Research On Influence Of Inverter Interfaced Distributed Generation On Voltage Sag And Its Optimal Configuration

With the increasing of automation production process and high-efficiency production equipment in the distribution network,users’ requirements for power quality are gradually increasing.Among many power quality problems,voltage dips have the most severe impact on widely used voltage-sensitive loads.Reasonably selecting the nodes with sensitive load connected to the power grid,installing voltage sag control equipment at the appropriate position in the power grid,and modifying the power grid are important measures to reduce the adverse impact of voltage sag on sensitive load.The premise of voltage sag prevention and control is to find the weak link in the power grid in an accurate way through voltage sag assessment,that is,to know the area where the voltage sag of the sensitive load access point is easy to occur after the fault occurs.At present,the distributed power supply has a high penetration rate in the distribution network,and the former will change the current distribution of the system during normal operation and failure.Therefore,distributed power supply is closely related to voltage sag evaluation of distribution network.Considering that Inverter Interfaced Distributed Generation(IIDG)based on power electronic device interface is the most widely used in distribution network,and its impact on voltage sag is the most significant,the distribution network with IIDG was researched.Different control strategies of a single inverter-type distributed power supply will change the corresponding characteristics of the fault,which in turn affects its ability to output reactive power and support the grid voltage.In the distribution network,multiple inverter-type distributed power sources can be connected to one point or distributed to multiple points.Different access methods will also affect the mitigation effect of voltage sag.The PSCAD simulation results show that the IIDG with advanced current-limit fault control strategy has low voltage ride-through capability and has the strongest mitigation effect on voltage sag.When the IIDGs are accessed to a single point in the middle of the feeder,or dispersed into the middle and the end,it will achieve best effect of increasing the voltage sag amplitude.At present,the voltage sag evaluation mostly adopts a single indicator on the power supply side or the user side,which lacks versatility and accuracy.In order to solve the above problems and to present the evaluation results more vividly,this paper defines the concept of voltage sag vulnerability domain,and its physical meaning refers to the area where the voltage sag of the whole network is the most serious once a fault occurs.The voltage sag vulnerability domain identification process includes important steps such as Monte Carlo simulation,voltage sag index evaluation and joint area of vulnerability generation.This paper focuses on the IIDG with low voltage ride through characteristic control strategy,and derives the iterative short circuit calculation method for distribution network,which is nested in Monte Carlo simulation.Four indicators of the grid side and the user side are selected to generate a comprehensive evaluation index set,and the combined weights are calculated based on AHP method and CRITIC method,and the voltage sags severity index(Voltage Sag Severity Index,VSSI)makes the assessment results more accurate and comprehensive.Based on the calculation results of the VSSI indicators of each node,the top 5 nodes are selected to obtain the joint area of vulnerability to form a voltage sag vulnerability domain.Proper configuration of the position and capacity of the inverter-type distributed power supply will maximize its mitigation of voltage sag.The voltage sag vulnerability domain,active network loss and economy are taken as the multiple goals of the optimal configuration of IIDG.The multi-objectives are dynamically weighted based on fuzzy Chebyshev planning,which overcomes the shortcomings of the lack of objectivity of the weighting method.An adaptive particle swarm optimization algorithm with fast and good convergence is used to solve the optimization model.The optimal configuration results of the IEEE30-node system show that the IIDGs distribution is near the nodes with the highest voltage sag,and the larger the distance from the main power source,the larger the capacity of the IIDG.After the optimal configuration,the voltage sag vulnerability domain is significantly reduced,mainly concentrated on the high voltage side and the ring portion near the low voltage side of the transformer.