Research On Droop Control Optimization Technology Of DC Microgrid

In order to solve the problem of distributed energy consumption,dc microgrid technology came into being.In its control technology,droop control,as a way to realize the control task without the need of communication network,has become the main control means of equipment-level control.However,in the system with line impedance and multi-load,the traditional droop control method can no longer meet the control demand of the output current regulation of the distributed unit and the dc bus voltage at the same time.Therefore,this paper designs a series of control strategies and optimization methods for the voltage control unit based on the basic droop control method.In the design of the overall control scheme,in order to restrain the influence of line impedance and local load on the system operation,firstly,the operation characteristics of a system with four distributed units and local load are analyzed,and then a local load equivalent method is proposed to simplify the process of topology and mathematical analysis,and provide an analysis tool for the later control scheme.Secondly,the principle that particle swarm optimization algorithm can be used with droop control is given.Then,an improved method of adaptive inertia weight and learning factor is proposed for the key parameters of the algorithm,and the method is applied to the droop control strategy of distributed cell.The strategy uses droop parameter to form the current distribution error and bus voltage deviation sub terms of the converter searching for the best sagging parameters under various working conditions by means of iteration.Theexperimental results show that the proposed strategy can accurately distribute the load current according to the proportion,and maintain the bus voltage at the rated value at the same time,and the control accuracy almost reaches zero error regulation,making full use of the advantages of the improved algorithm,such as high convergence accuracy and fast speed.In order to solve the problem of short battery life caused by the imbalance of instantaneous charge(SOC)of each energy storage unit,a So C self equalization strategy is proposed,which is improved based on the original droop control method,and then the SOC equalization speed is adjusted by introducing the equalization speed coefficient.Secondly,in order to solve the problem of bus voltage deviation caused by time-varying droop coefficient,the whole control scheme is integrated into bus voltage regulation,and then a bus voltage sectional slope compensation method based on improved particle swarm optimization algorithm is proposed.This method uses the idea of differential calculus,divides the bus voltage curve of energy storage system into several small sections of slope function,and uses the improved algorithm to find the slope function Find the bus voltage value of each time node to establish the slope function,and then compensate the deviation through the function.The experimental results show that the bus voltage is well recovered,and the energy storage units can effectively complete the SOC equalization task under the constraints.Finally,a complete islanding operation model of DC microgrid is established,considering the factors such as line impedance and local load,and using the above scheme to coordinate the control of each module.