HEFEI, China, Dec. 02, 2021 /PRNewswire/ —With the increase of the proportion of new energy resources access, the operation mode of traditional power system that mainly based on thermal synchronous generators is changing. In the past, when the proportion of new energy resources was relatively low, its grid-connected performance had a limited impact on the grid, and its impact capacity was limited by its small capacity scale. Even if it fluctuated, it would not have a great impact on the strong grid. But now, with the rapid increase of new energy resources penetration, its grid-connected performance will directly affect the safe operation of the grid. Therefore, issues related to grid friendliness have been put on the agenda.
The short circuit ratio (SCR) of grid is an important index to measure the strength of grid. In the case of low SCR, any disturbance injected by inverter will be amplified by weak grid. Therefore, it becomes more difficult for power stations to maintain steady-state operation, complete transient fault through and maintain power quality under weak power grid. However, if the performance of any aspect is not up to standard, it may lead to problems or accidents such as off-grid, vibration, harmonic increase and even equipment damage.
Currently, the traditional grid-following (GFLI) inverter has been widely used in grid-connected photovoltaic applications, but it is easy to be unstable because of the low grid strength. Although the inverter manufacturers continue to optimize the grid-connected algorithm to adapt to the weak grid, with the increase of new energy resources access ratio, the grid strength continues to decline, blindly adapting to the weak grid cannot solve the fundamental problem, and how to increase the grid strength becomes particularly important. Although grid-forming (GFMI) technology originated from off-grid applications, with the gradual promotion and use of this technology in grid-connected applications, it has become a potential solution for unstable and low-strength systems. Through PSCAD model, this paper verifies how GFMI converter + energy storage battery can strengthen the system strength and improve the inertia of the system, and promote the system to be more stable.
Based on PSCAD model, this report verifies the influence of GFMI inverter + battery energy storage solution on power grid system through three modeling cases. Through simulation results, the following two conclusions can be drawn:
·GFMI inverter + battery energy storage solution can increase the strength (SCR) of the grid system. Under the background that the proportion of new energy access may reach 80% in the future, this is particularly important for remote areas or areas with weak grid strength. It can enhance power quality and reduce the influence of power grid fluctuation.
·GFMI inverter is similar to synchronous generator operation mode, which can add inertia link in inverter control system and improve inertia of new energy resources grid-connected system. When the grid load suddenly changes, it can make active response faster and slow down the frequency decline speed, and play a role in stabilizing the grid frequency and relieving the grid congestion.
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