Research Of A Modified Switched-coupled-inductor Quasi-Z-source Inverter

Aiming at the deficiency of quasi Z source inverter for lack of boost capacity,this thesis summarizes the solutions of enhancing the quasi Z source inverter boost ability by transplanting traditional DC-DC voltage boost technic into quasi Z source inverter.A new type of quasi Z source inverters is obtained by topology deduction.The voltage and current stresses of components and the voltage gain of the new type quasi Z source inverters are calculated.There is a topology among the new type of quasi Z source inverters named modified switched-coupled-inductor quasi Z source inverter MSCL-qZSI whose structure and components are similar to the existing SCL-qZSI and m SSCL-qZSI.To highlight the superiority of MSCL-qZSI,the comparisons of component voltage and current stresses and voltage gain and efficiency with SCL-qZSI and m SSCL-qZSI have been conducted.The result shows that the voltage gain as well as component voltage and current stresses of the three inverters are comparable except the current stress of coupled inductors.The current stress of coupled-inductor in MSCL-qZSI is far lower than that of SCL-qZSI and m SSCL-qZSI,which leads to the efficiency of MSCL-qZSI is higher than that of SCL-qZSI and m SSCL-qZSI.Due to the output voltage of photovoltaic arrays or fuel cells has a large fluctuation,the closed loop control design for MSCL-qZSI is needed.Firstly,the state space average method was used to establish the model,then the input variables needed to realize output stability control were analyzed,then the system compensation was corrected by PID compensator,and finally the closed loop control effect of PID was verified by building Simulink simulation model.The result shows that the output voltage of MSCL-qZSI can not be controlled stably by controlling the voltage of capacitor C₂while can be controlled stably by total voltage of capacitor C₁ and C₂.When the closed-loop simulation control analysis is finished,the hardware design of MSCL-qZSI is carried out,which mainly sonsists of three parts:（1）the design of main circuit;（2）the design of auxiliary circuit;（3）the design of controller.The design of coupled inductor,the design and selection of inductor and capacitor,and the selection of switch and diode,and the design of L-C filter are all based on the parameter of components of the main circuit.After the parameter of relevant components is designed,the selection of controller and the priciple of closed-loop control are stated.Before conducting the experimental test,the designed circuit was simulated by Saber simulator and the simulation waveforms of key components when operating in stable state were collected.Finally,a 1000 W prototype was established in the laboratory and the experimental waveforms of key components were gathered.The experimental results turned out that:（1）the experimental waveforms were consist with that of Saber simulations;（2）the efficiency measured in experiment was consist with that of theorial analysis which was confirmed by establishing the prototype of SCL-qZSI and m SSCL-qZSI,and MSCL-qZSI had the highest efficiency;（3）the effectiveness of PID parameters that was obtained by state space average method modeling and stability analysis was confirmed by closed-loop control experiment.