Abstract: In order to study the low frequency pressure oscillation of a flow adjustable gas generator in solid rocket ramjet，gas generator dynamic mathematic model was built and the open-loop frequency character of the pressure closed-loop control system was analyzed. Describing function method was used to analyze the relation of servo system hysterics nonlinear and pressure oscillation. Pressure oscillation frequency and amplitude were achieved by calculating the node of hysterics nonlinear describing function negative reciprocal character and open-loop frequency character. In general，the calculated results agree well with the test results. The pressure oscillation problem was solved by correcting open-loop frequency character of the controller to avoid it intersecting with hysterics nonlinear describing function negative reciprocal. Experimental results show that this method has the smaller pressure oscillation of less than 2%.

Key words: Solid rocket ramjet；Gas generator；Pressure fluctuations；Describing function

摘要： 针对固体火箭冲压发动机用流量可调燃气发生器压力低频波动问题，建立燃气发生器动态数学模型，分析压力闭环控制系统的开环频率特性。采用描述函数法分析伺服机构滞环非线性与压力波动之间的关系，通过计算滞环非线性描述函数负倒数特性与开环频率特性交点获得压力波动频率与幅值。理论计算结果与试验结果相符，通过改进控制器校正开环频率特性避免与滞环非线性描述函数负倒数相交解决压力波动问题，实验数据显示压力波动可以减小到2%以内。

关键词: 固体火箭冲压发动机；燃气发生器; 压力波动 ；描述函数