Impedance Source Network Research Articles

New Magnetically Coupled Impedance (Z-) Source Networks

Various magnetically coupled impedance source (MCIS) networks have been proposed in the literature for increasing voltage gain and modulation index simultaneously while reducing the number of passive components used in the converter. However, applications of such networks have been limited by their discontinuous currents drawn from the sources and/or high stresses experienced by their components. This paper thus proposes three new MCIS networks named, respectively, as quasi-Y-source, quasi-Γ-Z-source, and quasi-T-source or quasi-trans-Z-source networks. These new networks inherit all advantages of the existing MCIS networks. In addition, they demonstrate advantages like continuous input currents, reduced source stresses, and lower component ratings that are not achievable by other existing networks. Further, dc-current-blocking capacitors used in the networks help to avoid saturation of magnetic core. Derivations of all two-winding MCIS networks, including existing and new networks, from the generalized three-winding MCIS networks are then systematically illustrated, before comparing them. Operational principles, mathematical derivations, simulation, and experimental results of all studied networks have been presented in the paper.

Novel Family of Single-Phase Modified Impedance-Source Buck-Boost Multilevel Inverters With Reduced Switch Count

This paper describes novel single-phase solutions with increased inverter voltage levels derived by means of a nonstandard inverter configuration and impedance source networks. Operation principles based on special modulation techniques are presented. Detailed component design guidelines along with simulation and experimental verification are also provided. Possible application fields are discussed, as well as advantages and disadvantages. Finally, future studies are addressed for the new solutions.

A Fault-Tolerant Strategy Based on Fundamental Phase-Shift Compensation for Three-Phase Multilevel Converters With Quasi-Z-Source Networks With Discontinuous Input Current

This paper proposes a new fault-tolerant strategy for a multilevel converter with an integrated impedance-source network. The proposed fault-tolerant strategy leverages the flexibility provided by the impedance-source network to implement the fundamental phase-shift compensation (FPSC) method in order to restore operation of a multilevel converter with one or more faulty switches to the prefault conditions. In case of a fault occurrence, the proposed fault-tolerant strategy makes the most use of the remaining converter capacity and generates balanced line-to-line voltages, while evenly distributing an inevitable voltage stress increase, over all converter switches. In this paper, first, a brief background about an impedance-source based cascaded H-bridge converter and a suitable modulation method for it is provided. Then, the FPSC method is explained and the proposed fault-tolerant strategy based on this method is introduced. Finally, several experimental results from a prototype converter are provided to validate the operation of the proposed strategy.

Comparison of Impedance-Source Networks for Two and Multilevel Buck–Boost Inverter Applications

Impedance-source networks are an increasingly popular solution in power converter applications, especially in single-stage buck-boost power conversion to avoid additional front-end dc-dc power converters. In the survey papers published, no analytical comparisons of different topologies have been described, which makes it difficult to choose the best option. Thus, the aim of this paper is to present a comprehensive analytical comparison of the impedance-source-based buck-boost inverters in terms of passive component count and semiconductor stress. Based on the waveform of the input current, i.e., with or without a transformer, and with or without inductor coupling, the impedance-source converters are classified. The main criterion in our comprehensive comparison is the energy stored in the passive elements, which is considered both under constant and predefined high frequency current ripple in the inductors and the voltage ripple across the capacitors. Two-level and multilevel solutions are described. The conclusions provide a “one-stop” information source and a selection guide of impedance-source-based buck-boost inverters for different applications.

Modeling, Analysis, and Parameters Design of LC-Filter-Integrated Quasi-Z -Source Indirect Matrix Converter

Through coupling the impedance network between the grid and the conventional indirect matrix converter (IMC), the LC -filter-integrated quasi-Z-source (qZS) IMC overcomes the 0.866 voltage gain limitation of the conventional IMC and also avoids the input filter that is required to mitigate current harmonics of the conventional qZS matrix converters. This paper further investigates the voltage boosting and LC filtering function of the LC -filter-integrated qZS IMC. The voltage gain, the filtering function, and qZS network parameters design are presented using a small-signal model and circuit analysis. Simulation and experimental results validate the built model, the voltage gain analysis, and the parameters design of this type of qZS IMC. The input current of the LC -filter-integrated qZS network is compared to the conventional Z-source and qZS IMCs to investigate the integrated LC filtering capability. The experimental results verify that the LC -filter-integrated qZS network provides the necessary filtering function. Thus, the traditional input filter can be eliminated, which reduces the cost, power loss, volume, and weight for the overall system, when compared with the other conventional topologies that require the input filter, even those with impedance-source networks.

Small-Signal Modeling and Comprehensive Analysis of Magnetically Coupled Impedance-Source Converters

Magnetically coupled impedance-source (MCIS) networks are recently introduced impedance networks intended for various high-boost applications. It employs coupled magnetic in the circuit to achieve higher voltage gain. Various MCIS networks have been proposed in the literature for myriad applications; however, due to effective role of system modeling in the closed-loop controller design, this paper is allocated to small-signal modeling and analysis of MCIS converters. The modeling is performed by means of the circuit averaging and averaged switch technique. A generalized small-signal derivation is demonstrated for pulse width modulation (PWM) MCIS converters and it is shown that the derived transfer functions can simply be applied to Y-source, Γ-source, and T-source impedance networks. Various transfer functions for capacitor voltage, output voltage, magnetizing current, input and output impedance are derived and have been validated through frequency and dynamic responses of computer simulation results. In addition, a comprehensive analysis has been done for all mentioned PWM MCIS converters regarding their circuit parameters. Furthermore, the effect of considering the equivalent series resistances of capacitor and inductor on the stability margin of MCIS converters is revealed in this paper. Finally, in order to validate the derived transfer functions and to consolidate the perfumed analysis, experimental results are presented for all mentioned MCIS converters.

New Operation Strategy for a Grid-Connected Three-Phase Three-Level NPC qZS Inverter Based on Power Losses

This paper proposes a new operation strategy for a three-phase three-level neutral-point-clamped quasi-impedance source inverter in a grid-connected mode. The strategy is intended for any inverter based on impedance source networks where the shoot-through states allow a wider input operation range. This feature is commonly requested in photovoltaic applications due to variations in the level of irradiance. Converters of that family have different control variables or degrees of freedom that can be used to boost the input voltage. In the first step, focus was on possible control variables for the design of the control strategy to regulate the active/reactive power. We used a power losses analysis to determine the most suitable variables in each input voltage interval. Our detailed description for the design of the control strategy is based on the well-known relationship in an electrical system between P - d and Q - V . Good performance of the full system was validated by simulations. DOI: http://dx.doi.org/10.5755/j01.eie.22.3.15316

A Review of Galvanically Isolated Impedance-Source DC–DC Converters

Impedance-source converters, an emerging technology in electric energy conversion, overcome limitations of conventional solutions by the use of specific impedance-source networks. Focus of this paper is on the topologies of galvanically isolated impedance-source dc–dc converters. These converters are particularly appropriate for distributed generation systems with renewable or alternative energy sources, which require input voltage and load regulation in a wide range. We review here the basic topologies for researchers and engineers, and classify all the topologies of the impedance-source galvanically isolated dc–dc converters according to the element that transfers energy from the input to the output: a transformer, a coupled inductor, or their combination. This classification reveals advantages and disadvantages, as well as a wide space for further research. This paper also outlines the most promising research directions in this field.

Z-Source Inverter: Topology Improvements Review

One of the most promising power electronics converter topologies is the Z-source inverter (ZSI). The ZSI is an emerging topology for power electronics dc?ac converters with interesting properties such as buck-boost characteristics and single-stage conversion. A two-port network, composed of two capacitors and two inductors connected in an X shape, is employed to provide an impedance source (Z-source) network, coupling the inverter main circuit to the dc input source. The ZSI advantageously uses the shoot-through (ST) state to boost the input voltage, which improves the inverter reliability and enlarges its application fields. In comparison with other power electronics converters, it provides an attractive single stage dc?ac conversion with buck-boost capability with reduced cost, reduced volume, and higher efficiency due to a lower component number. For emerging power-generation technologies, such as fuel cells, photovoltaic (PV) arrays, and wind turbines, and new power electronic applications such as electric and hybrid vehicles, the ZSI is a very promising and competitive topology [1]-[4].

Research on Shoot-Through Zero Vector of Impedance Source Linearization Control Strategy

Z-source inverter takes advantage of a distinctive impedance source network and modulation method of shoot-through vector, and achieves the function of buck/boost DC - AC inverter in the single stage system at the same time, which is suitable for grid-connected PV systems with large input voltage variations. The purpose of this study is to draw a unified method of shoot-through vector and grid inverter of the z-source inverter, apply the method of state-space averaging for the modeling analysis of the z-source inverter and give a complete mathematical model. Based on which and according to the nonlinear control theory and making use of the linearization of affine nonlinear model of the z-source inverter, we can get the specific derivation of equation. The results of the simulation and experiment show that according to the linearization of the shoot-through vector with affine nonlinear model for the z-source, we can make the system have the characteristics of fast and accurate tracking, small overshoot, small DC voltage, AC current ripple and small THD, and it has a certain practical value.

PISB Control of Single Phase Quasi Impedance Source DC-DC Converter

The objective of the proposed topology for buck boosts energy conversion with a reduced ripple in the output voltage and current. The proposed topology contains quasi impedance source network which has one diode, two capacitors, two inductors are used to maintain continues current on the primary side by implementing simple boost PWM technique with PI controller. By PISB (Proportional Integral Simple Boost) control method, the proposed DC-DC converter gets high efficiency, nearly twofold increased gain, over twofold boost factor and reduced ripple in the output voltage compared with the conventional method.

Hysteresis current control with distributed shoot‐through states for impedance source inverters

SummaryThis paper presents a hysteresis current control technique with shoot‐through states distribution. This control algorithm could be applied to three‐level and multi‐level inverters with any impedance source network where reference current control signal along with shoot‐through states are required. Possible modifications of the presented algorithm are discussed. The steady‐state analysis was made to explain the operation principle of the algorithm. As a result, the link between the band ratio of the hysteresis current controller, the input voltage, and the desired DC‐link voltage was obtained. All theoretical predictions were proved by simulation and experimental results. Future applications are discussed.Copyright © 2015 John Wiley & Sons, Ltd.

Impedance-Source Networks for Electric Power Conversion Part II: Review of Control and Modulation Techniques

Impedance-source networks cover the entire spectrum of electric power conversion applications (dc-dc, dc-ac, ac-dc, ac-ac) controlled and modulated by different modulation strategies to generate the desired dc or ac voltage and current at the output. A comprehensive review of various impedance-source-network-based power converters has been covered in a previous paper and main topologies were discussed from an application point of view. Now Part II provides a comprehensive review of the most popular control and modulation strategies for impedance-source network-based power converters/inverters. These methods are compared in terms of theoretical complexity and performance, when applied to the respective switching topologies. Further, this paper provides as a guide and quick reference for researchers and practicing engineers in deciding which control and modulation method to consider for an application in a given topology at a certain power level, switching frequency and demanded dynamic response.

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

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.

Effects of Leakage Inductances on Magnetically Coupled Y-Source Network

Coupled inductors have been used with impedance-source networks, extended from the earlier Z-source network, to keep their shoot-through times short, while providing high-voltage gains. A commonly stated requirement for these networks is that their magnetic couplings must be strong or their leakage inductances must be small. This is often difficult to achieve in practice especially at high switching frequencies. It is therefore necessary to understand the effects that leakage inductances have on the performance of these converters. In this letter, we address these issues for the latest Y-source network, showing in particular that voltage spikes will appear across its switching devices in some, but not all, cases. Experimental results verifying the findings have been obtained and presented at the end of this letter.

Y-Source Impedance Network

A novel A-source impedance network is proposed in this letter. The A-source impedance network uses an autotransformer for realizing converters for any application that demand a very high dc voltage gain. The network utilizes a minimal turns ratio compared to other magnetically coupled impedance source networks to attain a high voltage gain. In addition, the proposed converter draws a continuous current from the source, and hence it is suitable for many types of renewable energy sources. The derived network expressions and theoretical analysis are finally validated experimentally with an example single-switch 400-W dc–dc converter. For the closed-loop control design and stability assessment, a small signal model and its analysis of the proposed network are also presented in brief.

Dual Z-Source Three Level Inverter Topology with Triplen Harmonic Elimination Employing Clamping Capacitor for Impedance Network for Open End Stator Winding Induction Motor

In open end stator winding three phase induction motor the two ends of all the phases of stator windings are connected to separate supplies. Open-end winding motors require either harmonic filters or isolation transformers to prevent currents of the triplen harmonic order flowing in the motor phases and the semiconductor devices. Separate dc supply is used for each inverter to block the flow of third harmonic currents. Z-Source Inverter will act as a booster inverter and also due to the presence of source impedance network, it provides ride through shoot through faults. A novel configuration of three level Neutral Point Clamped (NPC) Multi level Inverter with source impedance network, in which impedance network is formed by using the capacitors of the NPC inverter is proposed in this paper. Therefore the numbers of capacitors are reduced and voltage unbalancing of capacitor can be minimized. The proposed configuration offers reduced size and better throughput. The simulation results for the same are presented in this paper.

Research on TZSI Control Method

In transformer-Z-source inverters (TZSI), the impedance networks consist of a transformer and one capacitor. While maintaining the main features of traditional Z-source network, the new networks exhibit some unique advantages, such as the increased voltage gain and reduced voltage stress in the voltage-fed TZSI, when the turns ratio of the transformer windings is over 1. This paper contributes to the ac small signal modeling and analysis of TZSI in continuous conduction mode. The ac small signal model considers the dynamics introduced by network uniquely contained in TZSI. And a double loop control method which is impedance source network output dc voltage and current loop has been proposed to realize the control of TZSI. Results of simulations and experiments are used to validate the control method and show that this method is correct and feasible.

Distributed Impedance Network (Z-Network) DC–DC Converter

This paper presents a novel dc-dc converter incorporating a distributed impedance-source network (Z-source network, or Z-network) to achieve the buck (step-down) and boost (step-up) function of a transformer-isolated dc-dc converter. In this paper, the distributed impedance source network composed of an array of inductors and capacitors is coupled between power source and main switching devices. The great and unique feature about the distributed impedance source network dc-dc converter is that unlike the traditional V-source or I-source converters, it can be open- and short-circuited without damaging switching devices. Therefore, the desired buck and boost function can be achieved. Moreover, converter reliability can be greatly improved. A dc-dc converter using this proposed concept is built and tested. Its performances are verified with experimental results.