Novel Development of A Fuzzy Control Scheme with UPFC’s For Damping of Oscillations in Multi-Machine Power Systems


This paper presents a novel development of a fuzzy logic controlled power system using UPFCs to damp the oscillations in a FACTS based integrated multi-machine power system consisting of 3 generators, 3 transformers, 9 buses, 4 loads & 2 UPFCs. Oscillations in power systems have to be taken a serious note of when the fault takes place in any part of the system, else this might lead to the instability mode & shutting down of the power system. UPFC based POD controllers can be used to suppress the oscillations upon the occurrence of a fault at the generator side or near the bus side. In order to improve the dynamic performance of the multi-machine power system, the behavior of the UPFC based POD controller should be coordinated, otherwise the power system performance might be deteriorated. In order to keep the advantages of the existing POD controller and to improve the UPFC-POD performance, a hybrid fuzzy coordination based controller can be used ahead of a UPFC based POD controller to increase the system dynamical performance & to coordinate the UPFC-POD combination. This paper depicts about this hybrid combination of a fuzzy with a UPFC & POD control strategy to damp the electro-mechanical oscillations. The amplification part of the conventional controller is modified by the fuzzy coordination controller. Simulink models are developed with & without the hybrid controller. The 3 phase to ground symmetrical fault is made to occur near the first generator for 200 ms. Simulations are performed with & without the controller. The digital simulation results show the effectiveness of the method presented in this paper.


  1. UPFC
  2. POD
  3. Fuzzy logic
  4. Coordination
  5. Controller
  6. Oscillations
  7. Damping
  8. Stability
  10. State space model




Fig. 1 : A 3-machine, 9-bus interconnected power system model with 4-loads without the controllers


Fig. 2: A 3-machine, 9-bus interconnected power system model with 4-loads & 2 POD-UPFC & the fuzzy controller



Fig. 3 : Simulation result of power angle v/s time (without Fuzzy-POD-UPFC)


Fig. 4 : Simulation result of power angle v/s time (with UPFC & fuzzy control)


Fig. 5 : Comparison of the simulation results of power angle v/s time (without UPFC & with UPFC & fuzzy control)


AFACTS based multi-machine power system comprising of 3 generators, 9 buses, 3 loads with and without the 2 Fuzzy-POD-UPFC controllers was considered in this paper. SIMULINK models were developed in MATLAB 7 with & without the Fuzzy- POD-UPFC controllers for the considered multi machine model in order to damp out the oscillations. The control strategy was also developed by writing a set of fuzzy rules. The fuzzy control strategy was designed based on the conventional POD-UPFC controller & put before the POD-UPFC in the modeling.

The main advantage of putting the fuzzy coordination controller before the POD-UPFC in modeling is the amplification part of the conventional controller being modified by the fuzzy coordination unit, thus increasing the power system stability. Simulations were run in Matlab 7 & the results were observed on the scope. Graphs of power angle vs. time were observed with and without the controller. From the simulation results, it was observed that without the Fuzzy-POD-UPFC controller, the nine bus system will be having more disturbances, while we check the power angle on the first generator.

There are lot of ringing oscillations (overshoots / undershoots) & the output takes a lot of time to stabilize, which can be observed from the simulation results. But, from the incorporation of the Fuzzy- POD-UPFC coordination system in loop with the plant gave better results there by reducing the disturbances in the power angle and also the post fault settling time also got reduced a lot. The system stabilizes quickly, thus damping the local mode oscillations and reducing the settling time immediately after the occurrence of the fault.

The developed control strategy is not only simple, reliable, and may be easy to implement in real time applications. The performance of the developed method in this paper thus demonstrates the damping of the power system oscillations using the effectiveness of Fuzzy-POD-UPFC coordination concepts over the damping of power system oscillations without the Fuzzy-POD-UPFC coordination scheme.


[1]. L. Gyugi, “Unified Power flow concept for flexible AC transmission systems”, IEE Proc., Vol. 139, No. 4, pp. 323–332, 1992.

[2]. M. Noroozian, L. Angquist, M. Ghandari, and G. Anderson, “Use of UPFC for optimal power flow control”, IEEE Trans. on Power Systems, Vol. 12, No. 4, pp. 1629–1634, 1997.

[3]. Nabavi-Niaki and M.R. Iravani, “Steady-state and dynamic models of unified power flow controller (UPFC) for power system studies”, IEEE’96 Winter Meeting, Paper 96, 1996.

[4]. C.D. Schauder, D.M. Hamai, and A. Edris. “Operation of the Unified Power Flow Controller (UPFC) under Practical constraints”, IEEE Trans. On Power Delivery, Vol. 13, No. 2. pp. 630~639, Apr. 1998.

[5]. Gyugyi, L., “Unified power flow controller concept for flexible AC transmission systems”, IEE Proc. Gener. Transm. Distrib., No.139, pp. 323-331, 1992