Mario Schweizer

SiC versus Si—Evaluation of Potentials for Performance Improvement of Inverter and DC–DC Converter Systems by SiC Power Semiconductors

Switching devices based on wide bandgap materials such as silicon carbide (SiC) offer a significant performance improvement on the switch level (specific on resistance, etc.) compared with Si devices. Well-known examples are SiC diodes employed, for example, in inverter drives with high switching frequencies. In this paper, the impact on the system-level performance, i.e., efficiency, power density, etc., of industrial inverter drives and of dc-dc converter resulting from the new SiC devices is evaluated based on analytical optimization procedures and prototype systems. There, normally on JFETs by SiCED and normally off JFETs by SemiSouth are considered.

Design and Implementation of a Highly Efficient Three-Level T-Type Converter for Low-Voltage Applications

The demand for lightweight converters with high control performance and low acoustic noise led to an increase in switching frequencies of hard switched two-level low-voltage 3-phase converters over the last years. For high switching frequencies, converter efficiency suffers and can be kept high only by employing cost intensive switch technology such as SiC diodes or CoolMOS switches; therefore, conventional IGBT technology still prevails. In this paper, the alternative of using three-level converters for low-voltage applications is addressed. The performance and the competitiveness of the three-level T-type converter (3LT2C) is analyzed in detail and underlined with a hardware prototype. The 3LT2 C basically combines the positive aspects of the two-level converter such as low conduction losses, small part count and a simple operation principle with the advantages of the three-level converter such as low switching losses and superior output voltage quality. It is, therefore, considered to be a real alternative to two-level converters for certain low-voltage applications.

Optimal Design of LCL Harmonic Filters for Three-Phase PFC Rectifiers

Inductive components such as line filter inductors or transformers occupy a significant amount of space in todays power electronic systems, and furthermore, considerable losses occur in these components. A main application of filter inductors are EMI filters, as e.g. employed for the attenuation of switching frequency harmonics of PFC rectifier systems. In this paper a design procedure for the mains side LCL filter of an active three-phase rectifier is introduced. The procedure is based on a generic optimization approach, which guarantees a low volume and/or low losses. Different designs are calculated to show the trade-off between filter volume and filter losses. The design procedure is verified by experimental measurements.

Comparison of the chip area usage of 2-level and 3-level voltage source converter topologies

In the low voltage converter range, 3-phase 3-level VSC topologies are not wide spread in industry because of the increased part count and higher costs, although they are more efficient for higher switching frequencies. In this paper an alternative 3-level topology referred to as T-type is presented, which is very high efficient for medium switching frequencies (4–20 kHz). Additionally, it is shown that the total silicon chip area of a 3-level topology can be lower than in a 2-level topology since the losses are distributed over more components leading to only a small increase in the junction temperature. This allows for the design of a chip area and cost optimized 3-level bridge leg module for the mass market.

Comparative Evaluation of Advanced Three-Phase Three-Level Inverter/Converter Topologies Against Two-Level Systems

Efficient energy conversion in low-voltage applications has gained more attention due to increasing energy costs and environmental issues. Accordingly, three-level converters have been discussed as an alternative to the standard two-level voltage-source converter because they offer an increased efficiency at higher switching frequencies. From a system perspective, the benefits of using three-level converters are not only limited to the converter itself, but there are additional positive impacts on the surrounding such as on the load machine losses or on the electromagnetic interference input filter volume. In this paper, a holistic comparison of advanced three-level topologies against the two-level topology is given. Simple analytical calculations and measurements show the benefits and the optimization potential concerning several aspects, such as the necessary semiconductor chip area, the harmonic losses in the load machine and in filter components, and the volume of passive components.

Towards a 99% efficient three-phase buck-type PFC rectifier for 400 V DC distribution systems

In telecom applications, the vision for a total power conversion efficiency from the mains to the output of PoL converters of 95% demands for an optimization of every conversion step, i.e. the PFC rectifier front-end should show an outstanding efficiency in the range of 99%. For recently discussed 400 V DC distribution bus voltages a buck-type PFC rectifier is a logical solution. In this paper, an efficiency-optimized, nearly 99% efficient, 5 kW three-phase buck-type PFC rectifier with 400 V output is presented. Methods for calculating losses of all components are described, and are used to optimize the converter design for efficiency at full load. Special attention is paid to semiconductor losses, which are shown to be dominant, with the parasitic device capacitance losses being a significant component. A prototype of the proposed rectifier is constructed which verifies the accuracy of the models used for loss calculation and optimization.

Conceptualization and Multiobjective Optimization of the Electric System of an Airborne Wind Turbine

Airborne wind turbines (AWTs) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power kite flying at high speed perpendicular to the wind. On the kite are mounted a turbine, an electrical generator, and a power electronics converter. The electric power generated is transmitted via a medium voltage cable to the ground. Because of the high flight speed of the power kite, several times the actual wind speed, only a very small swept area of the turbine is required according to Betzs Law and/or a turbine of low weight for the generation of a given electric power. Moreover, because of the high turbine rotational speed, no gear transmission is necessary and the size of the generator is also reduced. For takeoff and landing of the power kite, the turbines act as propellers and the generators as motors, i.e., electric power is supplied so that the system can be maneuvered like a helicopter. In the present work, the configuration of power electronics converters for the implementation of a 100 kW AWT is considered. The major aspect here is the trade-off between power-to-weight ratio (W/kg) and efficiency. The dependence of cable weight and cable losses on the voltage level of power transmission is investigated, and a comparison is made between low voltage (LV) and medium voltage (MV) versions of generators. Furthermore, the interdependence of the weight and efficiency of a bidirectional dual active bridge dc-dc converter for coupling the rectified output voltage of a LV generator to the MV cable is discussed. On the basis of this discussion, the concept offering the best possible compromise of weight and efficiency in the power electronics system is selected and a model of the control behavior is derived for both the power flow directions. A control structure is then proposed and dimensioned. Furthermore, questions of electromagnetic compatibility and electrical safety are treated. In conclusion, the essential results of this paper are summarized, and an outlook on future research is given. To enable the reader to make simplified calculations and a comparison of a CWT with an AWT, the aerodynamic fundamentals of both the systems are summarized in highly simplified form in an Appendix, and numerical values are given for the 100 kW system discussed in this paper.

Comparison and implementation of a 3-level NPC voltage link back-to-back converter with SiC and Si diodes

This paper presents a high efficiency 10 kVA high-frequency input and output Si IGBT and SiC Schottky diode 3-level neutral point clamped voltage dc-link back-to-back converter (3LNPC-VLBBC). A switching frequency of 48 kHz makes the converter suitable for driving high-speed and low-inductive machines. A detailed loss analysis reveals that only four of the six diodes in a 3-level bridge-leg have to be replaced by SiC diodes to enable high efficiency operation if an appropriate modulation scheme is used. A comparison with an All-Si 3-level converter shows a reduction of the semiconductor losses by 10% at the nominal operating point. In addition, a semiconductor chip area based comparison is presented, showing the chip area partitioning of the individual semiconductor types and the corresponding costs for different implementations. The payback time for the additional costs resulting from replacing the Si diodes in the 3-level converter by SiC diodes due to energy savings is estimated. Finally, experimental results of the prototype are provided.

Conceptualization and multi-objective optimization of the electric system of an Airborne Wind Turbine

Airborne Wind Turbines (AWT) represent a radically new and fascinating concept for future harnessing of wind power. This concept consists of realizing only the blades of a conventional wind turbine (CWT) in the form of a power kite flying at high speed perpendicular to the wind. On the kite are mounted a turbine, an electrical generator and a power electronics converter. The electric power generated is transmitted via a medium voltage cable to the ground. Because of the high flight speed of the power kite, several times the actual wind speed, only a very small swept area of the turbine is required according to Betzs Law and/or a turbine of low weight for the generation of a given electric power. Moreover, because of the high turbine rotational speed, no gear transmission is necessary and the size of the generator is also reduced. For takeoff and landing of the power kite, the turbines act as propellers and the generators as motors, i.e. electric power is supplied so that the system can be maneuvered like a helicopter. In the present work the configuration of power electronics converters for the implementation of a 100kW AWT is considered. The major aspect here is the trade-off between power-to-weight ratio (W/kg) and efficiency. The dependence of cable weight and cable losses on the voltage level of power transmission is investigated, and a comparison made of low voltage (LV) and medium voltage (MV) versions of generators. Furthermore, the interdependence of the weight and efficiency of a bidirectional Dual Active Bridge dc-dc converter for coupling the rectified output voltage of a LV generator to the MV cable is discussed. Based on this, the concept offering the best possible compromise of weight and efficiency in the power electronics system is selected and a model of the control behavior is derived for both power flow directions. A control structure is then proposed and dimensioned. Furthermore, questions of electromagnetic compatibility and electrical safety are treated. In conclusion, the essential results of the work are summarized and an outlook on future research is given. To enable the reader to make simplified calculations and a comparison of a CWT with an AWT, the aerodynamic fundamentals of both systems are summarized in highly simplified form in an Appendix, and numerical values are given for the 100kW system discussed in this work.

Comparison of 2- and 3-level active filters with enhanced bridge-leg loss distribution

In this paper an efficiency comparison between 3-phase shunt active filters derived from the 2-level VSC, the 3-level NPC, Active NPC (A-NPC) and the T-type VSC is presented. In order to address the loss distribution issue of the 3-level topologies, while keeping the efficiency of the system high, a space vector modulation scheme incorporating a special clamping of the phase is proposed. It is shown that 3-level active filters can have their losses well distributed over the chip dies, leading to only a small difference in their operating temperatures. Additionally, a semiconductor area based comparison is used to further evaluate the studied active filter systems. Finally, experimental results obtained with a 12kVAr/48kHz 3-level NPC based shunt active filter employing custom SiC power modules are presented in order to demonstrate the performance and feasibility of this solution.