Resonant LLC Converter Switching to Limit 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 converter with a control unit that controls primary and secondary side switches to regulate output voltage, featuring an overshoot control operation where secondary side switches are set to low or OFF during load transients to quickly reduce voltage spikes, and a transition operation to smoothly return to steady-state operation.
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 simple 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 simple control circuitry without requiring complex high-bandwidth control loops
2Productivity
If multiple PWM modules are used in interleaved LLC converters to improve power delivery, then the converter capacity is increased, but delay times in updating PWM outputs increase and synchronization becomes more difficult
Solution Approach 1:
The control unit synchronizes the operation of multiple PWM modules by merging their control signals through a centralized control mechanism. This ensures that all interleaved converter phases update their PWM outputs simultaneously, eliminating synchronization delays and maintaining precise timing coordination across multiple power delivery channels
3Speed
If the control loop bandwidth is increased to reduce voltage overshoots, then the response speed to load transients is improved, but the control system becomes more complex and difficult to synchronize
Solution Approach 1:
The control unit dynamically adjusts the duty cycle of primary side switches in real-time based on detected load transient conditions. This dynamic control approach achieves fast response speed to voltage overshoots without requiring a permanently high-bandwidth control loop, thereby maintaining simpler system architecture while improving transient response performance
Data Source
Figure 1
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Figure 3a~3c
AI summary
The invention concerns a converter (1), especially a resonant LLC converter, comprising a transformer (2) comprising a primary side (3) and a secondary side (4); a primary side circuit (5) comprising primary side switches (6) connected to the primary side (3) of the transformer (2); a secondary side circuit (7) comprising secondary side switches (8) connected to the secondary side (4) of the transformer (2); and a control unit (10) configured to control the primary side switches (6) and the secondary side switches (8); wherein the control unit (10) is configured to perform a steady-state operation in which a switching frequency of the primary side switches (6) and of the secondary side switches (8) is controlled to regulate output voltage (Vout) of the converter (2); and the control unit (10) is configured to perform an overshoot control operation in which an output voltage spike during a load transient is reduced by setting a control signal for the secondary side switches (8) to low or OFF. The invention also concerns a control method for driving a converter (1).