The inherent unlimited high switching frequency of the sliding mode controller (SMC) is limited by practical constraints of the hysteresis modulation (HM) technique. The inductor current and output voltage of a converter can be regulated using a combination of HM-SMC. However, HM-SMC results in a variable switching frequency operation, which is not preferred due to Electromagnetic Interference (EMI) issues. In this paper, an interval fuzzy controller is designed and developed as a solution to enable HM-SMC. In addition, a robust sliding surface is proposed, which provides an improved dynamic response. The two proposed controllers’ compatibility with one another has been tested via experiments such as a step change in input voltage, load resistance variation, and finally, a step change in output voltage reference value. The test results validate that while the interval type-2 fuzzy maintains a constant switching frequency with acceptable dynamic responses, it successfully regulates the state variables of the system. A comparison of the performance of the proposed control method with existing techniques in the literature is presented.

In this paper, a modified fast terminal sliding mode control (FTSMC) with a fixed switching frequency is proposed for regulating the output voltage of the DC-DC buck converters. The design steps of the proposed FTSMC such as the selection of sliding surface, switching control strategy, existence, robustness, and stability analysis are presented in detail. To overcome the variable switching frequency in FTSMC, a frequency control loop is designed. Moreover, the proposed FTSMC with fixed switching frequency can be implemented by using only one voltage sensor. Hence, the proposed control method not only offers a fast dynamic response and fixed switching frequency but also simplifies the controller design in practical implementation. The effectiveness of the proposed control methods has been investigated by experimental studies. The results reveal that the proposed methods exhibit a good performance under both steady-state and dynamic transients caused by the variations in load resistance, input voltage, and reference voltage. Moreover, the proposed method is compared with four existing methods.

Sliding mode control (SMC) is widely used for permanent magnet synchronous motor (PMSM) drives because of its robustness against disturbances and parameter uncertainties. However, the reaching law still faces a trade-off between fast convergence and chattering suppression. Reaching laws based on the signum function usually provide rapid convergence but induce severe high-frequency oscillations, whereas smooth or exponential modifications may reduce discontinuity at the expense of slower transient response or excessively large control gains. To address these limitations, this paper proposes a novel sine-logarithmic reaching law combined with a power-rate term for PMSM sliding mode control. The proposed structure avoids both the conventional smooth and exponential approximations commonly used in the literature. A theoretical analysis is presented, and the convergence behavior is characterized in terms of practical finite-time stability. The effectiveness of the proposed reaching law is evaluated in MATLAB/Simulink through comparative PMSM simulation studies, including start-up, steady-state, load-disturbance, parameter-variation, and total harmonic distortion (THD) tests against representative reaching laws from the literature. The simulation results indicate that the proposed method provides a favorable trade-off among rapid reaching, chattering attenuation, steady-state accuracy, and harmonic performance. These findings suggest that the proposed reaching law is a competitive alternative for PMSM sliding mode control.

The use of SMC in the speed control of PMSM has attracted considerable attention in the literature due to its strong robustness against parameter uncertainties and external disturbances. However, the design of the reaching law in SMC remains a critical challenge, mainly because of the chattering phenomenon. Numerous configurations have been proposed, and one of the recently proposed approaches involves defining the error term within the reaching law structure instead of the sliding surface. On the other hand, the approach of integrating the error term directly into the reaching law rather than into the sliding surface has not been sufficiently investigated in terms of its specific impact on control performance. This study provides an in-depth investigation to fill this gap by comparing different reaching law structures—with and without error term integration—on a PMSM drive. A series of comprehensive tests, including steady-state, load torque disturbances, reference speed variations, and a parametric variation are conducted to compare error-based reaching-law structures with sliding-surface-based designs. The results show that defining the reaching law in terms of the sliding surface or the error term leads to distinct effects on the performance characteristics of the control system. These findings serve as a valuable reference for the development of high-performance reaching-law schemes for PMSM and various nonlinear systems, in terms of design considerations for the use of the error term.