Research On Opearation Mode And Control Strategy In Microgrid

Nowadays, with the fossil energy sources exhausting and rapid economic development, the whole society’s demand is fast growing, in order to solve the contradiction, distributed generation as the core of the new energy generation technology has received been more and more attention.Micro-grids can provide green, clean power with high quality for remote mountainous areas, islands, schools, factories where are far away from traditional power grid. Different from traditional power system, with the widely application of power electronics equipments, we can use them to be power networking interfaces.This paper have a major research on operation mode of parallel inverters with droop control and the inverter and synchronous generator parallel coordination control strategy at AC bus microgrid, including the voltage and frequent control with droop control inverter, the smooth translation between isolated and grid, the proportion of grid-forming units and grid-connecting units, the frequent recovery of grid-forming unit and the coordination operation strategy of the grid-forming inverter and synchronous generator.This paper introduces droop control theory of three-phase inverter, and does deep analysis on P-f and Q-V droop control characteristics. Based on this, it studies the issue of load share and averaged current control among power modules in the paralleled power system, and adds an integrator on reactive voltage control loop to inhibit the reactive circulation. Through simulation on critical proportion between grid-forming units and grid-connecting units on the premise the microgrid works steadily. Aiming at inverters parallel system and synchronous generators parallel system, this paper designs smooth switching controller between island and grid-connected modes, so as to switch between the two modes. Meanwhile, it studies system voltage-frequency recovery strategy based on the characteristic of frequent and voltage amplitude deceasing with the active power and reactive power demanding. And this paper designs the power controller and pre-synchronous controller, so as to reduce the impact of current and reactive shock. Finally, the simulation results verifies the validity of above control strategies.Finally, in Ali area, Tibet, for example, this paper analyses the current energy supply and demand situation in Ali, based on AC micro-grid, it proposes a construction scheme which contains small-scale hydropower, photovoltaic grid forming-unit, PV grid connecting-unit, diesel engines and spare backup battery systems. The Simulink models are built to study coordinated operation strategies of the whole system, and it analyses transient stability in different conditions: solar radiation falls and load mutations. The results verifies the stability of the system. After above theoretical analysis, this paper gives a reasonable construction scheme in Ali area, Tibet.