Resonant Converter Dead-Time Control for Light-Load Voltage Regulation
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Solution Overview
Problem
Resonant converters face limitations in controlling output voltage, particularly at light or zero-load conditions, due to the inability to increase switching frequency infinitely, leading to excessive power delivery and undesirable voltage fluctuations, which existing methods like Burst Mode Control and phase-shift methods fail to address effectively.
Innovation Solution
Introducing a method that varies the normalized conduction time of power switches inversely with switching frequency and sets a large dead time, allowing the resonant converter to operate in Pulse Frequency Modulation mode, thereby controlling output voltage by adjusting the power level delivered to the secondary winding, even at low or zero power levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the switching frequency is increased to control output voltage at light load conditions, then the output voltage regulation is improved, but the switching losses increase and zero-voltage switching conditions are compromised
Solution Approach 1:
The patent applies dynamics by making the dead time variable rather than fixed. The dead time is dynamically adjusted based on the switching frequency and load conditions, allowing the system to adapt to different operating points. This dynamic adjustment enables the system to maintain zero-voltage switching conditions across a wide frequency range while achieving precise output voltage regulation at light loads.
Solution Approach 2:
The patent changes the parameter of dead time from a fixed value to a variable parameter that depends on switching frequency and resonant frequency. By expressing dead time as a function of these frequencies rather than a constant value, the system can optimize performance across different operating conditions, reducing switching losses while maintaining voltage regulation precision.
2Ease of operation
If a fixed dead time is used in resonant converters, then the circuit operation is simplified, but the output voltage cannot be properly regulated at light or zero-load conditions
Solution Approach 1:
The patent transitions from a static dead time approach to a dynamic one where dead time is continuously adjusted based on operating conditions. This dynamic behavior allows the circuit to maintain simplicity in implementation while achieving precise voltage regulation across all load conditions, including light and zero-load scenarios where fixed dead time fails.
Solution Approach 2:
The patent implements feedback by using the switching frequency and resonant frequency information to automatically adjust the dead time. This feedback mechanism ensures that the dead time is optimally set for current operating conditions without requiring complex external control, thereby maintaining ease of operation while improving voltage regulation precision.
3Measurement precision
If existing control methods like Burst Mode Control or phase-shift methods are used, then some voltage regulation is achieved, but they fail to effectively address voltage fluctuations and excessive power delivery at light loads
Solution Approach 1:
The patent changes the fundamental parameter of dead time from fixed to variable, which fundamentally alters the converter's behavior at light loads. This parameter change enables the system to deliver near-zero power when needed while maintaining stable output voltage, overcoming the limitations of burst mode and phase-shift methods that cannot adequately control voltage fluctuations at light loads.
Solution Approach 2:
The patent utilizes periodic action by operating in pulse frequency modulation mode where the switching frequency varies periodically to regulate output voltage. Combined with variable dead time, this periodic frequency adjustment allows precise control of power delivery at light loads while maintaining voltage stability, addressing the shortcomings of other periodic control methods.
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 enables precise control of output voltage, reduces switching losses, and maintains zero-voltage switching conditions, offering a simpler and more effective solution for resonant converters, especially in light-load applications.
Implementation Method 1
a resonant tank having a resonant frequency... a period of a mutual resonance of a resonant tank
Implementation Method 2
the parasitic capacitors of the switches may be discharged prior to turning on the switches, resulting in lossless switching and known as Zero-Voltage Switching (ZVS)
Implementation Method 3
a transformer positioned between the resonant tank and an output rectifier... a primary winding coupled to the resonant tank and a secondary winding coupled to the output rectifier
Data Source
AI summary
Methods and systems for controlling an output voltage of a resonant converter during a light load condition. One such method includes generating a normalised conduction time of the resonant converter that varies inversely with a switching frequency of the resonant converter by continuing to operate the resonant converter in a Pulse Frequency Modulation mode at a low switching frequency that is similar to the resonant frequency. The method also includes controlling a power level delivered to a secondary winding of a transformer positioned between a resonant tank and an output rectifier of the resonant converter by regulating the normalised conduction time, where the delivered power level is variable based on load conditions. The method further includes generating an output voltage using the output rectifier wherein the magnitude of the output voltage corresponds to the power level delivered to the secondary winding.