Study On Simulation And Control Of Integrated Helicopter/Transmission/Engine System With Variable Rotor Speed

In order to further improve the performance of helicopter, the rotor morphing technologies are getting more attention in the helicopter investigation and the variable rotor speed technology is a primary branch of the rotor morphing technologies. In the current application, the variable rotor speed is generally realizing by adjusting the turbo-shaft engine speed. Since the specific fuel consumption of modern gas-turbine engines is optimum within a narrow speed range, it's difficult to achieve a variable rotor speed in that way. Therefore, the integrated helicopter/transmission/engine system model and control methods are investigated to simulating a variable rotor speed process.Firstly, with a helicopter as the research object, a complete model is established based on the blade element analysis and flight dynamics, then the hover instability of helicopter and the variation relationship of trim results with variable rotor speed are studied. A turbo-shaft engine Component-Level-Model is built with volume dynamics theory and a stage-stacking method is applied to modify the characteristics of the compressor. Then a comprehensive rotorcraft propulsion system model is composed of these two parts and the simulation results show that the model is agreed with helicopter and engine theory.Secondly, by analyzing the mechanism to achieve a variable rotor speed, a method to simulate the process of it by Continuously Variable Transmission is proposed. A CVT model by energy method is appended to the helicopter propulsion system model, and the rotor speed could be shifted with a variable gear ratio. The rotor speed shifting control is analyzed by the numerical simulation experiments and the results show that the rotor speed could be continuously changed up to 25 percent.At last, to solve the problem that the fuel control system with collective pitch feedforward is not applicable during the rotor speed shifting process, a ADRC cascade control scheme with torque feedforward is designed with which the overshoot of power turbine speed is reduced to 3.5% at a high manever. After comparing the difference of the helicopter and engine performance in the variable rotor speed processes with two different implementation methods, a combined control method is proposed and the simulation results show that the later benefits more in the rotor speed shifting process.