Study On The Coordination Control For Island Renewable Energy Generators

With the energy and environment problem becoming increasingly severe, research on renewable energy power generation is getting more and more significant in the power industry around the world. Island contains lots of renewable resources such as wind, sunlight, current, etc. Since island power supply needs long-distance electricity transmission therefore suffering high costs, ocean strategy implementation is greatly limited in China. Because of global energy crisis, it’s a trend to develop technology of island renewable energy power supply and establish island grids. Funded by the national863projects, the proposed Zhairuo Island power system project will mainly focus on the development and utilization technology of island renewable energy in order to ensure that the island grid can run reliably and connects flexibly to external grid in harsh environment. The island grid is designed to run in three modes:maximum power output mode, scheduling mode and islanded mode.This paper studys coordination control for island renewable energy generators based on the Zhaoruo Island power grid. According to its running modes, this paper proposed a two-layer control scheme in order to achieve unit-network coordinated operation. In the upper level, a controller is used to coordinate the lower level controllers residing in each units and in the network. This upper level controller is much more similar to an AGC controller, achieving the function of secondary’ frequency control; while the lower level controllers serve as the primary controller and realize the command from upper level. This paper provides a algorithm called "equal-ratio"when calculating power allocation for each generator, achieving the normal scheduling of generators effectively. Considering the disadvantage of switching control strategy when the grid is switching between grid-tie mode and islanded mode, it proposed that all generators operate under droop mode to achieve load sharing. The output of energy storage devices under droop control becomes unstable when facing extreme cases, so this paper presents a algorithm of switching droop control and PQ control seamlessly.Firstly, this paper set up mathematical model of DFIG, photovoltaic generator and hybrid energy storage, as well as the complete renewable energy island grid simulation model based on the actual parameters of the grid. Then, simulation analysis was carried out in several typical mode of operation (grid-tie mode, islanded mode and switching from grid-tie mode to islanded mode), and the results show the correctness of model established and the effectiveness of the coordination control strategy proposed in this paper.