In a central receiver solar power plant, heliostats are arranged with respect to the central receiver so as to reflect the rays from the sun onto the power tower with high precision by tracking the sun in both the azimuth and elevation directions. The master control system of a solar power plant consists of different levels. The first level is local control; it takes care of the positioning of the heliostats when the aiming point and the time are given to the system, and informs upper level about the status of the heliostats field. The second logic level makes some important dispatch calculations of heliostats field. The most popular linear two-axis local driving system of heliostat consists of two linear driving actuators, the driving mechanism with rotary joints, and the controller. Traditional methods for heliostat design are often based on a sequential approach in which the mechanical structure is designed first and then the control system is advised. In order to reach the optimal design of heliostats, an integrated design approach that concurrently considers the interactions between the mechanical and control subsystems is necessary. In this article, an integrated design methodology of heliostat drive system is presented.
The methodology is based on modeling and simulation. The dynamic models that describe the behavior of the mechanical and control components are presented. These models involve mechanical and control design variables such as the motor parameters, power screw (including back lash), heliostat mass, load forces, and wind forces. Matlab, Solidwork, and Simulink are chosen to apply PID tracking control to heliostats, due to the ability to arbitrarily model complex mechanical systems, directly import properly constructed, third-party 3D CAD models, simulate integrated control, handle a variety of robotics nomenclature, and other features. The present methodology is employed for integrated design of a single facet small size heliostat with mirror area of 3 m2.The methods described in this article also show a way to rapidly simulate novel and complex heliostat geometries. Analysis of the heliostat drive system performance and dynamic characteristics according to mechanical and control design variables is conducted for the purpose of control system design and performance optimization. The drive system performance is evaluated in terms of positioning tracking errors, system response, and control system behavior. It is shown that the mechanical characteristics of the ball power screw actuator such as ball-screw diameter, lead, overall flexibility, stiffness, backlash, and inertia significantly influence the performance of drive system.
