Quasi Z-Source AC-AC converter system connected in series With Dynamic Voltage Restorer(DVR) capability Jun-Hyun Eom - Department of Electrical Engineering Graduate, School Chonnam National University-SOUTH KOREA

동적전압보상 기능을 갖는 출력이 직렬 결합된 Quasi Z-소스 AC-AC 컨버터
 Quasi Z-Source AC-AC converter system connected in series With Dynamic Voltage Restorer(DVR) capability Jun-Hyun Eom
 Department of Electrical Engineering Graduate, School Chonnam National University (Supervised by Professor Young-Cheol Lim)

(Abstract)
 Recently, different with the conventional load, the present load devices such as computers, Automated production equipments, precision electronic devices are very sensitive to the power quality. These load devices sensitive to the power quality are increasing sharply and people are paying more and more attention to the AC-AC power conversion devices like instantaneous voltage-compensators, phase-shifters, electronic transformer which are installed in the side of power system or consumers. Similarly, the AC chopper, PWM AC-AC converter, matrix converter and Z-Source AC-AC converter also belong to the AC-AC power conversion devices referred above. among these devices, due to the latest research method, the Z-Source AC-AC converter has quite simply structure and control method and is possible to boost output voltage in phase and boost or buck output voltage out of phase with respect to input voltage.

Nevertheless, since the Z-Source AC-AC converter operates in DCM (Discontinuous Current Mode), stress of the elements is bigger compared with the case of CCM(Continuous Current Mode) and it's very disadvantageous viewed from the waveform. It is probable to solve the problems referred above by Quasi Z-Source AC-AC converter. However, the operation of buck mode is impossible, even though it's possible to boost or buck the output voltage out of phase and boost the output voltage in phase.

In this study, a single-phase quasi Z-source AC-AC converters with a series connection of the output terminals is proposed. The proposed system has configuration that the input terminals of two quasi Z-source AC-AC converters are connected in parallel and its output terminals are connected in series. for output of in-phase buck mode with respect to the input ,the intersection switching control is presented and the current flow in both of the out phase mode and in phase mode and the output voltage's forming process was shown.

In addition, a DVR(Dynamic Voltage Restorer) though using a single-phase quasi Z-source AC-AC converter connected with the output terminals in series is proposed. In general, among the problems which cause the lower quality, the Voltage Swell or Voltage Sag could be the major one which brings great influence to the consumers with high frequency and sensitive load. The Voltage Swell which is the increasement of the supply voltage's magnitude in duration of 0.5∼30[cycles] while the voltage magnitude is 1.1∼1.8[p.u] of nominal voltage and the Voltage Sag which is the drop of the supply voltage's magnitude in duration of 0.5∼30[cycles] while the voltage magnitude is 1.1∼1.8[p.u] of nominal voltage can lead to the accidents happening in most of the nearby distribution circuits. Such Voltage Swell or Voltage Sag causes the misoperation or suspension of work and bring about Nevertheless, since the Z-Source AC-AC converter operates in DCM (Discontinuous Current Mode), stress of the elements is bigger compared with the case of CCM(Continuous Current Mode) and it's very disadvantageous viewed from the waveform.

It is probable to solve the problems referred above by Quasi Z-Source AC-AC converter. However, the operation of buck mode is impossible, even though it's possible to boost or buck the output voltage out of phase and boost the output voltage in phase.
In this study, a single-phase quasi Z-source AC-AC converters with a series connection of the output terminals is proposed.

LINK ORIGINAL EN LA WEB
http://ocean.kisti.re.kr/downfile/volume/kipe/JRJJC3/2013/v18n4/JRJJC3_2013_v18n4_322.pdf