Hybrid fractional modified skyhook controller optimized by particle swarm optimization for railway secondary lateral suspension

Abstract

The suspension system is one of the mechanical systems in railway vehicles that offers greater ride quality to enhance ride comfort for passengers. However, the existing suspension system in a railway vehicle has a limitation in absorbing vibratory motion due to the lateral track irregularity. The unwanted vibratory motion reduces the ride performance of the railway vehicle system, thus leading to discomfort for railway vehicle passengers when excessive track interference occurs. Following this, it is essential to minimize unwanted vibratory motion so that the level of passenger comfort can be improved. The overall goal of the study is to enhance the railway vehicle ride performance by implementing a semi-active secondary suspension system via magneto-rheological (MR) fluid damper. Initially, a seventeen degrees of freedom (DOF) railway vehicle simulation model was developed which included the motions of lateral body acceleration (yc), yaw angle (Psi c, Psi b1, Psi b2) and roll angle of vehicle body and two bogies, (Theta c, Theta b1, Theta b2) as well as lateral acceleration (yw1, yw2, yw3, yw4) and roll angle (Theta w1, Theta w2, Theta w3, Theta w4) of four wheelsets. The effects of primary and secondary suspension elements were analysed using MATLAB/Simulink software and the result identified that the lateral damper for secondary suspension improved the railway vehicle body’s comfort level more than others by around 69.6% based on yc of the vehicle body. The study was then continued with the development of a small-scale railway vehicle test rig. The parameters for the test rig were obtained via dimensionless analysis study known as Pascal Modified method. Next, the experimental setup, calibration, modelling, and validation works on MR damper had been performed, and the force tracking control performance was assessed by using step, sinewave and saw-tooth inputs. After the small-scale railway vehicle test rig and MR damper models were validated, the performance of the proposed control strategy, specifically Body-based Modified Skyhook (BD-MS), Bogie-based Modified Skyhook (BG-MS), and Hybrid Body-based Bogie-based Modified Skyhook (HBB-MS) controllers optimized by Particle Swarm Optimization (PSO) were also examined against the passive system. The simulation results showed that the performances of BD-MS, BG-MS and HBB-MS controllers respectively improved until 13.9%, 61.6%, 85.1% reduction of yc, 17.1%, 26.4%, 69.9% reduction of Theta c, and 18.5%, 29.6%, 58% for reduction of Psi c. Lastly, the suspension system was further controlled by using a Hybrid Body-based Bogie-Based Fractional Modified Skyhook (HBB-FMS) controller to study the potential benefit of fractional gain in improving the railway vehicle body responses. The findings from the simulation work showed that the HBB-FMS controller provides better performance of about 43.5% in yc, 31% in Theta c, and 44.9% in Psi c against the HBB-MS controller. Therefore, it can be concluded that the semi-active suspension system with HBB-FMS controller was found effective in enhancing the ride performance of the railway vehicle by mitigating the unwanted vibratory motion on the railway vehicle body due to lateral track irregularities.