Modeling and Mechanism Investigation of Inertia and Damping Issues for Grid-Tied PV Generation Systems with Droop Control

Abstract

Inertia effect and damping capacity, which are the basic characteristics of traditional power systems, are critical to grid frequency stability. However, the inertia and damping characteristics of grid-tied photovoltaic generation systems (GPVGS), which may affect the frequency stability of the grid with high proportional GPVGS, are not yet clear. Therefore, this paper takes the GPVGS based on droop control as the research object. Focusing on the DC voltage control (DVC) timescale dynamics, the mathematical model of the GPVGS is firstly established. Secondly, the electrical torque analysis method is used to analyze the influence law of inertia, damping and synchronization characteristics from the physical mechanism perspective. The research finds that the equivalent inertia, damping and synchronization coefficient of the system are determined by the control parameters, structural parameters and steady-state operating point parameters. Changing the control parameters is the simplest and most flexible way to influence the inertia, damping and synchronization ability of the system. The system inertia is influenced by the DC voltage outer loop proportional coefficient Kp and enhanced with the increase of Kp. The damping characteristic of the system is affected by the droop coefficient Dp and weakened with the increase of Dp. The synchronization effect is only controlled by DC voltage outer loop integral coefficient Ki and enhanced with the increase of Ki. In addition, the system dynamic is also affected by the structural parameters such as line impedance X, DC bus capacitance C, and steady-state operating point parameters such as the AC or DC bus voltage level of the system and steady-state operating power (power angle). Finally, the correctness of the above analysis are verified by the simulation and experimental results.

Analysis of Inertia Characteristics of Direct-Drive Permanent-Magnet Synchronous Generator in Micro-Grid

“…According to the system structure diagram shown in Figure 2 and Equations (8), (15) and 21, the equivalent Heffron-Philips model can be obtained, as shown in Figure 9. For the same reason, it can be known from Equations (19)(20)(21) that the droop control analog grid has a certain inertia effect. Equation 21denotes that the equivalent inertia coefficient is affected by the following factors: the droop coefficient D and the cutoff frequency ωc.…”

“…In WT's micro-grid system, energy storage devices (WTs rotors, DC side capacitors) can be used to provide additional inertia for the system under the action of additional virtual inertia control [10][11][12][13][17][18][19][20]. At the same time, the micro-grid under the droop control can also provide a certain inertia [19,25].…”

“…The technological economy of the effect generation method fully and accurately understands the inertial characteristics of the direct-drive WT power system, which lays a foundation for the low-cost inertial control of the WT power system. In [19,20], the grid-connected converter of the inertia and damping characteristics are analyzed by using the electric torque analysis method. References [21,22] combined the converter with energy storage devices to examine the effects of two different control strategies on the inertia and damping characteristics of grid-connected energy storage systems.…”

Analysis and Simulations of the Primary Frequency Control during a System Split in Continental Europe Power System

“…Moreover, another element of novelty consists in the analysis of the system-split condition itself. Indeed, many authors have investigated CE area stability, discussing the abilities of different generation technologies to provide a frequency containment reserve [5][6][7] or the role of battery energy-storage systems [8][9][10], however, the event of system split is barely studied. The rest of the paper is divided as follows: Section 2 provides an overview of relevant aspects of the primary frequency control in the CE system, focusing in particular on the frequency-containment reserve process and the use and computation of the power-frequency characteristic; Section 3 describes the specific details of dynamic modelling and simulation of the CE power system, discussing the required extensions and adaptations of the dynamic model made by the authors for the development of an accurate simulation of the separation event; analysis and simulations of the system split in the CE synchronous area are reported in Section 4, pointing out the importance of a proper temporal distribution of power imbalances and defensive actions; Section 4 reports the results of extended analyses done with the validated models, examining variant scenarios of missing defensive actions, reduced system inertia and comparison with the reference incident; finally, in Section 5, the main results of the work are summarized with conclusive comments and remarks.…”

Characteristics of Parallel Inverters Applying Virtual Synchronous Generator Control

“…In [10] and [11], the equivalent inertia of a doubly-fed induction generator (DFIG) based wind turbine system and a photovoltaic (PV) system provided by a modified phase-locked loop (PLL) rather than a VSG are investigated, respectively. In [12], the DC-link capacitor in a grid-connected PV system is used to provide the virtual inertia, where the equivalent inertia, damping, and synchronizing coefficients are derived by a torque analysis to represent the characteristics of the PV system. The same method is adapted by [13] to study the VSG.…”