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Friday, 15 June 2018

An Interline Dynamic Voltage Restoring and Displacement Factor Controlling Device (IVDFC)


An interline dynamic voltage restorer (IDVR) is invariably employed in distribution systems to mitigate voltage sag/swell problems. An IDVR merely consists of several dynamic voltage restorers (DVRs) sharing a common dc link connecting independent feeders to secure electric power to critical loads. While one of the DVRs compensates for the local voltage sag in its feeder, the other DVRs replenish the common dc-link voltage. For normal voltage levels, the DVRs should be bypassed. Instead of bypassing the DVRs in normal conditions, this paper proposes operating the DVRs, if needed, to improve the displacement factor (DF) of one of the involved feeders. DF improvement can be achieved via active and reactive power exchange (PQ sharing) between different feeders. To successfully apply this concept, several constraints are addressed throughout the paper. Simulation and experimental results elucidate and substantiate the proposed concept.
1.      Displacement factor improvement
2.      Interline dynamic voltage restorer (IDVR)
3.      Interline dynamic voltage restoring and displacement factor controlling (IVDFC)
4.      PQ sharing mode



 Fig. 1. Single line diagram of an IPFC in transmission system.


Fig. 2. Per-phase PQ sharing mode simulation results: (a)–(c) for first case and (d)–(f) for the second case.

Fig. 3. Per-phase simulation results for voltage sag condition at: (a) feeder 1 and (b) feeder 2.

Fig. 4. Per-phase experimental and corresponding simulation results for DF improvement case: (a) and (b) receiving feeder; (c) and (d) sourcing feeder (time/div= 10 ms/div).

Fig. 5 Per-phase experimental results and corresponding simulation results for voltage sag case: (a) and (b) at feeder 1 and (c) and (d) at feeder 2 (time/div = 10 ms/div).

Fig. 6 Per-phase experimental results and corresponding simulation results for voltage swell case at: (a) and (b) feeder 1 and (c) and (d) at feeder 2 (time/div = 10 ms/div).

This paper proposes a new operational mode for the IDVR to improve the DF of different feeders under normal operation. In this mode, theDFof one of the feeders is improved via active and reactive power exchange (PQ sharing) between feeders through the common dc link.
The same system can also be used under abnormal conditions for voltage sag/swell mitigation. The main conclusions of this work can be summarized as follows:
1) Under PQ sharing mode, the injected voltage in any feeder does not affect its load voltage/current magnitude, however, it affects the DFs of both sourcing and receiving feeders. The DF of the sourcing feeder increases while the DF of the receiving feeder decreases.
2) When applying the proposed concept, some constraints should be satisfied to maintain the DF of both sourcing and receiving feeders within acceptable limits imposed by the utility companies. These operational constraints have been identified and considered.
3) The proposed mode is highly beneficial if the active power rating of the receiving feeder is higher than the sourcing feeder. In this case, the DF of the sourcing feeder will have a notable improvement with only a slight variation in DF of the receiving feeder.
The proposed concept has been supported with simulation and experimental results.
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