Research On High Performance Control Of Onboard Electro-mechanical Servo System

The onboard servo system plays an important role in the flight performances and safety and is a key component of various flight vehicles.With continuously increasing the space scale and speed range of modern flight vehicles,high dynamic pressure causes a large load and rotational inertia of the rudder and makes a higher demand on power density,control precision,dynamic characteristic and fault tolerance of the servo system.Thus,the replacement of the hydraulic systems by developing electro-mechanical servo systems has nowadays become a research spot and development trend in the fields of aeronautics and astronautics.High reliability fault tolerance technology,high dynamic control method,and high efficiency driving strategy are the key issues in this endeavor.The purpose of this study is to improve the fault tolerance,dynamic characteristics,steady-state performance and system efficiency of the onboard electro-mechanical servo system,and the major contributions are summarized as follow:Firstly,in order to improve the fault tolerant capability of the servo system,a dualredundant electro-mechanical actuator(EMA)with no-force disputation is proposed.The cross-feedback technique is used in the speed coordinated control to enhance the transient behavior under fault condition and to increase the system bandwidth.The characteristic model of the proposed EMA is established and an on-line fault detection algorithm based on the characteristic model is proposed.This strategy solves the problems of high false alarm rate,long detection time and low detection rate,which exist in a traditional model monitoring method,due to the rate saturation nonlinearity and the wide range of uncertain aerodynamic loads.Secondly,in order to improve the dynamic characteristics of the system and to avoid the overshoot and oscillation,a proximate time-optimal multi-mode control strategy based on the characteristic model is designed for the positon control.It not only considers the influence of the inner loop characteristic on the control,but also changes the nominal optimal switching line to the switching region,and consequently achieves a fast response and smooth operation.For the speed control,a compound controller of synchronous motor is proposed.By designing the independent rotational transforms,respectively,for the feedforward and feedback channels,we solve the difficulty of the conventional feedforward control to reflect the phase characteristics of the signal at high motor speed.A constant-torque current control strategy is also proposed in order to eliminate the commutation torque ripple and to improve the system power density.Thirdly,in order to realize highly efficient operation of the high power electromechanical servo system,a novel adaptive compound control strategy of current phase angle is designed.Its compound structure integrates an adaptive feedforward controller and a proportional-integral(PI)feedback controller and controls the internal power-factor angle fast and accurately.The feedforward controller,adjusted by the DC-link current and the motor speed as auxiliary variables,regulates the current phase angle adaptively.Consequently,the current amplitude is significantly reduced by controlling the internal power factor to 1.In addition,a fault-tolerant measurement of the internal power factor angle is provided to reliably detect the current phase angle.Furthermore,a real-time calculation method for rotor position based on low resolution sensor is presented to realize high-precision detection of rotor angle.Fourthly,in order to improve the comprehensive performances of the field-oriented control(FOC),a novel control law based on current compound control structure in d-q axis is proposed.The dynamics and control precision of the rotational speed and the current of d-q axis is improved by decoupling feedforward compensator and the feedback controller.Besides,a d-q current direct detection method of the permanent magnet synchronous motor is also put forward to solve poor fault-tolerance of the conventional coordinate transform when the current senor fails or the measured signal is disturbed.Finally,the simulated and experimental results are given,verifying the effectiveness of all the proposed servo control methods.