An Enhanced Voltage Sag Compensation Scheme for Dynamic Voltage Restorer

IEEE Transactions on Industrial Electronics, 2013

ABSTRACT

This paper deals with improving the voltage quality of sensitive loads from voltage sags using dynamic voltage restorer (DVR). The higher active power requirement associated with voltage phase jump compensation has caused a substantial rise in size and cost of dc link energy storage system of DVR. The existing control strategies either mitigate the phase jump or improve the utilization of dc link energy by (i) reducing the amplitude of injected voltage, or (ii) optimizing the dc bus energy support. In this paper, an enhanced sag compensation strategy is proposed that mitigates the phase jump in the load voltage while improving the overall sag compensation time. An analytical study shows that the proposed method significantly increases the DVR sag support time (more than 50%) compared with the existing phase jump compensation methods. This enhancement can also be seen as a considerable reduction in dc link capacitor size for new installation. The performance of proposed method is evaluated using simulation study.

 

KEYWORDS:

  1. Dynamic voltage restorer (DVR)
  2. Voltage source inverter (VSI)
  3. Voltage sag compensation
  4. Voltage phase jump compensation.

 

SOFTWARE: MATLAB/SIMULINK

  

BLOCK DIAGRAM:

Fig. 1. Basic DVR based system configuration

 

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results for the proposed sag compensation method for 50% sag depth. (a) PCC voltage, (b) load voltage, (c) DVR voltage, (d) DVR active and reactive power, and (e) dc link voltage.

Fig. 3. Simulation results for the proposed sag compensation method for 23% sag depth. (a) PCC voltage, (b) load voltage, (c) DVR voltage, (d) DVR active and reactive power, and (e) dc link voltage.

 

CONCLUSION

In this paper an enhanced sag compensation scheme is proposed for capacitor supported DVR. The proposed strategy improves the voltage quality of sensitive loads by protecting them against the grid voltage sags involving the phase jump. It also increases compensation time by operating in minimum active power mode through a controlled transition once the phase jump is compensated. To illustrate the effectiveness of the proposed method an analytical comparison is carried out with the existing phase jump compensation schemes. It is shown that compensation time can be extended from 10 to 25 cycles (considering pre sag injection as the reference method) for the designed limit of 50% sag depth with 450 phase jump. Further extension in compensation time can be achieved for intermediate sag depths. This extended compensation time can be seen as considerable reduction in dc link capacitor size (for the studied case more than 50%) for the new installation. The effectiveness of the proposed method is evaluated through extensive simulations in MATLAB/Simulink and validated on a scaled lab prototype experimentally. The experimental results demonstrate the feasibility of the proposed phase jump compensation method for practical applications.

 

REFERENCES

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  • G. Nielsen, F. Blaabjerg and N. Mohan, “Control strategies for dynamic voltage restorer, compensating voltage sags with phase jump,” in Proc. IEEE APEC, 2001, pp. 1267–1273.
  • D. Li, S.S. Choi, and D.M. Vilathgamuwa, “Impact of voltage phase jump on loads and its mitigation,” in Proc. 4th Int. Power Electron. Motion Control Conf., Xian, China, Aug. 14–16, 2004, vol. 3, pp. 1762– 176.
  • Sullivan, T. Vardell, and M. Johnson, “Power interruption costs to industrial and commercial consumers of electricity, IEEE Trans. Ind App., vol. 33, no. 6, pp. 1448–1458, Nov. 1997.
  • Kaniewski, Z. Fedyczak and G. Benysek “AC Voltage Sag/Swell Compensator Based on Three-Phase Hybrid Transformer With Buck- Boost Matrix-Reactance Chopper”, IEEE Trans. Ind. Electron., vol.61, issue. 8, Aug 2014.

 

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