**HYBRID Z-SOURCE BOOST DC-DC CONVERTERS**

** **

*Abstract*

This paper presents a new family of hybrid Z-source boost dc-dc converters intended for photovoltaic (PV) applications, where the high step-up dc-dc converters are demanded to boost the low source voltages to a predefined grid voltage. Because the boost capabilities of the traditional Z-source networks are limited, the proposed converters are composed of combine traditional Z-Source networks in different ways to enhance the boost abilities of the traditional Z-source networks. The new version of the proposed Z-source converters are termed hybrid Z-Source boost dc-dc converters to satisfy the traditional benefits of Z-source networks with stronger voltage boost abilities which can also be applied to dc-ac, ac-ac, and ac-dc power conversions. The performances of the proposed converters are compared with other Z-source networks behaviors. The simulation and experimental results of the proposed converters are validated at different operating conditions.

**EXISTING SYSTEM: **

The concept of Z-source network was firstly proposed by F. Z. Peng. As shown in Fig. 2, the Z-source network is an X-shaped impedance network, which can be applied to dc-ac, dc-dc, ac-ac, and ac-dc power conversion. The Z-source inverter (ZSI) can utilize the shoot-through state which is not allowed in the traditional voltage-source inverters (VSIs) to boost the voltage. In addition, the buck voltage inversion ability is also retained. The ZSI has rapidly become a research hotspot because of its buck-boost inversion ability. Though with the aforementioned advantages, the original ZSI also has some drawbacks, such as discontinuous input current, high voltage stresses and limited boost factor 1/(1-2*D* 0278-0046 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. *s* ) (*D* is the shoot-through duty cycle). Moreover, the dc voltage source and the inverter bridge do not share a common ground. To overcome the limitations in the original ZSI, various novel impedance-source network topologies have been presented in numerous studies. A the modified Z-source network topologies, quasi-Z-source network is a simple but efficient solution. It can be seen from Fig. 3 that the quasi-Z-source inverters (qZSIs) can be classified into continuous-current qZSI and discontinuous-current qZSI. For easier referencing, their impedance networks are respectively referred to as quasi-Z-source network I and quasi-Z-source network II. The two proposed quasi-Z-source networks have the same boost factors as the traditional Z-source network, ). But they have some advantages over the traditional Z-source network, such as continuous input current, common ground between the voltage source and the inverter bridge, and reduced capacitor voltage stress.

**PROPOSED SYSTEM: **

Three new hybrid Z-source dc-dc converters are presented in *V*** in** this paper, which can be categorized as hybrid two-quasi-Z- source boost dc-dc converter, hybrid three-quasi-Z-source boost dc-dc converter and hybrid Z-source/quasi-Z-source boost dc-dc converter. The topologies of these converters are presented in the following sections.

*A. Hybrid two-quasi-Z-source boost dc-dc converter*The hybrid two-quasi-Z-source boost dc-dc converter is shown in Fig. 4, which consists of a hybrid two-quasi-Z-source network (

*L*1 –

*D*1 –

*C*1 –

*C*2 –

*L*2 –

*C*3 –

*D*2 –

*C*4 –

*L*), an active switch

*S*, an output diode

*D*3 , and an output capacitor

*C*3 . It can be seen from Fig. 4 that the proposed hybrid Z-source network is obtained by replacing inductor

*L*in the quasi-Z-source network I with the quasi-Z-source network II, which adds an inductor

*L*, two capacitors (

*C*3 and

*C*4 ), and a diode

*D*2 3 to the quasi-Z-source network I. The hybrid two-quasi-Z-source network has higher step-up ability (voltage gain

*M*= 1/(1-3

*D*)) than that of the quasi-Z-source network I (

*M*= 1/(1-2

*D*

*s*

*s*)) and inherits the merits of the quasi-Z-source network I, such as continuous input current and common ground between the input and output.

**CONCLUSIONS **

A family of hybrid Z-source boost dc-dc converters for PV power systems has been presented in this paper. The proposed converters use the hybrid Z-source networks, which are obtained by combining the traditional Z-source networks. Apart from the high step-up abilities, the proposed hybrid Z-source networks retain all the advantages of the traditional Z-source networks, such as continuous input current, reduced capacitor voltage stress and common ground between the voltage source and the inverter bridge. The topologies, operating principles and comparison with other Z-source networks are presented in this paper. Finally, the simulation and experimental results verify the features of the proposed converters.

**REFERENCES **** **

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