# A Study of Order Modification for Reactive Power Support by Wind Farm during Communication Failure
## 2 System Description
### Proposed Modification Algorithm  
To achieve a continuous assignment plan along with a wide area-based generation system, a self-modification method for the communication state has to be composed. The major issue for a large-scale wind farm is calculation reliability. Therefore, repetitive emergency responses for every single communication error could potentially have negative connotations in terms of reliability. As mentioned above, an active modification method will be introduced in this section for reducing emergency operations, caused by a variety of issues. Figure 3 shows the concept of a self-modification process of reactive power allocation plan. As the allocation method is based on a loss minimization plan, the adjacent wind turbines from the connection point provide a large portion of the reactive power supply. As mentioned previously, this proportional value is usable in converter operations during communication failure. However, owing to practical issues, some turbine units may become unable to provide reactive power. In this state, without modification by a central subsystem, the previously calculated proportions will be classed as an improper signal, and unable to handle the voltage variation at certain nodes. To compose an appropriate compensation plan, the self-modification algorithm has to take these potential conditions into account. The modification plans need to be amended with imposed values and measurable data, like the composed equation. In the case of the equation seen in the previous section, the main improvement is the availability of an autonomous modification method for reactive power supply when voltage variation conditions occur. However, this simple updating plan cannot satisfy the relevant quantities when power conversion devices at the turbines are unavailable. The inclusion of further processes, such as calculating the state of the upper unit, can lead to appropriate proportion modifications, offering a smoother reactive management plan without the need for additional support. This modification is represented by Equations (10) and (11). \[\eta^{\prime}{}_{ln}=\eta_{ln}+\eta_{com}\quad(0\leq\eta^{\prime}_{ln}\leq 1) \tag{10}\]  
\[\eta_{com}=\frac{\left(I_{QU}-I_{Q\delta}\frac{I_{pl}}{I_{ps}}\right)\cdot \frac{\Delta U_{pre}-\Delta U}{U}-\Delta Q_{n\cdot n+1}}{Q_{req}} \tag{11}\]  
Figure 4 shows the whole reactive power control algorithm, including the proportion modification processes. As an option of the WFMS, the supervisory controller can check the current status, and define a curtailment value to confirm the reactive power reserve. The reactive power reserve in this paper follows the power factor (_pf_) limitation scheme, as shown in Equation (12). The operator can check the reactive power reserve using the maximum value for the real power that is individually designated from the power prediction process. \[|Q_{eva}|=\sqrt{1-pf^{2}}\cdot S_{pcs} \tag{12}\]  
where, \(Q_{eva}\) is the available reactive power reserve, and \(S_{pcs}\) is the power conversion capacity of the converter (MVA). After calculating the proportion of each wind turbine, the imposed optimization process can be used as a selectable option by the system controller. Each wind turbine receives the calculated signal as a reference value, and utilizes it in a reactive current control process, before the next order is imposed. Unless it is considering an unpredictable state, the order will reflect the unprepared voltage condition, and the modification can be processed by the re-calculation in the algorithm. The proposed section is applied in stages, taking three conditional statements into account. An initial non-response in communication logic acts as a trigger signal to the proposed control part. If there is a discrepancy in the networking subsystem, the self-modification logic will check the voltage variation to determine whether to revise the references or not. As mentioned above, the modification process is divided into categories of simple reference modification and proportional change.