Abstract
This paper proposes a dynamic high-type control (DHTC) method based on an interval type-2 fuzzy logic controller (IT2FLC), which is used in the photoelectric tracking system to improve the steady-state accuracy and response speed. Adding integrators to the traditional multi-loop feedback control loop can increase the system type, thereby speeding up the response speed and improving the steady-state accuracy, but there is a risk of integral saturation. Switching the type dynamically according to the system state can avoid integral saturation while retaining the advantages of the high-type. Fuzzy logic control (FLC) can dynamically change the output value according to the input change and has the advantages of fast response speed and strong ability to handle uncertainties. Therefore, in this paper, the FLC is introduced into the high-type control system, and the output of the FLC is used as the gain of the integrator to control the on-off to achieve the goal of dynamic switching type, which is successfully verified in the experiment. IT2FLC introduces a three-dimensional membership function, which further improves the FLC’s ability to handle uncertainties. From the experimental results, compared with T1FLC, IT2FLC’s ability to handle uncertainties is significantly improved. In addition, in order to speed up the calculation speed of IT2FLC, this paper proposes an improved type-reduction algorithm, which is called weighted-trapezoidal Nie-Tan (WTNT). Compared with the traditional type-reduction algorithm, WTNT has faster calculation speed and better steady-state accuracy, and has been successfully applied to real-time control systems, which has good engineering application value. Finally, in order to reduce the interference of human factors and improve the automation level of the system, a multi-population genetic algorithm (MPGA) is used to iteratively optimize the parameters of the FLC, which improves the output accuracy. On the experimental platform of the flexible fast steering mirror (FFSM), the control effects of the traditional controller, T1FLC and IT2FLC are compared, which proves that the IT2FLC-DHTC system has a faster response performance, higher steady-state accuracy, and stronger ability to handle uncertainties.
Highlights
Photoelectric servo tracking equipment is widely used in beam control systems, such as adaptive optics, free-space communication, line of sight stabilization, etc., and has important application value in military and civilian fields [1–3]
Tang constructed a PID-I system and added an integrator to the PID controller to achieve high-type control [1], and Papadopoulos et al constructed the explicit analytical PID tuning rules for the design of type-III control loops based on the principle of the symmetrical optimum criterion [11], but they did not achieve the goal of changing the type in real time according to the system status, and there is a hidden danger of integral saturation
Since the output of the interval type-2 fuzzy logic controller (IT2FLC) set in this paper is discretized, it is not necessary to discuss the reduction of the continuous domain as in the literature [28,29], which simplifies the calculation
Summary
Photoelectric servo tracking equipment is widely used in beam control systems, such as adaptive optics, free-space communication, line of sight stabilization, etc., and has important application value in military and civilian fields [1–3]. Dynamic high-type technology refers to dynamically connecting and disconnecting one or more integrators based on the original multi-loop feedback system to improve the response speed and steady-state accuracy while ensuring that the system does not have integral saturation. In the study of DHTC, Qin et al used T1FLC to construct the T1FLC-DHTC structure, which realized automatic switching of system types [18], but the control parameters of T1FLC completely relied on artificial settings, and in the real unstructured dynamic environment and many specific applications, the traditional T1FLC will face many uncertainties, mainly including measurement noise, friction, and rule base differences, etc. The FLC changes the system type in real time according to the system status, which achieves the purpose of improving the steady-state accuracy and speeding up the response speed, and avoids the hidden dangers of system oscillation and integral saturation caused by the increase of type.
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