Research On The Economic Operation Control Technology Of AC-DC Hybrid Microgrid

With the development of social economy,the power supply mode in today’s society is also gradually changing.The grid’s power supply demand is shifting toward regionalization,economization,and environmental protection.AC/DC hybrid microgrids combine the benefits of both DC and AC microgrids.It has become an essential component of the electricity system due to its ability to meet people’s economic and environmental needs.Today’s microgrids operation control,on the other hand,solely considers the primary regulation of power and voltage of distributed generations,ignoring the economic issues posed by the disparities in power generation costs across distributed generations.Furthermore,fault current peaks in the grid due to high impedance ground faults are modest and difficult to identify from typical grid operating states,resulting in long-term concealed issues for grid operation control.In this paper,microgrids operation control and protection approach to address economic and safety issues in microgrids operation control are given attention,as well as giving a reliable solution for grid operations that is both safe and stable.First,this paper proposes a cost micro-increment-based reference power optimal iterative algorithm for improving conventional droop control at the hybrid microgrids control level.The algorithm separates hybrid microgrids operation control into two levels: intra-subgrids and inter-subgrids.It enables the microgrid’s operation control to realize active power allocation among distributed power sources according to capacity,as well as the grid to allocate active power according to cost,taking into account the cost coefficient of each distributed generation,to realize economic operation control,thanks to the two-layer structure.Furthermore,the droop control algorithm is improved,and secondary control is added to assure grid frequency and bus voltage stability,resulting in grid stability.Second,to ensure the stability of the hybrid microgrid in response to unexpected conditions,a hybrid microgrid protection scheme based on Variational Mode Decomposition(VMD)is proposed in this paper.The scheme divides the protection of hybrid microgrid into DC subgrid protection and AC subgrid protection.Among them,the fault protection of AC subgrid adopts VMD-based differential current protection method to improve the performance of AC subgrid in case of short-circuit faults.This method can accurately distinguish and detect high impedance faults and ensure the correct action of relays.To address the problem of difficult detection of high-impedance ground faults in DC subgrids,this paper proposes a fault detection method based on VMD-SSA,which uses a variational mode decomposition method to collect the rate of change of the fault current,optimizes the quadratic penalty term of the decomposition process and the number of decomposition variables using a sparrow search algorithm,and calculates the kurtosis energy under the component of maximum kurtosis as the threshold,i.e.,the index of fault detection.Compared with the variational mode decomposition method optimized by particle swarm algorithm and genetic algorithm,the sparrow search algorithm improves the sensitivity of fault detection,reduces the tolerance,and realizes reliable protection of microgrid.Lastly,an AC-DC hybrid microgrid simulation model is developed using the Simulink modeling platform to validate the proposed control algorithm’s control impact in inter-subgrid and intra-subgrid microgrid control,as well as the protection effect of the AC and DC subgrids.Finally,it is proved that the suggested protection algorithm can accomplish cost-effective and stable operation in a hybrid AC-DC microgrid while also improving grid accuracy for high impedance fault detection.