| One of the most important features in the modern power system is the formation of large-scale interconnected power system. The interconnecting of the regional power grids can be used to disperse the peak time, reducing the installed capacity of generators, play a role of energy optimization and quality and reliability of the power supply for the power system. On the other hand, the network structure of the power system will be more complex than before with the interconnecting of the regional power grids. And the safety and stability of interconnected power system will be weakened too. The China State Grid is in the critical period of developing from regional power grids to interconnected power grids throughout the country now. There are several kinds of methods for connecting the regional power grids, like the connection of the AC line, the connection of the DC line, the connection of the AC-DC paralleling and so on. With the steady implementation of the strategy of transporting the power from West China to East China, the HVDC technology is already widely applied in China. If there are emergency situations in the interconnected grid, the transmit power of HVDC can be rapidly controlled to supplying power and damping the oscillation as a method of emergency control. The course and current situation of HVDC development is introduced in the paper. The significance and research status of emergency DC power support is also described.The mathematical model of steady-state for the converters which are the core devices in the HVDC system and the control system of HVDC is introduced in the paper. And the various models of HVDC systems for the flow calculation and transient stability analysis and their characteristics is described. Their application occasions and limitations are also analyzed. According to the actual operating conditions of HVDC systems in Middle China-North China integrated Grid, the control function module of emergency DC power supply is designed in the definition environment for users in PSASP to create the conditions for the transient stability simulation analysis with the joint of the function of emergency DC power support.The safety and stability level of Middle China-North China integrated Grid with the UHVAC put into operation is analyzed when there are serious problems in the AC line and the HVDC system the in the paper. The mechanism of improving the stability of interconnected power system by the emergency DC power supply is studied too. The feasibility of emergency DC power support of Multi-circuit Sending HVDC system in Central China Grid is analyzed and studied according to a lot of simulation and calculation. And the effects on improving stability of HVDC power support with rapid valve operation of generators is studied for the integrated power grid in the paper. The superiority on improving stability and reducing economic losses of the grid is found from the program above.The emergency DC power support strategy is also studied in detailed in the paper. The effects on the power angle stability of interconnected power system by the factors of start time, support rate, support amount and duration of emergency DC power support is mainly analyzed and studied. |
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