Single-Stage AC-DC Converter With Soft Switching and Integrated PFC
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Solution Overview
Problem
Conventional AC-DC power conversion systems require two stages, including a Power Factor Correction (PFC) circuit and an isolated DC-DC converter, leading to inefficiencies, hard switching losses, noise interference, and the need for additional inrush current limiting circuits, which increase system complexity and cost.
Innovation Solution
A single-stage AC-DC converter topology using two bridge arms with switching devices and an isolation transformer, achieving soft switching operation and eliminating the need for inrush current limiting circuits by controlling the input current to follow the AC input voltage waveform through resonant or PWM control, combined with a full bridge rectifier on the secondary side for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-stage converter circuit (PFC circuit + isolated DC-DC converter) is used, then power factor correction and isolated DC to DC conversion can be achieved, but system complexity and cost increase due to additional components and circuits
Solution Approach 1:
The patent combines the PFC circuit and isolated DC-DC converter into a single integrated converter circuit. The circuit uses a bridge rectifier followed by a single isolated DC-DC converter stage that performs both power factor correction and voltage conversion functions simultaneously, eliminating the need for separate PFC and DC-DC stages while maintaining both functionalities.
Solution Approach 2:
The isolated DC-DC converter stage is designed to perform multiple functions: it provides power factor correction by controlling the input current waveform, performs isolated voltage conversion from the rectified DC voltage to the desired output voltage, and regulates the output voltage through feedback control. This multi-functional design replaces the need for dedicated PFC circuitry.
2Ease of operation
If conventional hard switching operation is used, then simple circuit operation is achieved, but switching losses and noise interference increase
Solution Approach 1:
The patent implements soft switching operation by periodically resetting the auxiliary winding voltage to zero before each switching transition. This is achieved by controlling the primary switch to turn off when the auxiliary winding voltage reaches zero, and then actively resetting it to zero before the next switching cycle begins, enabling lossless switching without complex resonance circuits.
Solution Approach 2:
The patent changes the switching timing parameter to achieve soft switching. By controlling the primary switch to turn off at specific moments when the auxiliary winding voltage is zero or being reset to zero, the switching transitions occur under zero-voltage conditions, eliminating switching losses and noise while maintaining simple circuit operation.
3Reliability
If inrush current limiting circuitry is added, then input power startup reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements self-limiting inrush current protection through the inherent characteristics of the circuit components. The series combination of the bridge rectifier and the isolated DC-DC converter creates natural current limiting during startup, and the control circuit monitors and regulates the inrush current without requiring additional dedicated inrush current limiting components.
4Device complexity
If a single-stage converter topology is used, then device complexity is reduced, but achieving both power factor correction and isolated DC to DC conversion becomes more difficult
Solution Approach 1:
The isolated DC-DC converter is designed with multi-functional capability to perform both power factor correction and voltage conversion. By controlling the switching duty cycle and timing, the single converter stage achieves unity power factor operation while simultaneously providing isolated DC to DC voltage transformation and regulation.
Solution Approach 2:
The patent employs feedback control to regulate the output voltage and maintain power factor correction in a single-stage converter. The output voltage is monitored and fed back to the control circuit, which adjusts the switching parameters to maintain both the desired output voltage level and the power factor correction function, enabling the single stage to perform multiple functions adaptively.
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
The solution enables efficient, low-noise, cost-effective, and compact AC-DC conversion with improved power factor correction and reduced circuit complexity, eliminating the need for separate PFC and DC-DC stages.
Implementation Method 1
an isolation transformer with its primary winding connected in series with a capacitor and then connected across the switching nodes of the two bridge arms
Implementation Method 2
The disclosed converter circuit provides soft switching operation
Data Source
AI summary
A high efficiency AC-DC converter with a single stage circuit on primary side to provide integrated functionalities of Power Factor Correction and isolated DC-DC conversion in combination with the isolation transformer and rectifier circuit on the secondary side. A plurality of operating methods of primary circuit are disclosed to realize the integrated power processing functions with zero voltage switching operation. A specific operating method of the secondary circuit is also disclosed for the system to maintain near unity power factor. In addition to the potential of reducing system cost, reducing space requirement and improving power conversion efficiency, the disclosed concept has also effectively eliminated the necessity of additional circuitry for inrush current limiting at startup of the input power.