Research On Voltage Stability Control Strategy Of Distribution Network With DG

After distribution generation is connected to the grid,the traditional passive network will be transformed into an active network,which has a certain impact on the power quality,voltage distribution and relay protection mode of the distribution network.Among them,voltage stability is closely related to system stability and user power quality,so it is necessary to meet the requirements of safe,stable and economic operation of power grid through appropriate control methods.This paper analyzes the voltage and control strategy of grid connected with DG in two different distribution network environments.The first distribution network situation is that the overall structure of the distribution network is relatively stable,and the voltage will not exceed the limit in a large range or for a long time,while the DG has high penetration.The second distribution network situation is that the power supply distance is long,the number of users is small,the voltage level is low,and the voltage quality of users is poor due to the long power supply distance.The main research contents are as follows:Firstly,the influence of DG including energy storage on distribution network voltage and network loss under different capacity,location and operation mode is analyzed quantitatively,and its variation law is deduced by formula.Since DG incorporation changes the original power flow and volt ampere characteristics of the system,the voltage stability indexes L and H of the distribution network are quantitatively analyzed.The general treatment of each type of node in power flow calculation after DG incorporation is given.Secondly,based on the DG high penetration distribution network environment in a certain area of Jiangsu Province,a multi time scale two-layer control strategy of distributed energy storage system is proposed.The double-layer control is implemented by upper and lower layers,and the upper layer is the stability control layer,which determines the total active / reactive power of the energy storage system when each node meets the voltage safe operation conditions and the voltage deviation is minimum.The lower layer is the optimal control layer,which optimizes the allocation of the upper layer results.The particle swarm optimization algorithm is used to solve the power of each energy storage unit when the loss rate of the active power network is the minimum and the new energy consumption rate is the maximum.The double-layer or single-layer optimization calculation is carried out in different time scales to meet the control objectives.In order to verify the rationality and effectiveness of the proposed control method,simulation calculations are carried out in the standard node system IEEE33 node and a distribution network node system in Jiangsu Province.The results show that this method can effectively reduce the voltage fluctuation,charge and discharge times of energy storage,improve the new energy consumption rate and reduce the active power network loss.Then,taking a sparse distribution network in Qinghai Province as the background,a comprehensive coordinated control strategy is proposed by combining the continuously adjustable power electronic voltage regulator with the traditional voltage regulator OLTC and CB.In the long time scale,according to the system state information and the load and DG prediction data,the discrete variables of OLTC and CB action values are convex relaxed by using the second-order cone programming under the equal interval optimal operation scale,and then the optimal solution is carried out to determine the action state and compensation amount.The real-time regulation in equal interval time scale is realized by PEVR.The voltage out of limit is judged by PEVR control system,and the compensation action value of each side is determined by particle swarm optimization and PEVR series parallel side control mode.The simulation results in IEEE33 node system and a region in Qinghai show that the proposed control strategy can improve the voltage quality of users in remote areas and reduce the switching times of traditional voltage regulator.