新能源电源接入不平衡配电网的短路计算方法

当新能源机组接入三相不平衡的配电网后,由于配电网不平衡元件在正、负、零序条件下难以解耦,将使得以传统对称分量法为基础的电网短路电流存在难以准确计算等问题,需要以相分量故障分析方法为基础进行计算。同时,新能源电源在电网故障条件下将进行低电压穿越运行,受其接入方式、低电压穿越控制策略及机组Crowbar保护等因素的影响,其短路电流特性将不同于传统同步电机,需要建立不同类型的新能源电源短路计算相分量模型。因此,文中首先根据不同类型新能源机组的低电压穿越控制策略综合分析了现有新能源电源等值计算模型,并建立了相应的短路计算相分量模型,然后基于传统相分量故障分析法,根据故障条件建立故障后的相分量导纳矩阵和电压方程,进而提出了含不同类型新能源接入不平衡配电网的短路计算方法。最后,通过仿真案例对所提方法的有效性进行验证。

Short-circuit Calculation Method for Unbalanced Distribution Network with Integration of Renewable Energy

When renewable energy units are connected to three-phase unbalanced distribution network, it is difficult to decouple unbalanced components of distribution network under positive, negative and zero-sequence conditions, which makes it difficult to accurately calculate the short-circuit current of power network based on traditional symmetric component method. It is necessary to calculate the short-circuit current based on phase component fault analysis method. At the same time, the renewable energy source will be operated at low voltage ride through(LVRT)mode under the condition of power grid fault. Influenced by its access mode, LVRT control strategy and Crowbar protection, the short-circuit current characteristics of the renewable energy source will be different from that of the traditional synchronous motor. It is necessary to establish phase component models for short-circuit calculation of different types of renewable energy sources. Therefore, this paper first synthetically analyses the existing equivalent calculation models of renewable energy sources according to the LVRT control strategies for different types of renewable energy units, and establishes the corresponding phase component model for short-circuit calculation. Then, based on the traditional phase component fault analysis method, the phase component admittance matrix and the voltage equation after fault are established according to the fault conditions. A short-circuit calculation method for unbalanced distribution networks with different types of renewable energy is proposed. Finally, the effectiveness of the proposed method is verified by a simulation case.