When integrated to the power system, large wind farms can pose voltage control issues among other problems. A thorough study is needed to identify the potential problems and to develop measures to mitigate them. Although integration of high levels of wind power into an existing transmission system does not require a major redesign, it necessitates additional control and compensating equipment to enable (fast) recovery from severe system disturbances. The use of a Static Synchronous Compensator (STATCOM) near a wind farm is investigated for the purpose of stabilizing the grid voltage after grid-side disturbance such as a three phase short circuit fault. The strategy focuses on a fundamental grid operational requirement to maintain proper voltages at the point of common coupling by regulating the voltage. The DC voltage at individual wind turbine (WT) inverters is also stabilized to facilitate continuous operation of wind turbines during disturbances.
- Wind turbine
- Doubly-fed Induction Generator
- Three phase fault
- Reactive power
Fig. 1. Block diagram of a Doubly-fed induction generator
Fig. 2 Test System
EXPECTED SIMULATION RESULTS:
Fig. 3. Voltage at the fault bus (Load bus) , Voltage at the fault bus (Zoomed version)
Fig. 4. Reactive power in the system with no compensating device, Reactive power in the system with mechanically switched capacitors
Fig. 5. Reactive and active power of the 25 MVA STATCOM for Case 3, AC and DC busbar voltages of the STATCOM for Case III.
Fig. 6. Reactive and active powers of only the STATCOM for Case 4, Reactive power and terminal voltage of only the the MSC for Case 4.
Fig. 7. Reactive powers of the system with a STATCOM and MSC
Fig. 8. Reactive power of the 125 MVA STATCOM for Case 5.
Wind turbines have to be able to ride through a fault without disconnecting from the grid. When a wind farm is connected to a weak power grid, it is necessary to provide efficient power control during normal operating conditions and enhanced support during and after faults. This paper explored the possibility of connecting a STATCOM to the wind power system in order to provide efficient control. An appropriately sized STATCOM can provide the necessary reactive power compensation when connected to a weak grid. Also, a higher rating STATCOM can be used for efficient voltage control and improved reliability in grid connected wind farm but economics limit its rating. Simulation studies have shown that the additional voltage/var support provided by an external device such as a STATCOM can significantly improve the wind turbine’s fault recovery by more quickly restoring voltage characteristics. The extent to which a STATCOM can provide support depends on its rating. The higher the rating, the more support provided. The interconnection of wind farms to weak grids also influences the safety of wind turbine generators. Some of the challenges faced by wind turbines connected to weak grids are an increased number and frequency of faults, grid abnormalities, and voltage and frequency fluctuations that can trip relays and cause generator heating.
- http://www.awea.org/newsroom/releases/Wind_Power_Capacity_012307. html, accessed Nov. 2007.
- Sun, Z. Chen, F. Blaabjerg, “Voltage recovery of grid-connected wind turbines with DFIG after a short-circuit fault,” 2004 IEEE 35th Annual Power Electronics Specialists Conf., vol. 3, pp. 1991-97, 20-25 June 2004.
- Muljadi, C.P. Butterfield, “Wind Farm Power System Model Development,” World Renewable Energy Congress VIII, Colorado, Aug- Sept 2004.
- M. Muyeen, M.A. Mannan, M.H. Ali, R. Takahashi, T. Murata, J. Tamura, “Stabilization of Grid Connected Wind Generator by STATCOM,” IEEE Power Electronics and Drives Systems Conf., Vol. 2, 28-01 Nov. 2005.
- Saad-Saoud, M.L. Lisboa, J.B. Ekanayake, N. Jenkins, G. Strbac, “Application of STATCOMs to wind farms,” IEE Proceedings – Generation, Transmission, Distribution, vol. 145, pp.1584-89, Sept 1998.