The flexible ac-transmission system (FACTS) family called distributed power flow controller (DPFC). The DPFC is derived from the unified power flow controller (UPFC) with eliminated common dc link. The active power exchange between the shunt and series converters, which is through the common dc link in the UPFC, is now through the transmission lines at the third harmonic frequency. The DPFC is to use multiple small size single phase converters instead of large size three phase series converter in the UPFC. The large number of series converters provides redundancy, thereby increasing the system reliability. As the D-FACTS converters are single phase and floating with respect to the ground, there is no high voltage isolation required between the phases. The cost of the DPFC system is lower than the UPFC. The DPFC has the same control capability as the UPFC, which comprises the adjustment of the line impedance, the transmission angle, and the bus voltage. Due to the high control capability DPFC can also be used to improve the power quality and system stability, such as low frequency power oscillation damping, voltage sag restoration or balancing asymmetry.
1. AC–DC power conversion
2. Load flow control
3. Power electronics
4. Power semiconductor devices
5. Power system control
6. Power-transmission control
Figure 1.DPFC configuration
EXPECTED SIMULATION RESULTS
Figure 2.Supply voltage during sag condition
Figure 3. Injected voltage during sag condition
Figure 4. Elimination of sag voltage
Figure 5. Supply voltage during swell
Figure 6. Injected voltage for swell
Figure 7. Elimination of swell voltage
The series converter of the DPFC employs the DFACTS concept, which uses multiple small single-phase converters instead of one large-size converter. It is proved that the shunt and series converters in the DPFC can exchange active power at the third-harmonic frequency, and the series converters are able to inject controllable active and reactive power at the fundamental frequency. The DPFC is also used to improving power quality problems such as sag and swell. The reliability of the DPFC is greatly increased because of the redundancy of the series converters. The total cost of the DPFC is also much lower than the UPFC, because no high-voltage isolation is required at the series converter part and the rating of the components of is low.
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