Research On Recovery Characteristics And Coordinate Orderly Recovery Strategy Of Multi-infeed HVDC System

The reverse distribution characteristics of energy and consumption contribute to the” the west to east” strategy of energy formation. Under the technical anvantages of its quick and flexible regulation, transmission distance without being limited by the synchronous operation stability, HVDC has been widely used in the background of power flow across regions, long distance, and large scale transmission. As the eastern coastal developed areas has a large load demand, some DC has been multi-infeed the same end of AC system. Until 2016, Guang Dong province has formed eight infeed DC receiving power grid. The problems between inverter station, such as the closely electrical distance, the highly infeed power energy and the weaker and weaker voltage support abilities, make stability of the multi-infeed HVDC system tend to complex. The recovery characteristics strategy of multi-infeed HVDC greatly influences the safe and stable operation of grid.This paper uses the theoretical analysis and and time domain simulation to analys the recovery characteristics and statergy of multi-infeed DC system. Firstly, the recovery characteristic of electical quantities,such as the transmission of active power and reactive power consumped by inverter,are analysed after the fault of receiving power grid. Secondly, the influence of DC control mode and control links is analysed on methanism. Then, the main oprating variables are disscussed based on normalized sensitivity methond, which may affect the recovery characteristic. The conclusion is that DC current makes the maximum influence to the system. Then, PI controlor and additonal delay link of VDCOL are controlled to adjust the recovery characteristics. Moreover, the parameters of PI and VDCOL links are coordinated optimizate to improve DC recovery characteristics. By the way, this page discussed how MIIF, MIESCR and DC transmission power can influence the probability of commutation failure and voltage supportcapability of receiving-end power grid for multi-infeed DC system, and then make a conclusion of MIIF critical exponent to distinguish communication failure and the relationship between MIESCR and voltage support capability.As far as "peak load shifting" for reducing the reactive power consumed by converter and avoiding subsequent commutation failure to reduce the interaction between DC systems are concerned, then the recovery stratagy,realized by coordinatting controlling the parameter of PI links and additonal delay link for VDCOL, is analysed based on MIESCR size. Then aiming at the shortcomings of the MIESCR, the multi-infeed DC system progressive staggering recovery index is put forward by using the contact among MIESCR, MIIF and active power transmission capacity.. Meanwhile, using dynamic reactive power peak size, the time demand of active power recovery to 90% of subsystems of multi-infeed DC systems and the whole reactive power demand of multi-infeed DC system to quantize the recovery performance of the system, The last, a seven-infeed DC receiving end simulation system is built on the PSCAD/EMTDC software to verify the effective of multi-infeed DC progressive staggering recovery strategy.