Blaabjerg, Frede

Liu, Ping

Qiu, Zhipeng

Shen, Yanfeng

Yang, Yongheng

Yuan, Jing

English

This paper proposes a modified inverter topology called Embedded Enhanced-Boost Z-Source Inverter (EEB- ZSI). Compared with the prior-art Enhanced-Boost Z-Source Inverter (EB-ZSI), the proposed topology features that the dc sources like PV panels can be embedded into a symmetrical impedance network. In this way, the dc current becomes continuous. More importantly, the voltage stress across the switching devices is lower, while a large conversion ratio is maintained. The proposed Z-source inverter is benchmarked with selected topologies in terms of the conversion ratio, voltage gain, and stresses on the devices. Simulation and experimental results are provided to validate the analysis

    Aalborg UniversitetAn Embedded Enhanced-Boost Z-Source InverterYuan, Jing; Yang, Yongheng; Liu, Ping; Shen, Yanfeng; Qiu, Zhipeng; Blaabjerg, FredePublished in:Proceedings of the IEEE International Power Electronics and Application Conference and Exposition (PEAC2018)DOI (link to publication from Publisher):10.1109/PEAC.2018.8590410Publication date:2018Document VersionEarly version, also known as pre-printLink to publication from Aalborg UniversityCitation for published version (APA):Yuan, J., Yang, Y., Liu, P., Shen, Y., Qiu, Z., & Blaabjerg, F. (2018). An Embedded Enhanced-Boost Z-SourceInverter. In Proceedings of the IEEE International Power Electronics and Application Conference and Exposition(PEAC 2018) (pp. 1-6). IEEE. https://doi.org/10.1109/PEAC.2018.8590410General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: November 24, 2020An Embedded Enhanced-Boost Z-Source InverterJing Yuan1, Yongheng Yang1, Ping Liu2, Yanfeng Shen1, Zhipeng Qiu3, Frede Blaabjerg11Department of Energy Technology, Aalborg University, Denmark2College of Electrical and Information Engineering, Hunan University, China3State Grid Jinan Power Supply Company, ChinaEmail: yua@et.aau.dk, yoy@et.aau.dk, pingliu@hnu.edu.cn, yaf@et.aau.dk, qzhpeng2005@126.com, fbl@et.aau.dkAbstract—This paper proposes a modified inverter topologycalled Embedded Enhanced-Boost Z-Source Inverter (EEB-ZSI). Compared with the prior-art Enhanced-Boost Z-SourceInverter (EB-ZSI), the proposed topology features that the dcsources like PV panels can be embedded into a symmetricalimpedance network. In this way, the dc current becomescontinuous. More importantly, the voltage stress across theswitching devices is lower, while a large conversion ratio ismaintained. The proposed Z-source inverter is benchmarkedwith selected topologies in terms of the conversion ratio, voltagegain, and stresses on the devices. Simulation and experimentalresults are provided to validate the analysis.Index Terms—Z-source inverter, embedded Z-source, highconversion ratio, continuous input currentI. INTRODUCTIONTraditional Voltage Source Inverters (VSIs) are widelyused in industrial applications, e.g., motor drives, distributedpower systems, and hybrid electric vehicles [1], which aretypically in the buck operation mode. Generally, a dc-dcboost converter is used to achieve a high conversion of the dcvoltage, which is then fed to an inverter. However, this two-stage power conversion increases the system cost and lowersthe efficiency. The Z-source inverter (ZSI) [2] shown in Fig. 1as a single-stage conversion, can effectively tackles thoseissues. Hence, many efforts have been made in recent yearsto enhance the performance of Z-source inverters by meansof topological innovations and advanced control strategies.Nonetheless, in order to increase the boost capability, morepassive components (e.g., inductors and capacitors) should beadded into the classic Z-source network shown in Fig. 1. Forinstance, a Switched-Inductor (SL) Z-source inverter(SL-ZSI)[3], as shown in Fig. 2, adopts two SL cells to replace thetwo inductors (L1 and L2) in traditional Z-source inverter, andthus leading to a higher conversion ratio. Based on the SL-ZSI topology, modified topologies were developed to furtherincrease the boost ratio. For instance, according to the quasiZ-source inverter, two SL qZSI topologies were proposed in[4] and [5].In addition, the boost capability can be improved by usingmore cascaded networks. In [6] and [7], the extended-boostZSI topologies are called diode-assisted or capacitor-assistedconverters for high boost ratios. A new family of high-boostZSIs with switched impedance is presented in [8] and [9].More specially, in [8], a topology with a switched impedancenetwork (EB-ZSI) was introduced, as shown in Fig. 3,which can achieve an even higher boost ratio due to theshorter shoot-through duration and a larger modulation index.However, the inverter volume also increases because of theextra inductors and/or capacitors.L1L2C1 C2DinVdcVinFig. 1. Classic three-phase Z-source inverter, where Vin is the input DCvoltage and Vdc is the DC-link voltage.L1L2C1 C2DinVdcVinL3D1D3L4 D5D4D6D2Fig. 2. Three-phase switched-inductor Z-source inverter [3].Additionally, the dc currents of ZSIs are normally choppeddue to the shoot-through operation. To address this problem,a number of embedded ZSI topologies were proposed [10],[11], which also achieve lower capacitor voltage ratings.A typical parallel-embedded Z-source inverter (E-ZSI) isexemplified in Fig. 4 , where it can be observed that twodc sources (e.g., PV panels) are directly connected in serieswith the inductors (i.e., (L1 and L2)) of the classic ZSI inFig. 1. This topology is especially suitable for PV or fuelcell systems.Inspired by the above, a new topology is proposed in thispaper by modifying the embedded Z-source and switchedZ-source, where Z represents impedance inverters. The pro-posed topology can achieve continuous dc source currentsand also reduce the voltage stresses with a relatively largeboost factor. In Section II, the operation principle of theproposed topology is presented. Comparisons with the con-ventional switched impedance networks and the embeddedZSIs are performed, and benchmarking results are given inSection III. Simulation and experimental results are provided978-1-5386-6054-6/18/$31.00 © 2018 IEEEL1C1D1C3DinL3D2L4L2C2 C4D3D4Vin VdcFig. 3. Enhanced-boost Z-source inverter [8].L1L2C1 C2DinVin/2 VdcVin/2 Fig. 4. Parallel-embedded Z-source inverter [10].in Section IV, which verify the improved performance ofthe proposed Z-source topology in terms of continuous dccurrents and also reduced voltage stresses. Finally, the paperis concluded in Section V.II. OPERATION PRINCIPLE OF THE PROPOSEDEEB-ZSI TOPOLOGYFig. 5 shows the topology of the proposed Embed-ded Enhanced-Boost Z-Source Inverter (EEB-ZSI), whichdemonstrates two symmetrical Z-source networks with em-bedded dc sources. The operation principle of the EEB-ZSIis the same as that of the conventional ZSI, there are twooperating states, i.e., the shoot-through state and non-shoot-through state.The equivalent circuits of the proposed Z-source converterin the shoot-through state and non-shoot-through state areshown in Figs. 6 and 7, respectively. It is assumed thatall capacitors (and inductors) in the proposed topology areidentical. Moreover, the dc sources in the two Z-impedancenetworks are the same voltage of 0.5Vin, with Vin being theinput voltage of the dc source before splitting . According tothe topological symmetry, it can be obtained thatVC1 = VC2 (1)VC3 = VC4 (2)in which VC1 , VC2 , VC3 , and VC4 are the corresponding volt-age across the capacitor C1, C2, C3, and C4. As mentionedabove, the operation can be separated into two states:L1C1D1C3DinL3Vin/2Vin/2D2L4L2C2 C4D3D4Vc1 Vc3Vc2 Vc3iL1iL2iL3iL4Vdca iabcFig. 5. Proposed three-phase embedded enhanced-boost Z-source inverter.L1C1 C3L3Vin/2Vin/2L4L2C2 C4Fig. 6. Shoot-through state of the proposed Z-source inverter.A. Shoot-Through StateAs shown in Fig. 6, D1 and D2 are ON with D3, D4,and Din being reverse-biased in the shoot-through state.Additionally, L1 and L2 are in parallel with C1 and C2,respectively. Then, it can be obtained thatVC1 = VC2 = VL1 = VL2 (3)where VL1 and VL2 are the voltage of the inductor L1 andL2, respectively.According to the Kirchhoff’s voltage law, the voltages onthe inductors L3 and L4 can be expressed asVL3 = VC3 + 0.5Vin (4)VL4 = VC4 + 0.5Vin (5)with VL3 , and VL4 being the inductor voltages in the shoot-through state.B. Non-Shoot-Through StateAs shown in Fig. 7, D3, D4, and Din are ON, and D1 andD2 are OFF. In one switching cycle, the inductor averagevoltage should be zero, and then applying the volt-secondbalance principle to all the inductors givesDVL1 + (1−D)VL1-NON = 0 (6)DVL3 + (1−D)VL3-NON = 0 (7)where VL1-NON and VL3-NON represent the inductor voltage onL1 and L3, respectively, during the non-shoot-through state,L1C1 C3L3Vin/2Vin/2L4L2C2 C4VdcFig. 7. Non-shoot-through state of the proposed Z-source inverter.and D is the duty cycle. With (3), (4), (6) and (7), VL1-NONand VL3-NON can be solved asVL1-NON = −D1−DVC1 (8)VL3-NON = −D1−D(VC3 + 0.5Vin) (9)Furthermore, according to Fig. 7, the following can beobtained by applying the Kirchhoff’s voltage law:VL1-NON + VC3 − VC1 = 0 (10)VL1-NON + VL3-NON − 0.5Vin + VC2 = 0 (11)VL1-NON − 0.5Vin + Vdc − VC3 = 0 (12)Accordingly, the capacitor voltage VC3 and the peak dc-linkvoltage V pdc can be expressed asVC3 =0.52D2 − 4D + 1Vin (13)V pdc =1−D2D2 − 4D + 1Vin = B · Vin (14)whereB =1−D2D2 − 4D + 1(15)is the boost factor.The peak of the inverter output voltage is expressed asV pac =MV pdc2=MBVdc2=GVdc2(16)in which G is the buck-boost factor, M is the modulationindex, and Vdc is the average dc-link voltage. The buck-boostfactor can be expressed with respect to the modulation indexM asG = MB =M22M2 − 1(17)III. COMPARISON OF THE PROPOSED EEB-ZSI WITHOTHER TOPOLOGIESA detailed comparison of the ZSI, E-ZSI, EB-ZSI andEEB-ZSI is performed, and the benchmarking results aresummarized in Table I. Fig. 8 shows the relationship betweenthe shoot-through duty ratio and the boost factor among thesetopologies. Although the boost factor of the proposed EEB-ZSI is slightly lower than the conventional EB-ZSI, it ismuch higher than the ZSI and the E-ZSI, as observed inFig. 8. In addition, Fig. 9 compares the voltage gains ofthe selected topologies in respect to the modulation index.Fig. 8. Boost factor comparison of the three Z-source inverters (i.e., theZSI, E-ZSI, and EB-ZSI) with the proposed inverter topology.Fig. 9. Voltage gain comparison of the three Z-source inverters (i.e., theZSI, E-ZSI, and EB-ZSI) with the proposed inverter topology.It can be seen in Fig. 9 that the voltage gain of the proposedimpedance-source topology is higher than the conventionalembedded ZSI and the classic ZSI. However, it achieves aslightly lower voltage gain when comparing with the EB-ZSI. Nevertheless, the proposed topology can achieve lowervoltage stresses, as shown in Figs. 10 and 11. The voltagestresses are defined as the ratio of the peak dc-link voltagetand capacitors voltage ot the minimum dc voltage. It canbe seen in Fig. 10 that the proposed EEB-ZSI has a betterperformance compared with other topologies in terms ofvoltage stresses over the power switches. The power switchstress of the proposed EEB-ZSI is almost the same as the EB-ZSI but much lower than the ZSI and E-ZSI for the samevoltage gain, as observed in Fig. 10. In addition, Fig. 11shows that the capacitor voltage stress of the proposed EZ-ZSI is less than the EB-ZSI, and thus, the capacitors withlower ratings can be used to reduce the cost and size forTABLE IBENCHMARKING OF SELECTED IMPEDANCE-SOURCE INVERTERS.ZSI [2] E-ZSI [10] EB-ZSI [8] EEB-ZSIB 11−2D11−2D12D2−4D+11−D2D2−4D+1G-M G = M2M−1 G =M2M−1 G =M2M2−1 G =M22M2−1Vs/GVdc 2− 1G 2−1G8G(√8G2+1+1)2−8G22G−1G√G2G−1Vc1 2/GVdc 1 2− 1G1+√1+8G24G12√2− 1GVc3 4/GVdc NA NA 1 1− 12GFig. 10. Comparison of switch stresses.Fig. 11. Capacitor voltage stress comparison of the EB-ZSI and the proposedEEB-ZSI.the same voltage gain. It is thus confirmed that the superiorperformance of the proposed topology over the EB-ZSI hasbeen achieved.TABLE IIEEB-ZSI PARAMETERS.Parameter Symbol Valuedc input voltage Vin 40 VEEB-ZSI inductance L 650 µHEEB-ZSI capacitor C 60 µFLoad inductance Rf 3 mHLoad resistance Lf 40 ΩSwitching frequency fs 5 kHzIV. SIMULATIONS AND EXPERIMENTAL TESTSIn order to validate the proposed EEB-ZSI topology,simulations and experimental tests are performed. Systemparameters are shown in Table II for both simulation andexperimental cases.A. Simulation ResultsThe proposed topology is simulated in the PLECS andMATLAB/Simulink with an open-loop control. The simu-lation results are shown in Fig. 12, where M = 0.775, D= 0.225, and Vdc = 40 V. According to (15), the boostfactor can be calculated as B = 3.85, and thus, the dc-linkvoltage should be boosted to 154 V (the peak). From thesimulation results, it is obvious that the capacitor voltagesof VC1 , VC2 , VC3 , VC4are, boosted to 77 V (VC1=VC2 ) and99 V (VC3=VC4 ), respectively, and the peak dc-link voltageVdc is boosted to 154 V, as expected. Additionally, all theinductor currents increase when the dc-link voltage remainszero during the shoot-through state, as shown in Fig. 12(b).This means that the DC currents are continuous. In orderto compare the capacitor stress between the EZ-ZSI andEEB-ZSI, another simulation is carried out and the resultsshow that the capacitor stress of the EZ-ZSI is higher thanthe proposed EEB-ZSI to achieve the same voltage gain,as indicated in Fig. 12(c). This is in agreement with thetheoretical analysis.B. Experimental ResultsAn experimental setup is built up in the lab to ver-ify the performance of the proposed topology. The entiresystem is controlled by a digital signal processor (DSP)TMS320F28335. The experimental results are shown in Fig.Fig. 12. Simulation results of the proposed Embedded Enhanced-Boost Z-source Inverter (EEB-ZSI), (a) the output leg voltage and load current inEEB-ZSI, (b) the dc-link voltage and inductor currents in EEB-ZSI, and (c)the voltages of the capacitors in the EZ-ZSI and the EEB-ZSI.13. The capacitor voltages VC1 , VC2 , and VC3 , VC4 are,boosted to 73 V (VC1=VC2 ) and 92 V (VC3=VC4 ), and thepeak dc-link voltage Vdc is boosted from 40 V to 148 V, asFig. 13. Experimental results of a three-phase EEB-ZSI system, (a) the dc-link voltage Vdc[100 V/div]and inductor currents iL1 , iL2 , iL3 , iL4 [5 A/div], (b) the dc-link voltage Vdc[100 V/div] and capacitor voltages VC1 , VC2 ,VC3 , VC4 [50 V/div].shown in Fig. 13(a). Compared with simulation results, theboost factor of the experimental results is slightly low dueto the effect of the parasitic components in the inductors andcapacitors. Moreover, the dc source currents in Fig. 13(a) arecontinuous. Notably, there are voltage spikes appearing in thedc-link voltage, as shown in Fig. 13. This is possibly due tothe electromagnetic interference, which should be improvedfurther.V. CONCLUSIONIn this paper, an Embedded Enhanced-Boost Z-sourceInverter (EEB-ZSI) was proposed. Compared with theEnhanced-Boost ZSI (EB-ZSI), the current from the dcsource in the proposed topology is continuous. Two dcsources are embedded into the symmetrical Z-source net-works in the proposed topology. Additionally, the capacitorvoltage stress of the proposed EEB-ZSI topology is lowerthan the EB-ZSI due to the embedded configuration. Sim-ulation and experimental results have demonstrated that theproposed topology has a similar boost capability as the EB-ZSI and better performance than the EB-ZSI in terms ofvoltage stresses of capacitors.REFERENCES[1] Z. Liang, S. Hu, H. Yang, and X. He, “Synthesis and design of theac current controller and impedance network for the quasi-Z-sourceconverter,” IEEE Trans. Power Electron., vol. 65, no. 10, pp. 8287–8296, Oct. 2018.[2] F. Z. Peng, “Z-source inverter,” IEEE Trans. Ind. Appl., vol. 39, no. 2,pp. 504–510, Mar. 2003.[3] M. Zhu, K. Yu, and F. L. Luo, “Switched inductor Z-source inverter,”IEEE Trans. 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