time the converter starts, including resonant capacitor initialization and gradual frequency/duty cycle ramping. This consistent preliminary action ensures that regardless of how frequent the startup events are, each startup begins in a controlled soft-switching state, preventing cumulative stress on components and maintaining high reliability even with frequent adaptations to load conditions.
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
The solution effectively avoids hard switching during startup, enabling smaller switch transistors and reducing the risk of damage, while ensuring a stable symmetric switching state is reached sooner, thus improving the reliability and efficiency of resonant converters.
Implementation Method 1
LLC resonant converters utilize the resonance between two inductors and a capacitor to provide natural soft switching
Data Source
AI summary
A method and semiconductor device for a resonant power converter includes logic circuitry that performs a dedicated startup sequence when power is first provided to the resonant converter. The logic circuitry can discharge the resonant capacitor, then iteratively pulse only an upper switch during a portion of the startup sequence, and measures the dead time between the half bridge signal starting to fall and the next time it finishes rising. If the dead time is greater that a startup exit value, which is based on the most recent upper switch on-time, then the upper switch on-time is incremented and the process is repeated until the dead time is less than the startup exit value, whereupon the startup logic transitions to conventional symmetric switching.