Dynamic Voltage Restorer Based on Three-Phase Inverters Cascaded Through an Open-End Winding Transformer

IEEE Transactions on Power Electronics, 2015

ABSTRACT

This paper investigates a dynamic voltage restorer (DVR) composed of two conventional three-phase inverters series cascaded through an open-end winding (OEW) transformer, denominated here DVR-OEW. The DVR-OEW operating with either equal or different dc-link voltages are examined. The proposed topology aims to regulate the voltage at the load side in the case of voltage sags/swells, distortion, or unbalance at the grid voltage. A suitable control strategy is developed, including space-vector analysis, level-shifted PWM (LSPWM) and its equivalent optimized single-carrier PWM (SCPWM), as well as the operating principles and characteristics of the DVR. Comparisons among the DVR-OEW and conventional configurations, including a neutral-point clamped (NPC) converter based DVR, are furnished. The main advantages of the DVROEW compared to the conventional topologies lie on: i) reduced harmonic distortion, ii) reduced converter losses, and iii) reduced voltage rating of the power switches. Simulated and experimental results are presented to validate the theoretical studies.

 

SOFTWARE: MATLAB/SIMULINK

 

 BLOCK DIAGRAM:

Fig. 1 Example of a typical application of DVR in Medium-Voltage (MV) distribution system..

 

EXPECTED SIMULATION RESULTS:

Fig. 2. System voltages for vca = vcb. (a) Grid voltages (egj). (b) DVR voltages at the secondary side of the injection transformers (vsj ). (c) Load voltages (vlj ). (d) Injected voltage (vp1) for one phase at the primary side of injection transformer.

 

Fig. 3. Pole voltages in one phase at inverters A (v1a0a) and B (v1b0b), respectively. (a) OEW inverter operates with alternatively leg of converter clamped in every half cycle. (b) OEW inverter operates by clamping inverter A.

 

CONCLUSION

In this paper a dynamic voltage restorer (DVR) obtained by means of the series connection of two three-phase inverters through an open-end winding transformer was presented. Two equivalent implementations with either level-shifted carrier PWM (LSPWM) or single-carrier PWM (SCPWM) strategy approaches were presented. The main advantages of the proposed topology, compared to conventional configurations with three legs (see Fig. 2(a)), six-leg (see Fig. 2(b)) and NPC (see Fig. 2(c)) lies on: (i) reduced harmonic distortion (operating at the same switching frequency), (ii) reduced converter losses (operating with the same harmonic distortion), (iii) reduced converter losses (with the same switching frequency), see Table III and (iv) reduced voltage rating of the power switches employed in the DVR. The operations with different dc-link voltages have been investigated and it is shown that much lower harmonic distortion can be obtained. The proposed DVR system is suitable for medium voltage application. Simulated and experimental results were also presented.

 

REFERENCES

  • Goharrizi, S. Hosseini, M. Sabahi, and G. Gharehpetian, “Threephase HFL-DVR with independently controlled phases,” Power Electronics, IEEE Transactions on, vol. 27, pp. 1706–1718, April 2012.
  • Biswas, S. Goswami, and A. Chatterjee, “Optimal distributed generation placement in shunt capacitor compensated distribution systems considering voltage sag and harmonics distortions,” Generation, Transmission Distribution, IET, vol. 8, pp. 783–797, May 2014.
  • N. M. Ho and H. S. H. Chung, “Implementation and performance evaluation of a fast dynamic control scheme for capacitor-supported interline DVR,” IEEE Trans. Power Electron., vol. 25, pp. 1975 –1988, Aug. 2010.
  • Rosas-Caro, F. Mancilla-David, J. Ramirez-Arredondo, and A. Bakir, “Two-switch three-phase ac-link dynamic voltage restorer,” Power Electronics, IET, vol. 5, pp. 1754–1763, November 2012.
  • Subramanian and M. Mishra, “Interphase ac-ac topology for voltage sag supporter,” Power Electronics, IEEE Transactions on, vol. 25, pp. 514 –518, feb. 2010.

Cascaded Open-End Winding Transformer based DVR

2016, IEEE

ABSTRACT

This paper introduces and generalizes a class of multilevel dynamic voltage restorer (DVR) for voltage sags/swells compensation of high-power sensitive loads. Such a device can improve the power quality of sensitive loads located in stiff systems. The proposed DVR is based on three-phase bridge converters series-connected by means of cascaded transformers using the concept of open-end winding (OEW). Hence, two DC links can provide either symmetrical (i.e., equal DC-link voltages) or asymmetrical (i.e., different DC-link voltages) operation of the DVR converters. Generalization for K-stages is presented as well. The proposed configuration is named as DVR-COEW (i.e., cascaded open-end winding). Such a topology permits to generate a maximized number of voltage levels per converter leg. The multilevel waveforms at the output voltages of the converter are generated by using a suitable PWM strategy associated with both: i) DC-link voltages ratio and ii) transformers turns ratio. Modularity and simple maintenance make the proposed DVRCOEW an attractive solution compared to some conventional configurations. The model and PWM control are addressed in this paper. Simulation and experimental results are presented.

 

KEYWORDS:

  1. Dynamic voltage restorer (DVR)
  2. Open-end winding (OEW)
  3. DC-link voltages
  4. Pulse Width Modulation (PWM)

 

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

Fig. 1. Example of a DVR-based system

 

EXPECTED SIMULATION RESULTS:

Figure 2. Phase-voltage of the resultant converter in phase-a (vra) for conventional and proposed DVRs considering an operation with 1-stage (i.e.,k = 1 with N1 = 1) having converters with a total of 6 legs. (a) Conventional DVR. (b) Proposed COEW-DVR and symmetrical DC-link voltages (i.e., DC link voltage ratio 1:1). (c) Proposed COEW-DVR and asymmetrical DC-link voltages (i.e., DC-link voltages ratio 2.:1)

Fig. 3. Figure 7. Phase-voltage of the resultant converter in phase-a (vra) for conventional and proposed DVRs considering an operation with 2-stages (i.e., k = 2) having converters with a total of 12 legs. (a) Conventional DVR with N1 = 1 and N2 = 3. (b) Proposed COEW-DVR and asymmetrical DC-link voltages (i.e., DC-link voltage ratio 2:1) N1 = 1 and N2 = 2. (c) Proposed COEW-DVR and asymmetrical DC-link voltages (i.e., DC-link voltages ratio 4:1) N1 = 1 and N2 = 2.

 

CONCLUSION

This paper has presented a cascaded open-end winding (COEW) transformer based DVR. The COEW-DVR configuration is generalized for k-stages. A comparison between the proposed and conventional (using HB [6]) configurations (operating with 1-stage) is summarized in Table IV. It can be seen that the proposed COEW-DVR has a better quality of output voltages when compared to the conventional one with HB [6]. This is observed by means of WTHD of the output resultant voltages vrj of the COEW-converter. Additionally, the lower values of WTHD at the output voltages permits the proposed COEW-DVR to reduce its switching frequency to match the same harmonic distortion value obtained for the conventional one. In this way, semiconductor losses would give a fair comparison. The semiconductor losses estimation was done by using the thermal module of PSIM, in which both configurations have operated under the same vrj magnitude and WTHD value. The power of the three-phase load was 6 kW. The conditions and more details for these comparisons under 1-stage operation are found in [19]. Hence, the semiconductor losses estimation for COEW-DVR with 1-stage operation are reduced up to 48.1% compared to the values obtained with conventional one. The losses comparison for 2 stages operation has been done as well. In that case, for the same switching frequency (i.e., fsw =10kHz) the proposed COEW-DVR has presented a reduction of 25% compared to losses obtained for conventional one.

 

REFERENCES

  • Koval and M. Hughes, “Canadian national power quality survey: frequency of industrial and commercial voltage sags,” Industry Applications, IEEE Transactions on, vol. 33, pp. 622–627, May 1997.
  • Affolter and B. Connell, “Experience with a dynamic voltage restorer for a critical manufacturing facility,” in Transmission and Distribution Conference and Exposition, 2003 IEEE PES, vol. 3, pp. 937–939 vol.3, Sept 2003.
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  • -m. Ho and H.-H. Chung, “Implementation and performance evaluation of a fast dynamic control scheme for capacitor-supported interline DVR,” Power Electronics, IEEE Transactions on, vol. 25, no. 8, pp. 1975–1988, 2010.
  • W. Li, P. C. Loh, F. Blaabjerg, and D. Vilathgamuwa, “Investigation and improvement of transient response of dvr at medium voltage level,” Industry Applications, IEEE Transactions on, vol. 43, pp. 1309–1319, Sept 2007.