# Optimal Modeling for Dynamic Response of Energy Storage Systems
## 2 Introduction and Building of Models for Energy Storage Systems
### Universal Model of WECC Energy Storage System
#### 2.1.3 REGC Module  
The REGC module is also known as the renewable energy generator/converter model. The same as the former two, it can be divided into an active power control loop and a reactive power control loop. The module control block diagram is shown in Figure 4. All parameters and their meanings in the REEC module are listed in Table 3. Its major function is to limit the surge current when the voltage is too low or too high and to convert the control commands into power grid signals imported into the simulation software.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Symbol** & **Description** \\ \hline
31 & \(I_{q3}\) & (Iq3 \(>\) Iq2), Reactive Power V–I pair, current (pu) \\
32 & \(V_{q4}\) & (Vq4 \(>\) Vq3), Reactive Power V–I pair, voltage (pu) \\
33 & \(I_{q4}\) & (Iq4 \(>\) Iq3), Reactive Power V–I pair, current (pu) \\
34 & \(V_{p1}\) & Real Power V–I pair, voltage (pu) \\
35 & \(I_{p1}\) & Real Power V–I pair, current (pu) \\
36 & \(V_{p2}\) & (Vp2 \(>\) Vp1), Real Power V–I pair, voltage (pu) \\
37 & \(I_{p2}\) & (Ip2 \(>\) Ip1), Real Power V–I pair, current (pu) \\
38 & \(V_{p3}\) & (Vp3 \(>\) Vp2), Real Power V–I pair, voltage (pu) \\
39 & \(I_{p3}\) & (Ip3 \(>\) Ip2), Real Power V–I pair, current (pu) \\
40 & \(V_{p4}\) & (Vp4 \(>\) Vp3), Real Power V–I pair, voltage (pu) \\
41 & \(I_{p4}\) & (Ip4 \(>\) Ip3), Real Power V–I pair, current (pu) \\
42 & T & Battery discharge time (-\(\zeta\)0) (s) \\
43 & \(SOC_{ini}\) & Initial state of charge (pu) \\
44 & \(SOC_{max}\) & Maximum allowable state of charge (pu) \\
45 & \(SOC_{min}\) & Minimum allowable state of charge (pu) \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._  
Figure 4: The REGC module control block diagram of a universal model of energy storage systems. Reprinted from Ref. [4] (Fig. 12), 2016, [PERSON].  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Symbol** & **Description** \\ \hline
1 & \(T_{q}\) & Converter time constant (s) \\
2 & \(rrpwr\) & Low voltage power logic (LVPL) ramp rate limit (pu/s) \\
3 & \(R_{slgt}\) & LVPL characteristic voltage 2 (pu) \\
4 & \(Z_{max}\) & LVPL characteristic voltage 1 (pu) \\
5 & \(L_{qq1}\) & LVPL gain (pu) \\
6 & \(V_{elim}\) & Voltage limit for high voltage reactive current management (pu) \\
7 & \(L_{qrpt1}\) & High voltage point for low voltage active current management (pu) \\
8 & \(L_{qrpt0}\) & Low voltage point for low voltage active current management (pu) \\  & & Current limit for high voltage reactive current management \\
9 & \(I_{elim}\) & (specified as a negative value) (pu) \\
10 & \(T_{llgt}\) & Voltage filter time constant for low voltage active current management (s) \\
11 & \(K_{lu}\) & Overvoltage compensation gain used in the high voltage reactive current management \\
12 & \(I_{qrmax}\) & Upper limit on rate of change for reactive current (pu) \\
13 & \(I_{qrmin}\) & Lower limit on rate of change for reactive current (pu) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parameters of the REGC module.