# Development of Energy Storage Systems for High Penetration of Renewable Energy Grids
## 2 Battery Energy Storage System (BESS) Frequency Regulation Technology
### Dynamic Regulation  
Dynamic regulation is a bidirectional frequency control strategy. The battery energy storage system actively adjusts its output power within 1 s based on the grid frequency  
Figure 1: The frequency versus output power for static regulation control.  
state, instantaneously compensating for active power to achieve grid frequency stability. As shown in Figure 2, the output power of the frequency operating curve for dynamic regulation control is shown. Dynamic regulation control has two types based on frequency control range, dReg 0.25 and dReg 0.50 [21]. The table of parameters for dReg 0.25 and dReg 0.5 are presented in Tables 1 and 2, respectively. The points in Figure 2 correspond to the corresponding symbols shown in Tables 1 and 2. In comparison, dReg 0.5 has a larger frequency operating range than dReg 0.25, indicating that dReg 0.25 has a larger parameter of droop gain.  
model of an electrically excited synchronous machine, considering electrical characteristics such as stator windings, rotor windings, excitation windings, and dampers. The DC side of the converter provides active power, while capacitors supply reactive power. The control logic of the virtual synchronous machine is implemented through digital signal processing control systems, which control the converter. Therefore, there is no physical mechanical component involved. Instead, a mathematical model within the controller outputs stable and dynamic responses of the virtual synchronous generator to simulate the response characteristics of a synchronous generator [22].  
Swing equation emulation is developed based on the concept of a virtual synchronous machine and aims to address the challenge of distributed generation resources that are not able to provide inertia effects. The idea of this concept is to incorporate short-term energy storage devices like batteries, capacitors, and supercapacitors into distributed generation resources. By employing appropriate power electronic converter control mechanisms, it achieves the capability to provide virtual inertia. The scholar [PERSON], leveraging the concept of a virtual synchronous machine, integrated the rotational kinetic energy equations into the control mechanisms of power electronic converters. This integration led to the derivation of virtual mechanical power equations, simulating the response of synchronous generators [23; 24].  
The control method of a synchronerter involves using the swing equations of a mechanical rotor to simulate the response characteristics of a synchronous generator. The electrical parameters of the synchronous generator are equivalently represented as part of the hardware circuit elements in the converter to provide virtual inertia. The impedance of the stator windings is equivalently represented as the inductance value of a filter, the phase voltage of the stator windings is equivalently represented as the voltage value of an output capacitor, and the back electromotive force generated by rotor movement is equivalently represented as the average voltage across switches. In the control system of a synchronerter, response parameters such as rotor inertia and damping constants are considered. Finally, control of the synchronerter is achieved through input variables such as the mechanical torque, rotor current, and mutual inductance between the rotor and stator [25].  
Considering the components, dynamic characteristics, and control response parameters of the three methods mentioned, Table 3 lists the components and control parameters for the consideration of virtual inertia in these three approaches.