Bridgeless PFC Circuit Zero-Crossing EMI Suppression
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Solution Overview
Problem
Bridgeless PFC converters experience higher electromagnetic interference (EMI) due to zero-cross transitions of the AC input, which can interfere with neighboring electronic components and degrade regulation, making traditional passive filters undesirable.
Innovation Solution
Incorporating current sources in parallel with switches of the low-frequency leg to control voltage transitions during AC zero crossings, reducing the rate of change in voltage and mitigating EMI without the need for large passive filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If bridgeless PFC converters are used to eliminate the AC rectifier bridge, then converter efficiency is improved and cost is reduced, but electromagnetic interference (EMI) increases during AC zero crossing transitions
Solution Approach 1:
The patent applies preliminary action by detecting AC zero-crossing transitions in advance and preemptively adjusting the switching states of the low-frequency leg switches and current sources before the voltage transitions occur. This proactive control prevents harmful EMI voltage spikes from occurring in the first place, rather than attempting to mitigate them after they occur.
Solution Approach 2:
The patent changes the operational parameters of the low-frequency leg by dynamically adjusting switch states and current source activation based on the AC input voltage phase. During zero-crossing transitions, the control circuit modifies the conduction states of switches S2 and S3, and activates current sources to limit the rate of change of voltage (dv/dt), thereby reducing EMI while maintaining power factor correction functionality.
2Object-generated harmful factors
If passive filters are used to reduce EMI, then electromagnetic interference is mitigated, but the system requires large filter components that increase device complexity and size
Solution Approach 1:
The patent replaces the traditional passive mechanical filter system with an active electronic control system. Instead of using large inductors and capacitors to filter EMI, the invention uses controlled switching of semiconductor devices and current sources to actively manage voltage transitions and suppress EMI at its source, thereby eliminating the need for bulky passive filter components.
Solution Approach 2:
The patent extracts the EMI mitigation function from the traditional passive filter approach and relocates it to the active control circuitry of the bridgeless PFC converter. By removing the dependency on external passive filters and integrating EMI control directly into the converter's switching control logic, the system achieves EMI reduction without adding external filter components.
Data Source
AI summary
A bridgeless power factor correction (PFC) circuit for reducing electromagnetic interference (EMI) is disclosed herein. A current source is placed in parallel with a switch of a low frequency leg. The current source may be turned on during zero crossings of the AC input voltage to limit current and reduce the rate of change in voltage. In turn, EMI may be advantageously reduced without the need for large passive filters or complicated circuitry.