Onur Demirel

Photovoltaic applications require stable output voltage regulation across a wide input voltage range and varying load conditions. The Zeta converter offers advantages for these applications; however, its fourth-order, switched, nonlinear dynamics create significant challenges for controller design. This study proposes a relative-degree-based discrete-time linear active disturbance rejection control (D-LADRC) strategy to address these complexities. This approach preserves the dynamics of the fourth-order Zeta converter and derives a second-order input–output model based on the relative degree. Dynamics not explicitly represented in the model are estimated by an observer and incorporated into the control action. The observer and controller are developed based on the second-order input–output model. A current-estimator-based linear extended state observer (CE-LESO), formulated in discrete time, uses the most recent output measurement at each sampling instant to estimate the total disturbance encompassing system dynamics, parametric uncertainties, and external disturbances. Comparative analysis with a PI controller indicates that D-LADRC provides faster reference tracking, reduced overshoot, and enhanced disturbance rejection in both simulations and experiments. D-LADRC also maintains consistent performance under inductance and capacitance uncertainties, as demonstrated by corner-case studies. The results support the effectiveness of the proposed approach for voltage regulation in Zeta converters used in photovoltaic applications.

This study provides a comprehensive analysis of estimation and discretization structures for discrete-time state observers applied to a continuous-time multiple-input single-output (MISO) DC–DC buck converter. The analysis focuses on model accuracy, estimation performance, noise sensitivity, and computational cost. The continuous-time state-space model of the power converter is established, and discrete-time models are derived using zero-order hold (ZOH), first-order hold (FOH), and the Tustin method. Discrete-time observers are formulated as prediction-estimator (PE) and current-estimator (CE) structures, reflecting the sequence in which measurement information is incorporated into the state estimation process. The ability of each discretization method to represent the continuous-time system dynamics is evaluated through frequency-response analysis, and the correspondence between continuous- and discrete-time models is assessed. The dynamic performance of the observer structures is compared based on estimation error and sensitivity to measurement noise. Furthermore, the arithmetic computational load per sampling period, execution times, and embedded hardware resource requirements of the discrete-time observer algorithms are analyzed. The results indicate that discrete-time observer performance should be evaluated not only by model accuracy, estimation error, and noise robustness, but also by real-time implementability and computational efficiency. Among the structures examined, the ZOH–CE variant is particularly suitable for embedded-system applications, achieving adequate model accuracy, good estimation accuracy, and noise robustness while minimizing arithmetic operations, execution time, and hardware resource usage. This study clarifies the trade-offs among model accuracy, estimation performance, noise robustness, and implementation cost in discrete-time observer design, and provides a comprehensive evaluation framework for selecting appropriate observer structures and discretization methods for real-time embedded power-electronics applications.

This study proposes a systematic approach for implementing discrete-time Linear Active Disturbance Rejection Control in the closed-loop regulation of power converters. The continuous-time Linear Extended State Observer was discretized using the zero-order hold method to obtain a current estimator-based Linear Extended State Observer that is suitable for real-time implementation. The design considerations for discrete-time Linear Active Disturbance Rejection Control, including the selection of observer and controller parameters and the sampling period, are addressed. For performance comparison, a PI controller was designed and implemented in discrete time. The control schemes were evaluated via MATLAB/Simulink (2025b) simulations and real-time closed-loop experiments on a microcontroller to assess the transient response, disturbance rejection capability, and steady-state accuracy of the buck converter. The simulation and experimental results demonstrate that the discrete-time Linear Active Disturbance Rejection Control incorporating a current-estimator-based Linear Extended State Observer significantly outperforms the PI controller in terms of transient response and disturbance rejection capability. From this perspective, this study provides a meaningful contribution to the limited literature on linear extended state observer-based discrete-time Active Disturbance Rejection Control methods.

This study presents a sliding mode controller design for DC motor speed control using optimization algorithms. The design of sliding mode controllers typically requires expert input during the parameter determination phase. Traditionally, these parameters are set through trial-and-error methods based on the experience of specialists. However, this approach can be both time-consuming and costly. The application of optimization methods automates the parameter-tuning process, reducing human intervention and, in turn, minimizing both design time and costs. The goal of this study is to enhance the performance of optimization methods by hybridizing them with chaotic systems. The random structures of chaotic systems allow optimization algorithms to explore a broader solution space, thereby improving their performance. The analyses conducted in this study reveal that hybrid chaotic algorithms outperform their original ones. The data indicate that the use of hybrid algorithms generally leads to a decrease in Steady-State Error. Additionally, it is observed that when all hybrid algorithms are employed, the sliding mode controller does not exhibit any overshoot. The results demonstrate that the sliding mode controller performs effectively, achieving low settling time, rise time, and steady-state error, while also preventing chattering. Among the methods examined, the sliding mode controller optimized with the Chaotic Henry Gas Solubility Optimization algorithm delivers the best performance, ensuring optimal system stability.

In disaster monitoring missions, unmanned aerial vehicles (UAVs) must cover large areas to assess the impact of a disaster. Critical to the success of such missions is the continuous transmission of Air Data and Attitude Heading Reference System (ADAHRS) data, along with stable RSSI and video feed transmission to the Ground Control Station (GCS). However, the vast coverage area poses a challenge, as omnidirectional antennas are limited by the UAV’s operational range. To overcome this limitation, a high-gain directional antenna is required, which needs to be constantly aimed at the UAV to maintain a stable connection. This study presents an antenna tracker, designed and implemented using an ATmega328P microcontroller, two servo motors, and a GPS receiver, providing two degrees of freedom. The tracker allows 180-degree rotation on the azimuth axis (yaw) and 90-degree rotation on the elevation axis (pitch). The system interface was developed using LabVIEW. Experimental results demonstrate that the proposed antenna tracker significantly extends the UAV’s operational range while maintaining a stable connection with minimal RSSI fluctuations compared to systems without an antenna tracker. The continuous availability of ADAHRS data, stable RSSI, and video feed ensures the success of critical mission operations.

Bu çalışma, optimizasyon algoritmalarının kaotik sistemlerle hibritlenerek kontrolcü tasarımı üzerindeki performanslarının iyileştirilmesi amaçlanmaktadır. Kontrol parametrelerinin optimum şekilde ayarlanması metodolojik yöntemlerle (Ziegler-Nichols, Adaptif vb) veya çoğunlukla uzman bilgisine dayalı deneme-yanılma yaklaşımlarla gerçekleştirilmektedir. Daha etkin çözümler sunabilmeleri açısından meta-sezgisel optimizasyon algoritmalarının kullanımı son yıllarda ön plana çıkmaktadır. Bu çalışma kapsamında, Parçacık Sürü Optimizasyonu ve bu algoritmanın kaotik sistemlerle entegre edilmiş versiyonu olan Kaotik Parçacık Sürü Optimizasyonu kullanılarak PID kontrolcünün parametreleri optimize edilmiştir. Optimizasyon sürecinde performans kriteri olarak Zaman Ağırlıklı Hatanın Karesinin İntegrali esas alınmıştır. Elde edilen bulgular, kaotik sistemlerin Parçacık Sürü Optimizasyon algoritmasına entegrasyonu, algoritmanın minimum değere yakınsama başarımını artırdığını ortaya koymuştur. Bu çalışma kaotik yapılarla hibritlenen optimizasyon algoritmalarının kontrol sistemlerinde başarılı bir şekilde uygulanabileceğini göstermiştir.

This paper proposes a bidirectional three-level T-type LLC resonant DC-DC converter operating with phase-shift control, which is simple and effective, variable frequency modulation to perform soft switching in a wide voltage ratio range and light loads, and pulse width modulation to reduce reactive circulating current. In this combined modulation method, three control parameters: switching frequency, the duty cycle of switches in the vertical arms, and phase shift between primary and secondary switches, are changed depending on the voltage conversion ratio and load. The circuit operates as LLC resonant in forward operation and series resonant in reverse operation. Thus, LLC and series resonant analyses of the proposed converter, operated in continuous current mode and buck mode, are presented. A simplified frequency domain analysis, including all harmonics, is used in the theoretical calculations. Thus, the control parameters are accurately calculated for forward and reverse operations. The current, voltage, and power formulas in the working principle of the converter are derived, and an analysis of the control parameters and zero voltage switching region is performed. Soft switching analysis is done by considering the junction capacitor of the MOSFET and the dead time. The theoretical performance of the proposed modulation method has been verified with a 2kW prototype. Soft-switching and loss analyses of the proposed converter have also been investigated under different load conditions and voltage conversion ratios. The proposed LLC resonant topology and modulation method improved significantly more efficiency than the phase-shifted modulated T-type converter under 30-100% load conditions.

Electromagnetic interference is the main problem in high switching power converters like DC-DC converters. One of the solution methods for electromagnetic interference reduction is to design a snubber circuit. The snubber circuit is a practical method to reduce fluctuations caused by parasitic components from the layout and non-ideal characteristics of switching devices. An effective snubber circuit design increases the converter's efficiency and reduces EMI noise. In this paper, electromagnetic interference is reduced using different snubber circuits in a three-level T-type isolated bidirectional DC-DC converter. The converter is simulated in PSIM to see the effectiveness of the noise reduction with the snubber circuits. CISPR 25 standard is used for the compliance assessment in the study.

This study presents a novel three‐level T‐type isolated bidirectional DC–DC converter (3LTT‐IBDC) for bidirectional DC power transfer. Owing to of the T‐type structure of the proposed converter it has less number of switches and thus, lower cost and higher efficiency, as well as easy control are the advantages of the proposed converter compared to three‐level counterparts. Additionally, 3LTT‐IBDC is more reliable than three‐level converters since unequal voltage blocking does not occur in T‐type structure. Moreover, the symmetrical operation of the isolation transformer due to three‐level symmetrical voltage waveform, lower voltage stress of switches and thus, higher efficiency are other advantages of 3LTT‐IBDC compared to two‐level counterparts. Here, the DC voltage gain and power transfer characteristic of the proposed converter for steady‐state operation and the expressions of the leakage inductance are derived. The proposed converter is simulated using PSIM. A 2‐kW prototype is built to verify the theoretical analysis of the converter. Theoretical and experimental results show a good agreement and validate the competency of the presented converter design. The efficiency of the proposed converter and switching transitions of the switches are analysed. The full load and maximum efficiency of the converter are measured as 96.27% and 96.81%, respectively.