Janis Zakis

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.

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.

Quasi-Z-source half-bridge DC-DC converter for photovoltaic applications

This paper presents a novel quasi-Z-source halfbridge galvanically isolated DC-DC converter intended for the photovoltaic applications. The topology could be envisioned as an alternative to the boost half-bridge DC-DC converter but the benefit of its symmetric structure reduces the threat of transformer saturation due to the dc flux. The proposed converter features the continuous input current and could be used either with one or two input voltage sources.

New high-gain step-up DC/DC converter with high-frequency isolation

This paper presents a new step-up DC/DC converter topology. The converter is intended for applications that require a high gain of the input voltage and galvanic isolation, i.e. power conditioning systems for alternative energy sources such as fuel cells. The operation principle of the converter is explained by help of a steady state analysis. Simulation results are presented and analyzed. Finally, the experimental results are provided and a modification possibility of the proposed converter is discussed.

Dynamic behaviour of qZS-based bi-directional DC/DC converter in supercapacitor charging mode

This paper presents a bi-directional quasi-Z-source inverter (qZSI) based DC/DC converter for supercapacitor (SC) interfacing in high power applications. In the SC charging mode the proposed converter acts as a conventional VSI based step-down converter, but in the energy recovery mode it acts as a qZSI-based step-up DC/DC converter. The paper analyzes and discusses the operation of the converter in the SC charging mode. The analysis of the static model of the converter as well as the Bode diagram are presented. Theoretical results are verified by experimental results on a 500 W prototype converter.

Experimental study of high step-up quasi-Z-source DC-DC converter with synchronous rectification

Quasi-Z-source DC-DC converters have attracted research interest due to their numerous advantages in emerging applications. However, they suffer from relatively low efficiency. This paper presents semiconductor loss breakdown of the quasi-Z-source DC-DC converter to show that conduction losses in semiconductors contribute most to overall losses. Synchronous rectification realized through replacement of diodes with N-channel MOSFETs was proposed to improve the converter efficiency in prior works. Our detailed experimental study of efficiency improvement with synchronous rectification was based on a 250 W prototype. Results were first obtained for replacement of diodes in the primary side only, then in the secondary side only. Finally, a converter that contains only controlled switches was evaluated. Efficiency curves measured were compared with those for the baseline diode-based topology. The experimental study was performed using operating points typical of photovoltaic module integrated converters.

Loss Reduction Method for the Isolated qZS-based DC/DC Converter

Abstract This paper presents an isolated quasi-Z-source inverter-based (qZSI) resonant DC/DC converter. The explanation of selection of the proposed topology is justified. Both the normal and the boost modes are discussed. Theoretical operation waveforms as well as basic expressions for the calculation of currents and voltages are proposed. A 1500 W laboratory prototype was built and experimentally verified at two operation points: that of light-load (300 W) and full-load (1500 W). All the experiments were also carried with resonant circuit and without it. The experimental results as well as performance of proposed qZSI based resonant DC/DC converter laboratory setup are presented and analyzed. Experimental and calculated characteristics showing the dependence of the load voltage and supply current on the load resistance in both modes were presented. The dynamic losses in the transistors were evaluated for the cases with the resonant circuit and without it. The main conclusions based on this study are summarized and the future tasks for development of proposed converter were defined.

Soft-switching capability analysis of a qZSI-based DC/DC converter

This paper analyzes the PWM control method for a new type of step-up DC/DC converters with galvanic isolation - the quasi-Z-source inverter (qZSI) based DC/DC converter. The PWM control method for qZSI with soft-switching capability is proposed and experimentally proved. The operation principles of discussed converter are explained. The experimental verification and analysis of top and bottom IGBTs of inverter bridge has been made. A prototype has been built in the laboratory and experiments are presented to analyse the soft-switching capability in loss reduction.