LLC Converter Ripple Reduction via Dual PI and Quasi-Resonant Control
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Solution Overview
Problem
Conventional LLC converters experience a 120-Hz ripple in output voltage and have a narrow frequency bandwidth, which is not adequately addressed by existing control methods such as PI control, especially for AC reference voltages.
Innovation Solution
The implementation of a control method that combines proportional-integral (PI) control with quasi-resonant control, using different sampling periods for each, to reduce 120-Hz ripple and increase the frequency bandwidth, with a controller that senses output voltage and adjusts switching based on both PI and quasi-resonant control to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PI control is used to control the output voltage, then DC output voltage accuracy is improved, but 120-Hz ripple in output voltage is not adequately reduced
Solution Approach 1:
The control system is segmented into two independent controllers: a PI controller for DC output voltage regulation and a quasi-resonant controller for 120-Hz ripple reduction. Each controller operates with its own sampling period and control loop, allowing them to address different aspects of output voltage regulation without interfering with each other's performance.
Solution Approach 2:
The patent merges PI control and quasi-resonant control into a unified dual-controller system. The PI controller handles DC voltage regulation while the quasi-resonant controller specifically targets 120-Hz ripple, and their control signals are combined to drive the converter switches, achieving both DC accuracy and ripple reduction simultaneously.
2Device complexity
If a single sampling period is used for both DC and AC control, then device complexity is reduced, but control performance for both DC voltage and 120-Hz ripple deteriorates
Solution Approach 1:
The system employs dynamic sampling periods for different control functions. The PI controller uses a longer sampling period suitable for DC voltage regulation, while the quasi-resonant controller uses a shorter sampling period optimized for 120-Hz ripple detection and correction. This dynamic differentiation of sampling rates allows each controller to operate at its optimal performance point.
3Manufacturing precision
If PI control bandwidth is increased to reduce 120-Hz ripple, then ripple reduction improves, but steady-state error for DC reference voltage increases
Solution Approach 1:
The control bandwidth is segmented into two distinct ranges: the PI controller operates with a bandwidth optimized for DC voltage regulation ensuring zero steady-state error, while the quasi-resonant controller operates at a higher frequency specifically targeting 120-Hz ripple. This segmentation allows each controller to have its bandwidth optimized for its specific function without compromising the other.
Data Source
AI summary
An LLC converter includes a transformer that includes a primary winding and a secondary winding, a resonant stage that includes the primary winding, a switching stage that includes switches and that is connected to an input voltage and the resonant stage, a rectifying stage that is connected to the secondary winding and that provides an output voltage, and a controller that senses the output voltage and that controls switching of the switches based on proportional-integral control of the output voltage to reduce errors in the output voltage with respect to a DC voltage and based on quasi-resonant control of the output voltage to reduce errors in the output voltage with respect to a range of voltages with a frequency bandwidth.