The output voltage of a photovoltaic panel is greatly affected by irradiance, temperature, shading, etc. A buck-boost type inverter is, therefore, required to accommodate the wide fluctuations in dc voltage. This article proposes a class of single-phase, single-stage buck-boost inverters employing five switches (implemented using power MOSFETs with external fast recovery diodes) to provide buck-boost operation for wide variations in photovoltaic (PV) output voltage. In this article, the proposed inverters are immune from current shoot-through problems associated with voltage source inverters, easing the requirement for PWM dead-times. They also provide a common-grounding feature between the grid-neutral and the negative-terminal of the PV panel, successfully suppressing the PV leakage current. In addition, they provide reactive power support. A simple input boost inductor-based buck-boost inverter is proposed with a wide gain range; other variants are also proposed based on the switched inductor, quadratic boost, and switched coupled-inductor, achieving higher boost voltage inversions with smaller values of duty ratio. Detailed circuit operations are presented based on proposed modulation strategies. Design guidelines/requirements of components and their comparisons are provided for all of the proposed inverters. The theoretical analysis and performance characteristics of all four topologies are experimentally validated using 400 VA laboratory prototype inverters.

In this paper, a family of single-phase single-stage high-gain dual-buck split-source inverters is proposed. The proposed inverters have combined the benefits of split-source inverter (SSI), dual-buck inverter (DBI) and high-gain dc-dc converters. Similar to the DBI, they provide high reliability by eliminating shoot-through issues, high switching frequency and efficiency by using power MOSFETs without leading the body diodes to reverse recovery issues, and decrease the PWM deadtime. In addition, voltage boost operation is achieved without using any additional active switch, which is in favor of lower control complexity. On the other hand, similar to the SSI, buck-boost dcac power conversion is realized in a single-stage. However, compared to the SSI, the proposed inverters achieve high voltage gain. As an example, the proposed switched-coupled-inductor split-source dual-buck inverter is analyzed and compared with the other proposed structures. To validate the theoretical analysis, a 300 W experimental prototype is designed and tested at 25-35 V input voltage, 155 Vpeak output voltage and 50 kHz.

This paper presents a family of NPC inverters consisting of single-phase, three-phase, and cascaded inverters. The proposed inverters have no short-circuit and dead-time issues, therefore no high voltage and current spikes are caused. Also, the dead-time in the switching signals can be eliminated or minimized. As a result, the magnitude of the output waveforms can be increased, and quality can be improved. Unlike the dual-buck NPC inverter, the voltage stress of all the semiconductor in the proposed inverter is lower, and unlike the split-inductor NPC inverter the proposed inverter provides reactive power. In this paper, the proposed three-level NPC inverter is analyzed, designed, and tested. The voltage stress of the semiconductor devices in the proposed inverter is half of the source voltage, whereas in the conventional dual-buck NPC inverter the voltage stress of the two external diodes is the source voltage. In addition to the aforementioned benefits, the proposed cascaded inverter reduces the total number of inductors. To verify the analysis, detailed simulation, and experimental results of the proposed three-level inverter with input voltage 640 V, output power 1.2 kW, and output voltage 220 Vrms are provided

A single-phase bipolar buck-boost direct pulse-width modulated (PWM) ac-ac converter is proposed, comprising of six IGBTs, a small film capacitor, and input/output LC filters. It can provide discrete non-inverting buck (NIBu) and boost (NIBo) operations with voltage gains of D and 1/(1-D), respectively. Moreover, it provides symmetric non-inverting buck-boost (NIBB) and inverting buck-boost (IBB) operations with voltage gains of D/(1-D) and -D/(1-D), respectively. It always supplies both continuous input/output currents, and it is suited well for reactive loads. It is immune from commutation problem and thus, has enhanced reliability, while avoiding the use of RC-snubbers or safe-commutation switching strategies. Various operating modes of the proposed converter make it suitable for diverse applications: 1) NIBu and NIBo can be used for application as direct ac voltage regulator. 2) Whereas, IBB operation can be utilized along with NIBu/ NIBo or NIBB operation to compensate both voltage sag and swell, when used as series voltage compensator based dynamic voltage restorer (DVR). 3) Symmetric NIBB/IBB operations can provide step-changed frequency output, similar to single-phase matrix converters (MCs), for applications as induction motor drive or high-gain ac-dc rectifier. Extensive operation analysis, component design guidelines and appropriate comparisons are provided, followed by experimental results.

A single-phase symmetric-bipolar-type high-frequency isolated buck-boost ac–ac (SBT-HFI-BBAC) converter is proposed. The converter is composed of two full-bridge inverter modules, input/output LC filters, and a high-frequency transformer (HFT) with series capacitors. It can provide identical noninverting and inverting buck-boost output voltages with symmetric-bipolar voltage gains of $ \pm D/({1 - D})$ . The frequency of the output voltage can also be adjusted in discrete steps, similar to single-phase matrix converters (MCs). It supplies continuous input and output currents and works well with nonunity power factor loads. The magnetizing current of the HFT has no line frequency component due to the presence of the series blocking capacitors. Moreover, due to the absence of ac switches, the converter has a simple commutation process, unlike conventional ac-ac/MCs. Two switching strategies are proposed; Strategy-I with fewer high-frequency switches and Strategy-II with reduced switch currents, providing more flexibility in switch power loss optimization. The proposed SBT-HFI-BBAC converter is well suited for application as a dynamic voltage restorer, compensating a wide range of grid voltage sags and swells, without the need for a low-frequency voltage injection transformer. Its step-changed frequency operation can also find use in various applications, such as high-gain ac–dc converters, traction systems, etc. A comprehensive description of circuit operation is presented along with component design guidelines and appropriate comparisons. Experimental verification results are provided using a 400-W laboratory test circuit.

Single-phase matrix converters (MCs) are undergoing a rapid development due to their bipolar voltage gain (as required in dynamic voltage restorer) and step-changed frequency operation (used in high step-up ac-dc rectifier, and to provide medium frequency isolation in traction and wind turbine converters, etc.). However, existing buck-boost MCs require high voltage/current rating devices, and suffer from large component voltage/current stresses and ripples, significantly degrading their efficiency. This paper proposes a highly-efficient single-phase buck-boost MC; consisting of eight IGBTs (implemented using two full-bridge IGBT modules), second-order input and output filters, and a small value film capacitor. Highly-efficient discrete inverting and non-inverting buck (DINIBu) and boost (DINIBo) operations are proposed (same as that of sixteen switches cascaded buck-boost MC), with significantly lower component voltage/current stresses and ripples. In addition, flexible inverting and non-inverting buck-boost (fINIBB) operations are also proposed with independent control of buck and boost duty ratios. All of the proposed operations are free of commutation issues, are compatible with reactive loads, and provide smooth input and output currents. Furthermore, all the switches have the same voltage stresses, and all four switches in a full-bridge module experience the same current stresses. Experimental results are presented, using a 400-VA laboratory prototype.