2018 Indian Control Conference (ICC) January 4-6, 2018. IIT Kanpur, India
Pre-Fuzzy-PID Controller for Effective Control of Electromagnetic Levitation System Ravi V. Gandhi and Dipak M. Adhyaru
Abstract— This paper proposes an effective control solution to achieve stabilizing control and tracking control with robustness against high valued disturbances in the area of Electromagnetic Levitation System (EMLS). EMLS is an openloop unstable and nonlinear test bench with input and state types of nonlinearities presents in the current control mode. Fuzzy-PID controller is designed and implement based on ITAE performance criterion to achieve satisfactory transient as well as steady state performance from EMLS. Pre-filter structure is added to smooth the system performance as well as to reduce the transient overshoot problem. The simulation results and different integral errors like ISE, ITAE and ISTE are presented to validate the effectiveness of the proposed research work under different initial conditions, various trajectories and different disturbances.
I. INTRODUCTION Electromagnetic Levitation System (EMLS) is one of the nonlinear, complex and unstable systems by nature. It is widely used as a test bench to develop control algorithms for many contactless practical applications as Magnetically Levitated (MAGLEV) trains, magnetic bearing, rocket launching system, wind turbines and many more [1]. EMLS in general consist of mechanical and electrical sub systems. Electrical subsystem has high speed dynamics and linear relationship between coil voltage and current of electromagnet [2], coil current can be treated as the main controlling variable. EMLS applications under Current control mode can be represented by a similar small scaled prototype structure as discussed in the next section. In, MAGLEV train applications, the airgap between track and electromagnet beneath the train is the primary controlled variable which is controlled by either coil voltage or coil current generated by electromagnet. In, this paper coil current is used as manipulating variable to control the airgap. Effective controller design becomes more difficult and challenging due to presence of input as well as state types of nonlinearities in the current controlled mode [3]. In most of the MAGLEV trains, there is always presence of external load disturbance in the acceleration dynamics due to track irregularities and uncertain passenger’s weight [4, 6].
*Resrach supported by Central Govt. of India under Visvesvaraya Fulltime Ph.D. scheme. Mr.Ravi V. Gandhi is a full-time Ph.D. scholar at Institute of Technology, Nirma University, Ahmedabad-382481, India. (Phone: +918000753097; e-mail:
[email protected]). Dr.Dipak M. Adhyaru is a Professor and Head of Instrumentation and Control Engineering at Institute of Technology, Nirma University, Ahmedabad-382481, India. (e-mail:
[email protected])
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Many researchers suggested the phase lead type of compensators to solve above mentioned problems [5, 7]. For stable suspension with position control and current control in cascade manner, lead compensator in outer loop and PI controller in inner loop is used [6]. Simulation results for conventional phase lead comparator shows presence of oscillations and nonzero steady state error. PD controllers are designed and implemented for the same applications which show better response compare to lead compensator [89]. LQR based PID controller [10], fractional ordered PID controller [2], IMC based PID controller [11] were proposed for stabilizing as well as tracking control while PID plus feedforward type hybrid controller for disturbance rejection control [12], were proposed separately for EMLS. Fuzzy logic based controllers have attracted the researchers so well till date due to many advantages compare to conventional controllers [23]. Also, fuzzy controllers can be easily clubbed with adaptive neural networks to get the best of both the controllers for the mechatronics applications [24].To take the maximum advantages of conventional PD controllers, fuzzy logic based PD controllers with human/operator knowlegde base were designed and implemented for many similar applications [13-15]. To achieve better stability and reliability compare to fuzzy-PD controllers, composite fuzzy-PID controllers were developed and implemented successfully with various tuning algorithms, structures and modes (i.e. discrete and continuous modes) in [16-19]. This paper proposes a pre-filter based simplified FuzzyPID controller design which fulfills the most of the control requirements very effectively for the EMLS as mentioned below: •
Stabilizing control under different initial conditions of airgap is obtained very smoothly without any transient or steady state problem.
•
Tracking control with sinusoidal and variable step change trajectories is achieved very smoothly.
•
Performance robustness against sinusoidal and random types of high valued payload and track disturbances is gained.
Organization of work flow is as follows: Section-II, describes the modeling of current controlled mode for EMLS. In section-III, conventional PID controller design and encountered problems are discussed. In section-IV, design of Pre-Fuzzy-PID controller is explained. In, section-V,
