A buck-boost ac-ac converter with inverting and non-inverting operations is proposed. It compensates both the voltage sag and swell when used as a dynamic voltage restorer. Its basic switching cell is a unidirectional buck circuit, owing to which it has no shoot-through concerns. It achieves safe commutation without using RC snubbers or soft commutation strategies. Further, it can be implemented with power MOSFETs without their body diodes conducting, and for current freewheeling external diodes of good reverse recovery features can be used to minimize the reverse recovery issues and relevant loss. The detailed theoretical analysis and experimental results of a 300-W prototype converter are provided.

This paper presents novel single-phase single-stage buck-boost inverters. The proposed inverters provide buck-boost operation for a wide variation of the input dc voltage. In addition, the proposed inverters are bidirectional and therefore can provide reactive power. Further, they require only one inductor. The proposed inverters also eliminate the common-mode leakage current problem by connecting output neutral to the midpoint of capacitors or directly to input voltage sources. Therefore, they are well suitable for photovoltaic applications. Although six switches are required, two switches are working at line frequency resulting in negligible switching loss. Of the four remaining switches, only two are switching under high frequency at a time depending on the half cycle of the output voltage. The circuit operations are demonstrated through the analysis of the proposed inverters. A 120 Vrms/ 60 Hz/ 400 W hardware prototype was constructed and tested. The experimental results verify the theoretical analysis.

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

In this paper, two single-phase single-stage split-inductor buck-boost inverters are proposed: type-I and II. The proposed type-I is unity power factor inverter, while the proposed type-II inverter is suitable for any power factor. Both topologies remove the shoot-through problem. Furthermore, the reverse recovery issues for all switches are eliminated; therefore, MOSFETs are used to obtain higher efficiencies. The proposed inverters operated at higher switching frequencies confer the additional benefit of smaller passive components. The current stresses of the two switches in the proposed type-I and II inverters are lower of the conventional boost inverter. The dead-time can be eliminated at both the high and line switching frequencies. In addition, the inductor conduction loss is minimized to improve efficiency. Moreover, the voltage stresses of the two switches in the type-I inverter can be much lower of its counterpart boost inverter. Most importantly, unlike the conventional high reliability inverters, the magnetic volume of the proposed high reliability type-I and II inverters is same of its counterpart boost inverter. The experimental results obtained for 500 W, 110 Vrms, 60 Hz hardware prototypes verify the analysis.

This paper proposes the new non-inverting buck-boost ac-ac converter, which can minimize the reverse recovery loss by disabling the body diodes of switches and using the external fast recovery diodes for its current freewheeling. In particular, the proposed ac-ac converter takes advantages of metal-oxide semiconductor field effect transistors (MOSFET) and external fast recovery diodes to achieve the high efficiency. Also, it has the high reliability without the shoot-through and dead-time considerations in the circuit. Moreover, it can be simply implemented without employing the conventional commutation control. This results in decreasing the control complexity. As its proper application, a new type of dynamic voltage restorer (DVR) based on the proposed non-inverting buck-boost converter is described. It enables to solve the voltage sag and swell problems by utilizing both positive and negative gains of converter. Then, the hardware prototype of proposed ac-ac converter and DVR are implemented to verify their practical effectiveness.

The output voltage of renewable energy sources is influenced by environmental conditions. To compensate for the variations of voltage, a buck-boost power conditioning system can be used. This paper presents a full-bridge single-inductor based buck-boost inverter. Its output voltage can be greater or lower than the input voltage depending on the controllable duty-ratio. This inverter features bidirectional and reactive power flow operations with no high-frequency common-mode voltage. The unique feature of the proposed inverter is using a single inductor in the power train, which enhances power density. Moreover, only two switches can operate at high frequency. This enables to make the inverter with the high efficiency and simple circuit configuration. Based on the proposed full-bridge inverter, a novel cascaded buck-boost inverter is also presented. It retains all the benefits of the proposed full-bridge inverter. The theoretical analysis of the proposed full-bridge inverter is firstly explained in detail. It is then extended to a cascaded inverter. Thereafter, the practical effectiveness of the proposed inverters is verified with the experimental tests by implementing the hardware prototypes of 110 Vrms, 60 Hz and 500 W for full-bridge single-inductor based buck-boost inverter, and 220 Vrms, 60 Hz and 1000 W for the cascaded inverter.