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Optimal Design & Fabrication of a Non-Flat Sun Sensor Array With Large Field of View

Yousefian, Peyman | 2016

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49427 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Durali, Mohammad; Jalali, Mir Abbas
  7. Abstract:
  8. Modern sensors consist of arrays of detectors specially arranged to enhance precision, capabilities, and field of view (FOV). Sensor arrays can have multiple functionalities such as the simultaneous detection of position and motion. We use a linear sensor model and develop an optimization method to design an array of photodiodes. Our objective function minimizes bias and variance estimations. We introduce a maximum likelihood technique to approximate and determine the bias caused by measurement errors, and verify our theory by statistically complete simulations. We apply our theory to design an optimal sun sensor. The sensor has a predefined conical FOV, and its accuracy is controlled by a set of directionally variable weighting parameters. This enables us to compute the optimal placements of photodiodes under various operational conditions. It is found that for a uniform accuracy distribution, both the variance and bias estimations can be exactly minimized for a given array configuration. For non-uniform accuracy distributions with rotational symmetries, when a higher accuracy is required around the centerline of the FOV, both errors attain their minima when the array configuration becomes inclined towards the center. In non-uniform and non-axisymmetric distributions, when a higher accuracy is imposed along a line or a path, the bias and variance errors differ significantly: while the variance minimization implies the concentration of the cells toward the path, the bias minimization yields a uniform distribution. The method presented in this study can be used in the optimal design of sun sensors for space systems and solar power plants. We report the design, fabrication and error analysis of a sun sensor array composed of six photodiodes. The sensor estimates the direction of the sun using a linear least squares method. The performance of the sensor is deteriorated by three major sources: fabrication errors, scattered environmental light, and inexact modeling of photodiodes. Using a calibration procedure and modeling the uniform component of the environmental light, we mitigate the first two errors and significantly reduce root mean squared error from 2.63 to 0.83. For a field of view of 110, the maximum estimation error also drops from 3.8 to 1.6. Through exact mathematical modeling of photodiodes, we demonstrate the feasibility of further reducing the root mean squared error, and discuss the effect of the maximum allowed angle of incidence on the sensor array performance. We propose a method to compute the optimum value of this angle and verify it experimentally. The effect of the number of illuminated photodiodes on the sensor accuracy is also investigated experimentally
  9. Keywords:
  10. Sun Sensor ; Bias ; Optimal Design ; Error ; Calibration ; Array ; Field of View (FOV) ; Wide View ; Nonflat Array

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