LLC Resonant Converter Dual Mode Control
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Solution Overview
Problem
LLC resonant converters experience unstable output voltage and reduced conversion efficiency due to distortion in the DC gain curve caused by parasitic capacitance when the load is light, leading to inefficiencies in power conversion.
Innovation Solution
A power conversion circuit that includes a switching circuit, a resonant circuit, a transformer, and a controller, where the controller selectively outputs either a frequency modulation signal or a pulse width modulation signal as a second control signal based on the working frequency to control the switching circuit, adjusting the switching frequency or duty cycle to stabilize the output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If frequency modulation is used to control the LLC resonant converter, then the output voltage stability is improved at light load, but the device complexity increases due to the need for dual control modes
Solution Approach 1:
The control circuit dynamically switches between frequency modulation mode and pulse width modulation mode based on the working frequency of the LLC resonant converter. When the working frequency is below the resonant frequency, frequency modulation is applied; when it exceeds the resonant frequency, pulse width modulation is applied. This dynamic adaptation resolves the contradiction by selecting the appropriate control mode for different operating conditions, improving output voltage stability without permanently increasing device complexity.
2Loss of energy
If the switching frequency is increased to improve conversion efficiency, then the conversion efficiency is improved, but the distortion caused by parasitic capacitance increases
Solution Approach 1:
The invention changes the control parameter from fixed frequency operation to variable frequency operation with dual modes. By monitoring the working frequency and switching between frequency modulation and pulse width modulation based on whether the working frequency is below or above the resonant frequency, the system optimizes the switching frequency to improve conversion efficiency while compensating for parasitic capacitance distortion effects.
Solution Approach 2:
The control circuit uses feedback from the working frequency detection to automatically select the appropriate control mode. The feedback mechanism compares the working frequency with the resonant frequency and adjusts the control strategy accordingly, enabling the system to maintain high conversion efficiency while minimizing the harmful effects of parasitic capacitance distortion.
3Speed
If pulse width modulation is used for control, then the response speed is improved, but the output voltage stability deteriorates at light load due to DC gain curve distortion
Solution Approach 1:
The system dynamically selects between frequency modulation and pulse width modulation based on the working frequency relative to the resonant frequency. At light load conditions where the working frequency is below resonance, frequency modulation is used to maintain stability. When the working frequency exceeds resonance, pulse width modulation is applied to provide faster response. This dynamic selection resolves the contradiction between response speed and output voltage stability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution improves the stability of the output voltage and enhances conversion efficiency by dynamically adjusting the control signal mode based on the load conditions, reducing distortion and overshoot, and shortening the settling time of the LLC resonant converter circuit.
Implementation Method 1
LLC resonant converters are widely applied in various applications since LLC resonant converters are suitable for a wide range of input voltages and high power outputs
Implementation Method 2
When the load is light, the DC gain curve at a high frequency is distorted resulting from the influence of parasitic capacitance in the LLC resonant converter circuit
Data Source
AI summary
A power conversion circuit includes a switching circuit, a resonant circuit, a rectifying circuit, a controller and a transformer including a primary winding and a secondary winding. The resonant circuit is electrically coupled to the switching circuit and the primary winding. The rectifying circuit is electrically coupled to the secondary winding. The controller is electrically coupled to the switching circuit and the rectifying circuit and configured to selectively output one of a frequency modulation signal and a pulse width modulation signal as a second control signal according to a working frequency of a first control signal.