In this paper, a new power frequency model for unified power flow controller (UPFC) is suggested with its dc link capacitor dynamics included. Four principal control strategies for UPFC series element main control and their impacts on system stability are discussed. The main control of UPFC series element can be realized as a combination of the four control functions. The supplementary control of UPFC is added for damping power oscillation. The integrated UPFC model has then been incorporated into the conventional transient and small signal stability programs with a novel UPFC-network interface. Computer tests on a 4-generator interconnected power system show that the suggested UPFC power frequency model and the UPFC- network interface method work very well. The results also show that the suggested UPFC control strategy can realize power flow control fairly well and improve system dynamic performance significantly.
Fig. 1. Transmission line with UPFC installed
Fig. 2. The main control and phasor diagram.
EXPECTED SIMULATION RESULTS:
Fig. 3. Plots of case 1a.
Fig. 4.Plots of case 1b.
Fig. 5. Plots of case 1c.
Fig. 6. Effects of supplementary control.
Fig. 7. Results of the suggested control scheme.
The suggested UPFC power frequency model and the developed UPFC-network interface method work very well in the study of power system dynamics with satisfied convergence and accuracy. Four principal main control strategies are discussed and the computer tests results support the discussion conclusion very well. The constant power flow control is good for steady state control and the constant series compensation control is useful for first swing stability. The supplementary control is very efficient in damping intcrarea power oscillation. The suggested UPFC control can realize the desired control strategy flexibly and improve system dynamic performance significantly.
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