中文摘要：

PID控制是反馈控制系统中最常用的控制方法，基于数字滤波技术设计的低通滤波PID算法通过滤掉误差信号中的噪音信号从而提高了算法的控制效果。介绍了HT-7密度控制系统结构，详细说明了该控制算法的原理及实现过程，该算法在HT-7密度控制系统中应用，得到了很好的控制效果。

英文摘要：

PID control is the disciplinarian frequently used in feed-back control system, and the low pass filtering PID algorithm based on the digital filtering technology is presented. The principle of this algorithm and its realization are described. The feedback control system for plasma density in HT-7 Tokamak is introduced. The algorithm enhances the control precision by filtering the noise intermingled in the error signal and is well used in the plasma density control system in HT-7 Tokamak.