| With the rapid development of the world economy and the increasing proportion of renewable energy resources connected to the grid,the uncertainties on the power supply and load of the power system are increasing day by day.Firstly,the location and construction period of new energy power stations,especially small and medium-sized distributed power sources,are relatively flexible.And the new energy itself also has characteristics of uncertainty,and uneven distribution of time and space,etc.The high proportion of new energy power to the power grid will make the operation characteristics of power system more complex and the operating environment more difficult to predict.Secondly,the active loads such as electric vehicles are increasing year by year,and the diversified loads are developing rapidly.So the long-term growth trend of load is becoming less predictable.In addition,the actual operating environment of power system,such as line maintenance and unit operation state,has an important impact on power system planning.So it is of great practical significance to take it into account in power network planning.Under the new situation of the above mentioned power system development,higher requirements are put forward for the flexibility as well as reliability of transmission network planning.In this paper,the incremental decision making of urban planning is introduced into the planning of power transmission network,and the method of incremental decision-making of power transmission network is proposed.Based on the reference power network model for determining optimal transmission capacity,the paper studies the power transmission network planning considering different factors.In order to explore the influence of different load levels on the planning results,this paper takes wind power integration as an example to establish a transmission network planning model that takes multi-load levels into consideration.And the iterative posteriori method of successive addition was applied in the n-1 security constraint test,which the most serious line over-limit cases were screened out in each iteration,and the corresponding line constraint were added to the original model until the safety check was met.Finally,six scenarios of different load levels are tested in the example analysis to verify the advantages and disadvantages of different load options in the planning.For the influence of line maintenance is ignored in the current network planning,this paper takes wind power integration as an example and proposes a transmission network planning model that considers the annual maintenance of line with the new energy resources.In the model,the multi-scenario technology is adopted to deal with the uncertainty of wind power output,and the nonlinear part in the constraint is linearized in order to transform the model into a mixed integer linear model.Finally,two situations of network planning are set in the case analysis.The results of the examples show that the model considering line maintenance in the planning is highly reliable and can deal with the line breaking accident during line maintenance under the guarantee of normal power supply.Considering the high proportion of renewable energy,this paper takes a large-capacity wind generation as an example,and takes into account the reactive power and voltage constraints of the system,and proposes an AC power flow model for transmission network planning considering unit operating status under the integration of new energy resources.In the planning model,the unit start-stop,ramp rate and minimum up/down time constraints are considered.And the multi-scenario technology was used to deal with the uncertainty of wind power output,and a series of linearization methods were used to transform the AC power flow model into a mixed integer linear model.Finally,the result of case analysis shows that a better planning scheme can be obtained by considering the unit operating state when a higher proportion of new energy is connected. |
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