Marek Adamowicz

New type T-Source inverter

This paper presents different topologies of voltage inverters with alternative input LC networks. The basic topology is known in the literature as a Z-source inverter (ZSI). Alternative passive networks were named by the authors as T-sources. T-source inverter has fewer reactive components in comparison to conventional Z-source inverter. The most significant advantage of the T-source inverter (TSI) is its use of a common voltage source of the passive arrangement. Experimental results for the TSI are in agreement with theoretical and simulated prediction.

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.

LCCT-Z-Source inverters

Many renewable generation units (e.g. PVs, fuel cells, small wind turbines) require integrated DC-AC converters providing efficient high step-up power conversion. On the basis of recent developments in impedance source (Z-source) inverters the present paper proposes an integration of quasi-Z-source inverter (qZSI) with a built-in high frequency transformer. Two new type LCCT-Z-Source inverters are presented by author. Proposed inverters characterize continuous input current, improved relationship between boost coefficient and modulation index and improved EMI performance. Application of four element (Inductor — Capacitor — Capacitor — Transformer) LCCT impedance network provides higher voltage gain than obtained in quasi-Z-source inverter. The advantage of proposed topology over other recently developed trans Z-source inverters (TZSI) is that two built-in capacitors block DC currents in transformer windings and prevents core saturation. Simulation and experimental results are shown to verify the proposed topologies.

Performance comparison of SiC Schottky diodes and silicon ultra fast recovery diodes

Advanced control systems combined with high speed gate driver circuits enable extremely high rate of change of power devices voltages, up to hundreds of kV/us. Short rise times of power devices could cause significant EMC problems, which are unacceptable in majority of power electronics applications. It is known that voltage variations during diode switch-off depend on how long it takes for the charge stored near the p-n junction to be recovered during voltage reversing. In fast switching applications good forward recovery characteristics are needed. The silicon carbide (SiC) diodes characterize almost zero reverse recovery charge. However the lossless operation in connection with extremely high dv/dt could cause the SiC diodes less effective in damping the voltage ringing. The compromise between high efficiency and low EMI emission is therefore the actual aim of the research. The paper compares the static and dynamic characteristics of ultra fast silicon (Si) and SiC Schottky diodes and presents the study of the mechanism of parasitic high frequency oscillations during turn-off transient.

Evaluation of SiC JFETs and SiC Schottky diodes for wind generation systems

Recent achievements related to the use of silicon carbide (SiC) devices in wind generation systems (WGSs) are presented in the paper. With applications in WGS, the choice of high-temperature, high-frequency SiC devices reduces the volume and size of power electronic converters, particularly their passive filters which dominate the weigh of the converter. The SiC-based power converters are expected to have three times lower losses than silicon-based AC-DC-AC converters currently applied to the wind turbines. Efficiency improvement can be particularly significant at low wind speeds where the WGS operates most of the time. The paper presents results obtained for the 30A 1200V generator side SiC JFET-based DC-AC converter with a switching frequency 100 kHz. The prototype was worked out and investigated at the Gdansk University of Technology. A special attention is paid to the performance of two stage DC-coupled gate driver circuit. Static and dynamic characteristics of 1200V SiC devices (JFETs and Schottky diodes) used in the WGS DC-AC converter are investigated. An approach to suppression of undesirable oscillations/EMI problems caused by the high dv/dt of SiC devices is presented.

New Alternative Passive Networks to Improve the Range Output Voltage Regulation of the PWM Inverters

This paper presents different topologies of buck-boost converters with passive input networks that have alternative topologies; this is known in the literature as a Z-source inverter. Alternative passive networks were named by the authors as T-inverters; these improve output voltage regulation of the PWM inverters. T-inverter has fewer reactive components in comparison to conventional Z-source inverter. The most significant advantage of the T-inverter is its use of a common voltage source of the passive arrangement. This solves many problems involving electromagnetic compatibility which are present in the Z-source inverter. Experimental results for the T-inverter are in agreement with theoretical and simulated predictions.

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.

High step-up continuous input current LCCT-Z-source inverters for fuel cells

Z-source inverters (ZSIs) are suited for applications which require a large range of voltage gain, such as in fuel cells. The present paper extends the concept of ZSIs. New type high step-up LCCT-Z-source inverter dedicated for fuel cells is proposed in the paper. Compared to recently proposed modifications of basic Z-source inverter the new topology has the advantages of available continuous input current, improved boost ratio and simple topology. Thanks to application of transformer with turns ratio higher than one the proposed LCCT-Z-source can operate with lower shoot-through ratio and higher modulation index compared to ZSI. The existence of two built-in DC-current-blocking capacitors connected in series with transformer windings prevents the transformer core from saturation. Simulation and experimental results are provided to verify the reliability of the proposed topology.

CCM and DCM operation analysis of cascaded quasi-Z-source inverter

This paper presents the steady-state analysis of the voltage-fed quasi-Z-source inverter (qZSI) with cascaded (two-stage) quasi-Z-source network (qZS-network). Cascaded qZS-network is derived by the adding of one diode, one inductor and two capacitors to the traditional qZSI. Main focus of this paper is on mathematical models of the cascaded qZS-converter. Static models were elaborated and analyzed for the continuous (CCM) and discontinuous conduction mode (DCM) of the converter. In order to verify the theoretical assumptions a prototype has been built. The experimental results are presented and analyzed.

Application of wireless communication to small WECS with induction generator

Wind energy conversion systems (WECS) seem to be self-evident elements of the future smart grids. Among many generator types the squirrel cage induction generator (SCIG) characterizes robustness and low cost. A full-scale power converter can perform smooth grid connection over wide speed range of multiple-stage geared SCIG. Increasing number of sensors can improve the WECS control and diagnostics but increasing number of thin wires i.e. between a nacelle and the converter housing can reduce reliability. A wireless communication using ADF7020 transceiver for data acquisition and transmission is proposed in the paper.