With the increasingly wide application of frequency control technology and the continuous improvement of application level, the accuracy requirements of frequency control system are also higher and higher. At present, many frequency control devices belong to open-loop control mode, which can not meet the requirements of high-precision control. In order to improve the control accuracy of the open-loop variable frequency governor, the system adopts a closed-loop system with encoder speed detection and high-performance FX2NPLC control.