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Author: search.filters.author.Cholahan, VarinSubject: search.filters.subject.fixed-time control

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    Fixed-Time Control of the Lifting Axis of a CNC Machine Using a Permanent Magnet Synchronous Motor and a Fixed-Time Nonlinear Observer
    (2026-07-01)
    Cholahan, Varin
    ;
    Tangsrirat, Worapong
    ;
    Pukkalanun, Tattaya
    This paper introduces an adaptive fixed-time position controller (AFxTPC) designed for the lifting axis servo mechanism of a computer numerical control (CNC) plasma machine. It integrates a permanent magnet synchronous motor, gearbox, and ball screw into a unified electromechanical model. The proposed AFxTPC combines a fixed-time terminal sliding surface function with adaptive fixed-time sliding mode control to achieve fixed-time convergence, precise tracking, and robustness in the presence of parameter uncertainties. A specially designed reaching law guarantees accurate trajectory tracking, while the fixed-time terminal sliding surface function effectively minimizes chattering near the sliding manifold. Importantly, a novel fixed-time nonlinear disturbance observer is developed to simultaneously estimate the unmeasured system states and lumped disturbances in real time within a guaranteed initial-state-independent settling time. These estimated values are explicitly fed back into controller for active disturbance compensation. The stability of the overall closed-loop system is rigorously established using Lyapunov stability theory. Simulation results demonstrate that the proposed observer-based controller achieves superior performance compared with conventional proportional–integral–derivative (PID) and standard sliding mode controllers. It exhibits zero steady-state error, reduced overshoot, minimal chattering, and strong robustness over a wide range of operating conditions.
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    Robust fixed-time control for DC-DC converter with matched and mismatched perturbations
    (2025-08-01)
    Cholahan, Varin
    ;
    Tangsrirat, Worapong
    This paper introduces a state-dependent variable exponent coefficient for fixed-time sliding mode control. The proposed state-dependent sliding surface ensures system stability and facilitates a rapid response within a fixed timeframe, while also addressing both matched and mismatched perturbations. This sliding mode control is applied to the DC-DC converter, a system that frequently encounters mismatched issues. By using the fixed-time concept, the designed sliding mode surface exhibits robustness, enabling it to manage both matched and mismatched perturbations within a fixed-time duration. We first present the average mathematical model for the continuous mode DC-DC converter. Next, a state-dependent sliding surface with a variable exponent coefficient is developed. Following next, the controller is designed to regulate the converter's voltage while effectively rejecting both matched and mismatched disturbances. The stability of the proposed approach is evaluated through the use of a Lyapunov function. Lastly, numerical simulations demonstrate rapid convergence and significant robustness against uncertainties in parameters, both matched and mismatched. When compared to other fixed-time and finite-time schemes, the proposed fixed-time controller is notable for its high efficiency and relatively straightforward control solution.
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    Robust Fixed-Time Speed Control of Electric Vehicles With Mechanical Transmission and Permanent Magnet Synchronous Motor Under System Uncertainties and Perturbations
    (2025-01-01)
    Cholahan, Varin
    ;
    Tangsrirat, Worapong
    Electric vehicles (EVs) are increasingly significant in modern transportation. This work presents the design of a robust fixed-time controller aimed at enhancing the efficiency of speed control in EVs, despite uncertainties and disturbances from the mechanical transmission system. The dynamic model of the transmission system includes a planetary gear and a differential gear, both of which are connected to a permanent magnet synchronous motor, a widely recognized popular power source for EVs. The model uncertainties and perturbations in the model are analyzed and integrated into the dynamic model to ensure high tracking accuracy. The fixed-time control laws are initiated to regulate machine speeds. To achieve accuracy in closed-loop stability, a disturbance observer is employed to estimate the total uncertainty and provide the lumped approximation as a control signal. The model integrating mechanical transmission with the electrical power source is formulated within a nonlinear control framework. The Lyapunov method is utilized to demonstrate the system’s stability. To ensure the design model fulfills the specified performance standards, numerical simulations are conducted to evaluate the transient responses of the dynamic system.
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    Robust Constant Exponent Coefficient Fixed-Time Control Based on Finite-Time Extended Sliding Mode Observer of Permanent Magnet Synchronous Motors
    (2023-11-01)
    Cholahan, Varin
    ;
    Wongvanich, Napasool
    ;
    Tangsrirat, Worapong
    This paper presents the Robust Constant Exponent Coefficient Fixed-Time Control (CECFSMC), an innovative control technique for precisely regulating the speed of a permanent magnet synchronous motor (PMSM) by utilizing fixed-time stability with constant exponent coefficients to provide not only faster convergence but also in a specific period of time. The effect of chattering is also lessened. To ensure that the designed controller produces the desired performance under bounded disturbances, a finite-time extended sliding-mode observer (ESMO) is also designed to estimate the PMSM velocity while also estimating lumped load disturbances. The considered PMSM is the surface-mounted PMSM. Finally, a numerical simulation with PMSM drive shows good robustness against load disturbances, better convergence, and a reaching time of less than 2 s, thereby demonstrating that the proposed fixed-time constant exponent coefficient offers good performance and is much simpler than the conventional finite-time method.