Dynamic modeling and control of an electromechanical control actuation system

Yerlikaya, Ümit
Electromechanical simulators, actuators are widely used in miscellaneous applications in engineering such as aircrafts, missiles, etc. These actuators have momentary overdrive capability, long-term storability and low quiescent power/low maintenance characteristics. Thus, electromechanical actuators are applicable option for any system in aerospace industry, instead of using hydraulic actuators. In the same way, they can be used in control actuation section of missiles to deflect flight control surfaces. Mostly used alternatives of control actuation system (CAS) are electromechanical, electrohydraulic and electrohydrostatic CASs. In this thesis, electromechanical control actuation systems that are composed of brushless direct current motor, ball screw and lever mechanism are studied. In this type of control actuation system, there are both nonlinearity and asymmetry which are caused by lever mechanism itself, saturation limits, Coulomb friction, backlash and initial mounting position of lever mechanism. In order to design controller and optimize controller parameters, all equations of motion are derived and so the detailed nonlinear and linear mathematical models of this system are obtained. The servo vi drive amplifier of motor is used in current mode. Between position and current loops, inner velocity loop is used to provide extra damping to the system and avoid unnecessary oscillations. Therefore, three control loops are used. By using linear model of electromechanical CAS, according to performance requirements, it is decided that PI and P-controller are sufficient for position and velocity control, respectively. The limitations that are imposed to controllers which have integral gain cause a residual error, so the controllers tend to overshoot target value in order to eliminate it. In order to solve this problem, an anti-windup method is applied. Then, the unknown controller parameters and anti-windup coefficients are found according to the performance requirements by using MATLAB Response Optimization Tools on the nonlinear model. During the optimization, the nonlinear relations and limitations on controller outputs are considered. A prototype of electromechanical CAS with ball screw and lever mechanism is manufactured. All unknown parameters such as dimensions, masses, inertias of components, viscous and Coulomb frictions and backlash of the system are identified. Identified Coulomb friction values are used for friction compensation in real-time application. Real-time tests are performed with optimized controller parameters and anti-windup coefficient by using xPC Target (MATLAB-Simulink). Finally, the nonlinear model of electromechanical control actuation system is verified by making real-time tests on the manufactured prototype with and without external load.  
Citation Formats
Ü. Yerlikaya, “Dynamic modeling and control of an electromechanical control actuation system,” M.S. - Master of Science, Middle East Technical University, 2016.