Computer Engineering

The need for effective design of satellite attitude control (SAC) subsystem for a microsatellite is imperative in order to guarantee both the quality and reliability of the data acquisition. A proportional-integral-derivative (PID) controller was proposed in this study because of its numerous advantages. The performance of PID controller can be greatly improved by adopting an integral time absolute error (ITAE) robust controller design approach. Since the system to be controlled is of the 4 th order, it was approximated by its 2 nd order version and then used for the controller design. Both the reduced and higher-order pre-filter transfer functions were designed and tested, in order to improve the system performance. As revealed by the results, three out of the four designed systems satisfy the design specifications; and the PD-controlled system without pre-filter transfer function was recommended out of the three systems due to its structural simplicity, which eventually enhances its digital implementation. 1. INTRODUCTION Satellites are exposed to many disturbances in space [1] which can adversely affect their attitude. The reliability of the microsatellite data acquisition is highly dependent on the quality of the SAC system because the attitude control system is crucial for accurate satellite operation [2]. Therefore, the needs for an accurate design of attitude control subsystem which guarantees the quality and reliability of the data. Several methods exist in the literature for achieving SAC. [3] and [4] proposed direct and modified adaptive controllers, respectively to mitigate different scenarios in spacecraft attitude control. Fixed-time [5], finite-time [6], adaptive gain based integral second order [7], fast terminal [8] and adaptive fast terminal [9] sliding mode techniques have been employed in rigid spacecraft attitude controller design. Several applications of PID controller for satellite attitude control can be found in the literature. PID attitude controller for a rigid body satellite designed using a combination of Kharitonov theorem and vectored particle swarm optimization method was presented in [10]. Spacecraft control torque and velocity constraints dependent sliding mode based robust PID attitude controller were presented by Y. Li et al. [11]. Latest research by [12-16] employed an observer-based PID controller to control the attitude of a rigid satellite with ON/OFF thruster actuator which showed improvement in attitude control performance. The optimal PID controller for SAC, designed by [17] gave acceptable results for both the settling time and percentage overshoot, even though the bounds of controller parameters were arbitrarily

MQ-series gas sensors are frequently used in gas concentration sensing owing to their high sensitivity and relatively cheap cost. Reportedly, both the sensor's circuit sensitivity () and power dissipation () are functions of sensor circuit load resistance (). However, there is no well-established standard method for determining value that can simultaneously yield maximum sensor circuit sensitivity () and acceptable for a given value of gas concentration. To obtain optimum , the dependence of and on for a given gas concentration was thoroughly investigated. The model equations for determining , and at (,) were derived and MQ-6 gas sensor's response to its associated gases was used for demonstrating the proposed method. Variations of both and with respect to were investigated when each of the associated gases has concentration of 1000 ppm. The sensor circuit optimal must satisfy the dual conditions of (i) S= and (ii) < set threshold. Results obtained from the analysis revealed that the values of , were 20, 24, 64, 120, and 152 kΩ for liquefied petroleum gas (LPG), CH 4 , H 2 , alcohol and CO respectively, corresponding to sensor powers of 0.3125, 0.2589, 0.0977, 0.0521, and 0.0411 mW.

MQ-series gas sensors are frequently used in gas concentration sensing owing to their high sensitivity and relatively cheap cost. Reportedly, both the sensor's circuit sensitivity () and power dissipation () are functions of sensor circuit load resistance (). However, there is no well-established standard method for determining value that can simultaneously yield maximum sensor circuit sensitivity () and acceptable for a given value of gas concentration. To obtain optimum , the dependence of and on for a given gas concentration was thoroughly investigated. The model equations for determining , and at (,) were derived and MQ-6 gas sensor's response to its associated gases was used for demonstrating the proposed method. Variations of both and with respect to were investigated when each of the associated gases has concentration of 1000 ppm. The sensor circuit optimal must satisfy the dual conditions of (i) S= and (ii) < set threshold. Results obtained from the analysis revealed that the values of , were 20, 24, 64, 120, and 152 kΩ for liquefied petroleum gas (LPG), CH 4 , H 2 , alcohol and CO respectively, corresponding to sensor powers of 0.3125, 0.2589, 0.0977, 0.0521, and 0.0411 mW.

Design of proportional-integral-derivative (PID) controller with proportional, integral, and derivative gains given by 𝑘𝑝, 𝑘𝑖 and 𝑘𝑑 respectively, for time-delay systems is presented in this study. The centroid of the convex stability region (CCSR) method in the 𝑘𝑖-𝑘𝑑 plane for fixed 𝑘𝑝 is used. PID controller design  for  time-delay  systems  in  the  𝑘𝑝-𝑘𝑖  plane  for  a  fixed  𝑘𝑑  and  𝑘𝑖-𝑘𝑑 plane for a fixed 𝑘𝑝 have been extensively researched. Despite the amenability of CCSR method to design of PID controller in the 𝑘𝑖-𝑘𝑑 plane for fixed 𝑘𝑝, its application in this regard has not been given serious attention. The stability region in 𝑘𝑖-𝑘𝑑 plane for fixed 𝑘𝑝 was determined and the required controller gains  in  the  region  were  determined  using  the  CCSR  method.  Using  the determined controller gains, the system closed loop unit step response for all the  considered  regions  was  plotted  on  same  axes.  Based  on  the  obtained results, different combinations of controller gains can be implemented depending  on  the  system  time  domain  performance  measures  (TDPMs) requirements. However, selection of an appropriate controller gains combinations, requires compromise among any of the conflicting TDPMs.

The development of structured methods for proportional-integral (PI) controller design for systems with time delay are proposed in this article. Several PI controller design methods for time-delay systems have been reported. However, combining two or more methods to form new ones have not been given serious attention. The system stability region in the controller parameters space was determined by plotting the stability boundaries. In this study, the controller gains were first obtained using genetic algorithm (GA), weighted geometric center (WGC), and centroid of convex stability region (CCSR). Thereafter, these gains were combined by finding the centroids of lines joining any of the two gain locations, and triangle whose vertices are the location of the three gains in the convex stability region, thus yielding four additional methods, M1, M2, M3, and M4. Compared to a particular existing method, some of the proposed methods yield faster response speed at the expense of reference i...