说明：  该函数用来计算任意函数的一阶偏导数(数值方法),基于K均值的PSO聚类算法,三相光伏逆变并网的仿真。
( This function is used to calculate the arbitrary function of the first order partial derivative (numerical methods), K-means clustering algorithm based on the PSO, Three-phase photovoltaic inverter and network simulation.)