During the design process of composite positioning control system (CPCS) for the DC motor, it was found that the dynamic response curves for the motor speed etc. were oscillated, and they showed a certain degree of instability. In order to explore the correlation between the oscillation and the internal structure of the CPCS, we analyzed and compared the dynamic response curves, the root locus maps, and the frequency characteristics on MATLAB. The result shows that by using the reduced-order method, the transferring function of the high-order control system can be simplified as a basic form of a real zero, a real pole and two pairs of complex conjugate poles. The root cause of the oscillation and the stability reduction of the CPCS system is the removal of the pair of complex conjugate poles that are closer to the origin. By increasing the real part or decreasing the imaginary part of another pair of complex conjugate poles, the system oscillation can be reduced or eliminated. This conclusion has important reference value of improving the control system's positioning accuracy and stability.%在直流电机复合定位控制系统(CPCS)设计过程中,发现电机速度等动态响应曲线发生振荡,表现出一定程度的不稳定性.为探究这一振荡与控制系统内在结构之间的关联性,使用MATLAB对PID及CPCS系统动态响应、根轨迹及频率特性等进行分析、比较.结果显示:高阶控制系统的传递函数总可以通过降阶等方式简化为具有1个实数零点、1个实数极点和2对复共轭极点的基本形式.其中离原点位置较近处的一对复共轭极点的移除是造成CPCS系统稳定性下降,产生振荡的根本原因.该振荡可通过增大另一对复共轭极点实部或减小虚部的方法予以降低或消除.这一结论对提高控制系统的定位精度和稳定性具有重要的参考意义.
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