Resonant Converter Time Modulation for Stable Light-Load Control
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Solution Overview
Problem
Conventional resonant converters, such as LLC converters, face limitations in providing high bandwidth due to the varying dynamics of the resonant tank, leading to instability and regulation failures under light load conditions.
Innovation Solution
The implementation of Time Modulation (modulating the period instead of frequency) associated with a variable frequency oscillator, such as a voltage-controlled oscillator, to optimize gain across different regulation points, thereby improving control loop stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resonant converters use standard linear PID/PFM control, then the control implementation is simple, but the closed-loop output impedance exhibits spikes at or near the switching frequency, resulting in limited bandwidth and potential instability
Solution Approach 1:
The patent changes the control parameter from linear frequency modulation to time modulation (modulating the period instead of frequency). This parameter transformation provides an inverse relationship between control and frequency, which flattens the closed-loop output impedance and eliminates spikes at switching frequency, thereby improving stability and bandwidth
Solution Approach 2:
The patent introduces dynamic control through time modulation that adapts the switching period based on error voltage, creating non-linear frequency gain that provides lower control loop gain below resonance and higher gain above resonance, optimizing stability across different operating conditions
2Reliability
If conventional resonant converters operate under light load conditions, then the varying dynamics of the resonant tank cause instability and regulation failures, but increasing control gain to improve stability may cause oscillations and fluctuating output voltages
Solution Approach 1:
The patent transforms the control approach by modulating time period instead of frequency, which provides an inverse relationship that naturally adjusts control gain across the operating range. This eliminates the need for artificial gain adjustment and prevents oscillations while maintaining stability under light load conditions
Solution Approach 2:
The patent implements preliminary stabilization by using time modulation to pre-adjust the control characteristics before instability occurs. The inverse relationship between control and frequency provides inherent damping that prevents the varying dynamics of the resonant tank from causing instability in the first place
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 provides non-linear frequency gain, allowing for lower control loop gain below resonance and higher gain above resonance, thereby enhancing the stability and efficiency of resonant power converter control.
Implementation Method 1
The conventional LLC converter is configured to reduce switching loss through zero-voltage switching (ZVS)
Implementation Method 2
The tank circuit filters out harmonics and provides a sinusoidal like voltage and current waveform
Data Source
AI summary
A power supply as discussed herein includes a controller. The controller receives an output voltage feedback signal outputted from a resonant power converter. The output voltage feedback signal tracks a magnitude of an output voltage outputted from the resonant power converter to power a load. An error voltage generator generates an error voltage signal based on a comparison of the output voltage feedback signal to a setpoint reference voltage. The output voltage feedback signal derives a control period setting from an error voltage. The controller controls switching of switches in the resonant power converter in accordance with the derived control period setting.