基于梯度法和最大熵方法的变循环发动机加速控制规律设计

Design of Variable Cycle Engine Acceleration Control Schedule Based on Gradient Method and Maximum Entropy Method

关键词:  变循环发动机  过渡态  梯度法  最大熵方法  几何调节规律

Key words:  Variable cycle engine  Transient  Gradient  Maximum entropy  Geometric adjustment law

摘要:

为了解决变循环发动机（VCE）加减速控制规律设计问题，提出了一种基于梯度法和最大熵方法的VCE加速控制规律优化设计方法。通过求加速时间对几何变量的导数确定几何变量调整的方向和步长，逐步得出加速过程的几何调节规律。计算VCE加速过程时，采用过渡态直接模拟方法保证发动机的喘振裕度、燃烧室油气比和涡轮进口总温均满足约束条件。在优化过程中，采用最大熵方法，令几何调节规律的熵值保持在较大的值，优化出的几何调节规律相对于只考虑时间梯度的结果更为合理，震荡幅度更小，更便于实际调节。计算结果表明，经过约15次优化，加速时间可以从6.2s缩短到4.1s，且优化出的几何调节规律更平稳。对优化的控制规律进行分段线性化，转速误差最大为1.4%，推力误差最大为1.8%，可以用于工程实践。本文提出的方法能够实现VCE加速过程几何调节规律优化设计。

Abstract:

In order to design the variable cycle engine（VCE） acceleration and deceleration control law， a VCE acceleration control law design method based on gradient method and maximum entropy method was proposed. This design method determines the direction and step length of the geometric variable adjustment by calculating the derivative of the acceleration time to the geometric variable and then gradually obtains the geometric adjustment schedule of the acceleration process. When calculating the VCE acceleration process， the transient-state direct simulation method were used to ensure that the engine’s surge margin， combustion chamber fuel-air ratio and turbine inlet temperature all meet their constraints. In the optimization process， the maximum entropy method is used to keep the entropy value of the geometric adjustment law at a high value. The optimized geometric adjustment schedule is more natural than the result of considering only the time gradient， the oscillation amplitude is smaller， and it is more convenient for practical adjustment. The calculation shows that generally after about 15 optimizations， the acceleration time can be shortened from 6.2s to about 4.1s， and the optimized geometric adjustment law is easy to adjust. Piecewise linear the optimized control law， the maximum speed error is 1.4% and the maximum thrust error is 1.8%， which can be used in engineering practice.This method can get the proper geometric adjustment law of VCE acceleration process.