Static Synchronous Generator Model: A New Perspective to Investigate Dynamic Characteristics and Stability Issues of Grid-Tied PWM Inverter

Abstract

With increasing penetration of the renewable energy, the grid-tied PWM inverters need to take corresponding responsibilities for the security and stability of future grid, behaving like conventional rotational synchronous generator (RSG). Therefore, recognizing the inherent relationship and intrinsic differences between inverters and RSGs is essential for such target. By modeling the typical electromechanical transient of grid-tied PWM inverters, this paper first proves that PWM inverters and RSGs are similar in physical mechanism and equivalent in mathematical model, and the concept of static synchronous generator (SSG) is thereby developed. Furthermore, the comprehensive comparison between RSG and SSG is carried out in detail, and their inherent relation is built. Based on these findings, the rationality and feasibility of migrating the concepts, tools, and methods of RSG stability analysis to investigate the dynamic behaviors and stability issues of SSG is therefore confirmed. Taking stability issues as an example, the criteria of small signal and transient stability of a typical grid-tied PWM inverter is put forward to demonstrate the significance of the developed SSG model (including synchronizing coefficient, damping coefficient, inertia constant, and power-angle curve), providing clear physical interpretation on the dynamic characteristics and stability issues. The developed SSG model promotes grid-friendly integration of renewable energy to future grid and stimulates interdisciplinary research between power electronics and power system.

Coordinated Control Schemes of Super-Capacitor and Kinetic Energy of DFIG for System Frequency Support

“…The detailed dynamic model of the complete DFIG system in this paper can be referred to [4,26,27], including the induction generator model, the drive train model, the back-to back converter model and the controller model. The controller of the complete DFIG system mainly contains the rotor-side converter (RSC) controller, the grid-side converter (GSC) controller and the pitch angle controller, which will be introduced in the following sections.…”

“…where f WT in (27) is the designed AC frequency deviation, which is an input signal of the emulated inertia control of WT. f is the defined cut-off frequency.…”

Phillips-Heffron model for current-controlled power electronic generation unit

“…In order to analyze the small-signal stability of modern power system with VSCs, a promising solution is to establish SG-equivalent model for the VSCs [8][9][10][11][12]. It is the classic Phillips-Heffron model, which characterizes the SG dynamics with inertia, synchronizing and damping coefficients [13,14].…”

“…As for the CC-VSCs, it is often regarded as an ideal current source and the dynamic of phase-locked-loop (PLL) is always overlooked. Such assumptions only hold true in strong grid with low penetration level of VSCs [11,19]. The CC-VSC is considered to affect the small-signal stability of the system indirectly just by altering the steady state operation point of the SGs [19].…”

“…The high-order mathematical model of the whole system is complicated, and the physical explanation of the VSC dynamic can hardly be recognized [26,27]. Thus it is inconvenience to obtain the direct principle for the parameter optimizations of the CC-VSC to improve the small-signal stability [11].…”