Miao Zhu

Switched Inductor Z-Source Inverter

On the basis of the classical Z-source inverter, this paper presents a developed impedance-type power inverter that is termed the switched inductor (SL) Z-source inverter. To enlarge voltage adjustability, the proposed inverter employs a unique SL impedance network to couple the main circuit and the power source. Compared with the classical Z-source inverter, the proposed inverter increases the voltage boost inversion ability significantly. Only a very short shoot-through zero state is required to obtain high voltage conversion ratios, which is beneficial for improving the output power quality of the main circuit. In addition, the voltage buck inversion ability is also provided in the proposed inverter for those applications that need low ac voltages. Similar to the classical Z-source inverter, the proposed concepts of SL Z-source inverter can be applied to various applications of dc-ac, ac-ac, dc-dc, and ac-dc power conversion. A detailed topology analysis and a generalized discussion are given. Both simulation and experimental results verify the analytical results.

Generalized multi-cell switched-inductor and switched-capacitor Z-source inverters

High performance voltage and current-source inverters (VSI and CSI) are widely required in various industrial applications such as servo-motor drives, special power supplies, distributed power systems and hybrid electric vehicles. However, the traditional VSI and CSI have been seriously restricted due to their narrow obtainable output voltage range, short-through problems caused by misgating and some other theoretical difficulties due to their bridge-type structures. The Z-source inverter was proposed to overcome the problems associated with the traditional inverters, in which the functions of the traditional dc-dc boost converter and the bridge-type inverter have been successfully combined. To further widen the operational range or gain of the Z-source inverter in both the voltage and current type configurations, the generalized switched-inductor and switched-capacitor impedance networks are proposed hereon. Both simulation and experimental testing have been conducted for validating the extra boosting introduced with some representative results captured and presented near the end of the paper.

Cascaded Multicell Trans-Z-Source Inverters

Inverters with high-output voltage gain usually face the problem of high-input current flowing through their components. The problem might further be exaggerated if the inverters use high-frequency magnetic devices like transformers or coupled inductors. Leakage inductances of these devices must strictly be small to prevent overvoltages caused by switching of their winding currents. To avoid these related problems, cascaded trans-Z-source inverters are proposed. They use multiple magnetic cells in an alternately cascading pattern rather than a single magnetic cell with large turns ratio. Simulation and experimental results have shown that the multicell inverters can produce the same high-voltage gain, while keeping currents and voltages of the components low. The inverters can also step down their output voltages like a traditional voltage-source inverter without compromising waveform quality.

Hybrid-Source Impedance Networks: Layouts and Generalized Cascading Concepts

Hybrid-source impedance networks have attracted attention among researchers because of their flexibility in performing buck-boost energy conversion. To date, three distinct types of impedance networks can be summarized for implementing voltage-type inverters with another three types summarized for current-type inverters. These impedance networks can in principle be combined into two generic network entities, before multiple of them can further be connected together by applying any of the two proposed generalized cascading concepts. The resulting two-level and three-level inverters implemented using the cascaded networks would have a higher output voltage gain and other unique advantages that currently have not been investigated yet. It is anticipated that these advantages would help the formed inverters find applications in photovoltaic and other renewable systems, where a high voltage gain is usually requested. Experimental testing for validating the extra boosting has already been conducted with some representative results presented at the end of this paper.

Topology analysis of a switched-inductor Z-source inverter

This paper presents a developed impedance-type power inverter that is termed switched-inductor Z-source inverter. To enlarge voltage adjustable ability, the proposed inverter employs a unique switched-inductor impedance network to couple the main circuit and power source. Compared with the classical Z-source inverter, the proposed inverter increases the voltage boost inversion ability significantly, and only a very short shoot-through zero state is required to obtain high voltage conversion ratios. In addition, the voltage buck inversion ability is also provided in the proposed inverter for those applications that need low ac voltages. Same to the classical Z-source inverter, the proposed concepts of switched-inductor Z-source inverter can be applied to various applications of dc-ac, ac-ac, dc-dc and ac-dc power conversion. A detailed theoretical analysis and the general discussion are given. Both simulation and experimental results verify the main analytical results.

Tapped-inductor Z-source inverters with enhanced voltage boost inversion abilities

This paper presents the concept of using a new tapped-inductor (TL) Z-source impedance network for implementing Z-source inverters. By replacing the original two inductors found in the classical impedance network with two modified 2-terminal TL cells, output voltage range of the new inverter can widely be expanded. This means a larger gain, which in principle, can be adjusted freely by varying the turn ratio of the TL and the inverter shoot-through duration, which is now much shorter than that found in the classical Z-source inverter. Shorter shoot-through duration is in fact preferred, since it leads to a larger modulation index, and hence a better output waveform quality. Theoretical analysis for explaining these operating features has already been discussed throughout the paper, before simulation results are presented for verifying them. The proposed TL-network can also be applied to the quasi Z-source inverters with certain unique advantages achieved. For illustration, two example topologies are presented with their performance characteristics discussed.

Remaining Inductor Current Phenomena of Complex DC–DC Converters in Discontinuous Conduction Mode: General Concepts and Case Study

Remaining inductor current phenomena occur in several dc-dc converters operating in discontinuous conduction mode, but they do not agree with the classical definition of the discontinuous conduction mode. Since these special phenomena often cause misunderstanding during theoretical analysis and engineering applications, a reexamination is performed in this paper. Based on the investigation of energy characteristics, a new explanation of the discontinuous conduction mode is proposed so that all discontinuous cases, including the remaining inductor current phenomena, can be unified by the proposed concepts. The paper presents the canonical explanation, existence conditions and main solving principles, which simplify the derivation process of steady-state performance of a complex dc-dc converter. Case study on a fifth order self-lift Luo converter and a seventh order re-lift SEPIC converter are performed, respectively, and the corresponding simulation results are shown to validate the theoretical analysis.

Enhanced-Boost Z-Source Inverters With Alternate-Cascaded Switched- and Tapped-Inductor Cells

In this paper, a number of alternate-cascaded switched-inductor and tapped-inductor networks have been proposed for Z-source inverters. The resulting topologies have enhanced voltage-boost capability while retaining the usual voltage-buck flexibility of a conventional voltage-source inverter. The enhanced capability is achieved by using lower rated components that can more readily be found. These components are assembled without direct series connection and hence avoid unbalanced voltage sharing problems and losses linked to balancing resistive circuits. The component count is, however, high, meaning that the proposed inverters should only be considered when a design requires multiple lower rated components rather than a few higher rated ones. Analysis, simulation, and experimental results have already validated the concepts discussed.

Enhanced Self-Lift Cûk Converter for Negative-to-Positive Voltage Conversion

This letter introduces a new step-up dc-dc converter that provides a negative-to-positive voltage-conversion path for the negative dc-voltage source. Compared with the classical Cûk and buck-boost converters, the proposed converter increases the voltage boost ability significantly using the switched capacitor and self-lift techniques. It is featured with single power switch operation, common ground, transformerless structure, and clear energy delivery process; therefore, the relative simple structure is beneficial to potential industrial applications in future. A detailed theoretical analysis for the continuous and discontinuous conduction modes is given, and the main general aspects for circuit design are derived. A preliminary system modeling based on the flow graph is also presented for reference. Both simulation and experimental results are provided to validate the analysis results.

Space vector pulse-width modulation based maximum boost control of Z-source inverters

In this paper, a novel maximum boost control method is presented based on the space vector pulse-width modulation (SVPWM) technique for the three-phase Z-source inverter (ZSI). Compared with the traditional carrier-based maximum boost control strategy, the proposed method has a wider linear operation range and is easier for digital implementation. Whats more, the number of switching transition in each switching cycle is reduced, which indicates less switching power losses. It will be beneficial for the further industrial applications of the ZSIs. The simulation results in Matlab/Simulink as well as comparative performance have been provided and discussed, which have validated all theoretical analysis in the paper.