# Dynamic Stability Analysis of Isolated Power System
## 1 Introduction  
In the changing geopolitical, economic, and diplomatic energy situation, each energy system must be able to maintain and ensure stability of the functioning of energy resources in critical conditions. Competences and ability to work independently of other energy systems must be strengthened in each electricity system.  
The structure of an isolated energy system consists of electricity sources, equipment, their protection and automation, and load. All system elements must ensure reliable and stable operation of the electrical power system [1, 2, 3, 4].  
In the event of a disturbance or system failure, any EPS can be divided into separate and self-contained parts--islands. A distributed or isolated electrical power system must ensure energy reliability, stability, and the ability to work in critical and extreme operating conditions [5, 6, 7, 8, 9].  
The stability of an isolated energy system is a very important indicator of reliability and quality. When analyzing the dynamic stability of an isolated EPS, it is necessary to assess whether the system will operate under extreme conditions for a short time or continuously. One of the key indicators of the dynamic stability of an EPS is the behavior of the generators under different network operating modes. Another very important point is the primaryand secondary power control of the generators. Finally, it is also important to consider the possibilities of using the operating functions of the HVDC BtB converter [10; 11; 12].  
This article describes research and develops mathematical models for the analysis of an isolated energy system. This analysis is based on and supplemented by previous calculations and experiments. The developed models can be used as a basis to analyze the dynamic stability of an isolated energy system. These numerical models combine the authors' experiences and scientific achievements in dynamic stability research [12; 13].  
Attention has mainly been paid to the application of primary and secondary frequency and the active and reactive power control functions in numerical models. The applicability of voltage control and HVDC BtB converter operation functions is especially relevant in the models. Depending on the complexity of the dynamic model, these features can be adapted to a variety of isolated EPS operating modes. All dynamic models are designed for symmetric EPS operation. The focus has been on frequency and inertia management and control of the isolated EPS. The influence of the different operating modes of the HVDC BtB converter on the stability of the isolated energy system is also very important [2; 3; 4; 5; 6; 7; 8; 9; 10].  
This paper is organized as follows. Section 2 describes the structure and the main parameters of the analyzed isolated power system. Analysis of the system's frequency dependence on a rapid load change is presented in Section 3. Section 4 is dedicated to an analysis of the impact of the HVDC BtB converter's settings on the system's response to a disturbance. The response of the system to the switching of the synchronous condensers is analyzed in Section 5. Section 6 presents research on the system's response to a load change when the HVDC BtB converter's frequency control function is on. Emergency operating modes--disconnection of the unit operating in pump mode and HVDC BtB converter disconnection--are considered in Section 7. Finally, in Section 8, the results are summarized, and conclusions are presented.