Research On Enhanced-Boost Bi-Directional Quasi/Series Z-Source Inverter With Novel Switched Inductor Cells

With the increment of renewable energy applications and the number of electric vehicles(EVs),renewable energy generation and EVs have become important measures for energy conservation and emission reduction.The Voltage Source Inverter(VSI)cascaded with a boost type bi-directional dc–dc converter is widely used to meet the wide voltage range requirement.However,the structure of two-stage energy conversion is generally much more complex than the single-stage energy conversion in the energy storage system.In 2002,the Z-Source inverter(ZSI)was proposed by Prof.F.Z.Peng.The Z-Source Network(ZSN)configuration makes the ZSI realize the boost function and dc –ac conversion in one active stage through Shoot-Through States(STS).However,the conventional ZSI has the following disadvantages.i)Due to the unidirectional power flow feature,the ZSI is unsuitable for the energy storage system.ii)The ZSI operates in an undesirable mode operation with unstable peak dc-link voltage.iii)During start-up,the ZSI suffers from large inrush current.iv)The boost ability of the conventional ZSI is limited by the low modulation index M and high voltage stresses of components.To solve aforementioned shortcomings,an enhanced-boost bi-directional Quasi/Series ZSI with novel switched inductor(SL)cells(named as Active-SLs QZSI)is proposed.The proposed active SL cell replaces three diodes in the conventional SL cell of the QZSI with two capacitors and one active sw itch,thus allowing bi-directional power flow and achieving higher boost factor.Compared with existing ZSIs,the proposed Active-SLs QZSI has less current stress of ZSN,higher efficiency and higher boost factor.To study operation principle of the proposed Active-SLs QZSI,steady-state model of proposed Active-SLs QZSI is established and possible modes operation are analyzed in details,which mainly includes inverter mode and rectifier mode operation.A Five-Segment SVPWM basd modified Space Vector Modulation(Five-Segment MSVM)is introduced to reduce the switching frequency of active switches of ZSN.Compared with existing SVPWM techniques,the current stress through inverter’s switches can be reduced by 3 times with the proposed Five-Segment MSVM.The switching frequency of three ZSN active switches is the same as that of inverter’s six switches with the Five-Segment MSVM.To mantain constant of the peak dc-link voltage with variable input dc voltage and reduce influence of the right half plane zero(RHZ),the peak dc-link voltage of the Active-SLs QZSI is controlled by the dual-loop dc-link feed-forward control strategy in this paper.The dynamic model of the Active-SLs QZSI is established initially.The design process of the dual-loop dc-link feed-forward control strategy is then presented in details.Simulations and experiments have been conducted in the laboratory to verify superiorities of the proposed Active-SLs QZSI(inverter mode operation;light load mode operation and rectifier mode operation).Both simulation and experimental results indicate that the proposed Active-SLs QZSI possesses bidirectional power flow capability with inherent inrush current suppression and avoid undesirable mode operation under light load mode operation.Besides,the effectiveness of the Five-Segment MSVM and the dual-loop dc-link feed-forward control strategy is validated.