This paper proposes an isolated single‐phase flexible buck‐boost ac–ac converter with an adjustable output frequency and optimized semiconductors count. One power switch only operates with a high switching frequency in each half‐cycle of the input voltage, and others operate with a low switching frequency equal to the output frequency. Thanks to this feature, the converter provides high efficiency, 95.5% in step‐down mode and 91.5% in step‐up mode. The galvanic isolation between the input and output sides is also regarded for the proposed topology by employing two coupled inductors. The converter has an inherent safe commutation by utilizing a simple modulation strategy. Thus, additional snubber circuits and complex commutation strategies are no longer required. The proposed converter does not require any input filter as it operates with the continuous input current. This paper presents the operating principle of the proposed topology in detail. For this purpose, a 200‐W experimental prototype has been designed to examine the performance of the suggested converter for different operating modes and output frequencies. Results confirm the theory and operation of the proposed topology.

This paper proposes a single‐phase q‐source AC‐AC converter with a wide and flexible voltage gain. The converter only incorporates two bidirectional power switches. This new topology has many bold features like continuous input current, non‐inverting boost, and inverting buck modes. The high voltage gain is achieved by utilizing a coupled inductor in the converter. The converter gain is increased by the turns ratio of the coupled inductor proportionately. The proposed q‐source comprises one input inductor, one coupled inductor, and one capacitor, which are less than other competitors. In order to reduce the voltage and current stresses on power semiconductors, a safe commutation strategy for the converter is also introduced that eliminates snubber circuits. The input and output filters are no longer required due to the proposed converter specifications. So the volume and cost of the converter are decreased significantly. The achieved efficiency equals 94.5% due to utilizing the proposed optimized topology and switching strategy. In this paper, the operating principle of the converter is presented in detail. An experimental prototype has been designed to examine the performance of the suggested converter. Results confirm the theory and operation of the proposed topology.

This paper proposes a new single‐phase direct step‐up ac–ac converter by modifying the p‐type impedance source. It provides a high boost factor as well as high efficiency, while only six parts are required to design it, involving just two bidirectional power switches. A safe commutation method has been applied to power switches to make the converter snubber‐free and high efficient. Input and output harmonic filters are no longer required since input and output currents variate continuously with small ripple and low total harmonic distortion (THD). The proposed topology only modulates the output voltage amplitude, not the phase and frequency, so the output frequency is identical to the input frequency and constant. Thus, it can be utilized in step‐up conversion applications, like inductive power transmission from low ac voltage sources. Input and output have the same ground, which is a good protective feature. In this paper, the operating principle of the converter is demonstrated. Experimental results have been represented to evaluate the performance of the converter. For this purpose, an experimental prototype has been fabricated. Results are investigated and compared with other previous step‐up ac–ac converters. Results confirm the theory, operating principle, and performance of the converter.

Bidirectional synchronized transfer (BST) in variable frequency drive (VFD) systems implies automatic synchronization with seamless transfer of the motor to the grid or take‐over of the motor from the grid. This feature is realized if the magnitude, frequency, and phase angle of the VFD voltage and the grid voltage are synchronized. So, an accurate synchronization algorithm is necessary. This paper proposes a new BST method based on the discrete Fourier transformation (DFT) that obtains the magnitude, frequency and phase angle of VFD and grid voltages precisely through determining the fundamental components. This new BST coordinates the output voltage of the VFD with the grid using two error amplifiers. Also, additional decoupling reactors or transformers are no longer required by using this method due to exact estimation and synchronization. Furthermore, the algorithm can be integrated into any motor control strategy. This paper presents the principle of the proposed BST comprehensively and evaluates it by experimental results. The algorithm is tested on an induction motor via a 13‐level cascaded H‐bridge (CHB) inverter and the V/Hz constant control. The effect of BST on the motor voltage and current, the inverter current and dc‐link voltage is also examined. Results confirm the proposed strategy.

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