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In a single-stage buck-boost quasi-switched boost inverter (qSBI), the shoot-through state insertion causes high amplitude common-mode voltage. Consequently, the qSBI becomes less attractive in transformerless photovoltaic (PV) systems. In this paper, a novel space vector pulse-width modulation for a modified qSBI is introduced to reduce the magnitude of common-mode voltage and push the modulation index up to 1. By properly choosing the shoot-through interval time, shoot-through states are considered to be inserted for boosting voltage and also reducing the THD value of the output voltage. The mathematical analysis and operating principles of the converter are discussed and verified through PSIM simulations. Finally, an experimental prototype is validated based on a TMS320F28335 DSP microcontroller and a DE0-Nano FPGA digital control platform. INDEX TERMS Z-source inverter, quasi-switched boost inverter, single-stage inverter, common-mode voltage, transformerless PV system, space vector pulse-width modulation.

Low voltage stress on the impedance source network devices is the main reason for the advent of DC-linked type quasi-switched boost inverters (DqSBIs). However, the DqSBI has become less attractive due to its low voltage gain. This paper presents a novel PWM control strategy for the DqSBI and its comparative performance evaluation to the conventional inverters. The modified PWM control strategy based DqSBI improves the voltage gain and reduces the conduction loss and the inductor current ripple. Circuit analysis and comparison study between the DqSBI, the quasi-Z-source inverters, and the two-stage inverter with a boost DC-DC converter are presented. 1-kVA three-phase inverter prototypes were set up to compare and evaluate the performance of the DqSBI with the improved PWM method for voltage gains of 0.85 to 1.6. The measured efficiency and total harmonic distortion (THD) values are also presented. INDEX TERMS Quasi-switched boost inverter, quasi-Z-source inverter, two-stage inverter, shoot-through, DC-linked type.

High-voltage gain conversion is necessary for several applications, especially for low voltage renewable source applications. In order to achieve a high-voltage gain, the presented paper proposes a class of transformerless DC-DC converters based on three switched-capacitor networks. The proposed converters have the following characteristics: reduced voltage stress on the capacitors and power devices; obtained high voltage gain with small duty cycle; and reduced conduction losses in the power switches. To verify the operation principle of the proposed converters, the detailed analysis in different conditions of the proposed converters and a comparison considering existing topologies are also discussed in the paper. Moreover, the parameter selection and controller design for the converters are determined. Finally, to reconfirm the theoretical analysis, both the simulation and experimental results taken from a 400 W prototype operating at 60 kHz are given.

In this study, an improved pulse width modulation (PWM) scheme was proposed for an active quasi-Z source inverter (AqZSI). Compared to the quasi-Z-source inverter (qZSI), the AqZSI with improved PWM strategy can operate in a wide range of input voltage with higher efficiency. Furthermore, the AqZSI can operate with a higher modulation index, a lower inductor current stress, and a reduced shoot-through current. A procedure flowchart is presented for the optimal selection of the shootthrough duty cycle, the switching ratio of the additional switch, and the modulation index for AqZSI. Moreover, some comparative results between the AqZSI, qZSI and conventional two-stage inverter with a boost DC-DC converter are shown in detail. Finally, 1.2 kVA SiC-based three-phase inverter prototypes are built to verify the agreement between theory and measurement.