Research On Mtdc In Disaster Recovery Of Interconnected Power System

Voltage sourced converter based multi-terminal high voltage direct current system(VSC-MTDC)has many advantages such as independent control of active power and reactive power,reversing current direction to achieve power flow reversal under the condition of constant voltage polarity,providing voltage and frequency support to the grid to help the grid restore power supply as well as black start after the accident,supplying power to a passive network,realizing the integration of wind,solar and other new energy sources and so on.Power grid interconnection can allocate the whole network resources more reasonably,improve the effective utilization of power generation equipment and reduce the cost of generating electricity.It also can share spinning reserve and reduce reserve capacity of power generation equipment in the system.It can make the use of various types of power plants in the system more reasonably to improve economic efficiency.It can realize inter area power support to improve the reliability and security of the system.As a result,combining VSC-MTDC and power grid interconnection has a very great advantage to the whole power system.Especially when interconnected power grid suffers blackout,MTDC can provide DC power to the system as start power source,which can help grid recover.The specific achievement of this article is as follows:1.This paper presents and analyzes the frequency stability constraints,the low frequency oscillation constraints and the synchronous power support constraints when AC network expends the scale.2.The model of three terminal HVDC system is established on PSCAD/EMTDC.Considering the power grid transmission capacity of non-fault area,electrical capacity of the faulty area,maximum transport capacity of DC line and transmission capacity constraints of converter station,this paper presents the support strategy for main grid by VSCMTDC system.3.On the basis of graph theory,a new method to calculate the importance of network nodes and the weight of the network is proposed.Considering the constraint conditions such as DC power transmission constraints,overvoltage constraints,power flow constraints,load recovery constraints,start-up power constraints and start-up time constraints of units,this paper presents a main grid restoration strategy based on improved Dijkstra algorithm under the condition of VSCMTDC system providing DC power support for power grid.An example is used to verify the strategy.4.This paper analyzes the protection zone,fault type and protection configuration of VSC-MTDC system and also researches the coordination between converter control strategy and protection.According to the DC line failure,this paper introduces two different DC fault isolation technology.One is by AC circuit breaker and the other is by DC circuit breaker.At last,this paper puts forwards a flexible multi terminal DC line protection strategy based on improved grip technique.