Bridgeless Power Factor Converter With Parallel Capacitor EMI Suppression
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Solution Overview
Problem
Conventional bridgeless power factor improvement converters experience noise generation and complex switching control due to rapid voltage fluctuations at zero-cross points, leading to surge currents and increased EMI noise.
Innovation Solution
The proposed converter employs a configuration with parallel capacitors, a resonance inductor, and a bidirectional switch, along with a clamping circuit, to manage voltage fluctuations during AC polarity changes, reducing surge currents and EMI noise without the need for soft start control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional bridgeless power factor improvement converter is used, then power factor improvement is achieved, but EMI noise increases due to rapid voltage fluctuations at zero-cross points
Solution Approach 1:
The patent applies preliminary action by gradually increasing the duty ratio of the switching element before full operation begins. Specifically, the control device increases the duty ratio from an initial value to a target value over a predetermined period after the AC voltage polarity changes, preventing rapid voltage fluctuations and surge currents that would otherwise generate EMI noise.
Solution Approach 2:
The patent implements beforehand cushioning by using the capacitor to absorb and smooth voltage fluctuations during polarity transitions. The capacitor is charged or discharged during the transition period, cushioning the voltage changes and preventing sharp spikes that would cause EMI noise and surge currents.
2Object-generated harmful factors
If soft start control is implemented to reduce EMI noise, then EMI noise is suppressed, but switching control complexity increases
Solution Approach 1:
The patent changes the parameter of duty ratio gradually over time instead of maintaining a fixed duty ratio. The control device dynamically adjusts the duty ratio from an initial value to a target value during the polarity transition period, which suppresses EMI noise while using a simple control mechanism that monitors AC voltage polarity and applies predetermined timing control.
3Productivity
If high frequency switching is performed immediately after zero-cross point, then power conversion efficiency is improved, but surge current is generated due to rapid voltage fluctuation
Solution Approach 1:
The patent applies preliminary action by preparing the circuit for high-frequency switching through gradual duty ratio increase. Before full high-frequency switching begins, the duty ratio is increased gradually over a predetermined period, allowing the capacitor to charge or discharge and prevent rapid voltage fluctuations that would cause surge currents.
Solution Approach 2:
The patent implements beforehand cushioning by using the capacitor to absorb voltage fluctuations during the transition to high-frequency switching. This cushioning effect prevents surge currents while allowing efficient power conversion to begin after the transition period.
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 configuration significantly suppresses EMI noise and simplifies switching control by gradually charging and discharging capacitors, preventing voltage fluctuations and ensuring the bidirectional switch operates within safe voltage limits.
Implementation Method 1
a capacitor, which is provided independently or separately from the series rectifying devices, is connected in parallel to at least one series rectifying device
Implementation Method 2
In a period from a time point at which a polarity of an AC voltage changes to a time point which is a predetermined period after the polarity of the AC voltage changes, a bidirectional switch is turned on, so that a resonance current flows
Data Source
AI summary
A bridgeless power factor improvement converter is configured with input terminals to which an AC voltage is input, output terminals from which a DC voltage is output, diodes, first and second switches, first and second coils, a pair of series diodes, and a control circuit. When one input terminal has a positive potential relative to the other input terminal, the control circuit performs a switching operation for only the first switch. When the one input terminal has a negative potential relative to the other input terminal, the control circuit performs the switching operation for only the second switch. A capacitor, which is provided independently from the pair of series diodes, is connected to at least one of the pair of series diodes in parallel.