Three-Level Stacked LLC Converter PWM for Fixed-Frequency Gain Control
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Solution Overview
Problem
Existing LLC resonant converters face challenges in achieving fixed switching frequency operation over a wide input or output voltage range, leading to complex design, poor EMI performance, and limited controllable voltage gain due to variable switching frequency, which complicates the optimization of magnetic components and gate driver circuitry.
Innovation Solution
A stacked structure LLC resonant converter with a pulse width modulation (PWM) control scheme that generates a three-level LLC resonant input voltage, allowing for fixed switching frequency operation without modifying the conventional topology, simplifying the design and reducing costs, and ensuring stability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pulse frequency modulation (PFM) control strategy is adopted for wide input/output voltage range applications, then the voltage gain requirement is met, but the switching frequency range becomes wide causing complex design and poor EMI performance
Solution Approach 1:
The patent implements dynamic switching between two full-bridge circuits (primary and secondary) based on operating conditions. The primary full-bridge operates during light-load conditions while the secondary full-bridge operates during heavy-load conditions, enabling the converter to adapt to wide input/output voltage ranges while maintaining fixed switching frequency and reducing design complexity
Solution Approach 2:
The patent divides the single full-bridge circuit into two separate full-bridge circuits (primary and secondary). This segmentation allows independent optimization of each bridge for specific operating conditions, with the primary bridge handling light-load and the secondary bridge handling heavy-load, thereby resolving the contradiction between wide voltage range adaptability and design complexity
2Device complexity
If phase shift modulation (PSM) is used to achieve fixed frequency operation, then switching frequency is fixed, but the controllable output voltage range is restricted due to difficulty in satisfying zero-voltage switching
Solution Approach 1:
The patent dynamically switches between primary and secondary full-bridge circuits based on load conditions. The primary full-bridge uses phase-shift modulation for light-load conditions to maintain fixed frequency, while the secondary full-bridge uses pulse-width modulation for heavy-load conditions to expand voltage control range, thus resolving the contradiction between frequency stability and voltage range
Data Source
AI summary
The invention discloses a novel control scheme/strategy for the stacked structure LLC resonant converter. The control scheme includes a control signal as a gating signal of the fourth switch, and gating signals of the first, second and third switches that are operably generated according to the gating signal of the fourth switch. The gating signals of the second switch has a same duty ratio as and a phase shift of 180 degrees from the gating signal of the fourth switch. The gate signals of the first and third switches are complementary with the gate signals of the second and fourth switches, respectively. By adopting the control strategy, a three level LLC resonant network input voltage is generated, which includes Vin, Vin/2 and 0.