Indrek Roasto

Quasi-Z-Source-Based Isolated DC/DC Converters for Distributed Power Generation

This paper presents new step-up dc/dc converter topologies intended for distributed power generation systems. The topologies contain a voltage-fed quasi-Z-source inverter with continuous input current on the primary side, a single-phase isolation transformer, and a voltage doubler rectifier (VDR). To increase the power density of the converter, a three-phase auxiliary ac link (a three-phase inverter and a three-phase isolation transformer) and a three-phase VDR are proposed to be implemented. This paper describes the operation principles of the proposed topologies and analyzes the theoretical and experimental results.

Step-Up DC/DC Converters With Cascaded Quasi-Z-Source Network

This paper is devoted to the step-up dc/dc converter family with a cascaded quasi-Z-source network (qZS-network). The cascaded (two-stage) qZS-network could be derived by the adding of one diode, one inductor, and two capacitors to the traditional quasi-Z-source inverter (qZSI). The proposed cascaded qZSI inherits all the advantages of the traditional solution (voltage boost and buck functions in a single stage, continuous input current, and improved reliability). Moreover, as compared to the conventional qZSI, the proposed solution reduces the shoot-through duty cycle by over 30% at the same voltage boost factor. Theoretical analysis of the two-stage qZSI in the shoot-through and non-shoot-through operating modes is described. The proposed and traditional qZS-networks are compared. A prototype of a step-up dc/dc converter with the cascaded qZS-network was built to verify the theoretical assumptions. The experimental results are presented and analyzed. Finally, a further optimization method of the cascaded qZS-network is proposed, and some practical design issues are discussed.

New Shoot-Through Control Methods for qZSI-Based DC/DC Converters

Shoot-through control methods for qZSI-based dc/dc converters are presented and studied. The major goal was to increase efficiency. A new modulation technique, pulse width modulation (PWM) with shifted shoot-through, is compared with the conventional PWM shoot-through control method. The new method reduces switching frequency of bottom side transistors and inherently features partial soft switching. Previous studies have shown that the biggest drawback of PWM control with shoot-through is unequal switching frequencies of transistors. One solution to that problem could be signal swapping that has been proposed by the authors of this paper. All control methods are first simulated and then experimentally verified on a test prototype.

Experimental study of shoot-through control methods for qZSI-based DC/DC converters

This paper proposes a novel step-up DC/DC converter with galvanic isolation - the quasi-Z-source inverter (qZSI) based DC/DC converter and discusses three different shoot-through PWM control methods suitable for this topology. The proposed converter is meant for applications where the wide range of voltage gain is demanded, e.g. with renewable energy sources (fuel cells, photovoltaic cells), in telecom, aerospace and some other applications. For the verification of theoretical assumptions the converter prototype was assembled and tested. Experimental waveforms of the converter operated with different shoot-through PWM control methods are compared and discussed. Design considerations for converter and different control signal generators are provided.

New bi-directional DC/DC converter for supercapacitor interfacing in high-power applications

This paper presents a new bi-directional DC/DC converter for supercapacitor interfacing in high-power applications. The converter acts as a VSI-based step-down DC/DC converter during the supercapacitor charging mode and as a qZSI-based step-up DC/DC converter during the energy recovery mode. To provide voltage matching and galvanic isolation the medium frequency transformer was implemented. To ensure higher voltage boost of the SC voltage during the discharge the qZSI with a two-stage quasi-Z-source (qZS) network was introduced. The paper analyzes and discusses the operation of the new converter mostly concentrating on the energy recovery (boost) mode. The operation of the two-stage qZS-network is analyzed in detail. Guidelines are presented for the new converter design. Finally, theoretical background was verified by the simulations.

Galvanically Isolated Quasi-Z-Source DC–DC Converter With a Novel ZVS and ZCS Technique

This paper focuses on the galvanically isolated quasi-Z-source dc-dc converter with a novel zero voltage and zero current switching technique. The unique feature of the impedance network lies in combining the buck-boost operation capability with the short- and open-circuit immunity of transistors; at the same time, it can perform zero voltage and zero current switching on the primary side. The boundary conduction mode of the current in the second inductor of the quasi-Z-source network was used along with snubber capacitors in the two out of four transistors and a special control algorithm to achieve full zero-switching operation of the inverter. Simulation and experimental results prove the discussed ideas. Possible modifications of the algorithm and future applications are also described.

An improved high-power DC/DC Converter for distributed power generation

This paper presents a new step-up DC/DC converter topology intended for the distributed power generation systems. The topology utilizes the voltage fed quasi Z-source inverter with continuous input current on the primary side, a single-phase isolation transformer and a voltage doubler rectifier. To increase the power density of the converter, implementation of the three-phase auxiliary AC-link (three-phase inverter and three-phase isolation transformer) and the three-phase voltage doubler rectifier are proposed by the authors. The paper describes the operation principles of the proposed topologies and analyzes the theoretical and experimental results.

Quasi-Z-source inverter based bi-directional DC/DC converter: Analysis of experimental results

This paper presents simulation and experimental results of a quasi-Z-source inverter (qZSI) based bi-directional DC/DC converter for supercapacitor (SC) interfacing. The bidirectional capability provides both the charging and discharging of the SC. During the charging mode the converter operates as a conventional VSI performing the voltage buck function, but during the discharging mode the converter operates as a qZSI based step-up DC/DC converter performing the voltage boost function. The proposed converter discussed was tested in both operating modes — SC charging and discharging. Theoretical assumptions are proved by the PSIM simulation results and verified experimentally on a 500 W laboratory prototype. The most important results obtained are outlined.

Two-stage quasi-Z-source network based step-up DC/DC converter

This paper presents an optimization possibility of the voltage-fed continuous input current quasi-impedance source inverter (qZSI) by the introduction of the two-stage quasi-Z-source network (qZS-network). The two-stage qZS-network could be derived by the adding of one diode, one inductor and two capacitors to the traditional qZSI. The proposed two-stage qZSI inherits all the advantages of the traditional solution (voltage boost and buck functions in a single stage, continuous input current and improved reliability). Moreover, the proposed solution features over 30% shoot-through duty cycle reduction for the same voltage boost factor as compared to the conventional qZSI. Theoretical analysis of the two-stage qZSI in shoot-through and non-shoot-through operating modes is presented. The proposed and traditional qZS-networks are compared. A prototype has been built to verify the theoretical assumptions. The experimental results are presented and analyzed. Finally, a further optimization method of the proposed two-stage qZS-network is discussed.

Analysis and evaluation of PWM and PSM shoot-through control methods for voltage-fed qZSI based DC/DC converters

Tim paper compares and analyzes two control methods (pulse width and phase shift modulation) for a new type of step-up DC/DC converters with galvanic isolation — the quasi-Z-source inverter (qZSI) based DC/DC converter. The proposed converter is suitable for applications, where the wide range of voltage gain is demanded, e.g. with renewable energy sources (fuel cells, photovoltaic cells), in telecom, aerospace and some other applications. For the verification of theoretical assumptions the converter prototype was assembled and tested. Experimental waveforms are compared and discussed.