Research On The Key Technologies Of Magnetic Integration In DC-DC Switched-Mode Power Converters

Integration is the trend of power electronics technology. Magnetic integrationtechnology is an important part of the research contents of the passive integrated powerelectronics. In this dissertation, the key technologies of magnetic integration in DC-DCswitched-mode power converters have been studied, including analysis method ofintegrated magnetics, zero current ripple design of Forward converter with magneticintegration, magnetic integration techniques of current doubler rectifier (CDR) converterand multi-phase interleaving parallel converters, AC winding loss mechanism andmodeling of multi-function integrated magnetics, near-field magnetic coupling utilizationand control technique, small signal modeling technique of power converter with magneticintegration.On the analysis methods of integrated magnetics, a general time-domain analysismethod has been developed based on analog analysis method with electrical circuit andmagnetic circuit. It helps to visually and conveniently establish the interface relationshipbetween parameters of electrical circuit and magnetic circuit, and then achieve thewaveforms of magnetic flux and electric current. Forward converter with magneticintegration is illustrated as example.There are two types of Forward converter with magnetic integration due to thedifferent magnetic integrated schemes. From point of view of the equivalent electricalcircuit model of integrated magnetics, the output current ripple reduction has beenanalyzed in Forward converter with the first magnetic integration. The feature of the outputcurrent ripple reduction of the active clamp Forward converter with the first magneticintegration has been discovered by the concept of current ripple steering mechanism. Themagnetic flux distribution and AC winding losses under zero current ripple design havebeen explained. Furthermore, the principle of the active clamp Forward converter with thesecond magnetic integration has been analyzed. As the two secondary windings have sameturn numbers, it can also get zero ripple output current performance, which is verifiedexperimentally. A novel integrated magnetics of CDR converter has been proposed by the removal ofone of the inductor windings. It shows that this scheme helps to simply the winding layout,reduce the leakage inductance between primary winding and secondary windings, andeventually improve power efficiency and power density. It is also found that the existingintegrated magnetics of Half-bridge CDR converter is that of Forward converter applied inthe double-end converter, which will provides new understanding of magnetic integrationin switched-mode power converter. Furthermore, an improved design with winding turnsratio of2to1between secondary windings has been proposed to make intrinsic stability ofphysical structure by only one air gap. At the same time, due to the reduction of air gapfringing flux effect and the improvement of winding ripple current, the efficiency of theimproved magnetic design in Half-bridge CDR converter can be increased by3.5%The features of coupled inductors in the application of2-phase voltage regulatormodule (VRM) have been analyzed. The influence of the coupling parameters on phasecurrent ripple has been established. A new dual resistance model has been proposed toembody the complex AC winding loss characteristics based on the deep analysis andunderstanding of phase current ripple. Furthermore, to reduce the high AC winding lossescaused by the currents of inductor component of Flyback transformer, a novel multi-phaseinterleaving Flyback converter with magnetic integration has been proposed. It helps tosuppress current high-order harmonics, reduce the winding losses and core losses, reduceswitching losses and improve the conversion efficiency.A new idea of near-field flux coupling of magentic integration has been proposed torealize magnetic integration by transformation and utilization of spatial magnetic fielddistribution among phase inductors in VRM. It helps to use simple magnetic structure tofigure out much complex structures. Magnetics with this technique will be simple and easyto achieve. Furthermore, applied to magnetics integrated CDR converter, the near fieldcoupling magnetic integration can help to make better understand on the operationmechanism of the existing integrated magnetics and reveal the intrinsic relationship amongdifferent integration schemes. It is proved that the reduction of the near-fieldmagneto-resistance can reduce excitation current, reduce AC winding losses and the corelosses and switching losses, and then improve efficiency of power converter.Finally, three small-signal modeling methods of switched mode power converter withintegrated magnetics have been respectively proposed, based on the different approaches toanalyze integrated magnetics and combined with the state space averaging method. Smallsignal control features in Forward converter and CDR converter with magnetic integration have been explored. These help to obtain the system transfer function and establish atheoretical basis for the systematic research of magnetic integration power converter.