The Study Of Power Control For ±500kV Double Hvdc System

Niuzhai-Conghua HVDC transmission project is one of the West-East electricity transmission key projects of China Southern Power Grid in the 12 th Five-Year Plan.It is the first double-circuit HVDC transmission project in China,which adopts the double-circuit transmission line on the same tower,use the same station at the rectifier and inverter,and share the same ground electrode.Niuzhai-Conghua HVDC transmission system set the double-circuit power coordinate control system,which is applied in HVDC transmission project for the first time.In this paper,a new hierarchical structure of the double-circuit HVDC transmission system is presented.The double-circuit power control of the double-circuit power coordinate control system is analyzed and studied in detail,including the distribution of double-circuit power,the convert principle of double-circuit control mode,the switch of double-circuit control mode,etc.At present,the effect of the current of Niuzhai-Conghua HVDC ground electrode has serious implications for the operation of oil and gas pipelines.The China South Grid(CSG)has taken some necessary temporary measures and emergency measures to effectively control the current of ground electrode.But these measures increased workload of the operators and at the expense of the operating characteristic of HVDC.The current distribution strategy of double-circuit power: first the power of every-circuit HVDC system is proportional to the sum of the DC voltage absolute value,and then each HVDC pole control system distribute the bipolar power command value between the two poles;in case of DC system failure(such as the most common block of monopole),the DC power is transferred to the other healthy pole,this strategy make sure the minimum current of ground electrode for every-circuit HVDC system,but not the minimum for double-circuit HVDC system.In order to avoid or reduce the influence caused by the grounding electrode current on oil and gas pipelines,we need to optimize the distribution strategy of double-circuit power.In this paper,through the research of double-circuit power coordinate control system,and optimize the distribution strategy of double-circuit power: take the pole of same name as a whole in the double-circuit HVDC system,internally the power is proportional to the DC voltage,and the double-circuit power is distributed to each pole directly;in case of DC system failure(such as the most common block of monopole),the DC power is transferred to the pole of same name,and then transferred to the pole of different name,the optimized distribution strategy can exert the advantages of double-circuit HVDC system in case of block of monopole,effectively reduce the current of ground electrode,and reduce implications for the oil and gas pipelines.This paper builds a simulation model with MATLAB to simulate the optimized distribution strategy.The results verify that the optimized distribution strategy is feasible and effective.The results will have certain significance to the actual project operation.