Current Ripple Suppression And Electro-thermal Analysis Of The Coupled Inductor For The Quasi-Z Source Inverters

The traditional voltage source inverter belongs to step-down inverter,while the quasi-Z source inverter overcomes some shortcomings of the traditional inverter and has the characteristics of voltage rise and fall.Compared with the Z source inverter,it also has the advantages of continuous input current and significant reduction of a capacitor voltage stress,which makes it have a broader application prospect in new energy fields such as fuel cell,photovoltaic power generation and electric vehicle drive.In this paper,the voltage source quasi-Z-source inverter are taken as the research object.Various input current ripple suppression strategies are analyzed.A novel design of coupled inductor is proposed to reduce the input current ripple of quasi-Z source inverter.The loss and temperature rise of coupled inductor are also studied.The correctness of the above strategies and theoretical analysis is verified by simulation and experiment.In this paper,the topology of voltage source quasi-Z-source inverter is analyzed in detail,and its different control strategies are introduced.The mathematical model of inductor current high frequency ripple is obtained by simplification and equivalence,and the basic principle of ripple suppression strategy is determined.Because of the special impedance network of quasi-Z-source inverter,capacitance can clamp the inductance voltage,which results in the real-time equalization of inductor L₁ and L₂.Based on this characteristic,inductor L₁ and L₂ can be coupled through iron core.When inductance L₂ is close to mutual inductance,the high frequency current ripple at the input end of the inverter can be theoretically eliminated.Therefore,a new design scheme of coupled inductor is proposed in this paper.The realization process of magnetic cores with different shapes is analyzed,and the input current ripple can be effectively reduced by reasonably setting the turns of two coils.For the core device of quasi-Z source impedance network,the excitation current pulsation through the winding will cause the magnetic field to change repeatedly,which will lead to more core and winding losses and then lead to heating.Therefore,this paper firstly analyses and compares the existing methods for calculating the loss and temperature rise of magnetic components.Then,in view of the application environment of quasi-Z-source inverters,the core works in a locally magnetized state with large DC bias,and repeats magnetization and demagnetization in both shoot-through state and non-through sections.The influence of different shoot-through duty ratio and switching frequency on core loss is analyzed by using the modified core loss calculation model and the temperature rise is calculated based on the traditional thermal circuit model.Finally,based on Ansys software platform,this paper builds a multi-physical simulation model of quasi-Z-source inverter,and uses DSP control module to build the experimental platform of the system.Experiments and simulation results show that the proposed high-frequency ripple suppression strategy is feasible and can effectively reduce the input current high-frequency ripple,and the scheme is simple and practical without adding additional devices.At the same time,the joint finite element simulation model takes into account the influence of electromagnetic heat on the circuit.The simulation and experimental results verify the correctness of thermal analysis,which can provide guidance for the design of heat dissipation structure of the system,especially the optimal design of the coupled inductor.