Increasing Power Density of Inductors using Electropermanent Magnets
Inductive components are used widely in the power grid for the purpose of controlling power flow, regulating fault current, and providing compensation. Magnetics are also a principal component of power electronics circuits. In both cases, inductor design focuses on achieving a desired impedance while maintaining the component within its saturation limits. Unfortunately, in many applications, the saturation limits of an inductor are often proportional to the size of the inductor.
This project aims to decrease the size of inductors while maintaining their power density using electropermanent magnets. The electropermanent magnet is used to counteract the internal flux of the inductor, thus altering the saturation characteristic of the inductor. Electropermanent magnets differ from electromagnets in that they have zero steady-state power losses and heating issues, while maintaining the ability to electronically control the magnetic field. Inductors are often times the largest component in a power converter. Therefore, reducing the size of the inductor could lead to smaller more cost effective inductive components currently being used in motors, switched mode power supplies and the power grid.
The top oscilloscope screen shot shows the inductorâ€™s saturation level of 3.44[A]. The second oscilloscope screen shot shows an increased saturation point of 4.76[A] when the inductor is paired with the electropermanent magnet.
The overall goal of this project is to provide new magnetic design parameters for more power efficient inductive components. These design parameters will provide guidelines for the inductor and the corresponding electropermanent magnet. Design variables for creating an energy efficient inductor include core dimensions, number of coil turns, airgap length, operating frequency and saturation levels. Design variables for the electropermanent magnet include, operational characteristics of permanent magnetic materials and their dimensions as well as energy required to alter the state of the electropermanent magnet. The electropermanent magnet-inductor pair design variables include optimal airgap between components for maximal flux cancellation and minimizing electromagnetic interference.
The internal flux of the electropermanent magnet-inductor pair were modeled using magnetic circuits and Finite Element Method Magnetics software. The saturation levels of the inductor were then tested using a custom designed PCB that includes dynamic switching capabilities of the electropermanent magnet. Currently, work is being done to switch the electropermanent magnet dynamically with a 60Hz current sine wave through the inductor. As the sine wave approaches its peak values the electropermanent magnet will switch on to adjust the inductor current so that it remains within its saturation limit.
How WBG Can Help
The Double Pulse Test is commonly used to measure characteristics of wideband gap devices. The test board designed for this project leverages the Double Pulse Test circuit to measure the saturation current levels of the inductor. Also, wideband gap devices were used in the H- Bridge to dynamically change the states of the electropermanent magnet. While wideband gap devices were not essential to this project, valuable experience with soldering and modeling these devices was obtained and will be applied in future work.
- Maeve Lawniczak