Research On Improved Droop Control Of Distributed Generation In Microgri

Distributed power generation can consume and utilize renewable energy sources through connection to microgrids.This approach to obtaining clean,low-carbon energy has received widespread attention from researchers around the world.In order to address the series of problems that arise from the fluctuation and intermittency of distributed power generation when it is connected to traditional power grids,energy storage systems are often connected to microgrid systems in practical engineering to ensure stable and reliable operation of the microgrid.This article focuses on the allocation of active and reactive power output of distributed power generation and energy storage systems in AC microgrids,analyzes and proposes improvements to the droop control method used when inverters are connected to microgrids.First,the classification of inverter control strategies in microgrids is briefly summarized,followed by theoretical derivation of the traditional droop control principle and analysis of the circulating current problem in microgrids.The mathematical modeling of the three-phase inverter circuit topology is carried out,and the transformation from stationary coordinate system to rotating coordinate system is performed.The design and analysis of the double-loop controllers for voltage outer loop and current inner loop used in the transformed model are performed to prove the effectiveness of the overall control model.Next,the impact of line impedance on the distribution of reactive power output of distributed power generation is analyzed.A distributed reactive power distribution strategy based on virtual impedance is proposed to address the problem that traditional droop control cannot reasonably allocate reactive power output due to differences in line impedance.The distributed consensus theory is explained,and the principle of adaptive virtual impedance adjustment for power regulation is analyzed.The dynamic consensus algorithm is then used to obtain the average power information required by the controller to update the adaptive virtual impedance value,achieving the goal of allocating reactive power output of each distributed power generation unit in proportion to its capacity.Distributed secondary voltage control is also introduced to compensate for the voltage drop caused by virtual impedance.The effectiveness of the proposed control strategy is verified through multiple simulation cases designed in MATLAB/Simulink under different conditions.Furthermore,a problem with traditional droop control is addressed,where the initial SOC(state of charge)values of energy storage systems are different and unable to allocate active power output according to the size of SOC,resulting in an SOC imbalance.A SOC rapid balancing improvement of droop control strategy is proposed by combining the characteristics of hyperbolic tangent function and droop coefficient.In which the average value of SOC of each energy storage unit is obtained using distributed consistency control method for improved equalization control.Under the proposed control strategy,each energy storage unit can allocate output power reasonably based on the size of SOC,and has a faster convergence speed than existing SOC balancing control methods,without exceeding the output power limit.Distributed secondary frequency control is also added to compensate for system frequency deviation and improve system stability.The effectiveness of the proposed improved droop control strategy is demonstrated through simulation comparisons of different SOC balancing controls using MATLAB/Simulink.Finally,a semi-physical experimental platform based on the NI-PXIe hardware platform and Star Sim software is built to conduct hardware-in-the-loop simulation experiments on the proposed distributed reactive power distribution strategy based on virtual impedance and the SOC rapid balancing improvement of droop control strategy.The experimental results are analyzed to further verify the effectiveness of the proposed control strategies.