A Control Strategy With Differential Power-flow Compensating Of Microgrid Under Symmetrical Fault Conditions

Microgrids have become an important carrier for effective absorption of distributed new energy generation.Its operation mode includes grid-connected mode and islanded mode.Different from grid-connected microgrids,islanded microgrids are not supported by the grid and are more prone to system instability due to power fluctuations or short-time faults,or even unable to maintain reliable power supply operations.Therefore,it is of great significance to study the fault ride-through control of the independent microgrid.This paper is based on the background of symmetrical faults occurring on the load side of the independent microgrid.According to the power transmission characteristics of the independent microgrid,the sensitivity of voltage to active power and reactive power is derived,and the influence curves of the changes in active and reactive power on voltage magnitude and phase angle are plotted respectively.It is concluded that the voltage magnitude of the microgrid is more sensitive to active power and less sensitive to reactive power in independent microgrids with a high ratio of resistance to inductance of the feeder impedance.Then the fault characteristics of the independent microgrid are analyzed,and it is concluded that the fault on the load side of the independent microgrid with a high line impedance ratio will lead to the power supply and demand imbalance in the fault area and voltage dip due to the limitation of micro source active power output of new energy power generation.To improve the above problems,a differential power-flow compensation control strategy based on the feeder impedance proposed in this paper not only uses micro source redundant power to realize dynamic compensation control of active power-flow to cope with the imbalance of power supply and demand in the fault area and the voltage dip in case of sudden fault on the load side,but also adjusts the coefficient of fault power-flow compensation according to the difference of micro source feeder impedance to optimize the distribution of fault power-flow and reduce feeder loss,so as to achieve the purpose of sharing fault power flow and suppressing inverter overcurrent.Comparing the MATLAB/Simulink simulation results of conventional distortion-free current limiting control and differential power-flow compensation control in the case of three-phase short-circuit faults on the load side of the microgrid,the results show that the control strategy proposed in this paper can effectively provide power support in the fault area and suppress voltage dip while optimizing the distribution of fault power-flow and reducing feeder losses.A small independent microgrid experiment platform composed of dual micro sources is built and a control circuit of DSP based on TMS320F28335 is designed to experimentally verify the effectiveness of the proposed differential power-flow compensation control strategy based on feeder impedance for improving power balance in fault areas and voltage support capability.