AC-DC Converter Control Method for THD and EMI Optimization
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Solution Overview
Problem
Controlling an AC-DC conversion circuit in critical conduction mode fails to simultaneously meet requirements for Total Harmonic Distortion (THD), Power Factor (PF), efficiency, and Electromagnetic Interference (EMI) due to varying switching frequencies and limitations in driver chip and circuit component capabilities.
Innovation Solution
A control method that adjusts the AC-DC conversion circuit's switching frequency and mode based on input voltages and loads, implementing different working modes such as Continuous Conduction Mode (CCM), Critical Conduction Mode (CRM), and Discontinuous Conduction Mode (DCM) to optimize THD, PF, and EMI performance by limiting the switching frequency within a preset range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the AC-DC conversion circuit is controlled to work in critical conduction mode (CRM) to improve switching frequency and power density, then the reverse recovery loss is eliminated, but the switching frequency varies largely and cannot be limited to a certain range
Solution Approach 1:
The patent applies dynamics by transitioning from a static single-mode approach to a dynamic multi-mode control strategy. The control system dynamically switches between CCM, CRM, and DCM based on real-time operating conditions (input voltage, output power, load), allowing the switching frequency to be actively managed within a target range while eliminating reverse recovery losses through selective CRM operation.
Solution Approach 2:
The patent changes the operational parameters by introducing multiple conduction modes with distinct characteristics. By adjusting the conduction mode parameter based on operating conditions, the system can control the switching frequency behavior - CCM provides frequency stability, CRM eliminates reverse recovery loss, and DCM reduces stress on components, thus resolving the contradiction between eliminating losses and stabilizing frequency.
2Device complexity
If the switching frequency is limited to a certain range due to driver chip and circuit component limitations, then the driving ability and component loss are managed, but the requirements of THD, PF, efficiency, and EMI characteristics cannot be met simultaneously
Solution Approach 1:
The patent segments the operating range into three distinct conduction modes (CCM, CRM, DCM), each optimized for specific performance requirements. This segmentation allows the system to meet multiple conflicting requirements simultaneously by operating in the most appropriate mode for each condition, rather than being constrained by a single frequency range limitation.
Solution Approach 2:
The patent implements multi-functionality by designing a control system that can operate in multiple conduction modes, making the AC-DC conversion circuit adaptable to various performance requirements. The universal control strategy can simultaneously optimize for THD, PF, efficiency, and EMI by selecting the appropriate mode, thus overcoming the limitations imposed by driver chip and component capabilities.
3Loss of energy
If the AC-DC conversion circuit operates in single critical conduction mode, then the reverse recovery loss is eliminated, but the switching frequency varies largely and cannot meet all performance requirements simultaneously
Solution Approach 1:
The patent transforms the static single-mode operation into dynamic multi-mode operation. The control system continuously monitors operating conditions and dynamically adjusts the conduction mode, enabling the circuit to adapt to different performance requirements while maintaining the benefits of CRM (reverse recovery loss elimination) when appropriate, and switching to CCM or DCM when frequency stability or other requirements take priority.
Data Source
AI summary
The present disclosure provides a control method for an AC-DC conversion circuit. The method includes: in an entire load range, acquiring circuit parameter information of the AC-DC conversion circuit; limiting an actual switching frequency or an actual switching period of the AC-DC conversion circuit within a preset working range according to the circuit parameter information. The AC-DC conversion circuit can meet requirements of Total Harmonic Distortion (THD), Power Factor (PF), efficiency and Electromagnetic Interference (EMI) and the like by adjusting the working information of the AC-DC conversion circuit through the preset working range.