IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 59, NO. 10, OCTOBER 2012 3727 Step-Up DC/DC Converters With Cascaded Quasi-Z-Source Network Dmitri Vinnikov, Senior Member, IEEE, Indrek Roasto, Member, IEEE, Ryszard Strzelecki, Senior Member, IEEE, and Marek Adamowicz, Member, IEEE Abstract—This paper is devoted to the step-up dc/dc converter family with a cascaded quasi-Z-source network (qZS-network). The cascaded (two-stage) qZS-network could be derived by the adding of one diode, one inductor, and two capacitors to the traditional quasi-Z-source inverter (qZSI). The proposed cascaded qZSI inherits all the advantages of the traditional solution (voltage boost and buck functions in a single stage, continuous input cur- rent, and improved reliability). Moreover, as compared to the con- ventional qZSI, the proposed solution reduces the shoot-through duty cycle by over 30% at the same voltage boost factor. Theo- retical analysis of the two-stage qZSI in the shoot-through and non-shoot-through operating modes is described. The proposed and traditional qZS-networks are compared. A prototype of a step-up dc/dc converter with the cascaded qZS-network was built to verify the theoretical assumptions. The experimental results are presented and analyzed. Finally, a further optimization method of the cascaded qZS-network is proposed, and some practical design issues are discussed. Index Terms—DC–DC power conversion, fuel cells (FCs), power conditioning units (PCUs), pulsewidth-modulated power convert- ers, rectifiers. I. I NTRODUCTION T HE voltage-fed quasi-Z-source inverter [(qZSI); Fig. 1(a)] has been reported to be suitable for different renewable power applications (fuel cells (FCs), solar panels, wind power generators, etc.) because of its unique capability of voltage boost and buck functions in a single stage [1]–[4]. If necessary, the qZSI can boost the input voltage by introducing a spe- cial shoot-through switching state, which is the simultaneous conduction (cross conduction) of both switches of the same inverter’s phase leg. This switching state is forbidden for the traditional voltage-source inverters (VSIs) because it causes the short circuit of the dc-link capacitors. In the qZSI, the shoot- Manuscript received December 2, 2010; revised May 6, 2011 and October 18, 2011; accepted November 15, 2011. Date of publication December 7, 2011; date of current version April 27, 2012. This work was supported in part by the Estonian Ministry of Education and Research under Project SF0140016s11 and in part by the Estonian Science Foundation under Grants ETF8538 and ETF8687. D. Vinnikov and I. Roasto are with the Department of Electrical Drives and Power Electronics, Tallinn University of Technology, 19086 Tallinn, Estonia (e-mail: dmitri.vinnikov@ieee.org; indrek.roasto@ieee.org). R. Strzelecki is with the Department of Ship Automation, Gdynia Maritime University, 81-225 Gdynia, Poland, and also with the Power Electronics Lab- oratories, Electrotechnical Institute, Po˙ zaryskiego 28, 04-703 Warsaw, Poland (e-mail: rstrzele@am.gdynia.pl). M. Adamowicz is with the Department of Mechatronics and High Volt- age Engineering, Gdansk University of Technology, 80-233 Gdansk, Poland (e-mail: madamowi@ely.pg.gda.pl). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIE.2011.2178211 Fig. 1. (a) Voltage-fed qZSI and (b) voltage-fed qZSI with the cascaded qZS- network. through states are used to boost the magnetic energy stored in the dc-side inductors L 1 and L 2 without short circuiting the dc capacitors C 1 and C 2 . This increase in magnetic energy, in turn, provides the boost of the voltage seen on the inverter output during traditional operating states. If the input voltage is high enough, the shoot-through states are eliminated, and the qZSI begins to operate as a traditional VSI. This paper discusses a method of performance improvement for the voltage-fed qZSI with continuous input current gained by the introduction of the cascaded quasi-Z-source network (qZS-network). The cascaded (two-stage) qZS-network is de- rived by the adding of one diode (D 2 ), one inductor (L 3 ), and two capacitors (C 3 and C 4 ) to the traditional qZSI, as shown in Fig. 1(b). The proposed cascaded qZS-network enables the duty cycle of the shoot-through state to be sufficiently decreased at the same voltage boost factor and component stresses as those of the traditional qZSI [5]–[9]. Due to the decreased shoot- through duty cycle, the values of the inductors and capacitors of the qZS-network could also be decreased. On the other hand, for the same component ratings and voltage and current stresses, the qZSI with the proposed cascaded qZS-network will ensure a higher voltage boost factor than with traditional solutions. 0278-0046/$26.00 © 2011 IEEE