Liudmila Smirnova

Study on Oscillations During Short Circuit of MW-Scale IGBT Power Modules by Means of a 6-kA/1.1-kV Nondestructive Testing System

This paper uses a 6-kA/1.1-kV nondestructive testing system for the analysis of the short-circuit behavior of insulated-gate bipolar transistor (IGBT) power modules. A field-programmable gate array enables the definition of control signals to an accuracy of 10 ns. Multiple 1.7-kV/1-kA IGBT power modules displayed severe divergent oscillations, which were subsequently characterized. Experimental tests indicate that nonnegligible circuit stray inductance plays an important role in the divergent oscillations. In addition, the temperature dependence of the transconductance is proposed as an important element in triggering for the oscillations.

Comprehensive investigation on current imbalance among parallel chips inside MW-scale IGBT power modules

With the demands for increasing the power rating and improving reliability level of the high power IGBT modules, there are further needs of understanding how to achieve stable paralleling and identical current sharing between the chips. This paper investigates the stray parameters imbalance among parallel chips inside the 1.7 kV/1 kA high power IGBT modules at different frequencies by Ansys Q3D parastics extractor. The resulted current imbalance is further confirmed by experimental measurement.

Round busbar concept for 30 nH, 1.7 kV, 10 kA IGBT non-destructive short-circuit tester

Design of a Non-Destructive Test (NDT) set-up for short-circuit tests of 1.7 kV, 1 kA IGBT modules is discussed in this paper. The test set-up allows achieving short-circuit current up to 10 kA. The important objective during the design of the test set-up is to minimize the parasitic inductance and assure equal current sharing among the parallel connected devices. Achieving of a low inductance level is very challenging due to the current and voltage ratings, the presence of series and parallel protection systems and the required access for a thermal camera. The parasitic extractor Ansys Q3D is used to estimate the parasitic inductances during the design. A new concept of round-shaped, low inductive busbars for an NDT set-up is proposed. Simulation results verified that both reduction of overall inductance and good uniformity in current sharing among parallel devices are achieved by utilizing a circular symmetry. Experimental validation of the simulation was performed using a preliminary set-up. Further, this concept can be implemented in the design of the busbars for the power converters, where the parallel connection of the switching devices is applied to obtain higher current levels.

Investigation on the short-circuit behavior of an aged IGBT module through a 6 kA/1.1 kV non-destructive testing equipment

This paper describes the design and development of a 6 kA/1.1 kV non-destructive testing system, which aims for short circuit testing of high-power IGBT modules. An ultra-low stray inductance of 37 nH is achieved in the implementation of the tester. An 100 MHz FPGA supervising unit enables 10 ns level control accuracy of the short-circuit duration, protection triggering, and acquisition of the electrical waveforms. Moreover, a protection circuit avoids explosions in case of failure, making the post-failure analysis possible. A case study has been carried out on an aged 1.7 kV IGBT power module. The case study shows the current and voltage waveforms during short-circuit, as well as the current mismatch among six inner sections, which demonstrate the capability and the effectiveness of the proposed setup in the short-circuit aspect reliability studies of MW-scale power modules.

Thermal Analysis of the Laminated Busbar System of a Multilevel Converter

Laminated busbar systems are commonly used in power electronic converters because of their low stray inductance. While the electromagnetic analysis of a busbar system is widely presented in the literature, there is a lack of accurate thermal modeling. In this paper, the thermal analysis of the busbar system is presented. An analytical lumped parameter thermal model (LPTM) of the busbar system is developed. The LPTM is applied to the fast estimation of the mean temperature and temperature-dependent power losses of the busbars by the proposed algorithm. Joule losses produced by nonsinusoidal currents flowing through the busbars in the converter are estimated. The skin and proximity effects, which have a strong influence on the ac resistance of the busbars, are considered in the loss estimation. Thus, a comprehensive electrothermal model of the busbar system is developed, which is of practical use in the converter design. It allows optimizing the stray inductance, material consumption, and cost of the busbar system as long as the specified temperature limits are not exceeded. The finite-element method thermal modeling validates the developed LPTM. Laboratory measurements in two operating points of the converter have been performed, and they show good correlation with the simulation results.

Identification of resonances in parallel connected grid inverters with LC- and LCL-filters

Modern high power grid inverters use usually LC-or LCL-filter at grid interface. Simpler L-filter does not prove sufficient harmonic attenuation without resulting in to very large and bulky filter components. Higher order filters realize better attenuation with smaller components. However, these filters introduce additional resonances to the system, which may cause instabilities without proper care. Connecting more than one inverter with individual LC- or LCL-filters in parallel will result in shifted resonances. The identification of the resonances in parallel connected LC- and LCL-filter system is essential for proper operation of the grid-connected inverter. For instance the efficiency of active damping is highly depended on the accurate knowledge of the filter resonances. In this paper the transfer functions for parallel-connected filter systems are derived and resonances analyzed. A method for resonance identification is presented.

Modular Multilevel Converter solutions with few Sub-Modules for wind power application

Modular Multilevel Converter (MMC) is a topology where series connection of Sub-Modules (SM) is used to achieve almost sinusoidal output voltage. The MMC converter with a large number of SMs is actively used in high voltage DC (HVDC) transmission systems where a bulky converter is not a difficult issue. In this paper the possibility to use a MMC with just a few SMs for wind power application with limited space in the nacelle is analysed. The current loading, electrical losses and thermal performance of the power devices in the converter solutions studied are analysed. It is shown that an MMC converter with full-bridge (FB) SMs has a more uniform loss and temperature distribution among the semiconductor devices than an MMC with half-bridge (HB) SMs. The reliability of the MMC converters is also investigated in terms of thermal loading.

Power semiconductor lifetime estimation considering dynamics of wind turbine

In the time of increasing power capacity of a single wind turbine, the wind power converter is considered as the most failure-prone component. Since, the wind turbine faces randomly varying wind speed, special grid conditions and faults, a strong effort is required to achieve highly reliable performance of power electronics. In order to predict the semiconductors lifetime, one must bring into focus the power converter mission profile and indicate the failure contribution by different loading conditions. Since, the previous studies have tended to focus only on specific or repeating loading conditions, a more complete and realistic mission profile needs to be generated. In this paper the focus is on the development of the model for the loading profile generation which takes into account the dynamics of the wind turbine. This model allows transforming the wind speed variations into the converter power variations. The lifetime is calculated for a three different IGBT joints, which are more prone to failure. The lifetime is expressed in terms of B10 lifetime.

Comparative analysis of LCL-filter designs for paralleled inverters

This paper presents LCL-filter configurations for parallel connected grid inverters. Three different configurations can be used in an LCL-filter implementation. All of these can be dimensioned to produce the same harmonic attenuation. However, the filter resonance frequencies and how they vary with respect to the number of inverters differs between the configurations. This paper presents and analyses three filter configurations and a comparative study is made. All three configurations are designed to produce the same attenuation. The amount of filter components and their relative dimensions are compared and differences in the effectiveness of the passive damping are discussed.