| Energy is an important guarantee for national economic development and improving people’s living standards.In recent years,because of the energy crisis and the increasingly serious environnmental pollution,coal,oil and other fossil energy are gradually being replaced with new energy.Solar energy for its unique advantage like clean,environment-friendly and never dry up,has attracted a great deal of attention.However,solar energy has a major feature that it is random and uncontrollable,and greatly influenced by weather factors,which will demand higher requirements to planning and design of grid-connected PV power plant.Distributed access method can make most use of solar energy resources,but then distribution network turns into multi-power network from a single power network,causing change of line power flow directions.Therefore,planning issue of distributed PV power plant connecting to the distribution network needs more meticulous and in-depth research.PV power plant output randomness model was researched in the paper,a method for its random simulation was proposed.Based on established PV power plant simulation model,effects were analyzed and researched for grid-connected PV power plant on aspects of distribution network power flow distribution,voltage distribution,short-circuit current and relay protection.In the end,a method was proposed for connecting to grid optimization planning with considering PV output randomness,location and capacity were optimized for distributed PV power plant connecting to grid.Specific contents are as follows:1.Characteristics of solar energy was analyzed,and then a calculation model of surface light intensity at different times was set up,surface light intensity distributions was also studied under different weather conditions.After studying photoelectric conversion model,the normalization beta distribution model of PV power was established while reference value is maximum output value.According to the light intensity statistical data,a parameter estimation method was proposed for beta distribution probability density function,and a method for stochastic simulation was included.Practical examples show that the method is effective.2.The effects of grid-connected PV power plant to the distribution network was studied,based on the effect considering the security constraints that need to pay attention to.Through analysis,studying changes that grid-connected PV power plant would bring to line power flow distribution and node voltage distribution.Analyses the characteristics of short circuit current for photovoltaic plant,studied short-circuit current of the line in distribution network including photovoltaic power plant in case of short-circuit fault,and difference from the original network short-circuit current and the impact to the normal operation of relay protection system.Based on establishing PV power plant physical simulation model,the simulation model was accessed to the typical IEEE33 distribution network for running simulation,studied the influence of grid-connected PV power plant to the parameters such as line power flow size and direction,node voltage distribution,system network losses.3.A grid-connected photovoltaic power plant design optimization method is proposed,with considering the PV power plant output random characteristics.The design optimization focus on grid-connected PV power plant location and capacity,to reduce power demand from main grid and reduce carbon emission for the purpose of optimizing,ensure the circuit breaker line flow unchanged,avoid influence to grid relay protection device.Sequential Monte Carlo probabilistic method was improved,so as to meet grid stochastic optimization problem,and improve efficiency.Constraints were put into optimizing target in terms of penalty function method to form a augmented objective function,and using Particle Swarm Optimization algorithm to solve the problem.Finally,typical example was applied to verify result of the optimization method. |
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