AC/DC Converter PFC Reduces DC Link Capacitor Size
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Solution Overview
Problem
Conventional AC/DC power converter circuits with power factor correctors (PFC) require large DC link capacitors to minimize ripples in the output voltage, which are expensive, have short lifetimes, and consume high leakage currents.
Innovation Solution
A power conversion circuit with a PFC and a DC/DC converter that uses a control circuit to regulate the input current based on a reference signal with a frequency dependent on the AC input voltage, allowing for a reduced capacitance of the DC link capacitor by generating a clocked voltage with a specific duty cycle to rectify the input power variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large DC link capacitor is used to minimize output voltage ripples, then the ripple amplitude is reduced, but the capacitor size, cost, and leakage current increase
Solution Approach 1:
The patent applies periodic action by synchronizing the DC/DC converter switching frequency with the AC input voltage frequency. The control circuit generates a reference signal at twice the AC frequency (100Hz or 120Hz) and uses this to modulate the switching duty cycle, creating periodic energy transfer that compensates for the rectifier output voltage ripples. This periodic synchronization allows the system to maintain stable output voltage with significantly reduced capacitor size.
Solution Approach 2:
The patent changes the operating parameters of the DC/DC converter dynamically based on the AC input voltage characteristics. The control circuit adjusts the switching frequency and duty cycle parameters in real-time to match the rectified voltage ripple frequency and amplitude. By adapting these parameters to the input conditions, the system achieves effective ripple reduction without requiring large fixed capacitance values.
2Stability of the object's composition
If a large DC link capacitor is used to minimize output voltage ripples, then the ripple amplitude is reduced, but the cost and lifetime are worsened
Solution Approach 1:
The synchronized periodic switching of the DC/DC converter creates controlled energy transfer cycles that prevent excessive voltage ripple buildup. By operating at frequencies synchronized with the rectifier output (100Hz/120Hz reference signal), the system maintains voltage stability through frequent small corrections rather than requiring a large capacitor to handle infrequent large corrections, thereby reducing capacitor stress and extending lifetime.
Solution Approach 2:
The control circuit performs preliminary action by anticipating the voltage ripple pattern based on the synchronized reference signal. It proactively adjusts the switching duty cycle in advance of voltage deviations, preventing ripples from growing to levels that would stress the capacitor. This predictive control reduces the energy storage burden on the capacitor, improving reliability.
3Stability of the object's composition
If a large DC link capacitor is used to minimize output voltage ripples, then the ripple amplitude is reduced, but the leakage current increases
Solution Approach 1:
The synchronized periodic operation creates frequent, small energy transfer cycles that maintain voltage stability without requiring large static charge storage. The capacitor operates at lower average voltage and current levels because the DC/DC converter actively manages ripple through periodic switching, reducing the leakage current that is proportional to the capacitor's voltage and charge.
4Weight of stationary object
If the DC link capacitor size is reduced, then cost and lifetime are improved, but output voltage ripples increase
Solution Approach 1:
The control circuit acts as an intermediary that actively manages the energy transfer between the rectifier and the reduced capacitor. By synchronizing the DC/DC converter switching with the rectifier output frequency and dynamically adjusting the duty cycle, the control circuit compensates for the reduced capacitor's inability to smooth ripples passively, maintaining output voltage stability despite smaller capacitance.
Solution Approach 2:
The periodic synchronized switching creates a rhythm of energy transfer that matches the rectifier output characteristics. This periodic action allows the reduced capacitor to be recharged and discharged in controlled cycles, preventing voltage from deviating excessively and maintaining stability without requiring large capacitance.
5Weight of stationary object
If the DC link capacitor size is reduced, then cost and lifetime are improved, but power conversion efficiency deteriorates
Solution Approach 1:
The control circuit dynamically changes the DC/DC converter operating parameters (switching frequency, duty cycle) to optimize efficiency at each moment. By synchronizing with the rectifier output and adjusting parameters in real-time, the system maintains high efficiency across varying load and input voltage conditions, compensating for the reduced capacitor's impact on overall power conversion efficiency.
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 solution reduces the size of the DC link capacitor while maintaining power conversion efficiency and minimizing output voltage ripples, thereby addressing the limitations of conventional systems.
Implementation Method 1
a power factor corrector with input terminals for receiving an AC input voltage, and output terminals for providing a first output voltage, and a DC/DC converter with input terminals coupled to the output terminals of the power factor corrector
Implementation Method 2
rectifying the clocked voltage using an inductive rectifier arrangement
Data Source
AI summary
Disclosed is a power converter including a power factor corrector and a DC/DC converter and a power conversion method.