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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
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Tangsrirat, Worapong
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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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FINITE-TIME NONLINEAR SPEED CONTROLLER OF PERMANENT MAGNET SYNCHRONOUS MOTOR USING C MEX S-FUNCTION
(2025-07-31)
Cholahan, Varin
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Rattanakun, Kritsana
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Tangsrirat, Worapong
Permanent magnet synchronous motor (PMSM) has high torque and possesses a simple structure relative to its capacity. It has been popularly applied in numerous industrial applications. Nonetheless, PMSM is sensitive to both internal and external disturbances. It exhibits significant nonlinearity and functions as a multi-variable coupling system. Therefore, a control system capable of delivering superior performance must be nonlinear. Owing to its considerable robustness capability, the sliding-mode control (SMC) technique is extensively utilized in this research. This work also demonstrates the use of C Mex S-function, the most efficient code-oriented tool, to simulate the operation of nonlinear systems. The C-Mex S-function is an effective and practical approach for developing models within the SIMULINK/MATLAB user interface environment and utilizing its requisite capabilities. Consequently, the nonlinear controller established in this study is carried out via the C-Mex S-function. Let’s manipulate the characteristics of the PMSM to converge to equilibrium within a finite time period. The tracking speed signal can be quickly followed with a high robustness against disturbances, uncertainties, and unmodeled variables. In addition, the Lyapunov function is employed to assess the stability of the developed SMC controllers, whereby the stable convergence property is demonstrated and proven. To illustrate the performance of the continuous fast-terminal sliding-mode control scheme, some simulation tests are performed on the speed regulation of the PMSM drive plant. The simulations are presented as code resembling the C programming language within SIMULINK/MATLAB. The findings show that the proposed controller achieves a speed overshoot of less than 3%, a settling time of approximately 0.15 seconds, and a steady-state error of less than 0.5 rad/s under a load torque of 1.5 Nm. These results highlight the high performance and robustness of the proposed speed controller.
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Observer-less Fixed-Time Speed Control For Permanent Magnet Synchronous Motors with matched-mismatched disturbances
(2025-01-01)
Cholahan, Varin
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Wongvanich, Napasool
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Tangsrirat, Worapong
This paper presents a state-dependent Variable Exponent Coefficient Sliding Mode Control (VECFSMC) By inducing fixed-time stability analysis, the proposed state-dependent sliding surface provides not only system stability but also a quick response in a fixed period of time as well as counteract with matched and mismatched disturbances. The proposed sliding mode control strategy does not use observers to estimate the disturbances. The designed sliding mode surface possesses robustness properties which is sufficient to cope with both matched and mismatch disturbances in a period of fixed time. Firstly, the mathematical model of permanent magnet synchronous motor and the mathematical background of variable exponent coefficient are demonstrated theoretically. Secondly, the state-dependent sliding surface with variable exponent coefficient is designed. The controller that can manipulate both the speed of PMSM and matched-mismatched disturbances is constructed. Lyapunov function is applied to assess the stability of the proposed method. Finally, a numerical simulation with PMSM drive shows fast convergence, good robustness against both matched and mismatched disturbances. The proposed fixed-time controller with this observer-less method offers high efficiency and offers not too complicated control solution comparing to the other fixed-time and finite-time methods with a small number of parameters.
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Robust Variable Exponent Fixed-Time Speed Control of PMSMs Based on a Fixed-Time Sliding Mode Observer
(2025-01-01)
Cholahan, Varin
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Wongvanich, Napasool
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Tangsrirat, Worapong
This paper presents a state-dependent variable exponent coefficient sliding mode control (VECFSMC). By inducing fixed-time stability analysis, the proposed state-dependent sliding surface provides not only system stability but also a quick response in a fixed period of time. To enhance the controller's ability to direct state trajectories along the sliding surface manifold towards equilibrium and attain the desired outputs despite the presence of disturbances, a fixed-time sliding-mode observer (FTSMO) has been created. The approach is assessed by Lyapunov stability analysis. Eventually, a numerical simulation of composited fixed-time Controller and fixed time Observer evidently shows fast convergence, high robustness against lump disturbances. The proposed technique, along with the fixed-time observer, achieves global fixed-time stabilization and offers straightforward implementation compared to other fixed-time methods, requiring the tuning of fewer parameters.
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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
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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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Practical Robust Fixed-Time Speed Control of Permanent Magnet Synchronous Motors with Adaptive Disturbance Rejection
(2025-01-01)
Wongvanich, Napasool
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Cholahan, Varin
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Tangsrirat, Worapong
The research presents an adaptive fixed-time speed controller of Permanent Magnet Synchronous Motors for a second-order nonlinear systems, grounded in practical fixed-time stability (CFTSMC). This approach employs a sliding mode surface with constant exponent coefficient designed to circumvent singularities and achieve a rapid convergence. Compared to more complex fixed-time controller, this method offers ease to implement. In addition, the maximum limits for control inputs are simply determined to avoid saturation problems. Subsequently, the stability of nonlinear speed control system is analyzed using well-kwon nonlinear Lyapunov technique. An adaption algorithm called adaptive disturbance rejection (ADR), is incorporated with a smooth tanh function to mitigate overall disturbances and chattering, thereby ensuring that the tracking error stays within a bounded residual region. Ultimately, numerical simulations are provided to demonstrate the efficacy of both controller and disturbance rejection approach.
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A Constant Exponent Coefficient Fixed-Time Control For Voltage Regulating DC-DC Converter
(2025-01-01)
Cholahan, Varin
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Wongvanich, Napasool
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Tangsrirat, Worapong
This research examines the voltage regulation capabilities of a DC-DC converter that employs the Fixed-Time control (FTSMC) method, incorporating a Constant Exponent Coefficient reaching law technique. The suggested approach is characterized by its simplicity, stability, and robustness, especially in the face of significant variations in load demands and input voltage. A state-space average dynamical model (SSA) is formulated. Initially, Continuous Conduction Mode (CCM) is established, followed by the development of the more advanced Discontinuous Conduction Mode (DCM). The nonlinear model considers two variables associated with the controlled voltage and the inductor coil current as state variables. To estimate unknown parameters, the feedback linearization method is applied. The dynamic system's output voltage is regulated using a Fixed-Time control technique. The proposed control system's stability is validated through the application of Lyapunov's theorem, which guarantees closed-loop stability. Finally, the simulation outcomes indicate the performance regulation relative to conventional linear controllers.
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A Novel Practical Fixed-Time Speed Control of Permanent Magnet Synchronous Motors with Input Saturation
(2025-01-01)
Cholahan, Varin
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Wongvanich, Napasool
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Tangsrirat, Worapong
In this article, we focus on a control problem for the speed control of a permanent magnet synchronous motor (PMSM). An antisaturation adaptive fixed-time nonsingular sliding mode control (AFFTNSM) with disturbance estimation compensation is designed for a class of second-order nonlinear systems to improve PMSM system performance. Firstly, a novel fast fixed-time nonsingular sliding mode surface is chosen based on the error dynamic equation. Then, a practical fixed-time sliding mode control algorithm is proposed where the stability of the proposed controller is demonstrated to show the convergence of the velocity tracking error to a neighborhood of the origin in fixed-time. The implementation of feedforward compensation of disturbance enhances the dynamic performance of the fast fixed-time nonsingular sliding mode control rule, resulting in reduced chattering phenomena. Numerical simulation results are provided to verify the efficiency of the proposed method.
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Robust Practical Fixed-Time Control and Application to DC-DC Buck Converter
(2024-01-01)
Wongvanich, Napasool
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Cholahan, Varin
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Tangsrirat, Worapong
This work presents an adaptive fixed-time speed controller of permanent magnet synchronous motors for a class of second-order nonlinear systems based on practical fixed-time stability, in which a sliding mode surface with a constant exponent coefficient is designed to avoid singularities and achieve a fast convergence rate. This method is easy to implement compared to other sophisticated fixed-time controllers. In addition, the upper bound of control inputs is selected to prevent saturation limitations. Following that, the Lyapunov function expresses the close-loop stability of a practical fixed-time controller. An adaptive disturbance rejection with smooth function is presented to attenuate the total disturbances, chattering, and steady-state error. The tracking error is integrated into a bounded residual region within a specified time. Finally, numerical simulations are given to verify the performance of both controller and disturbance rejection mechanisms.

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