## 3 Establishment of the Database Used in the Proposed Preventive Control Strategy
### Step 3  
In Step 3, the offline database concerning frequency response is established. This database includes the historical system operating data, the used \(\mathbf{P_{BESS}}\), \(\mathbf{P_{DLC}}\) and \(\mathbf{P_{EDRP}}\) and corresponding \(\mathbf{f_{min}}\) under the \(N\)-1 contingency event. The offline database is utilized to train the \(\mathbf{f_{min}}\), \(\mathbf{k_{BESS}}\), \(\mathbf{k_{DLC}}\) and \(\mathbf{k_{EDRP}}\) forecasting modules. For the BESS method, the battery is considered as a back-up power source, which is directly controlled by system operators [8; 27]. Many researches investigate the control methods for battery outputs and those methods affects the frequency support capability of BESS [21; 28; 29]. This work assumes that the BESS will provide the active power output directly when a contingency is detected and it assumes the battery response time to be 100 ms [4; 30]. Figure 6 shows an example for frequency response with and without using BESS--the solid red line and the dash red line represent the frequency response with 0 and 0.8 MW BESS, respectively. In this operating status, the relation between the power output from BESS and frequency nadir is summarized in Table 1 and it can be described by a linear regression with the slope of 0.0368. Figure 6: The contingency simulation with/without BESS power support. Furthermore, the DLC method provides load participants with incentive payments or rate discount and it allows system operators directly shuts down or cycles participants' certain electrical appliance [9; 10; 11; 12; 13; 14]. The certain electrical appliance (e.g., air conditioners and water heaters) can be directly shed via the load-relay or load-controller. Whether the load-relay or load-controller is activated or not, load participants receive the incentive payments or rate discount. Many researchers investigated different UFLS relay settings and the corresponding frequency support capability by DLC [3; 31; 32; 33]. This work assumes the load participants to provide the UFLS service using the rate of change of frequency relay. Figure 7 shows an example for frequency response with and without the use of DLC--the solid red line and the dash red line represent the frequency response with 0 and 0.8 MW DLC, respectively. Within the same operating status, the relation between the amount of load shedding and frequency nadir is summarized in Table 2 and it can be described by a linear regression with the slope of 0.037. \begin{table}
\begin{tabular}{c c c} \hline
**BESS Output** & **Frequency Nadir** & **Frequency Support** \\
**(MW)** & **(Hz)** & **(Hz/0.1 MW BESS)** \\ \hline
0 & 57.1103 & - \\
0.1 & 57.1471 & 0.0368 \\
0.2 & 57.1839 & 0.0368 \\
0.3 & 57.2206 & 0.0367 \\
0.4 & 57.2574 & 0.0368 \\
0.5 & 57.2941 & 0.0367 \\
0.6 & 57.3309 & 0.0368 \\
0.7 & 57.3676 & 0.0367 \\
0.8 & 57.4044 & 0.0368 \\
0.9 & 57.4410 & 0.0366 \\
1.0 & 57.4779 & 0.0369 \\
1.1 & 57.5146 & 0.0367 \\
1.2 & 57.5513 & 0.0367 \\
1.3 & 57.5880 & 0.0367 \\
1.4 & 57.6246 & 0.0366 \\
1.5 & 57.6613 & 0.0367 \\ \hline \end{tabular}
\end{table} 
Table 1: The frequency support capability of BESS—case study. Figure 7: The \(N\)-1 contingency simulation with/without DLC load shedding. The EDRP method provides load participants with incentive payments or rate discount; it notifies participants 15 min to 2 h ahead and requests for voluntary load-reduction service [9; 10; 11; 12; 13; 14; 15]. By implementing the proposed preventive control method and the short-term renewable and load forecasts, system operators can predict and reduce a certain amount of load in advance [9; 14; 16; 17], regardless either a contingency event really occurs or not. In this work, the EDRP scheme notifies load participants 15 min in advance, which is common for a general EDRP scheme. Figure 8 shows an example for frequency response with and without using EDRP--the solid red line and the dash red line represent the frequency response with 0 and 3.6 MW EDRP load-reduction, respectively.