| Distributed Generation(DG),as a supplement and support of centralized power system,has its unique advantages in investment cost,environmental compatibility,reliability of power supply and flexibility of power generation mode.However,high permeability DG access to distribution network will inevitably change the power flow of the system and cause a series of power quality problems,especially the voltage quality will have a significant impact.Reasonable DG configuration can enhance the advantages and avoid the disadvantages,so this paper makes a thorough study on the influence of DG on distribution network voltage and its optimal configuration.Firstly,according to the simplified distribution network model with DG,the influence mechanism of DG on distribution network voltage distribution and voltage fluctuation is analyzed theoretically.The static voltage stability of distribution network is analyzed,and the static voltage stability index based on the existence of power flow solution is given.The influence of DG on distribution network voltage is not only traditional but also unique.Finally,the main factors affecting voltage distribution,static voltage stability and voltage fluctuation are DG access location,capacity,power factor and access mode.Then the DG and energy storage components are modeled.Taking photovoltaic power generation system and wind power generation system with strong power fluctuation as examples,the working principles of these two DGs are analyzed,and the specific models of photovoltaic and wind power systems are built based on PSCAD/EMTDC platform.The correctness of the models is verified by simulation of their output characteristics.In addition,the accumulator and supercapacitor in energy storage elements are also studied.Their PSCAD models are established and their charging and discharging characteristics are verified by simulation.Then using IEEE33-bus standard distribution system model,the effects of DG access location,access capacity and power factor on voltage distribution and static voltage stability are simulated and analyzed.The voltage distribution and static voltage stability of DG single-point centralized access and multi-point decentralized access are compared and analyzed.It is pointed out that DG can improve voltage level and voltage stability,but it is not configured.When it causes voltage overrun and other problems.For voltage fluctuation,the variation of DG output and node voltage fluctuation caused by fluctuation of illumination intensity and wind speed are studied.The results show that the voltage fluctuation at grid-connected point is the most serious.The influence of DG start-up and shutdown on voltage fluctuation is also considered.It ispointed out that DG start-up and shutdown have a great impact on power grid.Finally,aiming at the optimal allocation of DG,a multi-objective optimal allocation model with minimum network loss,maximum voltage stability margin and minimum voltage deviation is established.At the same time,the multi-objective optimization is transformed into single-objective optimization by using the theory of fuzzy sets,and the adaptive mutation particle swarm optimization algorithm is used to solve the problem.Taking IEEE33 bus standard distribution system model as an example,the optimal access location and capacity of DG are obtained by solving the problem in this paper,which improves the overall performance of the system.After the location and capacity of DG are determined,the output fluctuation of DG is suppressed by hybrid energy storage system.The hybrid energy storage control strategy based on EEMD and fuzzy control is adopted.The high frequency component of fluctuating power is borne by supercapacitor,the secondary high frequency component of fluctuating power is borne by battery,and the low frequency component is connected to the grid.The correctness of the hybrid energy storage system and its control strategy is proved by an example analysis,which makes it possible for DG to access large capacity. |
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