Grid-Connected And Off-Grid Switching Control Technology Of Regional Power Grid Under High Permeability Of New Energy

In order to adapt to the layout of the existing energy structure,the regional power grid,which combines various distributed power sources such as fuel,light and storage,emerges as the times require.It can provide users with electric energy nearby,reduce large-scale long-distance transmission of electric energy,and improve energy utilization efficiency.At the same time,due to the access of a large number of new energy units to the regional power grid,the region presents weak inertia characteristics.When the regional power grid is connected to the grid,the stability of the large power grid is guaranteed.Once the unplanned island occurs,it is separated from the support of the large power grid,and the frequency will produce huge fluctuations,affecting the stability of the system operation.The weak inertia characteristics of the regional power grid lead to more prominent frequency security and stability when switching between grid-connected and off-grid.In this paper,the regional power grid under the high permeability of Huai ’an new energy is taken as the research object,and the smooth switching control method of regional power grid is studied.In this paper,the following specific work has been carried out on the above problems:(1)Topology and control strategy of regional power grid under high permeability of new energy.Firstly,the topology of the regional power grid under the high permeability of the actual Huai ’an new energy is constructed.The power supply in this structure mainly includes the gas turbine power generation system,the photovoltaic power generation system and the energy storage power generation system.Secondly,the mathematical model and control strategy of each power supply are analyzed.The gas generator set adopts the conventional unit based on the synchronous generator to directly integrate into the power grid.The photovoltaic power generation system adopts a two-stage power generation structure.The pre-stage Boost boost circuit adopts the Maximum Power Point Tracking(MPPT)control,and the post-stage inverter adopts PQ control.To maximize the power output,the energy storage system adopts PQ control to ensure the constant power output.Finally,a dynamic simulation model of regional power grid with practical engineering significance is established.(2)Research on frequency characteristics of high proportion of new energy regional power grid under off-grid.Firstly,according to the operation characteristics of Huai ’an regional power grid,the switching characteristics of the system when the gas turbine is used as the main power supply are analyzed.According to the frequency characteristics of the gas turbine under different capacity and different inertia time constants,the safe operation interval of the single-machine on-load system under the grid-connected and off-grid operation is given.Secondly,taking some regional power grids in Huai ’an as the research object,several output models with different penetration ratios of new energy under conventional control are established,and their frequency characteristics are analyzed.Through simulation,the difference of grid-connected and off-grid frequency characteristics between singlemachine load system and high-proportion new energy access system is compared,and the influence of high-proportion new energy access on the frequency characteristics of regional power grid system under grid-connected and off-grid is analyzed.Finally,the simulation research on the safe operation interval of the system under different output ratios of new energy is carried out.(3)The time-sharing switching control strategy based on master-slave structure.Firstly,the control strategy of ’ coordinated control of new energy stations-adaptive control of regional power grid ’ is proposed,and the architecture of coordinated control system of regional power grid is established,which solves the problem of slow response speed of traditional new energy stations.Secondly,a time-sharing switching control strategy based on master-slave structure is proposed.When the power imbalance occurs in the regional power grid after the disconnection of the tie line,the time-sharing adjustment control measures are taken to adjust the system power in multiple time periods.Finally,through simulation verification,the conventional one-time adjustment and the timesharing adjustment control measures proposed in this paper are compared and analyzed.The results show that the time-sharing adjustment strategy can reduce the secondary impact of frequency and realize the smooth switching between grid-connected and off-grid.