LLC Converter Load Transient Response via Resonant Capacitor Sensing
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Solution Overview
Problem
LLC converters face slow load transient response due to controller saturation and the need for additional costly components like optocouplers or current sense transformers, which are not responsive enough for efficient operation.
Innovation Solution
A current sensing circuit coupled with a boost controller is used to indirectly sense load current across a resonant capacitor, transmitting this information to a DSP to adjust the PFC circuit setpoint voltage, eliminating the need for a current sense transformer and enhancing response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate optocoupler circuit or current sense transformer is used to sense load current, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the load current sensing function from traditional separate components (optocouplers, current sense transformers) and integrates it into the resonant capacitor voltage detection. By measuring the voltage across the resonant capacitor, the system indirectly obtains load current information without requiring additional sensing components, thus reducing device complexity while maintaining measurement capability
Solution Approach 2:
The resonant capacitor serves multiple functions: it is part of the LLC resonant circuit for power conversion and simultaneously acts as a sensing element for load current detection. The voltage across this single component provides both operational control information and load current information, eliminating the need for dedicated sensing components and reducing overall system complexity
2Loss of information
If traditional optocoupler or transformer-based sensing is used, then load current information can be transmitted, but response time is too slow for efficient LLC operation
Solution Approach 1:
The patent replaces traditional electromagnetic sensing mechanisms (optocouplers, current sense transformers) with direct voltage detection across the resonant capacitor. This substitution eliminates the inherent delay in electromagnetic coupling and signal transmission, providing instantaneous load current information that enables faster control response in LLC converters
Solution Approach 2:
The resonant capacitor voltage serves as an intermediary that directly reflects load current conditions. Instead of using separate sensing components that require signal conditioning and transmission, the voltage across the resonant capacitor provides immediate load information that can be directly used by the control system, significantly improving response time
3Loss of energy
If PFC output voltage is adjusted during load transients, then efficiency is improved, but output voltage sags due to slow boost response
Solution Approach 1:
The patent implements preliminary action by detecting load current changes through the resonant capacitor voltage and proactively adjusting the PFC output voltage setpoint before significant voltage sag occurs. The control system anticipates the need for voltage adjustment by monitoring the instantaneous load conditions, enabling the PFC circuit to prepare and respond faster, thus maintaining efficiency while preventing output voltage droop
Data Source
AI summary
Methods and systems for improving load transient response in LLC converters are provided herein. The method includes coupling a current sensing circuit to an output of the LLC converter, sensing load current of the LLC converter, and increasing a setpoint voltage for a power factor correction (PFC) circuit output based on the sensed load current.