Power Factor Correction Circuit Dynamic Switching Frequency Control
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Solution Overview
Problem
Conventional power factor correction circuits fail to sufficiently reduce normal mode noise and require large filter circuits due to a simple proportional change in switching frequency with AC power supply voltage, leading to inefficiencies and increased size.
Innovation Solution
A power factor correction circuit with a control circuit that dynamically adjusts the switching frequency of the semiconductor switch to maximize when the ripple of the current through the inductor or its third-order harmonic component is at its peak, optimizing noise reduction and allowing for a smaller filter circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If switching frequency is changed proportionally to AC power supply voltage magnitude, then normal mode noise is dispersed with respect to frequency, but noise reduction is insufficient and large filter circuits are required
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable based on the instantaneous magnitude of the AC power supply voltage. The control circuit dynamically adjusts the switching frequency to track the voltage magnitude, ensuring optimal noise dispersion across different operating conditions. This dynamic adjustment allows the system to adapt to changing voltage levels rather than using a fixed or simply proportional frequency relationship.
Solution Approach 2:
The patent changes the switching frequency parameter in response to changes in AC power supply voltage magnitude. By establishing a specific functional relationship between voltage magnitude and switching frequency (where frequency is set to a predetermined value when voltage reaches a predetermined magnitude), the system optimizes noise characteristics. This parameter change strategy enables better noise reduction performance without requiring oversized filter circuits.
2Object-affected harmful factors
If switching frequency is increased to reduce normal mode noise, then noise reduction improves, but switching loss increases
Solution Approach 1:
The patent optimizes the switching frequency parameter based on the AC power supply voltage magnitude. Instead of using a fixed high frequency that would always reduce noise but increase switching loss, the system adjusts the frequency to match operating conditions. When voltage magnitude is high, the frequency is set to a predetermined value that provides adequate noise reduction while avoiding excessive switching loss. This conditional parameter adjustment resolves the trade-off between noise reduction and energy 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 approach effectively reduces normal mode noise and enables a more compact filter circuit by controlling the switching frequency based on input/output voltage ratios or duty ratios, enhancing noise reduction and reducing the overall apparatus size.
Implementation Method 1
the inductor 31, the semiconductor switch 33, the diode for rectification 34 and the smoothing capacitor 35 constitute the boost chopper, which repeats storing and releasing energy to/from the inductor 31 by turning the semiconductor switch 33 ON/OFF, so as to boost the voltage
Implementation Method 2
the distortion of the input current is suppressed by the switching operation of the boost chopper
Implementation Method 3
20 is a full wave rectifier circuit constituted by a diode bridge
Data Source
AI summary
A power factor correction circuit includes a rectifier that rectifies AC power supply voltage, a series circuit of an inductor and a semiconductor switch connected between the rectifier circuit output terminals, and a series circuit of a diode and a smoothing capacitor connected to both ends of the semiconductor switch, a load connected to both ends of the smoothing capacitor, so that the power factor on the input side of the rectifier circuit is corrected by the switching operation of the semiconductor switch. This power factor correction circuit includes a control circuit that controls the switching frequency of the semiconductor switch such that the switching frequency becomes maximum when the ripple of a current flowing through the inductor becomes maximum. According to this power factor correction circuit, normal mode noise can be reduced, and the size of a filter circuit can be decreased.