In this paper, a new topology for cascaded multilevel inverters based on quasi Z-source converter is proposed. In the proposed topology, the magnitude of output voltage is not limited to dc voltage source, while the magnitude of output voltage of conventional cascaded multilevel inverters is limited to dc voltage source. In the proposed topology, the magnitude of output voltage can be increased by controlling the duty cycle of shoot-through (ST) state, transformer turn ratio, and the number of switched inductors in the Z-source network. As a result, there is no need for extra dc–dc converter. In the proposed topology, the total harmonic distortion (THD) is decreased in comparison with the conventional Z-source inverters. The proposed topology directly delivers power from a power source to load. In addition, in the proposed basic unit, higher voltage gain is achieved in higher modulation index which is an advantage for the proposed base unit. The performance of the proposed topology is verified by the experimental results of five-level single-phase inverter.
In different industrial and mission oriented applications, redundant or standby semiconductor systems can be implemented to improve the reliability of power electronics equipment. The proper structure for implementation can be one of the redundant or standby structures for series or parallel switches. This selection is determined according to the type and failure rate of the fault. In this paper, the reliability and the mean time to failure (MTTF) for each of the series and parallel configurations in two redundant and standby structures of semiconductor switches have been studied based on different failure rates. The Markov model is used for reliability and MTTF equation acquisitions. According to the different values for the reliability of the series and parallel structures during SC and OC faults, a comprehensive comparison between each of the series and parallel structures for different failure rates will be made. According to the type of fault and the structure of the switches, the reliability of the switches in the redundant structure is higher than that in the other structures. Furthermore, the performance of the proposed series and parallel structures of switches during SC and OC faults, results in an improvement in the reliability of the boost dc/dc converter. These studies aid in choosing a configuration to improve the reliability of power electronics equipment depending on the specifications of the implemented devices.
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