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In this paper, a new class of dc–dc converter topologies based on capacitive link dc–dc converters—Ćuk, SEPIC, and Zeta converters—that operate under the critical conduction mode has been proposed. The proposed converters are the extensions of quasi-square-wave zero-current-switching converters, which use an auxiliary circuit to provide zero-current and zero-voltage switching for all semiconductor switches at both turn on and turn off transitions and eliminate voltage ringing across the output switch. Using the proposed auxiliary circuit, the value of dv/dt has been diminished; hence, the EMI of the proposed topology is significantly reduced compared to the conventional quasi-square-wave zero-current-switching converters. To verify the operation of the proposed converter and confirm its advantages, an experimental prototype has been implemented, and the experimental results and the efficiency of the proposed converter have been compared with the conventional quasi-square-wave zero-current-switching converters. [ABSTRACT FROM AUTHOR]

This paper proposes a high-power-density and reliable inverter topology, which transfers the maximum power of a PV array to the load in one power conversion stage. The single-stage power conversion, along with the soft-switching capability of the proposed three-phase PV inverter promises high efficiency at all operating points. Instead of a capacitive dc link that decouples the dc–dc converter and the voltage source inverter in traditional two-stage PV inverters, a high-frequency capacitive ac link is employed in the proposed inverter, which enables exploiting a very small film capacitor, rather than a bulky electrolytic capacitor, for transferring power. Eliminating electrolytic capacitors prolongs the lifetime of this inverter. Considering the long lifetime of PV modules, this feature is of high importance in PV applications. The high-frequency ac link also allows using high-frequency transformers for providing galvanic isolation. Therefore, this inverter is expected to have a very high power density. This paper presents principles of the operation and control, design, and analysis of this inverter, and verifies the performance of the inverter through two prototypes: a 2-kW Si-based prototype and a 2-kW SiC-based prototype operating at different switching frequencies. [ABSTRACT FROM AUTHOR]

A single-stage three-phase ac–ac converter benefiting from a high-frequency alternating link voltage is proposed in this paper. In this converter, a very small film capacitor can transfer the energy from the input to the output, owing to the high-frequency alternating voltage of the link. This eliminates the need for large electrolytic capacitors that are typically used in dc-link ac–ac converters. Moreover, a compact high-frequency transformer at the link can replace the bulky low-frequency transformers, in case isolation is required. These features increase the power density as well as reliability of the proposed converter in comparison with the conventional dc-link converters. The number of required switches in the proposed converter is 12, which is less than the number of switches needed in matrix converters, leading to lower switching and conduction losses. Despite being single-stage, the proposed ac–ac converter is capable of both stepping up and stepping down the voltage and also frequency transformation. This eliminates the need for using cascaded power converters. In this paper, the operation principles of the proposed ac–ac converter are investigated, and variable switching frequency and fixed switching frequency control methods for operating this converter are introduced. The performance of the converter is verified through simulation and experiment. [ABSTRACT FROM AUTHOR]

In this study, a novel T-type topology for single-phase direct AC/AC conversion is proposed. In this topology, frequency changing takes place directly (without common DC voltage bus) through three converters that are connected in a T structure. Unity input power factor and precise output voltage and frequency regulation is achieved through appropriate control of these three converters. H-bridge converters can be used in each branch of T to make the proposed converter. The converter is controlled such that the average active power of each H-bridge remains zero. Therefore, capacitors are implemented in DC links of H-bridges. Moreover, using half-bridge converters, instead of Hbridge ones, for T branch converters, leads to an AC/AC converter with only six semiconductor switches. Also, multilevel inverters, specially cascaded H-bridge can be used in branches of T. This will lead to a multilevel AC/AC converter that is suitable for high-power applications such as intertie connections and high-power motor drives. Principle of operation and control schemes of the converter are then explained. Simulation and experimental results verify the performance of the converter while operating as a power supply at different frequencies. [ABSTRACT FROM AUTHOR]

This study proposes a new fault detection method for modular multilevel converter (MMC) semiconductor power switches. While in common MMCs, the cells capacitor voltages are measured directly for control purposes, in this study voltage measurement point changes to the cell output terminal improving fault diagnosis ability. Based on this measurement reconfiguration, a novel fault detection algorithm is designed for MMCs semiconductor power switches. The open circuit and short circuit faults are detected based on unconformity between modules output voltage and switching signals. Simulation and experimental results confirm accurate and fast operation of the proposed method in faulty cell diagnosis. Implementation simplicity, no need to extra voltage measurements and multi faults detection ability are some other advantages of the proposed method. [ABSTRACT FROM AUTHOR]