Tanel Jalakas

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.

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.

Development of 50-kW Isolated DC/DC Converter with High-Voltage IGBTs

The 6.5 kV insulated gate bipolar transistor (IGBT) is a new promising power device for high-voltage high-power applications. Due to its increased voltage blocking capability, the new HV IGBT can serve as a good replacement for GTO and IGCT thyristors in medium or medium-to-high power applications. One of its general application fields is railway traction. The paper discusses design and development considerations of the 50-kW auxiliary power supply to be used in 3.0 kV DC commuter trains. Focus is on the implementation of 6.5 kV IGBTs in the primary inverter of APS to improve overall power density, system integrity as well as reliability of the whole system. For instance, topology selection, analysis and simulation of functional blocks of a converter for different operation points are described. A prototype of half-bridge isolated DC/DC converter with two 6.5 kV 200 A IGBT transistors was designed and built. Some design considerations are specified in the paper.

Development of Auxiliary Power Supplies for the 3.0 kV DC Rolling Stock

The paper discusses design and development problems of auxiliary power supplies (APS) with output powers up to 100 kW to be used in 3.0 kV DC commuter trains. Focus is on the implementation of 6.5 kV IGBTs in IHVM of APS. Using single 6.5 kV IGBT module instead of several series-connected IGBTs or even converters helps to achieve more reliable, efficient, compact and lightweight design than ever. For the APS with output power up to 100 kW, the simple half-bridge topology and two 200 A 6.5 kV IGBTs (one for the TOP and one for the BOT switch) it is sufficient to fulfill all the design requirements. Given paper generally deals with topology selection, analysis of switch losses and cooling of HV IGBT as well as with control and protection of the new power supply. Some generalizations and practical considerations are given.

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.

QZSI DC/DC converters in input-series output-parallel connection for distributed generation

This paper presents the configuration and control strategy for an input-series- and output-parallel-(ISOP) connected isolated DC/DC converter. The constituent modules are voltage-fed quasi-Z-source inverters with a single-phase isolation transformer and a voltage doubler rectifier. Experimental measurements with common duty cycle in open loop operation mode are shown in order to observe divergence of the system caused by the parasitic elements of the converters. In order to ensure the proper operation of the system, inverters input voltage sharing must be ensured. The control strategy is based on a common voltage control loop to regulate the output voltage and the input voltage balancing is ensured by means of the addition of a voltage control loop in the remaining converters.

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

This paper presents a new step-up DC/DC converter topology with high-frequency isolation intended for residential fuel cell power systems. In contrast to traditional voltage source converters, the proposed topology utilizes the impedance network represented by a combination of two inductors and two capacitors on the input side of the DC/DC converter. Due to the specific feature of boosting input voltage by introducing a shoot-through operation mode, the new converter provides a more reliable, simpler and cheaper solution than offered by those recently available for residential fuel cell power systems. The paper describes the design methodology, analyzes the experimental results and discusses the optimization possibilities of the proposed topology.

Feasibility study of half- and full-bridge isolated DC/DC converters in high-voltage high-power applications

This paper discusses the half- and full-bridge DC/DC converter topologies for high-power (200 kW) high-voltage (3.6 kV) applications. Focus is on the primary part of these topologies, i.e. the feasibility of replacement of two high-voltage IGBTs in the full-bridge by two high-voltage film capacitors in the half-bridge. The implementation of a half-bridge topology will lead to a sufficient simplification of a power scheme layout as well as control and protection algorithms. The full-bridge topology gives a clear advantage of the twofold reduced current of inverter switches, thus providing a possibility of implementation of smaller devices for the same transferred power as compared to a half-bridge.

Electric vehicle fast charger high voltage input multiport converter topology analysis

This paper describes a novel topology for a multiport electric vehicle battery charging converter. Due to high energy demand and high input currents, a fast-charging station is placed close to the substation that contains a low frequency transformer. Inside the fast-charging station, an intermediate DC-bus connects energy storages, a supply grid rectifier and charging converters. Low voltage (570 V) causes high currents and results in high losses at busbars, magnetic components and semiconductor devices. We propose a high voltage input multiport converter topology with a high frequency isolation transformer for a fast charger of an electric vehicle. High input voltage enables currents and conduction losses to be kept low in the charging converter until the very last conversion stage that is connected to the electric vehicle battery. Also, the dimensions of magnetic components are reduced due to high frequency. Grid-side converter is realized using the back to back cascaded converter topology. Charging converters can be realized with the current doubler rectifier topology and bidirectional with a controllable full bridge rectifier/inverter as in this operational mode it has an advantage over a current doubler. The quasi Z source could be used as a filter/boost circuit. The proposed charging station topology was verified by computer simulations.

Analysis of implementation possibilities and benefits of three-level half-bridge NPC topology in static auxiliary converters for rolling stock

This paper is focused on the high-voltage (≥2 kV) high-power (≥20 kW) isolated DC/DC converters for the rolling stock applications. The 3.3 kV IGBT based three-level half-bridge neutral point clamped (NPC) inverter topology was analyzed as an alternative to the two-level half-bridge with 6.5 kV IGBTs. The properties of primary switches, theirs selection procedure as well as inverter loss distribution and design challenges of both concurrent topologies were evaluated and compared.