Research On High-frequency Power Magnetic Components With Permanent Magnet Bias In Power Electronics

With the development of power converters toward the minimization,high-efficiency and low-profile, the power density becomes higher and higher. So,it is required to have much more power density for the magnetic component. DCpower chokes, as one of the most important magnetic components, to enhancetheir power density or to decrease their volume becomes an importantdevelopment tendency.One method to achieve this goal is to develop the magnetic materials withhigher flux saturation abilities. But this consideration is limited by the currentmagnetic material technology and production level. Another method is to utilizepermanent magnet material to introduce an opposite magnetic flux pre-bias tocancel the flux excited by the winding currents to further increase thecurrent-carrying abilities and reduce the volume of the DC chokes. The paper isfocused on the study of how to utilize the excellent magnet properties of thesintered NdFeB permanent magnet in its applications in the DC chokes.Firstly, the different magnet materials are evaluated, such as ferrite magnet,AlNiCo, SmCo, bounded NdFeB and sintered NdFeB for their magnetizing property,thermal property and de-magnetizing property, among these, sintered NdFeB is verysuitable for the pre-bias applications in high-frequency DC chokes with its good properties.However, how to utilize the good properties of sintered NdFeB and at the meantime toovercome its disadvantage with great eddy current losses under high-frequency excitationdue to its high conductivity will bring us a good way to use magnet pre-bias technique inhigh-frequency DC chokes.A scheme is proposed for using sintered NdFeB as pre-bias magnet and relative corestructure. Together with the suitable parameters design with the core structure, the AC fluxproduced by the AC current in the choke winding cannot basically pass through the coreportion where the magnet is located, but the pre-bias DC flux produced by the magnet canget through the core portion where the winding is located. So the eddy current loss andthermal de-magnetizing effects can be avoided in the magnet, the de-magnetizing by theshock pulse current can also be avoided. The benefits by the permanent magnet pre-bias technique are as below:1、The core size and weight can be reduced and winding mean length can also bereduced with less DC resistance and DC winding loss while the inductance andcurrent-carrying ability keeping the same;2、The power density can be increased double while the core size and weight is keptthe same or just slightly increased;3、The height of the planar inductor can be obviously further reduced when thepre-bias magnet technique is used in the planar magnetics applications.The magnetic circuit analysis, electromagnetic field simulation and parameters designare performed in the paper for applications in the DC power chokes, transformers inflyback topology, and planar inductor. The detail comparison designs, inductor samplemakings and tests in the circuits show that the magnet pre-bias scheme is right in theory,effective and available in practical applications. The technique is especially suitable for theDC choke application with ferrite core, large DC current and high-frequency operation.