| UHVDC transmission is an important way to optimize the allocation of energy resources.Northeast China Power Grid is a regional power grid with high wind energy reserve.Its wind abandonment rate has been high for a long time due to the lack of large-capacity power outgoing channels.At the end of 2017,the Jarud-Qingzhou ±800kV UHVDC transmission project was put into operation to solve this problem.Although the project provides a way for local wind energy absorption,it challenges the safe and stable operation of the system at mean time.Because the total installed capacity of Northeast Power Grid is small and the support construction of Jarud converter station is imperfect,once DC blocking fault occurs,all areas of the network will suffer serious impact.At this time,adopting reasonable emergency control strategy will play a key role in maintaining the safe and stable operation of the system.Electrical dissection theory is a method to analyze the source-flow coupling factors of network.It can be used to answer the question "Where does the power flow come from and where it goes".According to the characteristics of Northeast China’s actual power grid,the method of electrical dissection is improved,which can make it practical in the study of practical problems.This paper presents a method to analyze the actual large-scale power grid based on the electrical dissection theory,and uses the method to analyze the source of DC power outgoing from the Northeast China Power Grid,which serves as the basis for formulating emergency control strategy.When the large capacity DC is blocked,a large amount of power surplus will be generated in the sending end system.Accurate and fast generator tripping measures become the key to maintain the safe and stable operation of the system.An emergency control strategy formulation method based on electrical dissection theory is proposed,and its superiority in power flow control is verified in the New England 39-bus system.The method is applied to the Northeast China Power Grid.Two examples of DC unipolar blocking and bipolar blocking are used to verify the method.The results show that the emergency control strategy based on electrical dissection theory can limit the impact of the fault to the line coupled with DC,and take into account the safety of the AC line near the converter station,and allocate part of the risk to the whole network.In order to meet the specific operating conditions of the system,optimize the control effect and reduce the economic cost,it is necessary to coordinate the provinces,lines and units of the system,and rationally adjust the emergency control strategy.From three aspects of inter-provincial coordination,wind-thermal power coordination and multi-DC coordination,the coordinated control strategy of power grid at the sending end after UHVDC blocking is proposed.Inter-provincial coordination makes full use of the power support capability between provincial networks to solve the problem of undercut caused by the problem of some units that can not be removed.Wind-thermal power coordination adopts the idea of preferential removal of wind power,and incorporates the units near the converter station with the risk of overvoltage into the cut-off strategy,thus avoiding the over-cut caused by wind generator disconnection.Multi-DC coordination can significantly reduce the total power of generator tripping,and reduce the economic losses caused by the start-up and shutdown of a large number of units.The example analysis shows that the coordinated control method based on electrical dissection theory can stabilize the system frequency and take into account the power flow distribution.This mehod can avoid large-scale power flow offset and effectively prevent cascading faults caused by power flow overstepping after DC blocking accident. |
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