This paper presents the control of DC-DC buck converter. The control strategy is based on the theory of discrete-time sliding mode control to ensure robustness against parameter variations and external disturbances. The output voltage regulation is achieved using a digital controller that combines discrete-time first-order sliding mode control with a discrete-time realization of the super-twisting algorithm, commonly used in second-order sliding mode control. The design of the proposed controller is performed using a discrete-time model of the DC-DC buck converter. Extensive simulations were conducted in Matlab/Simulink to validate the performance of the control algorithm under varying load conditions and input voltage fluctuations. A comparative study between conventional PI controller and the proposed discrete-sliding mode based controller in tracking of various voltage references under action of disturbances is given.

U radu se upoređuju tri metode za estimaciju i kompenzaciju poremećaja u diskretnim sistemima sa kliznim režimom (KR). Prva metoda koristi Luenbergerov opserver poremećaja, druga - nominalni model upravljanog objekta, a treća - integral signala klizne funkcije. Cilj rada je da pokaže ekvivalentnost navedenih metoda u primeni na diskretne sisteme upravljanja sa KR u nominalnim uslovima na jednostavnom sistemu upravljanja objektom prvog reda tipa čistog integratora. Poseban doprinos rada je modifikovani estimator poremećaja koji kombinuje Luenbergerov estimator sa estimatorom na osnovu integrala klizne funkcije. Teorijski rezultati su ilustrovani simulacionim eksperimentima.

This study offers experimental testing of commercial and laboratory inverters, utilized in a laboratory prototype of an urban microgrid. Operation of grid inverters supplied by PV arrays in urban environments, encounters challenges such as partial shading and soiling. Emulation of the current-voltage characteristics of PV arrays enables repeated and reliable testing of inverter operation under irregular supply conditions. It has been shown that finding the maximum power point can be challenging under conditions of partial shading and soiling. Additionally, meeting the grid quality standards for the delivered power represents a challenge. Satisfying these requirements can be achieved through careful design of LCL filters at inverter output terminals, but further improvement can be achieved only through an adequate selection of the primary controller. To further improve the quality of grid currents, the possibility of applying innovative control algorithms has been demonstrated for laboratory inverters. Application of sliding mode controllers, besides ensuring system robustness, can prevent overshoots and fault responses from the current protection circuit by introducing a specific anti-windup structure.

A new design approach to discrete time sliding-mode-based controllers with disturbance compensation is proposed in this paper. The approach is applicable for linear time invariant plants with matched disturbances. Starting from the known methods for disturbance estimation (i) using discrete time nominal plant model and (ii) using original sliding mode control design method, full integration of those two algorithms into single one is proposed. Besides, the proposed algorithm can be additionally simplified for a small sampling time. The simplified algorithm does not directly depend on the equivalent control but only on the present and previous values of the sliding variable and previous value of the control. The obtained results are compared with the corresponding system with disturbance estimator based on sliding variable measurement. It is established that both methods give identical results in the nominal case. The method is illustrated in a positional servo system design. Comparative analysis of different methods is done by computer simulation.

Application of a discrete time (DT) sliding mode controller (SMC) in the control structure of the primary controller of a three-phase LCL grid inverter is presented. The design of the inverter side current control loop is performed using a DT linear model of the grid inverter with LCL filter at output terminals. The DT quasi-sliding mode control was used due to its robustness to external and parametric disturbances. Additionally, in order to improve disturbance compensation, a disturbance compensator is also implemented. Also, a specific anti-windup mechanism has been implemented in the structure of the controller to prevent large overshoots in the inverter response in case of random disturbances of grid voltages, or sudden changes in the commanded power. The control of the grid inverter is realized in the reference system synchronized with the voltage of the power grid. The development of the digitally realized control subsystem is presented in detail, starting from theoretical considerations, through computer simulations to experimental tests. The experimental results confirm good static and dynamic performance.

This article proposes a new robust dead‐beat controller for multivariable systems using multirate sampled data. Applying a discrete‐time higher order sliding mode control approach, the proposed dead‐beat controller design uses the state‐space nominal model (model without disturbances) of the system and its controllability indices to compute the state feedback matrix. The obtained control annihilates the system state in a minimal number of sampling periods. For example, a heuristic procedure for selecting a sampling time is considered in order to keep maximal amplitudes of control inputs within the allowable limits. Since the dead‐beat control has poor robustness, a new discrete‐time supertwisting disturbance observer is used to suppressed disturbance effects. Stability analysis of the proposed observer has shown that it is suitable for Lipschitz type of disturbances. The sampling period of the disturbance observer is generally smaller than the control sampling period. Properties of the proposed control system are demonstrated in simulation examples.