适应非光滑特性的交直流混合电力系统状态估计

交直流混合电力系统中的有载调压变压器(on-load-tap-changer, OLTC)和换流器模型存在大量限幅、死区等非光滑特性，如何处理换流器引入的分段函数约束是当前状态估计的研究难点。构建了OLTC的混合整数非线性(mixed integer nonlinear programming, MINLP)模型，通过控制二次侧电压水平得到OLTC挡位的估计值。针对换流器采用分段函数描述包含限幅、死区等下垂控制特性的问题，提出采用近似拟合函数将分段函数光滑化。与采用MINLP描述分段函数的方法相比，所提模型显著提高了计算效率。通过3节点和IEEE14节点交直流混合系统算例，验证了所提状态估计模型的正确性和实用性，同时分析了拟合系数对状态估计的影响。算例表明，所提模型增强了状态估计处理不良数据的能力，提高了对非光滑特性的适应能力，在保证计算精度的前提下能够提高状态估计的收敛性。

State estimation for an AC/DC hybrid power system adapted to non-smooth characteristics

In an AC/DC hybrid power system, converter and on-load-tap-changer (OLTC) models have a large number of non-smooth characteristics such as limits and a dead zone. How to deal with the piecewise function constraints introduced by a converter is a difficult problem in existing state estimation. A mixed integer nonlinear programming (MINLP) model of OLTC is proposed and tap position is estimated by controlling the secondary voltage level. Given that the converter uses piecewise functions to describe droop control characteristics including limits, dead zone and so on, the piecewise functions are smoothed by approximate fitting functions. The proposed model significantly improves the computational efficiency compared with the method of using MINLP to describe piecewise functions. The correctness and practicability of the proposed SE model are verified on a 3-bus system and IEEE14-bus AC/DC hybrid systems, and the influence of the fitting coefficient on state estimation is analyzed. Numerical examples show that the proposed model can enhance the ability of state estimation to deal with bad data and improve the adaptability to non-smooth characteristics. The convergence of state estimation is improved as well as ensuring calculation accuracy. This work is supported by the National Natural Science Foundation of China (No. 52177125 and No. 51707196).