# Optimal Power Dispatch of an Offshore Wind Farm under Generator Fault
## 1 Introduction  
With the recent rapid development of wind energy, the form of wind energy has gradually developed from distributed onshore to centralized offshore. Most Wind Farms (WFs) are directly connected to the grid. Therefore, for the grid, it is more desirable to treat WFs like conventional power plants. In other words, the ideal WF should operate as a conventional power plant [1]. In addition to the uncontrollable and variable wind resources, WFs have many different characteristics compared to conventional power plants as follows:  
* The operating environment of a WF is very harsh. That will increase the failure rate of the components of a Wind Turbine (WT). Therefore, more attention should be paid to the influence of the fault and failure of WTs on WFs. * WFs usually consist of dozens of independent WTs. WF operators need to coordinate and manage all the WTs to meet the requirements from the grid. * There is an aerodynamic interaction among the WTs. The wake effect can cause 30-50% power loss of WFs and increase the fatigue loads of the downstream WTs [2]. The optimal operation of individual WTs cannot result in the optimal operation of the whole WF with respect to power production or loads. From the characteristics of WFs described above, it can be seen that the Wind Farm Control (WFC) considering faults is very necessary to optimize the WF performance and accommodate the unexpected faults, especially for offshore WFs. The wind resources at sea are abundant, and the capacity of the WT is usually large. Unplanned maintenance caused by faults will result in large power losses. Moreover, offshore WTs have high maintenance costs, and the maintenance is affected by many weather factors, such as wind speed and wave height. Therefore, if there is an effective WFC, under the premise of ensuring the safety of the WT, it can not only protect the faulty WT, but also track the power demand from the Transmission System Operator (TSO) as much as possible. It will be able to reduce the power losses caused by the faulty turbine, as well as lower the maintenance costs. Active Power Regulation (APR) of WFs as a part of WFC has been an important topic of research in recent years. The wake effect is one of the causes of WF power loss. Many researchers have focused on how to reduce the wake effect to improve the power generation [3; 4; 5]. This concept was named Active Wake Control (AWC) in [6]. Two different methods are commonly used. One method is axial induction control, which is more widely used [4; 5]. In general, axial induction control achieves the control objectives by adjusting the Tip Speed Ratio (TSR) and the pitch angle of the WT blades. It is not as effective at improving power as other methods. The implementation of axial induction control requires access to the original control system of the WT. This will pose a threat to the safety of the WT. Therefore, the axial induction control can only be adopted by the manufacturer. Otherwise, the potential voiding of the warranty of the WT will be an unavoidable problem. The other method is yaw-based AWC. In this method, the upstream WT is operated with rotor yaw misalignment to divert the wake away from the downstream WT [7]. This method is very effective for improving the power of the WF. However, the weakness of this method is that it will increase the fatigue loads of the individual WTs [8]. Moreover, in practice, due to the slow response speed of the yaw control, the WT may not be able to track the yaw angle reference in time. In addition to these two methods, the easiest way to implement WFC is power dispatch, which optimizes the WF power by adjusting the power reference of the individual WTs. It is more of a WF management than a WFC one. This method does not affect the WTs' original control system. Although this method cannot increase the WF power as much as the former methods, it is highly feasible and more suitable for practical application. Therefore, this paper adopted the power dispatch method to optimize the power of the WF in the fault condition.