The key characteristics of the sliding mode control (SMC) are the ability to manage unmodeled dynamics with rapid response and the inherent robustness of parametric differences, making it an appropriate choice for the control of power electronic converters. However, its drawback of changing switching frequency causes critical electro-magnetic compatibility and switching power loss issues. This paper addresses the problem by proposing a dynamic integral sliding mode control for power converters having fixed switching frequency. A special hardware test rig is developed and tested under unregulated 12.5-22.5 V input and 30 V output. The experimental findings indicate excellent controller efficiency under wide range of loads and uncertain input voltage conditions. In addition, the findings indicate that the closed-loop system is robust to sudden differences in load conditions. This technique provides an improvement of $24.52$ % in the rise time, $20.10$ % in the settling time and $42.85$ % in robustness of the controller as compared to conventional controllers. Furthermore, the comparison with the existing fixed-frequency sliding mode control techniques is presented in a tabular form.

The rapid decrease in conventional energy resources and their harmful impact on the environment has brought the attention of the researchers towards the use of renewable energy technologies. The renewable energy systems are connected to Direct Current (DC) micro-grids via power electronic converters where the load conditions are unknown and network parameters are uncertain. These conditions call for the use of robust control techniques such as Sliding Mode Control (SMC) in order to regulate the grid voltage. However, SMC has a drawback of operating the power converter at variable switching frequency which results in degrading the power quality. This paper introduces a fixed frequency sliding mode controller that does not suffer from this predicament. A novel double integral type switching manifold is proposed to achieve voltage regulation of a DC micro-grid, in the presence of unknown load demands and un-modeled dynamics of the network. Rigorous mathematical analysis is carried out for the stability of the closed loop system and the technique is experimentally validated on position of a DC micro-grid using a specially designed test rig. For benchmarking purposes, a conventional Proportional Integral (PI) controller is also implemented. An improvement of 2.5% in rise time, 6.7% in settling time and reduction of voltage dip by 31.7% during load transaction is achieved as compared to the PI controller. The experiment confirms the hypothesis that fixed frequency SMC shows better performance than its counterpart in the phase of introduced disturbances.

In this article, we propose an analysis and controller design of a bidirectional bridgeless single-stage dc/ac converter with high-frequency link and low part count. The dual-phase-shift control is proposed to control and modulate the ac power and to minimize the root mean square (rms) of the transformer current. Furthermore, the phase-shift angle is chosen to assure wide range of zero voltage switching (ZVS) turn- on of all the switching devices. The proposed controller has a reduced total harmonic distortion (THD) at the output ac current without zero-crossing spikes. A continuous-time average model that well predicts both transient- and steady-state relations between the high-frequency ac link and the dc side is needed to simplify the controller design. Since complex discrete-time models were used in the previous pieces of literature, simple and powerful continuous-time tools were not used to design the closed-loop system. In this article, a novel continuous-time generalized average model is proposed. The derived model precisely predicts the high-frequency state variables of the converter, including a simple formula for the transformer current rms value. The formula is used to minimize the transformer current to reduce the losses. Moreover, the transient analysis and the closed-loop control design are presented. A prototype circuit is tested to verify the performance of the proposed control scheme with the proposed isolated single-stage dc/ac converter.

This article proposes a single stage AC/AC converter with a high frequency-link which is suitable for multi-level converters. The proposed topology is a direct AC/AC converter without commutation problems which solves the common issue of direct AC/AC converters. Moreover, four-quadrant switches commonly used in matrix converters, and unfolding bridges normally essential in conventional circuits, are unnecessary in the proposed circuit, which enhances the efficiency and cost. The converter control strategy is adapted based on a single-phase shift technique with constant switching frequency and 50% duty cycle. The control strategy achieves a wide range of ZVS turn-on without any auxiliary circuit. Furthermore, the high-frequency transformer (HFT) is free from line-frequency components with minimized RMS value of current. Hence, a HFT with reduced size can be realized. The converter also has a low THD load current. A new continuous-time transient model of the proposed converter is proposed based on the Generalized Average Model (GAM). The derived model is used to design the proposed phase-shift controller. Moreover, a detailed closed-loop transient analysis is presented. A prototype circuit is implemented to validate the theoretical analysis and the feasibility of the proposed converter.

In the last few years, the switching frequency of power electronic converters is extended to the several MHz range. ISM frequency bands are specified in this range for power electronic applications. Most converter circuits, such as resonance and soft-switching circuits require an accurate modeling of the circuit components, such as the high frequency inductors and transformers. This paper focuses on the evaluation of a practically simple but accurate high frequency transformer model. In first, a three-capacitor lumped model is chosen due to its simplicity as well as to the physics-oriented concept. Furthermore, the extraction of the parameters is straightforward. It is found that splitting the leakage inductances in two halves based on the winding capacitance would make the model more accurate for modeling high frequency characteristics. The paper analyzes the model and provides a closed form transfer function for the input impedance and the voltage gain. To verify the model, different kinds of transformer hardware are fabricated, and their input impedances are measured from 1 MHz to 30 MHz, which includes three ISM bands. The measurements are then compared with the impedance function developed from the model. The model shows well-matching with the measurement as compared to the conventional models. Finally, the model is validated experimentally by designing an isolated 13.56 MHz Class-E power conversion circuit, which includes a transformer with soft-switching. The soft-switching is designed based on the conventional, three-capacitor and the proposed model, respectively. The proposed model provides more accurate design for the inverter assuring soft-switching and optimum performance of the circuit.