Power Converter Common Mode Filter Saturation Prevention
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Solution Overview
Problem
The existing power converter systems with PWM rectifying and inverter circuits and common mode filters face issues with magnetic saturation of the common mode choke coil due to differing switching frequencies, leading to increased common mode voltage and conduction noise, which compromises the filtering effect and results in magnetic saturation.
Innovation Solution
A power converter design that sets the switching frequencies of the PWM rectifying and inverter circuits such that the common mode choke coil does not saturate, including a common mode filter with a capacitor and a PWM rectifying circuit operating at a first carrier frequency and a PWM inverter circuit operating at a second carrier frequency, where the frequencies are set to prevent magnetic saturation, and optionally setting the resonance frequency of the common mode filter to twice or more the switching frequency to further prevent saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the switching frequency of PWM rectifying and inverter circuits is increased to reduce noise, then noise suppression improves, but the common mode choke coil becomes more likely to saturate
Solution Approach 1:
The patent applies dynamics by making the switching frequencies of the PWM rectifying circuit and PWM inverter circuit adjustable and independent of each other. By dynamically optimizing the frequency relationship (setting them to different frequencies rather than fixed equal frequencies), the system reduces common mode voltage peaks while maintaining effective noise suppression, preventing magnetic saturation of the common mode choke coil.
Solution Approach 2:
The patent changes the parameter of switching frequency from a fixed equal value for both circuits to different adjustable values. By setting the PWM rectifying circuit frequency and PWM inverter circuit frequency to different values, the common mode voltage waveform changes, reducing peak values and preventing magnetic saturation while maintaining noise suppression effectiveness.
2Reliability
If the cross section or number of turns of the common mode choke coil is increased to prevent saturation, then magnetic saturation prevention improves, but the filter size increases
Solution Approach 1:
The patent changes the operating parameters of the PWM circuits (switching frequencies) rather than changing the physical dimensions of the common mode choke coil. By optimizing the frequency relationship between rectifying and inverter circuits, the common mode voltage peaks are reduced, allowing the use of a smaller choke coil that prevents saturation without increasing filter size.
3Power
If the switching period is extended or dc voltage is increased, then power conversion capability improves, but the common mode choke coil becomes more likely to saturate
Solution Approach 1:
The patent applies dynamics by independently adjusting the switching frequencies of the PWM rectifying and inverter circuits. This dynamic frequency optimization reduces common mode voltage peaks even when operating at higher power levels or longer switching periods, preventing magnetic saturation while maintaining power conversion capability.
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 design effectively prevents magnetic saturation of the common mode choke coil, reducing noise and allowing for size and cost reduction of the filter components by ensuring the common mode voltage does not exceed saturation levels, thereby maintaining effective noise suppression.
Implementation Method 1
defining a voltage applied to the common mode choke coil as VLC1 and the number of turns of the common mode choke coil is N, a magnetic flux φLC1 of the core is expressed by Equation 1
Implementation Method 2
when the magnetic flux density of the common mode choke coil exceeds a saturation magnetic flux density Bmax, the inductance is reduced drastically, so that it no longer serves as a common mode filter
Implementation Method 3
a common mode filter including a common mode choke coil and a capacitor
Data Source
AI summary
A power converter is provided with a rectifying circuit, an inverter circuit, and a common mode filter including a common mode choke coil and a capacitor. The switching frequency of a PWM rectifying circuit is set at three times the switching frequency of a PWM inverter. Alternatively, the resonance frequency of the common mode filter is set at twice the carrier frequency of the rectifying circuit or the PWM inverter circuit or more.