Research On Secondary Voltage Regulation Strategy Of Synchronous Fixed-Frequency Microgrid

Microgrid technology based on distributed power generation can comprehensively utilize a variety of renewable energy to meet the diversified power demand of users,and effectively improve the power supply reliability of users.When the microgrid is in island mode,using droop control strategy in the inverter can improve the flexibility and reliability of the microgrid.However,changes of load can cause voltage and frequency offset in the microgrid.Currently,the existing synchronous fixed-frequency microgrid solves the frequency offset and frequency stability problems in the microgrid,but the voltage offset problem is still prominent.Aiming at the above problems,this paper investigates a creative secondary voltage regulation strategy of synchronous fixed-frequency microgrid.First of all,the general control methods of microgrid are compared and analyzed,and the characteristics and application scenarios of these control methods are summarized.Focusing on the problem of voltage offset in the synchronous fixed-frequency microgrid using current-voltage(I-U)droop control under the island mode,a secondary voltage regulation strategy of synchronous fixed-frequency microgrid based on local information is proposed.In particular,the droop curve is adjusted according to the real-time voltage at the outlet of the distributed generation(DG)to realize the secondary regulation of the DG output voltage,which makes the voltage at the load end always within the set range.In order to ensure the synchronization of DG voltage regulation action,a droop curve synchronization adjustment method based on satellite time service signal is proposed.To be specific,taking the satellite time service signal as the benchmark for each DG,the DG outlet voltage is compared with the voltage threshold at the same time,that is,the DG actions are synchronized.For the condition of unknown line impedance,voltage regulation is given priority,and the method of dynamic voltage regulation of DG is presented to stabilize the output voltage of DG within the allowable range.Then,the small signal model of synchronous fixed-frequency microgrid based on I-U droop control is established.The small-signal model of inverter output filter and network link,low-pass filter and droop control link,current loop control link and microgrid system are derived.Using the small signal model,the eigenvalue is calculated,and the corresponding eigenvalue trajectory is drawn by changing each control parameter.Finally,the influence of filter parameters,current loop PI parameters and droop coefficient on system stability is explored,which can provide reference standards for subsequent simulation and experimental parameter design.The simulation by Matlab/Simulink and experimental verification are carried out for the secondary voltage regulation strategy of synchronous fixed-frequency microgrid proposed in this paper.The simulation and experimental results show that after increasing/decreasing the load power,the secondary voltage regulation method proposed in this paper can make the load terminal voltage always within the set voltage threshold range,which significantly verifies its effectiveness.The method proposed in this paper improves the autonomous operation capability of the all-inverter microgrid,which means a valuable and vital exploration for the “Double-High-Plan” distribution network operation mode in the future.