دانلود رایگان مقاله انگلیسی توپولوژی بهبود یافته برای مبدل های AC / DC چندگانه در سیستم های HVDC و VFD - نشریه IEEE

Abstract

An improved topology for a multi-pulse AC/DC converter-based on 6-pulse rectifier modules operating in a degraded mode is described. Its main application is HVDC and VFD systems, where reliability, availability, and maintainability are the most critical requirements. A new concept called, “threephase electronic Z/z transformers,” which provides separated voltages with reconfigurable phase-shifting angles and voltage ratios, is discussed. The number of acceptable faulty rectifier modules is defined at the design stage. Such features enable AC/DC rectifier systems to be modular and reconfigurable. In contrast with conventional topologies, the proposed structure can operate optimally as an 18-pulse, 12-pulse, or 6-pulse rectifier in faulty conditions of local transformers or rectifier modules. An implementation method for a degraded 24-pulse rectifier with its control architecture including the Z/z transformers’ command unit is discussed. A 1.5 kV, 18 kVA, 18-pulse AC/DC converter associated with a real-time system control is designed and tested. Promising results validate the new concept.

VI. CONCLUSION

This paper proposed an improved topology of a multi-pulse AC/DC rectifier system to enable a degraded mode operation of VFD and HVDC systems with a faulty transformer or rectifier module but with acceptable grid side current distortion. The analyzed system is based on a 24-pulse rectifier system with four separated three-phase transformers, which are called electronic Z/z transformers, since their phase shifting angles and voltage ratios are reconfigurable through electronic command. The proposed configuration improves the conventional structure of a 24-pulse rectifier system, introducing the ability to adjust and improve the grid side current distortion in a degraded mode.

The principle and an implementation method of the proposed electronics Z/z transformer has been discussed. Moreover, the integration of the Z/z transformer command unit within the control architecture for VFD and HVDC systems has been presented. Finally, a reduced scale laboratory experimental setup rated 18 kVA, 1.5 kV and 18-pulse converter has been built and tested to confirm the accuracy of the investigations.

In future, the effects of the additional switches on the dynamic performances of the AC/DC rectifier system will be investigated.