Liisa Liivik

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.

Synchronous rectification in quasi-Z-source converters: Possibilities and challenges

This paper addresses an approach to improve the efficiency of the quasi-Z-source (qZS) converters. By replacing the qZS diode by the n-channel MOSFET, the power loss over a diode can be reduced in a qZS network. The paper presents operation basics of the approach, analysis and comparison of the power losses of the traditional and proposed designs and experimental validation of the theoretical assumptions.

Four Novel PWM Shoot-Through Control Methods for Impedance Source DC-DC Converters

This study proposes four novel pulse width modulation (PWM) shoot-through control methods for impedance source (IS) galvanically isolated DC-DC converters. These methods are derived from a PWM control method with shifted shoot-through introduced by the authors in 2012. In contrast to the baseline solution, where the shoot-through states are generated by the simultaneous conduction of all transistors in the inverter bridge, our new approach is based on the shoot-through generation by one inverter leg. The idea is to increase the number of soft-switched transients and, therefore, decrease the dynamic losses of the front-end inverter. All the proposed approaches are experimentally verified through an insulated-gate bipolar transistor-based IS DC-DC converter. Conclusions are drawn in accordance with the results of the switching loss analysis.

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.

Asymmetrical quasi-Z-source half-bridge DC-DC converters

This paper presents a novel quasi-Z-source half-bridge DC-DC converter family derived by a combination of the single-switch qZS DC-DC converter and the half-bridge galvanically isolated DC-DC converter. The novel topologies have only two active switches and are a cheaper alternative to the galvanically isolated quasi-Z-source DC-DC converters with a full-bridge switching stage. Such promising features as circuit simplicity, low cost, high efficiency, and high reliability are attributed to the new alternative solution. A 200W prototype was assembled and tested. Simulation and experimental results are presented to verify the step-up performance of the topology.

Impedance-source galvanically isolated DC/DC converters: State of the art and future challenges

Impedance-source switched mode converters are an emerging technology in electric energy conversion. They overcome limitations of conventional solutions by the utilization of specific impedance-source networks. Previous review papers cover impedance-source networks. Focus of this paper is on the topologies of the impedance-source galvanically isolated DC/DC converter. These converters are particularly appropriate for distributed generation systems with renewable or alternative energy sources which require input voltage regulation in a wide range. This paper presents a concise review of basic existing topologies for researchers and engineers. All the reviewed topologies of the impedance-source galvanically isolated DC/DC converter are classified by the element that transfers energy from the input to the output: a transformer or a coupled inductor. This classification undoubtedly reveals wide space for further research and the most promising research directions in this field.

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.

Multi-mode quasi-Z-source series resonant DC/DC converter for wide input voltage range applications

This paper examines the quasi-Z-source series resonant DC/DC converter as a candidate topology for the PV module integrated converter (MIC) with an extended input voltage regulation range. The converter features multi-mode operation by combining the shoot-through pulse-width modulation and ordinary phase-shift modulation to realize the boost and buck operating modes, respectively. Our experiments confirmed that the proposed MIC is capable of ensuring the ripple-free output voltage of 400 V within the input voltage range of 10...60 V. In contrast to the traditional series resonant converter, the MIC proposed is characterized by fixed-frequency operation over the entire range of input voltage variations. It requires only generic semiconductor devices and thus is a cost-effective solution.

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

This paper discusses the performance improvement method of the recently popular galvanically isolated quasi-Z-source DC-DC converter. In order to decrease the conduction losses in the quasi-Z-source network and voltage doubler rectifier the replacement of diodes by the N-channel MOSFETs was analyzed. The proposed approach was validated by the computer simulations in PSIM environment with accurate models of the semiconductors based on the device datasheet values. Finally, the power losses and resulting efficiency of the proposed quasi-Z-source DC-DC converter with synchronous rectification were compared to those of the traditional topology.

Comparative Analysis of Semiconductor Power Losses of Galvanically Isolated Quasi-Z-Source and Full-Bridge Boost DC-DC Converters

Abstract This paper compares semiconductor losses of the galvanically isolated quasi-Z-source converter and full-bridge boost DC-DC converter with active clamping circuit. Operation principle of both converters is described. Short design guidelines are provided as well. Results of steady state analysis are used to calculate semiconductor power losses for both converters. Analytical expressions are derived for all types of semiconductor power losses present in these converters. The theoretical results were verified by means of numerical simulation performed in the PSIM simulation software. Its add-on module “Thermal module” was used to estimate semiconductor power losses using the datasheet parameters of the selected semiconductor devices. Results of calculations and simulation study were obtained for four operating points with different input voltage and constant input current to compare performance of the converters in renewable applications, like photovoltaic, where input voltage and power can vary significantly. Power loss breakdown is detailed and its dependence on the converter output power is analyzed. Recommendations are given for the use of the converter topologies in applications with low input voltage and relatively high input current.