LLC Converter Envelope Control for Ripple Suppression and Bandwidth
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Solution Overview
Problem
Existing LLC converter control methods face challenges in improving system control bandwidth, dynamic performance, suppressing input low-frequency ripple, and current sharing performance, particularly in multi-phase operations.
Innovation Solution
A control circuit for LLC power converters employs a sampler to sample the output voltage, a feedback signal mixer to mix it with a reference voltage, and an envelope controller to generate a clock signal based on a sensed current, which drives power switches to stabilize output voltage and improve control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct frequency control (DFC) is used, then the control circuit is simple to implement, but the system control bandwidth cannot be improved and dynamic performance is poor
Solution Approach 1:
The control method is segmented into two independent parts: voltage feedback for frequency control and current feedback for envelope control. This segmentation allows each control loop to operate independently, improving overall control bandwidth without increasing circuit complexity significantly.
Solution Approach 2:
An envelope detector is introduced as an intermediary component to extract the envelope signal from the resonant current. This intermediary enables the system to achieve improved dynamic performance by providing separate current feedback control without requiring direct complex control circuitry.
2Reliability
If current mode control (CCM) is used, then additional control capability is provided, but additional hardware is required and circuit complexity increases
Solution Approach 1:
The resonant current itself serves as the feedback signal through the envelope detector, eliminating the need for separate current sensing hardware. The system uses its own internal signals for control, reducing additional hardware requirements while maintaining improved control performance.
Solution Approach 2:
The envelope detector serves multiple functions: it extracts the envelope signal for current feedback control, generates timing signals for the controller, and provides overcurrent protection. This multi-functionality reduces the need for separate dedicated components, thereby reducing overall circuit complexity.
3Reliability
If conventional control is used, then the converter operates normally, but input low-frequency ripple cannot be suppressed and current sharing performance in multi-phase operation is poor
Solution Approach 1:
Current feedback through the envelope detector provides real-time information about resonant current variations. This feedback mechanism enables the controller to actively suppress input low-frequency ripple by adjusting switching frequency in response to current variations, improving operational stability while eliminating harmful ripple effects.
Data Source
AI summary
A control circuit for a power converter includes a plurality of power switches, a resonant network coupled with the plurality of power switches, and an output circuit coupled with the resonant network. The control circuit comprises a sampler configured to sample an output voltage provided by the output circuit to generate a sampled output voltage and a feedback signal mixer configured to mix the sampled output voltage with a reference voltage to generate a mixed feedback signal. An envelope controller is configured to generate an envelope signal based on a sensed current flowing through the resonant network and generate a clock signal based on the mixed feedback signal and the envelope signal. A drive module is configured to generate a plurality of drive signals based on the clock signal and control the plurality of power switches based on the plurality of drive signals.