Research On The Key Techniques Of Multi-resonant DC-DC Converter And Magnetic Integration

Distributed renewable energy can be utilized through the DC microgrid system,which can greatly improve its own absorption and utilization rate.Therefore,a certain voltage support is provided for the large power grid.In addition,various kinds of DC loads,such as information communication equipment,electric vehicles,intelligent household appliances,are efficiently access to the DC microgrid architecture.By this way,their corresponding flexible management can also be harvested.However,with the DC voltage going toward a lower level,the performance of DC-DC converter,which serves as the key interface in the system,deserves much close attention.Under this condition,a dual-capacitor-inductor-transformer(D-CLT)multi-resonant soft-switching DC-DC converter with a unique zero voltage gain point is proposed in this paper.Moreover,an improved equivalent modeling method is presented to promote the calculating accuracy of DC voltage gain and guide the parameter design as well.To fulfill the requirements of high frequency,high efficiency and miniaturization,the corresponding magnetic integration design scheme is further studied.The major works are organized as below:(1)The derivation method of multi-resonant DC-DC converter topologies with a zero voltage gain point is proposed.The inherent limitations of DC voltage gain are analyzed for a typical LLC resonant converter.A unique notch filter structure is constructed to achieve the above zero voltage gain point.Meanwhile,a dual transformer structure is also combined with the notch filter to deduce the multi-resonant unit with a zero voltage gain point.As a result,the converter is able to attain the flexible voltage regulation ability and inherent over-current protection feature as well.Besides,a family of multi-resonant DC-DC converters with zero voltage gain is obtained.(2)A D-CLT multi-resonant soft-switching DC-DC converter is proposed.The zero voltage gain is achieved by employing a notch filter structure.Through the adoption of an additional high-frequency transformer,the converter is capable of realizing the effective transmission of the fundamental and the third-order harmonic active power at the same time.By this means,the reactive circulation within the resonant unit is highly reduced to improve the conversion efficiency of the proposed converter.In addition,an improved equivalent modeling method is proposed for the multi-resonant DC-DC converter.Compared with the traditional fundamental harmonic approximation method,the proposed method not only takes the influence of higher-order harmonic components into account,but also considers the phase angle difference between voltage and current of the nonlinear output unit.In this way,the calculation accuracy of DC voltage gain is improved.Finally,a relatively simple parameter design method is proposed for the multi-resonant converter with multiple components.The comparison of voltage stresses on the resonant capacitors in the multi-resonant unit is conducted.It facilitates the device selection and reduces the overall system cost as well.The simulation results verify the rationality and feasibility of the proposed design method.(3)A magnetic integration design method is presented according to the magnetic flux cancellation principle.A new type of matrix transformer structure is obtained by reasonable winding distribution and splitting the transformers with high turns ratio and then combing them into one.At the same time,the transformer windings adopt a four layer printed circuit board(PCB)structure,which further reduces the manufacturing cost.In addition,both of the mathematical model and T-type equivalent circuit of the transformers are established in this paper.The feasibility and outstanding advantages of the magnetic integration scheme are derived from the mathematical expressions.Furthermore,by integrating two separate transformers into one ‘U-I-U’ core structure,the total volume and core loss of magnetic components are effectively reduced.Finally,the feasibility and correctness of the proposed magnetic integration scheme are validated by building a finite element simulation model and a loss comparison model of the magnetic components.(4)Experimental prototypes of the proposed multi-resonant DC-DC converters are built in this paper.And the corresponding comparative experiments are carried out.Firstly,one group of comparative experiments verify the inherent over-current protection ability of the proposed multi-resonant converter.In addition,the ability of transferring the fundamental and the third-order harmonic active power within the entire switching frequency range is also verified.Secondly,some comparative experiments are carried out with and without using the magnetic integration scheme.The experimental results show that high conversion efficiency is achieved in the entire load range with the proposed magnetic integration scheme.