H.-P. Nee

• PhD
• Professor at KTH Royal Institute of Technology

Accurate modeling of switching loss is critical for silicon carbide mosfet s as well as power converters. However, previous “static” time-independent models did not consider the impact of gate oxide degradation on switching performance during long-term operation. This article proposes a “dynamic” time-dependent analytical model considering thresh...

For filling higher input voltage requirement, the input-series system based on attainable power devices is prevalent in industry. Specifically, its auxiliary power supply (APS) is self-powered from submodule (SM) capacitance on medium/high voltage occasions, for easing the common mode noise and insulation problems as well as facilitating the modula...

Various methods have been discussed in the literature regarding enabling the over-current (OC) capability of silicon carbide (SiC) MOSFETs. SiC MOSFETs can operate at up to 250 °C without failure. One of their features is to permit transient operation at elevated temperatures. This is possible if the stress on the gate oxide and packaging can be ke...

Gate oxide degradation under dynamic gate stress has been demonstrated as a reliability issue for SiC MOSFETs recently. Investigating the influence of dynamic drain-source voltage stress ( V_DS ) and load current ( I_L ) involved in switching operation on gate oxide degradation is very significant to identify the way for effec...

The demand for highly efficient and dynamic electric vehicles (EVs) has increased dramatically. The traction inverter, a pivotal component in an EV powertrain, plays a crucial role. This study is dedicated to designing a traction inverter with focus on achieving high efficiency and elevated power density and mitigating electromagnetic interference...

This article presents a novel scheme for condition monitoring of dc-link capacitors in modular multilevel converters (MMCs). The proposed solution uses estimated capacitance values of the dc-link capacitors for indicating their state-of-health (SoH). Moreover, a comparative approach is proposed where the estimated capacitance of all submodule capac...

An increasing share of fluctuating and intermittent renewable energy sources can cause over-currents (OCs) in the power system. The heat generated during OCs increases the junction temperature of semiconductor devices and could even lead to thermal runaway if thermal limits are reached. In order to keep the junction temperature within the thermal l...

Grid-forming converters can emulate the behavior of a synchronous generator through frequency droop control. The stability of grid-forming modular multilevel converters can be studied via the impedance-based stability criterion. This paper presents an ac-side impedance model of a grid-forming modular multilevel converter which includes a complete g...

This article presents a novel method for accurate online extraction of semiconductor ON-state resistance in the presence of measurement noise. In this method, the ON-state resistance value is extracted from the measured ON-state voltage of the semiconductors and the measured load current. The extracted ON-state resistance can be used for online con...

This article presents a novel scheme for condition monitoring of dc-link capacitors in modular multilevel converters (MMCs). The proposed solution uses estimated capacitance values of the dc-link capacitors for indicating their state-of-health (SoH). Moreover, a comparative approach is proposed where the estimated capacitances of all submodule capa...

The fault clearance time in the power system can vary from a few milliseconds to a few hundred milliseconds. Power electronics converters should be able to provide the increased current during faults without failing due to thermal limits. Hence, the heat generated in the semiconductor chip due to the over-current (OC) should be removed as soon as i...

Gate oxide degradation has been one of the major reliability challenges of SiC MOSFETs. Comprehensive and accurate localization of gate oxide degradation under bias temperature instability (BTI) conditions is important to improve device reliability. The split C-V (gate-source capacitance C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns...

The stability of a power electronicssystem can be assessed by means of the impedance-based stability criterion. Impedance modeling is a useful tool to analyze the effect of different circuit parameters and control schemes on the behavior of a converter. Modeling the input impedance of a power electronics converter is often successful when having fu...

Recent advancements in the silicon carbide (SiC) power semiconductor technology offer improvements for high-power converters, where today silicon (Si) devices are still dominant. Bipolar SiC devices feature particularly good conduction capability while blocking high voltages. With expected advances in SiC material quality and processing technology,...

In this paper, proton implantation with different combinations of MeV energies and doses from 2×10⁹ to 1×10¹¹ cm⁻² is used to create defects in the drift region of 10 kV 4H-SiC PiN diodes to obtain a localized drop in the SRH lifetime. On-state and reverse recovery behaviors are measured to observe how MeV proton implantation influences these devic...

The wireless control of modular multilevel converter (MMC) submodules was recently proposed. The success of the control depends on specialized control methods suitable for wireless communication and a properly designed wireless communication network in the MMC valve hall while aiming for low latency and high reliability. The wireless communication...

Inverter-based generators (IBGs) are becoming popular in modern power systems. When the penetration of IBGs is increasing in power systems, new stability, protection, and monitoring challenges are introduced in the grid. Grid-forming (GFM) control of converters is seen as a promising solution for future power grids to overcome particular stability...

This paper presents an online condition monitoring (CM) scheme for semiconductors used in modular multilevel converters (MMCs) that comprise cascaded H-bridge submodules. The CM algorithm is based on detecting changes in the ON-state resistance of the semiconductors over time. The proposed method is shown to successfully perform a curve-tracing of...

With the increase in penetration of power electronic converters in the power systems, a demand for over-current/overloading capability has risen for the fault clearance duration. This article gives an overview of the limiting factors and the recent technologies for the over-current performance of SiC power modules in power electronics converters. I...

Recent developments in medium-voltage (MV) silicon and silicon carbide (SiC) power semiconductor devices are challenging state-of-the-art converter and auxiliary power supply (APS) designs. The APS is an important converter component, which energizes the gate-drive units and, therefore, has an influence on the overall reliability and efficiency of...

Enhanced active resonant (EAR) DC circuit breakers (DCCBs) are a novel type of DCCB that use a discharge closing switch as interruption medium. A technical limitation of discharge closing switches is the minimum voltage across the main gap required for successful triggering. A novel commutation process creating the minimum voltage internally is pro...

Wireless control of modular multilevel converter (MMC) submodules can benefit from different points of view, such as lower converter cost and shorter installation time. In return for the advantages, the stochastic performance of wireless communication networks necessitates an advanced converter control system immune to the losses and delays of the...

Phase-modular buck–boost dc/ac inverters extend the voltage conversion range of conventional buck-type inverter topologies, and accordingly offer significant advantages for variable-speed motor drives powered from dc sources with wide-voltage-ranges like fuel cells or batteries. In this letter, two new modulation schemes are applied to the six-swit...

In future HVDC systems, many DC circuit breakers (DCCBs) will be required. In this paper, an advanced test circuit for DCCBs is described. A DC source is combined with a capacitor bank. In contrast to other test circuits, the proposed test circuit allows to replicate constant DC and temporary faults. In addition to conventional faults, this enables...

The wireless control of modular multilevel converter (MMC) submodules might offer advantages for MMCs with a high number of submodules. However, the control system should tolerate the stochastic nature of the wireless communication, continue the operation flawlessly or, at least, avoid overcurrents, overvoltages, and component failures. The previou...

Wireless control of modular multilevel converter (MMC) submodules has been offered recently with potentially lower cost and higher availability advantages for the converter station. In this paper, the wireless control of MMC submodules under ac-side faults is investigated. The central controller of the MMC is equipped for the unbalanced grid condit...

DC grid has become an important application in power transmission. However, the exist works only have the method to obtain the droop coefficient in a radial topology. Also, this droop coefficient is for V-I droop control. There is no such like method to obtain the droop coefficient for the P-V droop control. This paper proposed a new method for a c...

Dynamic avalanche (DA) phenomena and current filament (CF) formation are two extreme conditions observed in high-power devices, setting the maximum limit on turn-on/off current capability and di/dt in silicon (Si)-based bipolar devices. The properties of the silicon carbide (SiC) material enable devices with increased resilience for DA and CF compa...

This paper presents an online health monitoring scheme for dc capacitors in modular multilevel converters(MMCs). The health monitoring algorithm is based on detecting changes in the dc capacitance value over time. The proposed algorithm only utilizes measurements that are typically available in flexible alternating current transmission systems (FAC...

Enhanced active resonant (EAR) DC circuit breakers (DCCBs) are a promising set of recently proposed DCCB concepts. As other DCCBs, EAR DCCBs still require a fast mechanical switch. The requirements on the actuator of the mechanical switch depend on the DCCB concept and the DC grid and are derived here for an EAR DCCB. Thomson-coil actuators can ope...

The junction termination extension (JTE) structures for ultrahigh-voltage (UHV) devices consumes a considerable part of the semiconductor chip area. The JTE area is closely related to chip performance, process yield and ultimately device cost. The JTE lengths for UHV devices (i.e., > 30 kV) are still unknown, not visible in the scientific literatur...

Recent advancements in silicon carbide (SiC) power semiconductor technology enable developments in the high-power sector, e.g., high-voltage-direct-current (HVdc) converters for transmission, where today silicon (Si) devices are state-of-the-art. New submodule (SM) topologies for modular multilevel converters offer benefits in combination with thes...

Technology-based computer-aided design models have been used to predict the static and dynamic performance of ultrahigh-voltage (UHV) 4H-silicon carbide (SiC) P-i-N diodes, insulated-gate bipolar transistors (IGBTs), and gate turn- off (GTO) thyristors designed for 20–50 kV blocking voltage capability. The simulated forward voltage drops of 20–50...

Wireless control of modular multilevel converter (MMC) submodules offers several potential benefits to exploit, such as decreased converter costs and ease in converter installation. However, wireless control comes with several challenging engineering requirements. The control methods used with wired communication networks are not directly applicabl...

Results are reported from a successful field test with a silicon carbide (SiC) metal‐oxide‐semiconductor field‐effect transistor (MOSFET) traction inverter. The train has been operated over a 3‐month period in the Stockholm metro system. Increased traction inverter power density has been achieved, with volume and weight reductions of 51% and 25%, r...

The dc-side admittance of a modular multilevel converter can be used in assessing the stability of the dc system by means of impedance-based stability criteria. An accurate mathematical representation of the small-signal admittance can be given using harmonic linearization. To this end, the effect of the internal dynamics of the converter, e.g., th...

The performance of theoretical ultra-high-voltage power semiconductor devices has been predicted by means of numerical simulations using the Sentaurus technology computer-aided design tool. A general silicon carbide punch-through insulated-gate bipolar transistor (IGBT) structure has been implemented with suitable physics-based models and parameter...

Single-stage DC-AC power converters are gaining higher attention due to their simpler structure compared to the two-stage equivalent solution. In this paper, a single-stage DC-AC converter solution is proposed for interfacing a low voltage (LV) DC source with a higher voltage AC load or grid, where this converter has a modular structure with multil...

Direct current circuit breakers (DCCBs) have become a large research topic and are considered one of the critical components for future DC grids. Proposed DCCB concepts may be grouped into hybrid DCCBs and active resonant DCCBs. In this work, the enhanced active resonant (EAR) DCCB family is introduced. EAR DCCBs combine elements of hybrid and acti...

In this paper, a technology computer-aided design (TCAD) model of a silicon carbide (SiC) insulated-gate bipolar transistor (IGBT) has been calibrated against previously reported experimental data. The calibrated TCAD model has been used to predict the static performance of theoretical SiC IGBTs with ultra-high blocking voltage capabilities in the...

This paper studies a new hybrid converter that utilizes thyristors and full-bridge (FB) arms for achieving higher power capability than the full-bridge (FB) modular multilevel converter (MMC) with reduced semiconductor requirements. The study covers the theoretical analysis of the energy balancing, the dimensioning principles, the maximum power cap...

The temperature evolution during a short-circuit fault in the dies of three different Silicon Carbide 1200-V power devices is presented. Transient electro-thermal simulations were performed based on the reconstructed structure of commercially available devices. The simulations reveal the location of the hottest point in each device. The nonisotherm...

Future meshed high-voltage direct current grids require modular multilevel converters with extended functionality. One of the most interesting new submodule topologies is the semi-full-bridge because it enables efficient handling of DC-side short circuits while having reduced power losses compared to an implementation with full-bridge submodules. H...

The central control of MMC becomes demanding in computation power and communication bandwidth as the number of submodules increase. Distributed control methods can overcome these bottlenecks. In this paper, a simple distributed control method together with synchronization of modulation carriers in the submodules is presented. The proposal is implem...

In this project, a Technology CAD (TCAD) model has been calibrated and verified against experimental data of a 15 kV silicon carbide (SiC) bipolar junction transistor (BJT). The device structure of the high voltage BJT has been implemented in the Synopsys Sentaurus TCAD simulation platform and design of experiment simulations have been performed to...

Converter–grid interaction is of great interest in a weak-grid condition. This paper presents a single-input single-output open-loop transfer function for the stability analysis of grid-connected voltage-source converters. Differing from the conventional input impedance method and the eigenvalue analysis, an alternative multi-input multi-output clo...

This paper proposes a novel power module concept specially designed for highly reliable silicon carbide power devices for medium- and high-power applications. The concept consists of two clamped structures: 1) a press-pack power stage accommodating silicon carbide power switch dies, and 2) perpendicularly clamped press-pack heatsinks, in which, the...

The modular multilevel converter is one of the most preferred converters for high-power conversion applications. Wireless control of the submodules can contribute to its evolution by lowering the material and labor costs of cabling and by increasing the availability of the converter. However, wireless control leads to many challenges for the contro...

One of the major challenges of DC circuit breakers is the required fast mechanical actuator. In this paper, a Thomson coil actuator system for a vacuum interrupter is designed. Active damping is used to decelerate the moving contacts. Challenges are discussed, especially concerning the power supply needed for the Thomson coil actuator. The design p...

Converter–grid interaction is of great interest in a weak-grid condition. In this paper, an alternative multi-input multi-output closed-loop system is developed for the stability analysis of grid-connected voltage-source converters. In contrast to the conventional dq-impedance model and the eigenvalue analysis, this model eventually yields a single...

A considerable part of the fuel energy in vehicles never reaches the wheels and entirely converts to waste heat. In a heavy duty vehicle (HDV) the heat power that escapes from the exhaust system may reach 170 kW. The waste heat can be converted into useful electrical power using thermoelectric generator (TEG). During the last decades, many studies...

In future high-voltage direct current (HVDC) systems, a large number of HVDC breakers will be required. In this paper, the influence of HVDC breakers on the transient performance of point-to-point HVDC links in both asymmetrical and symmetrical monopolar configuration with half-bridge modular multilevel converters is studied with simulations in PSC...

This paper investigates the benefits of using high-voltage converter cells for transmission applications. These cells employ ultrahigh-voltage SiC bipolar power semiconductors, which are optimized for low conduction losses. The Modular Multilevel Converter with half-bridge cells is used as a test case. The results indicate a reduction of converter...

In this paper, a novel $dv/dt$ filter is presented targeted for 100 kW to 1 MW voltage source converters using silicon carbide (SiC) power devices. This concept uses the stray inductance between the power device and the converter output as a filter component in combination with an additional small RC-link. Hence, a lossy, bulky and costly filter in...

This paper presents an experimental methodology for the characterization of thermomechanical displacement and friction properties in a free-floating press-pack structure, and evaluation of the tensile stress on the semiconductor die through simulation of different mechanical and thermal loading conditions. The press-pack structure consists of a sin...

The demand for high-efficiency power converters is increasing continuously. The switching losses are typically significant in power converters. During the switching time, the component is exposed to a considerable voltage and current causing power loss. The switching time is limited by parasitic inductance produced by traces and interconnections in...

The temperature evolution during a short-circuit in the die of three different Silicon Carbide1200-V power devices is presented. A transient thermal simulation was performed based on the reconstructedstructure of commercially available devices. The location of the hottest point in the device iscompared. Finally, the analysis supports the necessity...

The breakdown voltages of the currently available 1.2 and 1.7-kV classes Silicon Carbide (SiC) transistors are not sufficient to operate under medium blocking voltages. On the other hand, the fabrication yields of the available high-voltage SiC transistors are still low, resulting in low current capabilities. Series-connection of several individual...