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

A new family of single-stage high-step-up boost voltage inverters based on transformers is proposed, called TZ-source inverters. By replacing two inductors in the classical Z-source inverter with two transformers, the proposed inverter produces a very high boost voltage gain when the turn ratio of the transformers is larger than 1. Compared to the trans-Z-source inverters, the proposed TZ-source inverter uses a lower transformer turn ratio, which reduces the transformer's size and weight while producing the same output voltage gain. The extension of the proposed inverter topology to dc-link-type and embedded-type topologies is presented. The operating principles, analysis, and simulation results are shown. To verify the performance of the proposed TZ-source inverter, a laboratory prototype was constructed and operated with 60-V dc input. The simulation and experimental results verified that the converter has high-step-up inversion ability.

TZ-Source Inverters

This paper deals with a new family of high boost voltage inverters that improve upon the conventional trans-Z-source and trans-quasi-Z-source inverters. The improved trans-Z-source inverter provides continuous input current and a higher boost voltage inversion capability. In addition, the improved inverter can suppress resonant current at startup, which might destroy the device. In comparison to the conventional trans-Z-source/-trans-quasi-Z-source inverters, for the same transformer turn ratio and input and output voltages, the improved inverter has a higher modulation index with reduced voltage stress on the dc link, lower current stress flow on the transformer windings and diode, and lower input current ripple. In order to produce the same input and output voltage with the same modulation index, the improved inverter uses a lower transformer turn ratio compared to the conventional inverters. Thus, the size and weight of the transformer in the improved inverter can be reduced. This paper presents the operating principles, analysis and simulation results, and compares them with those of the conventional trans-Z-source/-quasi-Z-source inverters. To verify the performance of the improved converter, a laboratory prototype was constructed based on a TMS320F2812 digital signal processor with 100 Vdc input and 115 Vrms output voltage.

Improved Trans-Z-Source Inverter With Continuous Input Current and Boost Inversion Capability

The properties of a single-phase quasi- $Z$ -source inverter (qZSI) and a single-phase quasi-switched boost inverter (qSBI), both of which are single-stage buck-boost inverters, are investigated and compared. For the same operating conditions, qSBI has the following advantages over qZSI: 1) Three capacitors are saved; 2) the current rating on both of its switches and diodes is lower; 3) its boost factor is higher with an equivalent parasitic effect; and 4) its efficiency is higher. However, qSBI has one more active switch and one more diode than $Z$ -source/qZSIs. In additi on, the capacitor voltage stress of qSBI is higher than that of qZSI. The dc and ac component circuit analysis, impedance design with low-frequency and high-frequency ripples, component stresses, and power loss calculation are presented. A prototype based on a TMS320F28335 DSP is built in order to compare the operating principle of qSBI and qZSI.

A Comparison Between Single-Phase Quasi- $Z$ -Source and Quasi-Switched Boost Inverters

The Z-source inverter is a relatively recent converter topology that exhibits both voltage-buck and voltage-boost capability. The Z-source concept can be applied to all dc-to-ac, ac-to-dc, ac-to-ac, and dc-to-dc power conversion whether two-level or multilevel. However, multilevel converters offer many benefits for higher power applications. Previous publications have shown the control of a Z-source neutral point clamped inverter using the carrier-based modulation technique. This paper presents the control of a Z-source neutral point clamped inverter using the space vector modulation technique. This gives a number of benefits, both in terms of implementation and harmonic performance. The adopted approach enables the operation of the Z-source arrangement to be optimized and implemented digitally without introducing any extra commutations. The proposed techniques are demonstrated both in simulation and through experimental results from a prototype converter.

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Space-Vector-Modulated Three-Level Inverters With a Single Z-Source Network

A modified single-phase quasi-Z-source ac-ac converter is proposed in this paper. The proposed converter has the main features in that the output voltage can be bucked or boosted and be both in-phase and out-of-phase with the input voltage. The input voltage and output voltage share the same ground, the size of a converter is reduced, and it operates in a continuous current mode. A safe-commutation strategy for the modified single-phase quasi-Z-source ac-ac converter is used instead of a snubber circuit. The operating principles and a steady-state analysis are presented. A laboratory prototype, tested using a resistive load, a passive load, and a nonlinear load, was constructed that used an input voltage of 70 Vrms /60 Hz in order to verify the performance of the modified single-phase quasi-Z-source ac-ac converter. The experimental results verified that the converter has a lower input current total harmonic distortion, a higher input power factor, and a higher efficiency in comparison to a conventional single-phase Z-source ac-ac converter. In addition, the experimental results show that the use of the safe-commutation strategy is a significant improvement, as it makes it possible to avoid voltage spikes on the switches.

A Modified Single-Phase Quasi-Z-Source AC–AC Converter

This paper documents a new three-switch, isolated boost dc–dc converter. The major features of the proposed converter are as follows: 1) continuous input current; 2) reduced one active switch, one additional diode, and one additional capacitor; 3) unchanged primary and secondary voltage waveforms of the transformer when the duty cycle is changed; and 4) removal of the snubber circuit. This paper presents the operating principles, analysis, parameter design guidelines, and simulation results for the proposed converter. To verify the performance of the proposed converter, a 400 W prototype was constructed with a 40–60 V dc input. A PID controller was used to maintain the dc output voltage at 400 V. The simulation and experimental results matched those of the theoretical analysis.

Isolated Boost DC–DC Converter With Three Switches

This paper discusses a commutation control method aimed at reducing the commutation torque ripple in sensorless drive of brushless direct current motors. These motors are generally used for low-cost applications because of relatively high efficiency and low manufacturing cost. On the other hand, they show a high torque ripple characteristic caused by nonideal commutation currents. This limits their application area, especially for low-voltage applications. In order to minimize torque ripple for the entire speed range, a comprehensive analysis of commutation torque ripple was made according to three commutation control methods whereupon an optimal current vector trajectory for low torque ripple was devised. The effectiveness of the proposed method was verified through simulation and experimental results.

Yong-Jae Kim

Papers

A Modified Single-Phase Quasi-Z-Source AC–AC Converter

Isolated Boost DC–DC Converter With Three Switches

Commutation Control for the Low-Commutation Torque Ripple in the Position Sensorless Drive of the Low-Voltage Brushless DC Motor