Research On Control Strategy Of Synchronous Fixed-Frequency Microgrid Based On Zero-Error Voltage U-I Drooping

With the development of society and economy,the problem of energy demand has become more and more prominent.There are many contradictions between the shortage of fossil energy and the continuous growth of power demand.The microgrid technology based on distributed power generation is one of the most promising applications in the current power system.Droop control is one of the most common control methods of parallel microgrid inverters,which can achieve the purpose of reasonable power distribution without communication.However,traditional droop control is based on the premise of high-voltage micro-grid and its line is inductive.If it is a low-voltage micro-grid,it is difficult for parallel inverters to achieve a reasonable distribution of output power.In this paper,combined with the development and application of synchronous phasor measurement(PMU)in the distribution network,in view of the voltage deviation and unbalanced power distribution problems in the traditional microgrid control,research on control strategy of synchronous fixed-frequency microgrid based on zero-error voltage U-I drooping is proposed.The synchronization clock and phase information obtained by the PMU are applied to the global synchronization reference signal of all inverters in the system to ensure that the parallel inverters in the microgrid can operate synchronously;different inverters can be completed with the help of the U-I droop relationship reasonable distribution of output power between devices,thereby simplifying the power and voltage frequency Corresponding relationship,reducing the difficulty of microgrid control.In this paper,the pulse per second of the PMU device is used as the synchronization reference signal,and all the distributed power sources are synchronized and adjusted by the PMU,so that the inverter generates a power frequency and in-phase synchronized voltage phasor,thereby alleviating the problems of power oscillation and parallel circulating current.Taking into account the shortcomings of traditional droop control strategies,a full inverter microgrid control strategy based on U-I droop is finally selected.The effective control of the inverter output power is achieved through the U-I droop control relationship,so that the parallel inverters in the microgrid can operate close to the form of a single inverter,which will make the power and voltage frequency The relationship is simplified and the control of the microgrid is easy.On the basis of traditional U-I droop control,a voltage recovery compensation control unit is designed to perform secondary zero-error voltage regulation to make up for the insufficiency of U-I droop control.In order to coordinate the relationship between differential voltage regulation and power distribution in the system,the PMU measurement information on the point of common coupling is used to calculate the line impedance parameters between the controlled inverter outlet and the point of common coupling in real time,and then through the virtual setting in the control strategy Impedance compensates for line impedance to achieve accurate power distribution.A microgrid simulation model was built in Matlab/Simulink simulation software,and simulation experiments were used to verify the effectiveness of the synchronous fixed-frequency microgrid islanding control strategy based on zero-error voltage U-I drooping regulation.