Dual-mode chokes teach old inverters new tricks: Page 3 of 3

April 01, 2019 //By Michael Freitag
Dual-mode chokes teach old inverters new tricks
Important changes in the way electricity is generated and used—such as increasing reliance on energy from renewable sources, the change to efficient variable-speed drives in industrial and domestic appliances, and adoption of hybrid or battery-electric vehicles—are increasing demands for electronic inverters that can be controlled to provide ac power at a desired voltage and frequency.

As far as the common -mode choke is concerned, identical currents flowing in opposite directions through the choke windings will create equal and opposite magnetic fields that cancel each other out. Therefore, the choke presents minimal impedance to the current flowing into the load and back through the return path. Differential noise refers to distortions that cause differences between these two currents. The magnetic fields due to these different signals will not cancel out; instead, they will present high impedance that attenuates the distortion.

 

Advanced filter technologies for lightweight inverters

Growing reliance on renewable energy, electric vehicles, and diverse motor drives continues to push demand for inverters that are compact, lightweight, and affordable. Consequently, the industry is looking for ways to reduce the size, weight, and cost of typically bulky components like filtering capacitors and chokes.


Fig. 4: Dual-mode chokes integrate three magnetic
components, saving solution size and part count.

Addressing this issues, proprietary ferrite core materials developed by KEMET help greatly reduce the size of standard chokes. In addition, they make it possible to create dual-mode chokes that combine common-mode and differential-mode filtering in the same package. The overall dimensions are similar to those of a comparable conventional common-mode choke. Figure 4 illustrates the principle.

KEMET also leveraged the extra design flexibility afforded by its proprietary materials to optimize the shape of these dual-mode chokes. The end result is significantly enhanced differential-mode (normal mode) noise suppression.


Fig. 5: Comparison of new dual-mode choke
versus conventional common-mode choke.

Figure 5 illustrates the high performance of the SSHB10 dual-mode chokes, presenting high impedance to both common-mode and differential-mode noise. The standard type, represented in this diagram by the SSHB10H-04320, is optimized for high-temperature performance. The SSHB10H-R04760 features a core material of increased permeability, which further boosts impedance to common-mode noise while maintaining identical differential-mode performance. Both chokes are rated for current up to 3 A.

 

Conclusion

Demand for compact, lightweight power inverters is expected to rise, across green-energy, industrial, and automotive markets. Advanced magnetic technologies that can significantly slim bulky noise filters and reduce component count now give designers extra freedom to achieve these goals.

 

About the author:

Michael Freitag is Director, Magnetics Product Management at KEMET Corp. - www.kemet.com

This article was first published in Electronic Design - www.electronicdesign.com


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