A New Class of Single-Phase High-Frequency Isolated Z-Source AC-AC Converters with Reduced Passive Components

 

Abstract

In this paper, a class of single-phase Z-source (ZS)  ac-ac converters is proposed with high-frequency transformer (HFT) isolation. The proposed HFT isolated ZS ac-ac converters possess all the features of their non-isolated counterparts, such as; providing wide range of buck-boost output voltage with reversing or maintaining the phase angle, suppressing the in-rush and harmonic currents, and improved reliability. In addition, the proposed converters incorporate HFT for electrical isolation and safety, and therefore can save an external bulky line frequency transformer, for applications such as dynamic voltage restorers (DVRs), etc. The proposed HFT isolated ZS converters are obtained from conventional (non-isolated) ZS ac-ac converters by adding only one extra bidirectional switch, and replacing two inductors with an HFT, thus saving one magnetic core. The switching signals for buck and boost modes are presented with safe-commutation strategy to remove the switch voltage spikes. A quasi-Z-source based HFT isolated ac-ac is used to discuss the operation principle and circuit analysis of the proposed class of HFT isolated ZS ac-ac converters. Various ZS based HFT isolated proposed ac-ac converters are also presented thereafter. Moreover, a laboratory prototype of the proposed converter is constructed and experiments are conducted to produce output voltage of 110 Vrms/60 Hz, which verify the operation of the proposed converters.

EXISTING  SYSTEM: 

The ZS network based concept is proposed by Peng in, where a ZS inverter is proposed with buck-boost voltage capability, and enhanced reliability. The ZS concept is also extended to ac-ac converters with various studies performed on single-phase ac-ac converters  and three-phase ac-ac converters . A single-phase ZS ac-ac converter is proposed , with benefits such as buck-boost voltage capability with reversing or maintaining phase-angle, smaller in-rush and harmonic current, and enhanced reliability. A single-phase qZS ac-ac converter, which retains all the benefits of the ZS ac-ac converter. It provides continuous input current, common grounds between input and output, and low voltage stress across capacitor. In, a single-phase modified qZS ac-ac converter is proposed, which has reduced number of passive components compared to the ZS and qZS ac-ac converters. The soft-commutation strategies for these ZS ac-ac converters are presented in, to eliminate switch voltage spikes. A coupled-inductor based single-phase gamma ZS ac-ac converter is proposed in, which can adjust the voltage gain by varying the turns ratio of coupled-inductor along with the duty ratio of the converter.   

PROPOSED  SYSTEM:

To overcome aforementioned drawbacks of the conventional non-isolated ZS ac-ac converters  and HFTI ZS ac-ac converters, a new class of single-phase ZS ac-ac converters is proposed with HFT isolation and reduced passive components. In addition to retaining all the features of the conventional ZS ac-ac converters, the proposed converters incorporate HFT for electrical isolation and safety. Therefore, they can save a large and costly external line frequency transformer, for applications such as DVRs, etc. The proposed HFTI ZS ac-ac converters use only one additional bidirectional switch compared to their conventional non-isolated counterparts, and have the same or less passive components requirement, as they add one HFT by eliminating two inductors (saving one magnetic core) from their non-isolated counterparts. The proposed converters save two capacitors and two inductors compared to the isolated ZS converters in, thus, reduce the cost, volume and losses. The switching strategies for buck and boost modes are presented with safe-commutation to remove the switch voltage spikes. A laboratory prototype of the proposed converter is also constructed and experiments are conducted to produce output voltage of 110 Vrms/60 Hz, which verify the operation of the proposed converters. 

CONCLUSIONS

In this paper, a new class of single-phase ZS ac-ac  converters is proposed with HFT isolation. The proposed HFTI ZS ac-ac converters have all the benefits of their conventional non-isolated counterparts such as; buck-boost voltage capability, reducing the in-rush and harmonic currents, and enhanced reliability. In addition, the proposed converters have HFT isolation, thus, do not need bulky external line frequency transformer to provide electrical isolation and safety for application as DVR. The proposed HFTI ZS ac-ac converters are obtained from conventional non-isolated ZS ac-ac converters by replacing two inductors with HFT (saving one magnetic core), and adding only one extra bidirectional switch.The switching strategies for buck and boost modes are presented with safe-commutation strategy to remove the switch voltage spikes without using snubber circuits. A qZS based proposed HFTI ac-ac converter is used to discuss the operation principle and circuit analysis of the proposed class of HFTI ZS ac-ac converters. Thereafter, various ZS based HFTI proposed ac-ac converters are also presented.  A laboratory prototype of the proposed converter is also constructed and experiments are conducted to produce output voltage of 110 Vrms/60 Hz, which verify the operation of the proposed converters.

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