In this paper, a method is presented to control offshore wind farm output power. This method is able to fix the wind farm output power even during wind speed variations. In the proposed method, the offshore wind farm is connected to the onshore grid through the high-voltage dc (HVdc) cable. Moreover, the power control of the wind turbines is achieved by controlling the HVdc convertors. In the proposed system, the generator side convertors have to control the active power absorbed from the wind, and the grid side ones are obtained to control the HVdc link voltage. The control system is based on applying the appropriate modulation index to the voltage source converters. Two control strategies are proposed and analyzed to control wind farm output power. The simulation results illustrate that the proposed method is able to smooth the output power of the offshore wind farms appropriately. The proposed wind farm configuration and the control system are validated by simulations in the MATLAB/Simulink environment.
- Current source inverter (CSI)
- Offshore wind farm
- Permanent magnet synchronous generator (PMSG)
- Voltage source converter (VSC)
Fig. 1. Proposed configuration of wind turbines connection.
EXPECTED SIMULATION RESULTS:
Fig. 2. (a) Wind speed variations (m/s). (b) Turbine rotational speed (rad/s).
(c) Turbine efficiency.
Fig. 3. HVdc link voltage.
Fig. 4. Wind farm output power.
In this paper, the configuration and control methods have been proposed for the offshore wind turbines, connected to the onshore grid. This method is capable to control and smooth the wind farm output power, injected to the onshore grid. The proposed system can mitigate the fluctuations of wind farm output power, even during wind speed variations. In other words, the wind farm can operate such as a PQ-bus. Moreover, two strategies (fixed power and MPPT) have been analyzed and compared with each other. Finally, the proposed method is compared with other similar works to smooth the output power of the wind farm. The main result is that the proposed method can smooth the output power better than the TSR, PAC, and OTC methods. But it is a bit weaker than the KEC method in power smoothing issue. Moreover, using this method, the wind farm is able to cooperate in frequency control of the onshore grid by controlling the desired active power, to improve the power system operation, which is the future work of the authors.
 J. O. Dabiri, “Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays,” J. Renew. Sustain. Energy, vol. 3, no. 4, p. 043104, 2011.
 J. Hua, “A floating platform of concrete for offshore wind turbine,” J. Renew. Sustain. Energy, vol. 3, no. 6, p. 063103, 2011.
 A. Urtasun, P. Sanchis, I. S. Martín, J. López, and L. Marroyo, “Modeling of small wind turbines based on PMSG with diode bridge for sensorless maximum power tracking,” Renew. Energy, vol. 55, pp. 138–149, Jul. 2012.
 (2007). Global Wind and Energy Council, Market Forecast 2010- 2014. [Online]. Available: http://www.gwec.net/fileadmin/documents/ Publications/GlobalWind2007report/market/forecast%2020102014
 M. Kesraoui, N. Korichi, and A. Belkadi, “Maximum power point tracker of wind energy conversion system,” Renew. Energy, vol. 4, no. 10, pp. 2655–2662, 2011.