Research On The Control Strategy For Regulating The Voltage And Frequency Of Islanding Microgrid

At present, the operation control strategy of micro grid has master-slave control, peer to peer control and hierarchical control. Master-slave control is so dependent on the main source that the reliability and redundancy is poor. In peer-to-peer control, micro source adopts droop control strategy which can achieve automatic power distribution. However there are problems such as reactive power sharing, voltage and frequency difference. In the low-voltage micro grid, the resistance component of the line impedance is much larger than that of the inductive component, so that droop control strategy for power coupling is serious. In hierarchical control, the underlying micro source controller can use master-slave control or peer-to-peer control. The central controller through the data exchange with the underlying micro source controller, can achieve voltage and frequency of secondary regulation, economic operation and other optimization operational objectives. Therefore, hierarchical control has important influence on the optimal operation of microgrid system.In low voltage microgrid, the distribution of active power on the feeder has great influence on the line voltage drop. The product of the active power transmission of every micro source and the resistance component of the line impedance is equal, which can improve the voltage distribution of micro grid. The microgrid in islanding mode use hierarchical control in this paper. Micro source controller adopts the improved droop control strategy, through continuously adjusting reference point of the no-load voltage and no-load frequency, to maintain the voltage amplitude stability of PCC in the ratings, to make the frequency of stable operation of micro grid to achieve rated frequency, to make the product of the active power transmission of every micro source and the resistance component of the line impedance equal, to make the voltage drop caused by line impedance on the feeder equal, and to make output voltage amplitude of micro source equal, which improves the voltage distribution of micro grid.Simulation and analysis is carried on through the MATLAB/Simulink software, which micro grid is composed of three micro sources. Experiment and analysis is carried on which micro grid is composed of two micro sources. The experiment is completed to achieve optimization distribution of active power and voltage and no-error frequency regulation. The experimental results show that the proposed hierarchical control strategy can significantly improve the voltage distribution and frequency stability of microgrid.