This paper presents a new component within the flexible ac-transmission system (FACTS) family, called distributed power-flow controller (DPFC). The DPF Controller is derived from the unified power-flow controller (UPFC). The DPFC can be considered as a UPFC with an 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 employs the distributed FACTS (D-FACTS) concept, which is to use multiple small-size single-phase converters instead of the one 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. Accordingly, 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. The principle and analysis of the DPFC are presented in this paper and the corresponding experimental results that are carried out on a scaled prototype are also shown.
- AC–DC power conversion
- Load flow control
- Power electronics
- Power semiconductor devices
Fig. 1. DPFC control block diagram.
EXPECTED SIMULATION RESULTS:
Fig. 2. DPFC operation in steady state: line current.
Fig. 3. DPFC operation in steady sta te:series converter voltage.
Fig. 4. DPFC operation in steady state: bus
Fig. 5. Reference voltage for the series converters. voltage and current at the Δ side of the transformer
Fig. 6. Step response of the DPFC: series converter
Fig. 7. Step response of the DPFC: linecurrent. voltage.
Fig. 8. Step response : active and reactive power injected by the series converter at the fundamental frequency.
Fig.9. Step response: bus voltage and current at the Δ of the transformer
This paper has presented a new concept called Distributed power flow controller. It emerges from the UPFC and inherits the control capability of the UPFC, which is the simultaneous adjustment of the line impedance, the transmission angle, and the bus-voltage magnitude. The common dc link between the shunt and series converters, which is used for exchanging active power in the UPFC, is eliminated. This power is now transmitted through the transmission line at the third-harmonic frequency. The series converter of the DPFC employs the D-FACTS concept, which uses multiple small single-phase converters instead of one large-size converter. The reliability of the DPFC is greatly increased because of the redundancy of the series converters. The total cost of this controller 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. The DPFC concept has been verified by an experimental setup. 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.
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