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.
Highlights
In recent years, with the increasingly serious problems of energy crisis and environmental pollution, the need for development of green and clean energy sources has become the consensus of the world [1,2,3]
This paper establishes the DC voltage control (DVC) timescale mathematical model of the grid-tied photovoltaic generation systems (GPVGS) based on droop control, and uses the electric torque method to reveal the factors and action rules that affect the inertia, damping and synchronization ability of the system from the physical mechanism perspective
The response time constant of current control is often designed around 10 ms, and those of DVC and PLL about ten times larger are selected [17]
Summary
With the increasingly serious problems of energy crisis and environmental pollution, the need for development of green and clean energy sources has become the consensus of the world [1,2,3]. In view of the inertia and damping mechanism research of renewable energy grid-tied power generation system, reference [9] makes full use of the idea of multi-time scale, grasps the time scale of interest, ignores other dynamic processes, and establishes the mathematical model of the system. In [14], the electric torque analysis method is used to analyze the inertia and damping characteristics of the grid-tied inverter itself, but the influence of the primary side energy was not considered. This paper establishes the DVC timescale mathematical model of the GPVGS based on droop control, and uses the electric torque method to reveal the factors and action rules that affect the inertia, damping and synchronization ability of the system from the physical mechanism perspective. It is beneficial to select appropriate control strategies and parameters, so that the GPVGS presents better inertia, damping and synchronization characteristics, to improve the stability of the power system
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