说明：  频率测量vi，包括ESTI、比例法、多项式逼近法、多周期平均计数法、仿真信号源、能量矩平衡、频率跟踪、三点法
(Frequency measurement vi, including ESTI, ratio method, polynomial approximation method, average more cycle counting method, the simulation signal source, energy moment balance, frequency tracking, three point method)