Buck-Boost AC/DC Converter Control for Inrush Current Limiting
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Solution Overview
Problem
Existing inrush current limiting methods, such as using Negative Temperature Coefficient (NTC) thermistors, result in reduced power conversion efficiency and higher internal operating temperatures, and can cause AC mains input brownouts or voltage interruptions due to reduced resistance when hot.
Innovation Solution
An inrush current limited AC/DC power converter apparatus utilizing a buck switch mode converter configured as a current source combined with a boost converter, which shares a zero crossing detection circuit to control switching actions, reducing power losses and component complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an NTC thermistor is used to limit inrush current, then inrush current is limited during initial power up, but power conversion efficiency is reduced and internal operating temperature increases due to power dissipation in the thermistor
Solution Approach 1:
The patent changes the operating parameters of the buck converter (switching frequency, duty cycle, current limits) dynamically during startup to limit inrush current without relying on passive thermistor resistance. The controller adjusts these parameters to achieve current limiting while maintaining high efficiency power conversion, eliminating the thermistor's power dissipation loss.
Solution Approach 2:
The patent replaces the passive mechanical/thermal inrush current limiting mechanism (NTC thermistor) with an active electronic control system (buck converter with controller). This substitution allows for precise current control through switching action rather than relying on temperature-dependent resistance, thereby eliminating continuous power dissipation in a resistive element.
2Reliability
If an NTC thermistor is used to limit inrush current, then inrush current is limited during initial power up, but AC mains input brownout or voltage dip may occur due to reduced thermistor resistance when hot
Solution Approach 1:
The patent implements feedback control through the controller that monitors input voltage and current conditions. When startup occurs, the controller detects voltage dips or brownout conditions and adjusts the buck converter's switching parameters accordingly to limit inrush current. This closed-loop feedback ensures current limiting is applied precisely when needed without causing mains voltage disturbances.
Solution Approach 2:
The patent employs dynamic control of the buck converter switching parameters during startup transient conditions. The controller dynamically adjusts switching frequency, duty cycle, and current limits based on real-time detection of startup conditions and mains voltage status, providing adaptive inrush current limiting that responds to changing conditions without causing brownout.
3Loss of energy
If a buck converter with switching action is used to limit inrush current, then power losses are reduced compared to thermistor approach, but device complexity increases due to additional switching components and control circuitry
Solution Approach 1:
The patent designs the buck converter to serve multiple functions: it provides inrush current limiting during startup, performs power factor correction, and delivers efficient power conversion during normal operation. By integrating these functions into a single converter topology with unified control, the patent reduces overall system complexity compared to having separate components for each function.
Solution Approach 2:
The patent merges the inrush current limiting function with the main power conversion function by using the buck converter for both purposes. The same switching components, inductor, and control circuitry are used for both startup current limiting and ongoing power conversion, eliminating the need for separate thermistor and control circuits.
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 effectively limits inrush current during initial power-up and brownout conditions with reduced power losses and lower operating temperatures, maintaining high power conversion efficiency and preventing AC mains input issues.
Implementation Method 1
A NTC thermistor is a variable resistor that decreases in resistance as its temperature increases in response to current flow through the power converter apparatus
Implementation Method 2
The switching action of the buck converter limits current on a cycle-by-cycle basis
Data Source
AI summary
A method and system for controlling and/or limiting inrush current is described. The system includes a buck converter section; a power factor conversion (PFC) boost converter section; and a storage capacitor section. In a first mode of operation, the boost converter section is disabled and the buck converter section is active and in a second mode of operation, the boost converter section is active and the buck converter section is disabled.