Uwe Drofenik

PWM Converter Power Density Barriers

Power density of power electronic converters in different applications has roughly doubled every 10 years since 1970. Behind this trajectory was the continuous advancement of power semiconductor device technology allowing an increase of converter switching frequencies by a factor of 10 every decade. However, todays cooling concepts, and passive components and wire bond interconnection technologies could be major barriers for a continuation of this trend. For identifying and quantifying such technological barriers this paper investigates the volume of the cooling system and of the main passive components for the basic forms of power electronics energy conversion in dependency of the switching frequency and determines switching frequencies minimizing the total volume. The analysis is for 5 kW rated output power, high performance air cooling, advanced power semiconductors, and single systems in all cases. A power density limit of 28 kW/dm3@300 kHz is calculated for an isolated DC-DC converter considering only transformer, output inductor and heat sink volume. For single-phase AC-DC conversion a general limit of 35 kW/dm3 results from the DC link capacitor required for buffering the power fluctuating with twice the mains frequency. For a three-phase unity power factor PWM rectifier the limit is 45 kW/dm3@810 kHz just taking into account EMI filter and cooling system. For the sparse matrix converter the limiting components are the input EMI filter and the common mode output inductor; the power density limit is 71 kW/dm3@50 kHz when not considering the cooling system. The calculated power density limits highlight the major importance of broadening the scope of research in power electronics from traditional areas like converter topologies, and modulation and control concepts to cooling systems, high frequency electromagnetics, interconnection technology, multi-functional integration, packaging and multi-domain modeling and simulation to ensure further advancement of the field along the power density trajectory.

Comparative evaluation of three-phase high-power-factor AC-DC converter concepts for application in future More Electric Aircraft

A passive 12-pulse rectifier system, a two-level, and a three-level active three-phase pulsewidth-modulation (PWM) rectifier system are analyzed for supplying the dc-voltage link of a 5-kW variable-speed hydraulic pump drive of an electro-hydrostatic actuator to be employed in future More Electric Aircraft. Weight, volume, and efficiency of the concepts are compared for an input phase voltage range of 98-132 V and an input frequency range of 400-800 Hz. The 12-pulse system shows advantages concerning volume, efficiency, and complexity but is characterized by a high system weight. Accordingly, the three-level PWM rectifier is identified as the most advantageous solution. Finally, a novel extension of the 12-pulse rectifier system by turn-off power semiconductors is proposed which allows a control of the output voltage and, therefore, eliminates the dependency on the mains and load condition which constitutes a main drawback of the passive concept.

Discontinuous Space-Vector Modulation for Three-Level PWM Rectifiers

This paper presents the implementation and experimental verification of two discontinuous pulsewidth modulation (DPWM) methods for three-phase, three-level rectifiers. DPWMs features, such as improved waveform quality, lower switching losses, reduced ac-side passive component size, are investigated and compared to the conventional continuous pulsewidth modulation (CPWM). These features allow higher power density and/or efficiency to be achieved and are important targets for the next generation of power rectifiers. The implementation of the two DPWM strategies is explained by means of space-vectors representation and modulation functions. A detailed analysis of both ac-side and dc-side current waveforms is presented, and there is excellent agreement between the analytical, simulated and experimental results for the mains current ripple amplitude and output center-point current over the practical modulation range. Finally, the control of the center-point voltage is discussed.

New physical model for lifetime estimation of power modules

In this paper a physical model for lifetime estimation of standard power modules is proposed. The lifetime prediction is based on the assumption that the solder interconnections are the weakest part of the module assembly and that the failure cause is the inelastic deformation energy accumulated within the solder material. Unlike the well-known Coffin-Manson model, the proposed model can be used to physically explain the dependency of lifetime on the various properties of a temperature profile i.e. frequency, dwell-ramp time, minimum/maximum temperature. The model is based on Clechs algorithm for simulation of stress-strain solder response under cyclical thermal loading and on the solder deformation mechanism map used to define the dominant failure mechanism under observed stress-temperature conditions. Either accelerated cycling tests or existing field databases are needed to parameterize the model. To verify the approach, the results of power cycling tests for a high power IGBT module found in literature are applied and the impacts of two mission profiles on the module lifetime are examined.

New wide input voltage range three-phase unity power factor rectifier formed by integration of a three-switch buck-derived front-end and a DC/DC boost converter output stage

A new three-phase unity power factor rectifier with a three-switch buck-derived input stage and a DC/DC boost converter output stage is presented. This system has a wide input voltage range and a continuous sinusoidal time behavior of the input currents lying in phase with the input voltages which is also guaranteed in case of a failure in one phase of the mains. The input currents are controlled using a switching state sequence showing minimum switching losses. A multi-loop system control is realized by an outer output voltage controller and an inner-loop buck+boost inductor current controller. Furthermore active damping of the input filter resonance is provided. For increasing the output power of the system a parallel connection of two interleaved units is proposed. There, a low input current ripple is achieved, and the cut-off frequency of the input filter can be shifted to higher frequencies (resulting in improved control dynamics and a more compact design downsizing of the inductors and of the input filter).

Comparative evaluation of three-phase high power factor AC-DC converter concepts for application in future more electric aircrafts

A passive 12-pulse rectifier system, a two-level, and a three-level active three-phase PWM rectifier system are analyzed for supplying the DC voltage link of a 5 kW variable speed hydraulic pump drive of an electro-hydrostatic actuator to be employed in future more electric aircrafts. Weight, volume and efficiency of the concepts are compared for an input phase voltage range of 98 V to 132 V and an input frequency range of 400 Hz to 800 Hz. The 12-pulse system shows advantages concerning volume, efficiency and complexity but is characterized by a high system weight. Accordingly, the three-level PWM rectifier is identified as most advantageous solution. Finally, a novel extension of the 12-pulse rectifier system by turn-off power semiconductors is proposed which allows a control of the output voltage and therefore eliminates the dependency on the mains and load condition which constitutes a main drawback of the passive concept.

Current handling capability of the neutral point of a three-phase/switch/level boost-type PWM (VIENNA) rectifier

In this paper the stationary operational behavior of a three-phase/switch/level PWM rectifier is analyzed for asymmetrical loading of the output partial voltages. For the considerations a sinusoidal mains current shape, resistive behavior of the mains current fundamental and constant pulse frequency are assumed. Based on analytical calculations it is shown that the average value of the neutral point current (which has to be formed for asymmetrical load) has an approximately linear dependency on the distribution of the overall relative on-time of the switching states of the system being redundant concerning the voltage formation between begin and end of a pulse half interval. The maximum admissible load of the neutral point (capacitive output voltage center point) is calculated. This load is given as a function of the amplitude of the mains current and the voltage transfer ratio of the system. The calculations are checked by results of a digital simulation of the system behavior. Furthermore, the increase of the rms value of the ripple of the mains current of the rectifier is analyzed as it results in forming of an average value of the neutral point current. As a basis for comparison, the ripple rms value is used which results in harmonic-(sub)optimal control and negligible average value of the neutral point current. Finally, the current stress on the power semiconductors and on the output capacitors of the system are compiled in the form of diagrams which can be applied directly for dimensioning the system.

Interactive Power Electronics Seminar (iPES)-a web-based introductory power electronics course employing Java-applets

This paper introduces the Interactive Power Electronics Seminar-iPES-a new software for teaching a basic course on power electronic circuits and systems. iPES is constituted by HTML text with Java-applets for interactive animation, circuit design and simulation and visualization of electromagnetic fields and is comprised of an easy-to-use self-explaining graphical user interface. The software does need just a standard web-browser, i.e. no installations are required. iPES can be accessed via the World Wide Web or from a CD-ROM in a stand-alone PC by students and professionals. Since the Java applets are simple to handle, a student can immediately start working and can fully concentrate on the theory of a problem. Due to the underlying software technology iPES is very flexible and can be used for on-line learning and be easily integrated into an e-learning platform. The aim of this paper is to give an introduction to the iPES-project and to show different areas covered. The e-learning software is available at no cost in English, German, Japanese and Korean. More translations, e.g. into Spanish and French will be available in the future. The web page is continuously updated in four-week intervals.

12-pulse rectifier for more electric aircraft applications

A high power density 10 kW three-phase 12-pulse rectifier is analyzed for applications in future more electric aircrafts. The experimental results, which are in good accordance with the theory, show high efficiency and low input current harmonics for a wide operating range. Furthermore, two novel rectifier topologies, which are formed by combining the passive 12-pulse rectifier with a boost stage on the DC side are proposed. This allows to guarantee a constant output voltage and/or to overcome the problem of the dependency of output voltage on the mains voltage amplitude and output power level.

Comparison of not synchronized sawtooth carrier and synchronized triangular carrier phase current control for the VIENNA rectifier I

Integrated control circuits being available for the input current control of single-phase power factor correctors are frequently applied also for realizing a simple current control for each phase of a three-phase PWM rectifier system. There, the input currents are controlled independently although the three phases are mutually coupled, i.e., the sum of the phase currents is forced to zero for missing connections between the mains star point and the output voltage center point. However, ignoring of the coupling of the three phases results in increased amplitudes of harmonics with switching frequency and/or in a significantly higher ripple of the rectifier input current. This is shown in this paper by a detailed analysis of different current control concepts for a three-phase three-switch three-level boost-type PWM rectifier (VIENNA Rectifier I) with unity power factor. The theoretical considerations are verified by digital simulations and an experimental analysis of a laboratory prototype and are valid in general for three-phase boost-type voltage DC link PWM rectifier systems.