Impedance networks cover the entire of electric power conversion from dc (converter, rectifier), ac (inverter), to phase and frequency conversion (ac-ac) in a wide range of applications. Various converter topologies have been reported in the literature to overcome the limitations and problems of the traditional voltage source, current source as well as various classical buck-boost, unidirectional, and bidirectional converter topologies. Proper implementation of the impedance-source network with appropriate switching configurations and topologies reduces the number of power conversion stages in the system power chain, which may improve the reliability and performance of the power system. The first part of this paper provides a comprehensive review of the various impedance-source-networks-based power converters and discusses the main topologies from an application point of view. This review paper is the first of its kind with the aim of providing a “one-stop” information source and a selection guide on impedance-source networks for power conversion for researchers, designers, and application engineers. A comprehensive review of various modeling, control, and modulation techniques for the impedance-source converters/inverters will be presented in Part II.

Impedance-Source Networks for Electric Power Conversion Part I: A Topological Review

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.

Switched Inductor Z-Source Inverter

This paper presents a comprehensive review of step-up single-phase non-isolated inverters suitable for ac-module applications. In order to compare the most feasible solutions of the reviewed topologies, a benchmark is set. This benchmark is based on a typical ac-module application considering the requirements for the solar panels and the grid. The selected solutions are designed and simulated complying with the benchmark obtaining passive and semiconductor components ratings in order to perform a comparison in terms of size and cost. A discussion of the analyzed topologies regarding the obtained ratings as well as ground currents is presented. Recommendations for topological solutions complying with the application benchmark are provided.

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Review and Comparison of Step-Up Transformerless Topologies for Photovoltaic AC-Module Application

This paper extends the impedance-source (Z-source) inverters concept to the transformer-based Z-source (trans-Z-source) inverters. The original Z-source inverter (ZSI) employs an impedance network of two inductors and two capacitors connected in a special arrangement to interface the dc source and the inverter bridge. It has buck and boost function that cannot be achieved by traditional voltage-source inverters and current-source inverters. In the proposed four trans-Z-source inverters, all the impedance networks consist of a transformer and one capacitor. While maintaining the main features of the previously presented Z-source network, the new networks exhibit some unique advantages, such as the increased voltage gain and reduced voltage stress in the voltage-fed trans-ZSIs and the expanded motoring operation range in the current-fed trans-ZSIs, when the turns ratio of the transformer windings is over 1. Simulation and experimental results of the voltage-fed and the current-fed trans-ZSIs are provided to verify the analysis.

Trans-Z-Source Inverters

This paper extends the impedance-source (Z-source) inverters concept to the transformer based Z-source (trans-Z-source) inverters. The original Z-source inverter (ZSI) employs an impedance network of two inductors and two capacitors connected in a special arrangement to interface the dc source and the inverter bridge. It has overcome the conceptual limitations of the traditional voltage-source inverter and the current-source inverter. In the proposed trans-Z-source inverters, the impedance network consists of a transformer and one capacitor. While maintaining the main features of the previously presented Z-source network, the new networks exhibit some unique advantages, such as the increased voltage gain in the voltage-fed trans-ZSIs and the expanded motoring operation range in the current-fed trans-ZSIs when the turns-ratio of the transformer windings is over 1. Simulation and experimental results of one of the voltage-fed trans-Z-source inverters are provided to verify the analysis.

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Trans-Z-source inverters

This paper proposes an improved Z-source inverter topology. Compared to the traditional Z-source inverter, it can reduce the Z-source capacitor voltage stress significantly to perform the same voltage boost, and has inherent limitation to inrush current at startup. The control strategy of the proposed Z-source inverter is exactly the same as the traditional one, so all the existing control strategy can be used directly. A soft-start strategy is also proposed to suppress the inrush surge and the resonance of Z-source capacitors and inductors. The operation principle of the proposed topology and comparison with the traditional topology are analyzed in detail. Simulation and experimental results are given to demonstrate the new features of the improved topology.

Improved Z-Source Inverter With Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

A new family of Z-source ac-ac converters with buck-boost ability are proposed, including four switches single-phase structure and six switches three-phase structure. New commutation strategies for these converters are proposed and safe commutation can be achieved without snubber circuit. The commutation strategies are easily to realize by sampling only voltage signals, and two switches are always turned on, so switching loss can be reduced. Analysis based on state-space averaging reveals the relationship between Z-source inductor current and filter inductor current as well as voltage ratio. The design considerations of voltage-fed single-phase topology are given as an example. Simulation results on the voltage-fed topologies and experimental results on voltage-fed single-phase topology verified the unique features of Z-source ac-ac converters and the proposed commutation strategies. These converters have merits such as less conduction and switching loss, less devices, therefore high efficiency and reliability can be achieved.

Z-Source AC–AC Converters Solving Commutation Problem

This paper proposes an improved Z-source inverter topology. Compared to previous Z-source inverter topology, it can reduce the Z-source capacitor voltage stress greatly, and has an inherent limitation to inrush current. The control strategy is exactly the same as the previous one, so all existing control strategies can be used directly. Soft-start strategy is also proposed to avoid the inrush current and resonance between the Z-capacitors and the Z-inductors. Comparison between the proposed and previous topologies is also presented. Analysis, simulation, and experimental results are presented to demonstrate the new features of the improved topology.

An Improved $Z$ -Source Inverter

This paper proposes a novel single-phase Z-source inverter topology with input and output sharing the same ground. It is simple in structure and only utilizes two switches while keeping the voltage transfer ratio the same as for the full-bridge inverter. One-cycle control is adopted. Highly efficient constant-frequency control can be achieved without an accurate model of the converter. The unique feature of the proposed topology is verified by operating principle, simulation and experimental results. This topology can be used in distributed power systems where dual grounding is needed.

Single-Phase Z-Source Inverter

A new family of Z-source AC-AC converters with buck-boost ability are proposed, including four switches single-phase structure and six switches three- phase structure. New commutation strategies for these converters are proposed and safe commutation can be achieved without snubber circuit. Analysis, simulation and experimental results on the voltage-fed Z-source AC- AC converters verified the analysis. These converters have merits such as less conduction and switching loss, less devices, therefore high efficiency and reliability can be achieved.

Chaohua Zhang

Papers

Improved Z-Source Inverter With Reduced Z-Source Capacitor Voltage Stress and Soft-Start Capability

Z-Source AC–AC Converters Solving Commutation Problem

An Improved $Z$ -Source Inverter

Single-Phase Z-Source Inverter

Z-Source AC-AC Converters Solving Commutation Problem