Research On Reactive Power Optimization Of An AC/DC Interconnected Power System Considering Daily Regulation Limits Of DC Transmission Power

With the development of HVDC technology, AC/DC interconnected power system plays a significant role in large-capacity and long-distance power transmission. For example, in the West-to-East power transmission of China Southern Grid, the capability of DC systems ac-count for about 60% of all the lines. Taking advantage of the flexible operation mode of HVDC systems and dispatching properly can effectively reduce the active power loss of the lines and improve the economic benefit of the grid operation. However, at present most of re-active power optimization algorithms of an AC/DC interconnected system are not enable to consider the restriction of daily DC transmission power regulation limits. The results may force the DC transmission lines change their active power harshly within daily operation, which would greatly affect the life of DC parts and the security of power system, then affect the practical application of reactive power optimization.In order to solve this practical problem, this paper is committed to the reactive power op-timization problem of an AC/DC interconnected power system incorporating daily regulation constraints of DC transmission power. By combining the nonlinear reactive power optimiza-tion and the stepwise approximation method, the three-stage algorithm of reactive power op-timization of an AC/DC interconnected power grid is formed, in which the restriction of daily DC power regulation limits is taken into account. The algorithm is divided into three stages, namely the continuous reactive power optimization calculation in 96 time sections, stepwise approximation of the DC transmission power and continuous reactive power optimization calculation under the determined DC transmission power in each time interval. Thus the problem of engineered application of reactive power optimization calculation for an AC/DC interconnected power grid is well solved.The test of the proposed method is carried out by system real-data from 500 k V main network frame of South China power grid to validate the reasonableness and effectiveness of the proposed method. At the same time, the impacts of the selected value of the different daily maximum regulation limits of DC transmission power on reactive power optimization calcu-lation are analyzed, such as comparison of active power loss in a whole day, actual power of AC transmission interfaces and voltage value of 500 k V nodes.