Resonant Converter Characteristic Frequency Control
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Solution Overview
Problem
Resonant converters face limitations in regulating output voltage during startup and shutdown, leading to excessive current stress, hard switching, and inability to linearly ramp-up or ramp-down due to limited frequency control range, resulting in potential power stage failures and output voltage ripple/oscillation.
Innovation Solution
Operating the resonant converter at its characteristic frequency (CRF) for zero-voltage-switching (ZVS) across a wide load and output voltage range, with closed-loop control for output voltage regulation during ramp-up, ramp-down, and steady-state conditions, and using burst mode to inhibit drive pulses during overvoltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the resonant converter operates with limited frequency control range, then the converter can maintain stable operation during normal conditions, but the converter cannot regulate output voltage to zero or low voltages during startup, resulting in excessive current stress and hard switching
Solution Approach 1:
The patent implements dynamic frequency adjustment where the switching frequency varies based on the output voltage level. During startup, the frequency is allowed to extend beyond the normal limited range to enable soft switching at low voltages. As the converter reaches steady state, the frequency is constrained to the optimal range for efficient operation. This dynamic adaptation resolves the contradiction between stability and versatility.
Solution Approach 2:
The patent changes the operating parameters (switching frequency and duty cycle) based on the operating condition. A startup mode is introduced where frequency and duty cycle parameters are adjusted independently from normal operation modes, allowing the converter to achieve soft switching across the full voltage range including zero and low voltages, thereby expanding the regulation range without compromising normal operation stability.
2Ease of operation
If pulse gating control is used to disable control pulses during output voltage overshoot, then the output voltage can be controlled during ramp-up/down, but the power stage operates in hard-switching conditions causing potential failures
Solution Approach 1:
The patent employs feedback control that monitors the output voltage and dynamically adjusts the switching frequency and duty cycle accordingly. During startup and transient conditions, the feedback loop maintains soft switching by adjusting the frequency to compensate for voltage changes, eliminating the need for pulse gating control that would force hard switching. This resolves the contradiction by maintaining both control capability and power stage reliability through continuous adaptive feedback.
3Adaptability or versatility
If switching frequency is increased to regulate output voltage over wide voltage range, then the converter gain can be reduced to zero for linear ramp control, but the switching frequency becomes theoretically infinite which is impractical
Solution Approach 1:
The patent implements a dynamic control strategy where the switching frequency is adjusted based on the required output voltage level and load conditions. Rather than requiring infinite frequency, the system dynamically selects appropriate frequency and duty cycle combinations to achieve the desired gain. During startup, the frequency is optimized for soft switching while the duty cycle provides the necessary gain adjustment, making the theoretically impractical infinite frequency approach practical through coordinated dynamic parameter adjustment.
4Manufacturing precision
If PWM mode is used during startup with constant maximum frequency, then a substantially linear startup can be achieved, but the output voltage exhibits excessive ripple/oscillation due to non-monotonic transfer function
Solution Approach 1:
The patent changes the control parameters dynamically based on the operating phase. During startup, the system uses frequency modulation with adaptive duty cycle adjustment rather than constant frequency PWM. The duty cycle is specifically adjusted to compensate for the non-monotonic transfer function characteristics, ensuring both linear startup and stable output voltage without excessive ripple. This parameter adaptation resolves the contradiction between startup linearity and voltage stability.
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
Enables controlled output voltage regulation, reduces switch stress, avoids body diode conduction, and extends the converter's regulation range, ensuring reliable operation and reduced ripple/oscillation across various operating conditions.
Implementation Method 1
operating the converter at its characteristic frequency (CRF) for zero-voltage-switching (ZVS) across a wide load and output voltage range
Data Source
AI summary
A method is provided of operating a resonant converter, the converter having a controller and power stage and providing an output voltage, by determining a characteristic frequency of the power stage. The characteristic frequency is defined as a natural oscillation frequency of the power stage observed right after the power stage control signals from the controller are disabled. The converter is operated at the characteristic frequency during ramp-up or ramp-down of the converter output voltage and/or during overload or input overvoltage conditions.