Mark-M. Bakran

A new HVDC-DC converter with inherent fault clearing capability

For the upcoming need to transfer bulk power over long onshore distances, HVDC power transmission is the preferred choice. However, components like HVDC-DC converters and a protection concept for DC line faults present challenges, that still have to be solved. As up today, the sections of a segmented DC transmission corridor would still be linked via an AC connection, leading to high transformation losses, and high investment costs. With the newly presented HVDC-DC auto transformer it is possible to directly link two DC lines with different voltage levels. In this paper the ability of this HVDC-DC converter to interrupt DC faults is investigated and compared to the state of the art topology of linking two DC lines via an AC connection.

A new family of modular IGBT converters for traction applications

Electrical locomotives and trains are nowadays driven by asynchronous motors, which are fed by voltage source inverters. The IGBT two level inverter allows a standardization of the topology and the control strategy over the whole power and voltage range. However, different application conditions (cooling, dc-link voltage, power range) lead to different converters. To allow a flexible converter design with proven components, a family of power electronic building blocks was developed, which uses 3.3 kV and 6.5 kV IGBT and achieves an output power of up to 3 MW

High power HVDC-DC converters for the interconnection of HVDC lines with different line topologies

The structural change in energy generation and distribution will demand that large amounts of power are transported over long onshore distances. High Voltage Direct Current (HVDC) power transmission is most suitable for that task since, compared to High Voltage Alternating Current (HVAC) power transmission, there are no stability issues and the transmission losses are much lower. However the junction points of a segmented HVDC transmission corridor still have to be realized as AC nodes, since missing components, like DC breakers and or efficient HVDC-DC converters prevent the direct interconnection of transmission segments to a radial or even meshed DC grid. With the new HVDC auto transformer topology the direct interconnection of HVDC lines with different voltage levels becomes feasible. In this paper the ability of this new HVDC-DC converter topology to connect different DC line topologies and to preserve the transmission redundancy in case of a DC pole malfunction is investigated.

Comparison of multisystem traction converters for high-power locomotives

The European railways are characterized by a wide range of supply voltage systems. To allow flexible operation of electrical locomotives and short stops at system borders, multisystem locomotives are necessary. The paper gives a comparison of different solutions for multisystem converters and introduces the most promising concept based on the latest high-power IGBT technology.

Challenges in using the latest generation of IGBTs in traction converters

Summary The voltage class 6.5kV was the last step to now cover completely the whole range of voltages for traction starting with 1.7kV and 3.3kV. This lead to the general introduction of the IGBT across the whole power range of traction. In first IGBT generations the Non Punch Through design dominated here. The latest generation of IGBTs feature characteristics like field-stop design or trench design. Thus high cosmic ray withstand capability can be combined with low VCesat. For the high-power high-voltage application as used in traction, the introduction of the field stop leads to a significant change in the switching behavior compared to the conventional NPT-design. It will be shown how the IGBT and diode turn-off characteristics change and how sensitive it is to parasitic circuit characteristics. Especially in high-power circuits with relatively large stray inductances, this is a device and application challenge. Further more it will be shown that the IGBT overvoltage during turn-off transients can be controlled only by using a highly dynamic gate driver. Since no active control ofthe diode turn-offis possible, the peak-voltage must be limited by appropriate circuit and device design. For new generations of IGBT and diode, this behavior should be considered carefully by the semiconductor development.

Design and Control of Fault-Tolerant Nonisolated Multiphase Multilevel DC–DC Converters for Automotive Power Systems

In this paper, a bidirectional, nonisolated dc-dc converter with several interleaved phases of multilevel modules for dual low-voltage automotive power systems is presented. Instead of using a two-level stage with short-circuit protection elements, a three-level module in a multiphase structure is proposed to achieve improved fault-tolerance. The dimensioning of the required flying capacitor for multilevel dc-dc converters is described. Further, benefits such as ripple reduction, automatic fault current limitation, and enhanced efficiency are achieved. Moreover, the control strategy for normal operation including the stability of the flying capacitor voltage as well as reconfiguration after semiconductor open- and short-circuit failure for ongoing degraded operation are explained.

Next generation of IGBT-modules applied to high power traction

Modern high power traction converters are equipped with IGBT-modules. For a reliable operation the modules have to fulfil the following requirements: High junction temperature limit, large safe operating area, high surge current capability and sufficient thermal cycling capability. In this paper current and next generation of IGBT modules will be characterised regarding the first three aspects.

Evolution of IGBT converters for mass transit applications

Since its invention in the early 1980s the IGBT has become the dominant power semiconductor in converters for mass transit applications. The paper describes the evolution of converter technology from special circuit configurations up to todays standard. The special requirements on high power IGBTs for traction are given with respect to electrical characteristics and above all load cycle capability. Various cooling systems, natural cooling, forced air cooling and water cooling compete and differ in converter output power but also in exploiting the thermal load cycle due to differing thermal capacitance. Here they are compared with respect to their performance in mass transit applications. In the end a comparison on basic system aspects involving converter control is given.

Optimized design of a Hybrid-MMC and evaluation of different MMC topologies

This paper investigates the combined use of basic cell types (half and full bridges) in a Modular Multilevel Converter in order to achieve an improved MMC performance. Based on an MMC without any additional features (only considering the power transmission capability), an optimal design is presented for additional capabilities such as DC fault ride-through capability or safe operation during reduced DC voltage. These different MMC configurations are compared to a Half and a Full Bridge MMC with regard to the total cost per transmitted power, which includes semiconductor losses and basic power electronic costs.

Online Junction Temperature Cycle Recording of an IGBT Power Module in a Hybrid Car

The accuracy of the lifetime calculation approach of IGBT power modules used in hybrid-electric powertrains suffers greatly from the inaccurate knowledge of application typical load-profiles. To verify the theoretical load-profiles with data from the field this paper presents a concept to record all junction temperature cycles of an IGBT power module during its operation in a test vehicle. For this purpose the IGBT junction temperature is measured with a modified gate driver that determines the temperature sensitive IGBT internal gate resistor by superimposing the negative gate voltage with a high-frequency identification signal. An integrated control unit manages the measurement during the regular switching operation, the exchange of data with the system controller, and the automatic calibration of the sensor system. To calculate and store temperature cycles on a microcontroller an online Rainflow counting algorithm was developed. The special feature of this algorithm is a very accurate extraction of lifetime relevant information with a significantly reduced calculation and storage effort. Until now the recording concept could be realized and tested within a laboratory voltage source inverter. Currently the IGBT driver with integrated junction temperature measurement and the online cycle recording algorithm is integrated in the voltage source inverter of first test vehicles. Such research will provide representative load-profiles to verify and optimize the theoretical load-profiles used in today’s lifetime calculation.