In this study, a controller is designed for a hydraulic actuator of a single axis durability test rig. The mathematical equations of the system are derived and a MATLAB Simulink® model is developed. The non-linear equations defining the system dynamics are linearized and the system is represented in state space. For the position control of the hydraulic actuator, a combined feedforward and feedback controller is designed. The feedforward controller estimates the force transmitted between the vehicle and the hydraulic actuator. Considering this force as a disturbance, a feedforward valve command signal is generated for compensation. In the design of feedback controller, the hydraulic actuator is considered independent of the load. Neglecting the valve dynamics and assuming the actuator chamber pressures are linearly dependent, a third order actuation system model is derived and a LQR controller is designed. In the design of LQR controller, the matrix penalizing the states is formed by approximating the impulse response of the closed loop system to an ideal second order response profile rather than by using iteration. The closed loop state space representation of the complete system is derived and its response is compared with the non-linear model.

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