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The low voltage ride through (LVRT) ability of PV inverter is very important to the safety and stability operation of grid. The current LVRT control strategy emphasizes reactive current support during voltage dip, and there is no active power requirement, so in the grid with high PV permeability, it is easy to cause large active power shortage during the voltage dip, then the frequency will decrease. In order to solve this problem, this paper analyzes the output characteristics of PV inverter using LVRT control strategy dominated by national standard, and the influence to frequency stability of grid with high PV penetration. Based on IEEE standard 3-machine 9- bus network frame, the grid frequency performance is simulated with the model of PV power station, The frequency variation during voltage dip using two typical LVRT control strategies were compared. At last, it is suggested to strengthen the active power support of PV power station during the grid dip, the output of reactive power and active power is guaranteed at the same time, the active and reactive power support to grid is realized, the LVRT performance of PV power station is improved to support grid.

Strain-induced martensite transformation (SIMT) commonly exists around a crack tip of metastable austenite stainless steels. The influence of the volume expansion of the SIMT on the hydrogen diffusion was investigated by hydrogen diffusion modeling around a crack tip in type 304L austenite stainless steel. The volume expansion changed the tensile stress state into pressure stress state at the crack tip, resulting in a large stress gradient along the crack propagation direction. Compared to the analysis without considering the volume expansion effect, this volume expansion further accelerated the hydrogen transport from the inner surface to a critical region ahead of the crack tip, and further increased the maximum value of the hydrogen concentration at the critical position where the strain-induced martensite fraction approximates to 0.1, indicating that the volume expansion of the SIMT further increased the hydrogen embrittlement susceptibility.

In recent years, photovoltaic (PV) power generation has developed rapidly at China and abroad. PV power generation is on the trend from auxiliary power supply to main power supply even leading power supply. Due to the fluctuation and intermittent characteristics of PV power generation, and zero inertia, the integration of large-scale grid-connected PV power generation may have a negative impact on the stability of the power system. Modeling grid-connected PV power generation systems is the key factor to investigate the influence between it and other parts of power system. Modeling of PV is also a hot issue that has been studied continuously for many years around the world. GE, WECC, CIGRE, CEPRI and so on have attached great importance to this issue and have published many research results. The existing research at China and abroad is reviewed in this paper, the existing problems are analyzed, and suggestions for future research are given.

Due to the renewable generation target and the continuously increasing electrical demand, a large number of wind farms and solar photovoltaic (PV)plants are being planned in China. As the electricity fault characteristics of inverter-interfaced renewable energy sources are different from the traditional synchronous generators. The fault circuit contributions are getting more and more attention from engineers. In this paper, the short-circuit calculation method considering dynamic reactive power support of renewable energy systems is proposed. Through a large number of calculations, the factors affecting short-circuit currents and trends of short-circuit current under different voltage drop depths are discussed. The results presented by this paper provide the reference for future research on control and protection of power systems with high penetration of renewable energies.

One of the main trends in the development of solar photovoltaic (PV) grid-connected technology is the grid code compliance assessment for grid connection of PV power plant. But it is difficult to obtain the dynamic performance of the PV power plant under different operation scenarios through field test. In particular, it is costly to obtain the characteristics of the point of connection of PV power plant. The paper introduces support tools for simulation-based dynamic characteristics analysis of grid connection of PV power plant. Firstly, the function and flow chart of the developed support tools is described in detail. Then, the photovoltaic inverter detailed modelled. Finally, the support tools are developed based on the Powerfactory C++ API and Python package. The tools have many automation features that can be applied to online services which have be installed in the clean energy big data center. Test results have illustrated that the support tools can reflect dynamic performance of grid connection of PV power plant and can provide a decision support for the renewable energy priority scheduling.

Tibet is known as the “Roof of the World” and is characterized by an abundance of renewable energy resources in the form of wind, geothermal, hydropower and, in particular, solar. Tibet power grid is a typical weak power system in terms of its network strength; however due to its abundant generating resources, power exportation to the neighboring grids takes a great proportion of its power output, which bring many challenges to the system stability. In recent years, a great threat on the Tibet power system security is posed by the large-scale development of photovoltaic (PV) power generation, and the main two aspects are: (1) the PV power output could drop about 50–70% within three seconds due to cloud cover; (2) the PV plants, without low voltage ride through (LVRT) inspection certification, have the risk to trip from the grid inoperation. This paper first presents theoretical and simulation analysis on the effects of cloud and LVRT capability on solar power outputs of the Tibet power system. The analysis results are validated by a LVRT field test on a typical PV plant in Tibet. Research results provide effective references for the power grid dispatching department on operating a power system with high penetration of solar power.