Research On Voltage And Frequency Recovery Control In Microgrid Based On Droop Characteristic

With the rapid development of the global economy and industrial technology, micro-grid technology has become one of the hot spots in the study of distributed systems. Distributed power generally connects with the power electronic interface in micro-grid, which can increase the flexibility and reduce the inertia of the system, but also increase the difficulty of the control in micro-grid. The droop control is used in order to make the power can be averaged, but at the expense of the stability index of voltage and frequency. Therefore, the research on the control of voltage and frequency is of great significance.In allusion to the resistance characteristics of the line impedance in micro-grid, the mathematical model of the three-phase inverter was established and the parameters of the three-phase inverter’s voltage and current double closed-loop feedback controller was designed in this paper, which can ensure the output impedance is resistive to facilitate the selection of droop characteristic. The difference of the droop control between the micro-grid and the traditional grid was analyzed based on the power transmission characteristics, then the droop control that suits for the low voltage micro-grid was adopted as the basis of the study in this paper. Due to the voltage and frequency deviation in droop control, especially when the micro-grid is operating in islanded mode, the stability of the system will be affected if the offset is too large. The voltage and frequency recovery control was used to guarantee the stability of the whole system in this paper. In the voltage recovery part, the master-slave control was adopted and the voltage compensation control items was joined in the main unit. In the meantime, the peer control and inertial element of reactive power were adopted by the frequency recovery part. So the voltage and frequency can be ensured to near the rated values when load mutation occurs, and the rationality of the method was analyzed in this paper. The simulation of the control strategy has been completed based on the MATLAB/Simulink platform, which was used to confirm the feasibility of the study in this paper.The experimental platform of micro-grid with DSP digital control was set up in this study, which was composed by three micro sources, and the experiment of the control method in this paper was completed based on the platform. The experimental results show that the voltage and frequency can have a good recovery on the basis of the stability of the system and the droop control can be improved as well as the stability of voltage, frequency and the entire micro-grid system can be ensured by the control strategy in this paper.