Research On The New Topology And Control Strategy Of Z Source Inverter

The Z source inverter can buck-boost energy by regulating the shoot-through duty(D),and improve the reliablity of the control systems by allowing the shoot-through states.Hence,it is widely used in motor drives,new energies,distributed power generation systems and fuel cell applicantions.Theoretically,infinite gain can be produced by Z source inverter like many other dc-dc boost topologies.However,it is not easy to implement.The ability of components set to electric pressure has limited the peak value of DC link voltage.Meanwhile,the coupling relationship between shoot-through duty(D)and modulation index(M)has restricted the maximum value of D.At the beginning of the study,the researches are mainly focused on using different control strategies to get shoot-through duty ratio(D)as large as possible under the same modulation index.But the space of enhancing boost factor is very limited in this condition.Then,more new Z source inverter structures have been proposed focused on higher boost factor and lower voltage stress.Meanwhile,the researches of application have been implemented to improve the perfermace of control systems.Therefore,the researches of Z source inverter are mainly focused on three aspects: the topology structure,the control strategy and the application technology.Supported by the National Natural Scinece Foundation of China(No.61271143),this dissertation addresses the fundamental theory and application technology of power converter based on Z source network.The main contents of this thesis are as following:(1)By combining switched-inductor with capacitor H-bridge circuit,a new quasi-switched inductor is designed.And then by replacing one inductor in classical Z source inverter by this new topology,a new Z source inverter,called asymmetric quasi switched inductor Z source inverter(AQSLZSI),is presented.The proposed inverter inherits the advantages of traditional Z source inverter and capacitor H-bridge circuit: simplified structure,reduced number of components,simplified control strategies,high boost factor.The operating principles of the proposed inverter are given,and performance analysis is provided.The simulation results of AQSLZSI and comparison with the SLZSI and Enhanced boost-ZSI are given in detail.Laboratory prototype is constructed.Experimental results confirm the theoretical analysis.(2)Three level neutral point clamped(NPC)Z source inverter is proposed to enhance voltage-boost by cascading two traditional Z source networks in series.Working principle and parameters designing of the NPC Z source inverter are given in detail.The advantages of Z source inverter,which can buck-boost energy and allow the shoot-through states,is inherited by this new proposed NPC Z source inverter.Meanwhile,high running efficiency and less harmonic content are obtained.Higher voltage with smaller shoot through and lower voltage stress on switch devices compared to traditional Z source inverter can be produced.The cascaded NPC Z source inverter model under Matlab/Sinmulink is built.The simulation results show that the boost factor has been increased from 1/(1-2D)for the traditional Z source NPC inverter to 1/(1-4D)for the proposed cascaded NPC Z source inverter.A prototype of the cascaded Z source NPC inverter is set up.The theoretical analysis of the features that the proposed NPC Z source inverter can increase the boost factor and expand the voltage regulation range of the inverter is verified by the experimental results.(3)The characteristics of cascaded Z source inverter and traditional control strategy are analyzed,a new maximum boost control is proposed.Based on SVPWM with third harmonic injection,all the zero vector states are replaced by shoot-through states.The switching frequency is reduced.Meanwhile,the shoot through duty cycle is improved effectively.Then,the boost factor is increased.Theoretical analysis is made,the formulas are deduced.Compared with the traditional Control strategy,under the same times of the voltage,maximum boost control with third harmonic injection improves the modulation significantly.Thus,the input range of the cascaded Z source inverter is extended.Simulation and experimental results are given to demonstrate the new features of the proposed control strategy.(4)A line modulation of SVPWM control algorithm used in Z source inverter is proposed.The dc bus voltage is regulated by the system output and the linear relationship is kept between the peak value of the output voltage and modulation index in the new proposed control strategy.Overmodulation is avoided.The ability of system output is enhanced.The system control algorithm is simplified.The cost of the system is saved,and the burden of system is reduced.This algorithm can improve the efficiency and the output power quality.To validate its advantages,analytical,simulation,and experimental results are also presented in the cascaded Z source inverter.(5)The number of pluses provided by incremental photoelectric encoder is limited due to the restriction of fabrication technology,the need of control performance in the servomotor system used vector control technology cannot be satisfied by the traditional incremental photoelectric encoder.A new simple linear equation based on the mathematical relationships of the sine and cosine electrical signals is described,an ultra-precise position estimation of the servomotor is proposed,and the resolution rotor angle is obtained by using reverse date fitting calculations.The performance of the proposed method was verified by using a practical system.The experimental results were in excellent agreement with theoretically anlysis.