Resonant LLC Converter Control for Load-Transient Overshoot
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Solution Overview
Problem
Existing converter control methods suffer from limited control loop bandwidth, leading to output voltage overshoots during dynamic load transients, and synchronization becomes difficult due to significant delay times in updating PWM outputs, especially in interleaved LLC converters.
Innovation Solution
A resonant LLC converter with a control unit that controls primary and secondary side switches, quickly reacting to load transients by setting secondary side switches to 'low' or 'OFF' during overshoot control operations, reducing output voltage spikes and preventing component damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional control methods with limited control loop bandwidth are used, then the converter can operate with simpler control circuitry, but output voltage overshoots occur during dynamic load transients
Solution Approach 1:
The control unit detects load transient conditions in advance and preemptively adjusts the duty cycle of primary side switches before the voltage overshoot fully develops. This preliminary action prevents the overshoot from reaching damaging levels while maintaining simpler control circuitry architecture.
Solution Approach 2:
The control unit continuously monitors output voltage and uses feedback signals to dynamically adjust switching parameters. When voltage overshoot is detected, the feedback mechanism triggers immediate duty cycle reduction, enabling effective overshoot control without requiring complex predictive algorithms.
2Power
If multiple PWM modules are used in interleaved LLC converters to increase power capacity, then the converter can handle higher loads, but delay times in updating PWM outputs increase and synchronization becomes more difficult
Solution Approach 1:
The control unit synchronizes all PWM modules by merging their control signals through a centralized coordination mechanism. This ensures that all interleaved phases update their PWM outputs simultaneously, eliminating synchronization delays and maintaining precise timing across multiple power stages.
Solution Approach 2:
The control system dynamically adjusts the switching phases and duty cycles of individual PWM modules based on real-time load conditions. This dynamic coordination allows the interleaved converter to maintain optimal performance across varying power levels while minimizing update delays through adaptive timing adjustment.
3Speed
If the control loop bandwidth is increased to reduce voltage overshoots, then the converter responds faster to load transients, but the system becomes more sensitive to noise and requires more complex compensation
Solution Approach 1:
The control unit detects load transient conditions in advance and preemptively adjusts the duty cycle of primary side switches before the voltage overshoot fully develops. This preliminary action prevents the overshoot from reaching damaging levels while maintaining simpler control circuitry architecture.
Data Source
AI summary
The disclosure concerns a resonant LLC converter, comprising a transformer comprising a primary side and a secondary side; a primary side circuit comprising primary side switches connected to the primary side of the transformer; a secondary side circuit comprising secondary side switches connected to the secondary side of the transformer; and a control unit configured to control the primary side switches and the secondary side switches; wherein the control unit is configured to perform a steady-state operation where switching frequencies of the primary side switches and of the secondary side switches are controlled to regulate an output voltage of the converter; and the control unit is configured to perform an overshoot control operation where an output voltage spike during a load transient is reduced by setting a control signal for the secondary side switches to low or OFF. The invention also concerns a control method for driving the above-mentioned converter.