Design Method And Practice Of Passive Components For High Power Density Grid-connected Inverters

The rapid development of society is promoting the transformation of energy.The installed capacity of renewable energy in China has repeatedly hit new highs in recent years.In the application of renewable energy conversion,inverters are important units for grid connection.With the changing application scenarios and installation conditions,efficiency is no longer the only indicator for evaluating the performance of grid-connected inverters,and high power density requirements are gradually becoming more important.In a single-phase grid-connected inverter,the DC side electrolytic capacitor and the AC output filter occupy a considerable volume.The use of active power decoupling technology and planar integration technology to reduce the volume of these two modules is a key measure to further improve the power density of single-phase grid-connected inverters.Firstly,in view of the bulky problem caused by the traditional DC-side electrolytic capacitors in single-phase grid-connected inverters,a design method of DC bus active power decoupling based on a full-bridge buffer is given.The topology structure and working principle are analyzed in detail,and the circuit parameters are designed and optimized from the practical application level.The two schemes of current hysteresis control and voltage control are further analyzed,and the voltage control scheme is optimized from the perspective of impedance characteristic matching,and the feasibility and beneficial effect of the two control schemes are verified by simulation.The ceramic capacitors and Ga N power transistors are selected for the physical prototype design.Aiming at the problems of high parasitic parameter sensitivity and low turn-on threshold of Ga N power transistors,a negative voltage turn-off drive circuit with half-bridge structure is designed.On this basis,a physical prototype is made.Through the grid-connected inverter experimental platform equipped with the active power decoupling prototype,it is verified that the scheme has different power factor operation capabilities and fast dynamic response performance to load changes.The volume of the 2k W active power decoupling prototype produced is 138cm~3,and the power density is 14.5W/cm~3,which is 3.3 times higher than the traditional electrolytic capacitor decoupling method,realizing the high power density optimization of the power decoupling module.Furthermore,in view of the bulky problem caused by the traditional wire-wound AC output filter in single-phase grid-connected inverters,a planar integrated design method of the AC output filter with a planar magnetic core combined with PCB windings is given.On the basis of high switching frequency of grid-connected inverter,the LCL filter structure is selected,and the parameter design process is given at the same time.The design method of the planar inductor is described in detail from the selection of the magnetic core and the design of the PCB winding structure,and the feasibility of the design is verified by the finite element analysis.The3D structure design method of the planar LCL filter is given based on the planar inductors and the SMD ceramic filter capacitors,and prototype is produced.Through the single-phase grid-connected inverter experimental platform equipped with the active power decoupling prototype,it is verified that the total harmonic distortion of grid current,the inductor current ripple ratio and the power factor of the designed planar integrated LCL filter meet the design standards.The volume of the produced 2k W AC filter prototype is 164.9cm~3,and the power density reaches 12.13W/cm~3,which is 1.9 times higher than the traditional wire-wound AC output filter,realizing the high power density optimization of the AC output filter.