Zenodo (CERN European Organization for Nuclear Research), Dec 1, 2022
Exact solution of a circuit model for a three-phase twelve-pulse rectifier with constant-voltage ... more Exact solution of a circuit model for a three-phase twelve-pulse rectifier with constant-voltage load and ac-side reactance for the continuous conduction mode is presented. Obtained results are compared to the results provided by sinusoidal approximation. It is shown that the sinusoidal approximation provides acceptable results at low output voltages, with the accuracy being decreased for the output voltages approaching to the discontinuous conduction mode boundary. In comparison to the exact solution, the sinusoidal approximation always provides slightly more optimistic prediction for the rectifier exploitation parameters. Computational complexity of the exact solution is the same as for the solution obtained applying sinusoidal approximation, having the same structure, but different parameters. In comparison to the six-pulse rectifiers of the same type, analyzed in previous publications, agreement between the solutions is better due to the increased pulse number and reduced harmonic content of the waveforms.
IEEE Journal of Emerging and Selected Topics in Power Electronics, Jun 1, 2022
Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequ... more Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequency transformers (MFTs) and enable the power transfer between galvanically isolated DC systems. Considering a typical SST isolation stage, i.e., a 166 kW unregulated series-resonant DC-DC converter acting as a DC transformer (DCX) with equal input and output MV DC voltages of 7 kV (1:1-DCX), we derive component-level and system-level performance limits of aircooled realizations with either an air-core transformer (ACT) or with a magnetic-core transformer (MCT). We describe the design of two fully rated MFT prototypes in detail and provide a comprehensive experimental characterization to validate the derived performance limits, including also the dielectric losses and the analysis of stray magnetic fields. The realized ACT and MCT prototypes achieve measured efficiencies of 99.5 % and 99.7 % at gravimetric power densities of 16.5 kW/kg and 6.7 kW/kg, respectively. Considering 10 kV SiC MOSFETs, calculated system-level efficiencies of the ACT-based and MCTbased 1:1-DCX result in 99.0 % and 99.2 % at the nominal operating point, with similar part-load efficiency characteristics. The paper concludes with an application-oriented qualitative evaluation of the two concepts.
State-of-the-art high power density AC/DC and DC/AC converter systems typically employ Triangular... more State-of-the-art high power density AC/DC and DC/AC converter systems typically employ Triangular Current Mode (TCM) modulation or conventional PWM. TCM is characterized by a wide variation of switching frequency over the mains period and ensures soft-switching in all operating points, but results in increased conduction and high-frequency losses due to the necessary large current ripple. In contrast, PWM with constant switching frequency features a lower RMS current and thus reduced conduction losses, but cannot achieve softswitching over the entire mains period and suffers from turn-on losses. In this paper it is investigated if an optimal combination of these two operating modes, i. e. an optimal adjustment of switching frequency and/or current ripple amplitude throughout the mains period, can lead to an increase in conversion efficiency and how such an Optimal Frequency Modulation (OFM) control scheme can be implemented in practice. The presented analysis is based on an ultra compact 2kW, 400V DC/AC converter system designed to overcome the GOOGLE Little Box Challenge.
The Flying Capacitor Converter (FCC) offers an attractive alternative to conventional 2-level con... more The Flying Capacitor Converter (FCC) offers an attractive alternative to conventional 2-level converter topologies due to the easily acquired high number of voltage levels and the increased effective switching frequency. However, balancing of the flying capacitor (FC) voltages is crucial in practice since a deviation from the nominal voltage levels increases harmonics in the output voltage and, more importantly, jeopardizes the integrity of the converter due to overvoltages across the power transistors. Modulation inherent FC balancing techniques (termed natural/passive balancing) have been thoroughly analyzed in literature, however only for stationary operating conditions. In this paper, the behavior of the FCC and the effectiveness of passive balancing will be analyzed in detail regarding specific operating conditions present in typical industry applications such as converter start-up, shut-down, standby and operation under fault conditions. The basis for the analysis is a 5-level, 2 kW FCC embedded in two typical industry applications: single-phase PV inverter and single-phase PFC rectifier.
are widely-used to compare power semiconductor materials and devices and to motivate research and... more are widely-used to compare power semiconductor materials and devices and to motivate research and development of new technology nodes. These material-and devicespecific FOMs, however, fail to directly translate into quantifiable performance in a specific power electronics application. Here, we combine device performance with specific bridge-leg topologies to propose the extended FOM, or X-FOM, a Figure-of-Merit that quantifies bridge-leg performance in multi-level (ML) topologies and supports the quantitative comparison and optimization of topologies and power devices. To arrive at the proposed X-FOM, we revisit the fundamental scaling laws of the on-state resistance and output capacitance of power semiconductors to first propose a revised device-level semiconductor Figureof-Merit (D-FOM). The D-FOM is then generalized to a multi-level topology with an arbitrary number of levels, output power, and input voltage, resulting in the X-FOM that quantitatively compares hard-switched semiconductor stage losses and filter stage requirements across different bridge-leg structures and numbers of levels, identifies the maximum achievable efficiency of the semiconductor stage, and determines the loss-optimal combination of semiconductor die area and switching frequency. To validate the new X-FOM and showcase its utility, we perform a case study on candidate bridge-leg structures for a three-phase 10 kW photovoltaic (PV) inverter, with the X-FOM showing that (a) the minimum hard-switching losses are an accurate approximation to predict the theoretically maximum achievable efficiency and relative performance between bridge-legs and (b) the 3-level bridge-leg outperforms the 2-level configuration, despite utilizing a SiC MOSFET with a lower D-FOM than in the 2-level case. INDEX TERMS AC-DC power converters, DC-AC power converters, multilevel converters, power semiconductor devices, semiconductor device modeling, switched capacitor circuits.
Dynamic on-resistance (dR on ), where the on-resistance immediately after turn-on is higher than ... more Dynamic on-resistance (dR on ), where the on-resistance immediately after turn-on is higher than the DC resistance, increases the conduction losses in power converters with gallium nitride high-electronmobility transistors (GaN HEMTs). There exist no direct dR on measurements in the literature above 1 MHz, leaving designers unable to predict conduction losses in emerging multi-MHz applications. We address this literature gap by collecting the first on-state voltage dR on measurements at multi-MHz frequencies, with a focus on the zero-voltage-switching conditions that are predominantly employed at high frequency. On the selected commercially-available HEMT with a breakdown voltage below 200 V, the dynamic contribution asymptotes above ≈ 2 MHz, a finding predicted by the slow time constants of the traps that cause dR on . For the tested HEMT, we find a maximum dR on increase over the DC resistance of 2× in a multi-MHz, zero-voltage-switched application. INDEX TERMS Dynamic on-state resistance, gallium nitride, power transistors, wide bandgap semiconductors.
Modern GaN and SiC power semiconductors require new experimental methods for determining switchin... more Modern GaN and SiC power semiconductors require new experimental methods for determining switching losses as the widely accepted double-pulse-test (DPT) fails to accurately capture the dissipated energy during a switching transition because of electrical measurement limitations imposed by the very fast switching of WBG devices. In this paper, a new calorimetric measurement principle which relies on temperature rise monitoring of an aluminum heat sink during continuous operation of the attached power semiconductor is presented. Unlike traditional calorimetric methods, a single measurement can be performed in minutes. Using the proposed measurement principle, a soft-switching performance evaluation of selected 600 V GaN, SiC and Si power transistors is provided.
2017 IEEE International Electron Devices Meeting (IEDM)
Novel heat removal and power delivery topologies are required to enable 'extreme 3D integration' ... more Novel heat removal and power delivery topologies are required to enable 'extreme 3D integration' with cube-sized compute nodes. Therefore, a technology roadmap is presented supporting memory-on-logic and logic-on-logic in the medium and long-term, by (i) dual-side cooling and integrated voltage regulators, and (ii) interlayer cooling and electrochemical power delivery.
Multilayer Ceramic Capacitors (MLCCs) are of paramount importance in electronics and ferroelectri... more Multilayer Ceramic Capacitors (MLCCs) are of paramount importance in electronics and ferroelectric Class II dielectrics enable outstanding energy-density values. However, the non-linear dielectric constant and associated low-frequency large-signal excitation losses of Class II MLCCs may cause critical overheating. A peak-charge based Steinmetz loss model entitled iGSE-C Q is known in literature and allows to accurately calculate MLCC low-frequency large-signal excitation losses under various operating conditions including biased and non-sinusoidal excitation voltage waveforms. Such a macroscopic iGSE-C Q model, however, is inherently limited to a specific MLCC, and in contrast to Steinmetz loss modeling for ferromagnetic inductor cores, the losses of other devices employing the same dielectric material cannot be predicted. Recent literature therefore proposed a microscopic and/or material specific MLCC Steinmetz Model entitled iGSE-C D which allows to calculate the losses of any MLCC of the same dielectric material based upon just a single set of Steinmetz parameters. However, due to the lack of information on the internal device geometry, the iGSE-C D could be verified only indirectly so far by means of a loss normalization based on the device capacitance and rated voltage. In this paper, we demonstrate the feasibility of a microscopic iGSE-C D MLCC loss model enabled by manufacturer data on the internal capacitor structure. The iGSE-C D is verified for two different MLCC series employing a conventional X7R dielectric and a novel Hiteca (with reduced non-linearity) Class II dielectric material with loss estimation error below 22%. This error results due to component tolerances and is acceptable, especially when compared to the loss calculation based on the datasheet information which can be off by up to a factor of ten. The analysis of the Hiteca dielectric reveals a frequency behavior different to the X7R material, and is discussed in the Appendix of this paper.
2021 13th International Symposium on Linear Drives for Industry Applications (LDIA)
Integrated Linear Rotary Actuators (LiRAs) offer a compact solution which can achieve high dynami... more Integrated Linear Rotary Actuators (LiRAs) offer a compact solution which can achieve high dynamics when coupled linear and rotary motions are required. As a further step in integration, the LiRA can be equipped with Active Magnetic Bearings, which however requires a special winding configuration and feedback control of the magnetically levitated mover's position to operate. In this paper a control-oriented analysis of a Self-Bearing (SB) Double-Stator (DS) LiRA is conducted, providing an insight on simultaneous bearing force and torque generation and deriving an electromechanical dynamic model which is linearized and used to design a 6-DoF cascaded position control system. This is then implemented in hardware and verified, bringing a prototype of the SB DS LiRA into full operation, tracking a linear-rotary mission profile with radial deviations of the levitated mover's position below 75μm.
e & i Elektrotechnik und Informationstechnik, 2022
Linear actuators (LAs) are used for applications that require repetitive linear motion, such as l... more Linear actuators (LAs) are used for applications that require repetitive linear motion, such as linear pumps and compressors, servo drives in industrial automation, and pick-and-place robots in the pharmaceutical and semiconductor industry. These LAs usually have mechanical ball or slide bearings, which require frequent maintenance due to signs of wear limiting the LAs’ usage in high-purity and high-precision processes of the latter applications.Therefore, this paper analyzes a novel LA with integrated magnetic bearings (MBs). It shows how the basic structure of the tubular LA is derived from a conventional rotary actuator. Afterwards, it explains the winding structures for the generation of the drive and bearing forces in detail, focusing on the impact of the linear motion on the bearing winding.Furthermore, two types of windings for the self-bearing LA, separated and combined, are analyzed and compared. It is shown that a combined winding structure leads to higher efficiency and a...
2021 IEEE 22nd Workshop on Control and Modelling of Power Electronics (COMPEL), 2021
The stability limits for an ultra-high bandwidth class-D power amplifier (100 kHz, 800 V DC-link,... more The stability limits for an ultra-high bandwidth class-D power amplifier (100 kHz, 800 V DC-link, 10 kW) are derived and characterized for two different use cases and for a given inductance of the line that connects the output of the converter to the load. In the first use case, the additional impedance due to the line is compensated and in the second use case, a controlled inner ohmic-inductive impedance is emulated by the converter. General stability analyses are conducted for simplified representations of the two control concepts, i.e., for compensating the line impedance and emulating an inner impedance. A detailed linearized model of the investigated power amplifier is used to evaluate the effectivenesses of both control concepts and to identify the stability boundaries that apply to the investigated converter system. By way of example, the compensation of the line impedance can decrease the total output impedance of the converter system due to a line inductance of 10 µH from 1.3 Ω to 0.37 Ω at 20 kHz. Furthermore, the compensation of the line impedance is found to be less prone to instability than the emulation of a defined inner impedance. With regard to the inner impedance emulation, the stability analysis discloses the dependency between the maximum allowable values of emulated inner inductance and inner resistance such that the system remains stable, which facilitates the evaluation of the implications of specific modifications of the converter hardware or changes of the structure of the control system on the stability boundaries. Without external inductance, a maximum inner inductance of 430 µH at the stability limit is achieved if the bandwidth of the impedance emulation is limited to 30 kHz. A detailed circuit simulation of the power stage and the digital control unit is used to verify the results of the analysis.
2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL), 2017
Integrated Voltage Regulators (IVRs) have become a viable solution for microprocessor's power... more Integrated Voltage Regulators (IVRs) have become a viable solution for microprocessor's power delivery. The active parts of the most recent IVRs are built in deep-submicron CMOS technologies and use stacked transistors to allow for the use of advanced low voltage devices with superior switching performance compared to the higher voltage long-channel devices. This paper evaluates three different topologies of CMOS half-bridge converters with respect to efficiency, implementation effort, suitability for on-chip integration, and multiphase applications: the conventional half-bridge converter, the half-bridge converter with conventional Active Neutral Point Clamping (ANPC), and a halfbridge converter with a modified circuit to achieve ANPC. In-depth analysis of the transient processes during switching for all three converters, based on Cadence simulations, reveal that both half-bridge converters with ANPC achieve proper balancing of the blocking voltages of the main transistors and ...
Zenodo (CERN European Organization for Nuclear Research), Dec 1, 2022
Exact solution of a circuit model for a three-phase twelve-pulse rectifier with constant-voltage ... more Exact solution of a circuit model for a three-phase twelve-pulse rectifier with constant-voltage load and ac-side reactance for the continuous conduction mode is presented. Obtained results are compared to the results provided by sinusoidal approximation. It is shown that the sinusoidal approximation provides acceptable results at low output voltages, with the accuracy being decreased for the output voltages approaching to the discontinuous conduction mode boundary. In comparison to the exact solution, the sinusoidal approximation always provides slightly more optimistic prediction for the rectifier exploitation parameters. Computational complexity of the exact solution is the same as for the solution obtained applying sinusoidal approximation, having the same structure, but different parameters. In comparison to the six-pulse rectifiers of the same type, analyzed in previous publications, agreement between the solutions is better due to the increased pulse number and reduced harmonic content of the waveforms.
IEEE Journal of Emerging and Selected Topics in Power Electronics, Jun 1, 2022
Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequ... more Solid-state transformers (SSTs) are employing compact high-power medium-voltage (MV) medium-frequency transformers (MFTs) and enable the power transfer between galvanically isolated DC systems. Considering a typical SST isolation stage, i.e., a 166 kW unregulated series-resonant DC-DC converter acting as a DC transformer (DCX) with equal input and output MV DC voltages of 7 kV (1:1-DCX), we derive component-level and system-level performance limits of aircooled realizations with either an air-core transformer (ACT) or with a magnetic-core transformer (MCT). We describe the design of two fully rated MFT prototypes in detail and provide a comprehensive experimental characterization to validate the derived performance limits, including also the dielectric losses and the analysis of stray magnetic fields. The realized ACT and MCT prototypes achieve measured efficiencies of 99.5 % and 99.7 % at gravimetric power densities of 16.5 kW/kg and 6.7 kW/kg, respectively. Considering 10 kV SiC MOSFETs, calculated system-level efficiencies of the ACT-based and MCTbased 1:1-DCX result in 99.0 % and 99.2 % at the nominal operating point, with similar part-load efficiency characteristics. The paper concludes with an application-oriented qualitative evaluation of the two concepts.
State-of-the-art high power density AC/DC and DC/AC converter systems typically employ Triangular... more State-of-the-art high power density AC/DC and DC/AC converter systems typically employ Triangular Current Mode (TCM) modulation or conventional PWM. TCM is characterized by a wide variation of switching frequency over the mains period and ensures soft-switching in all operating points, but results in increased conduction and high-frequency losses due to the necessary large current ripple. In contrast, PWM with constant switching frequency features a lower RMS current and thus reduced conduction losses, but cannot achieve softswitching over the entire mains period and suffers from turn-on losses. In this paper it is investigated if an optimal combination of these two operating modes, i. e. an optimal adjustment of switching frequency and/or current ripple amplitude throughout the mains period, can lead to an increase in conversion efficiency and how such an Optimal Frequency Modulation (OFM) control scheme can be implemented in practice. The presented analysis is based on an ultra compact 2kW, 400V DC/AC converter system designed to overcome the GOOGLE Little Box Challenge.
The Flying Capacitor Converter (FCC) offers an attractive alternative to conventional 2-level con... more The Flying Capacitor Converter (FCC) offers an attractive alternative to conventional 2-level converter topologies due to the easily acquired high number of voltage levels and the increased effective switching frequency. However, balancing of the flying capacitor (FC) voltages is crucial in practice since a deviation from the nominal voltage levels increases harmonics in the output voltage and, more importantly, jeopardizes the integrity of the converter due to overvoltages across the power transistors. Modulation inherent FC balancing techniques (termed natural/passive balancing) have been thoroughly analyzed in literature, however only for stationary operating conditions. In this paper, the behavior of the FCC and the effectiveness of passive balancing will be analyzed in detail regarding specific operating conditions present in typical industry applications such as converter start-up, shut-down, standby and operation under fault conditions. The basis for the analysis is a 5-level, 2 kW FCC embedded in two typical industry applications: single-phase PV inverter and single-phase PFC rectifier.
are widely-used to compare power semiconductor materials and devices and to motivate research and... more are widely-used to compare power semiconductor materials and devices and to motivate research and development of new technology nodes. These material-and devicespecific FOMs, however, fail to directly translate into quantifiable performance in a specific power electronics application. Here, we combine device performance with specific bridge-leg topologies to propose the extended FOM, or X-FOM, a Figure-of-Merit that quantifies bridge-leg performance in multi-level (ML) topologies and supports the quantitative comparison and optimization of topologies and power devices. To arrive at the proposed X-FOM, we revisit the fundamental scaling laws of the on-state resistance and output capacitance of power semiconductors to first propose a revised device-level semiconductor Figureof-Merit (D-FOM). The D-FOM is then generalized to a multi-level topology with an arbitrary number of levels, output power, and input voltage, resulting in the X-FOM that quantitatively compares hard-switched semiconductor stage losses and filter stage requirements across different bridge-leg structures and numbers of levels, identifies the maximum achievable efficiency of the semiconductor stage, and determines the loss-optimal combination of semiconductor die area and switching frequency. To validate the new X-FOM and showcase its utility, we perform a case study on candidate bridge-leg structures for a three-phase 10 kW photovoltaic (PV) inverter, with the X-FOM showing that (a) the minimum hard-switching losses are an accurate approximation to predict the theoretically maximum achievable efficiency and relative performance between bridge-legs and (b) the 3-level bridge-leg outperforms the 2-level configuration, despite utilizing a SiC MOSFET with a lower D-FOM than in the 2-level case. INDEX TERMS AC-DC power converters, DC-AC power converters, multilevel converters, power semiconductor devices, semiconductor device modeling, switched capacitor circuits.
Dynamic on-resistance (dR on ), where the on-resistance immediately after turn-on is higher than ... more Dynamic on-resistance (dR on ), where the on-resistance immediately after turn-on is higher than the DC resistance, increases the conduction losses in power converters with gallium nitride high-electronmobility transistors (GaN HEMTs). There exist no direct dR on measurements in the literature above 1 MHz, leaving designers unable to predict conduction losses in emerging multi-MHz applications. We address this literature gap by collecting the first on-state voltage dR on measurements at multi-MHz frequencies, with a focus on the zero-voltage-switching conditions that are predominantly employed at high frequency. On the selected commercially-available HEMT with a breakdown voltage below 200 V, the dynamic contribution asymptotes above ≈ 2 MHz, a finding predicted by the slow time constants of the traps that cause dR on . For the tested HEMT, we find a maximum dR on increase over the DC resistance of 2× in a multi-MHz, zero-voltage-switched application. INDEX TERMS Dynamic on-state resistance, gallium nitride, power transistors, wide bandgap semiconductors.
Modern GaN and SiC power semiconductors require new experimental methods for determining switchin... more Modern GaN and SiC power semiconductors require new experimental methods for determining switching losses as the widely accepted double-pulse-test (DPT) fails to accurately capture the dissipated energy during a switching transition because of electrical measurement limitations imposed by the very fast switching of WBG devices. In this paper, a new calorimetric measurement principle which relies on temperature rise monitoring of an aluminum heat sink during continuous operation of the attached power semiconductor is presented. Unlike traditional calorimetric methods, a single measurement can be performed in minutes. Using the proposed measurement principle, a soft-switching performance evaluation of selected 600 V GaN, SiC and Si power transistors is provided.
2017 IEEE International Electron Devices Meeting (IEDM)
Novel heat removal and power delivery topologies are required to enable 'extreme 3D integration' ... more Novel heat removal and power delivery topologies are required to enable 'extreme 3D integration' with cube-sized compute nodes. Therefore, a technology roadmap is presented supporting memory-on-logic and logic-on-logic in the medium and long-term, by (i) dual-side cooling and integrated voltage regulators, and (ii) interlayer cooling and electrochemical power delivery.
Multilayer Ceramic Capacitors (MLCCs) are of paramount importance in electronics and ferroelectri... more Multilayer Ceramic Capacitors (MLCCs) are of paramount importance in electronics and ferroelectric Class II dielectrics enable outstanding energy-density values. However, the non-linear dielectric constant and associated low-frequency large-signal excitation losses of Class II MLCCs may cause critical overheating. A peak-charge based Steinmetz loss model entitled iGSE-C Q is known in literature and allows to accurately calculate MLCC low-frequency large-signal excitation losses under various operating conditions including biased and non-sinusoidal excitation voltage waveforms. Such a macroscopic iGSE-C Q model, however, is inherently limited to a specific MLCC, and in contrast to Steinmetz loss modeling for ferromagnetic inductor cores, the losses of other devices employing the same dielectric material cannot be predicted. Recent literature therefore proposed a microscopic and/or material specific MLCC Steinmetz Model entitled iGSE-C D which allows to calculate the losses of any MLCC of the same dielectric material based upon just a single set of Steinmetz parameters. However, due to the lack of information on the internal device geometry, the iGSE-C D could be verified only indirectly so far by means of a loss normalization based on the device capacitance and rated voltage. In this paper, we demonstrate the feasibility of a microscopic iGSE-C D MLCC loss model enabled by manufacturer data on the internal capacitor structure. The iGSE-C D is verified for two different MLCC series employing a conventional X7R dielectric and a novel Hiteca (with reduced non-linearity) Class II dielectric material with loss estimation error below 22%. This error results due to component tolerances and is acceptable, especially when compared to the loss calculation based on the datasheet information which can be off by up to a factor of ten. The analysis of the Hiteca dielectric reveals a frequency behavior different to the X7R material, and is discussed in the Appendix of this paper.
2021 13th International Symposium on Linear Drives for Industry Applications (LDIA)
Integrated Linear Rotary Actuators (LiRAs) offer a compact solution which can achieve high dynami... more Integrated Linear Rotary Actuators (LiRAs) offer a compact solution which can achieve high dynamics when coupled linear and rotary motions are required. As a further step in integration, the LiRA can be equipped with Active Magnetic Bearings, which however requires a special winding configuration and feedback control of the magnetically levitated mover's position to operate. In this paper a control-oriented analysis of a Self-Bearing (SB) Double-Stator (DS) LiRA is conducted, providing an insight on simultaneous bearing force and torque generation and deriving an electromechanical dynamic model which is linearized and used to design a 6-DoF cascaded position control system. This is then implemented in hardware and verified, bringing a prototype of the SB DS LiRA into full operation, tracking a linear-rotary mission profile with radial deviations of the levitated mover's position below 75μm.
e & i Elektrotechnik und Informationstechnik, 2022
Linear actuators (LAs) are used for applications that require repetitive linear motion, such as l... more Linear actuators (LAs) are used for applications that require repetitive linear motion, such as linear pumps and compressors, servo drives in industrial automation, and pick-and-place robots in the pharmaceutical and semiconductor industry. These LAs usually have mechanical ball or slide bearings, which require frequent maintenance due to signs of wear limiting the LAs’ usage in high-purity and high-precision processes of the latter applications.Therefore, this paper analyzes a novel LA with integrated magnetic bearings (MBs). It shows how the basic structure of the tubular LA is derived from a conventional rotary actuator. Afterwards, it explains the winding structures for the generation of the drive and bearing forces in detail, focusing on the impact of the linear motion on the bearing winding.Furthermore, two types of windings for the self-bearing LA, separated and combined, are analyzed and compared. It is shown that a combined winding structure leads to higher efficiency and a...
2021 IEEE 22nd Workshop on Control and Modelling of Power Electronics (COMPEL), 2021
The stability limits for an ultra-high bandwidth class-D power amplifier (100 kHz, 800 V DC-link,... more The stability limits for an ultra-high bandwidth class-D power amplifier (100 kHz, 800 V DC-link, 10 kW) are derived and characterized for two different use cases and for a given inductance of the line that connects the output of the converter to the load. In the first use case, the additional impedance due to the line is compensated and in the second use case, a controlled inner ohmic-inductive impedance is emulated by the converter. General stability analyses are conducted for simplified representations of the two control concepts, i.e., for compensating the line impedance and emulating an inner impedance. A detailed linearized model of the investigated power amplifier is used to evaluate the effectivenesses of both control concepts and to identify the stability boundaries that apply to the investigated converter system. By way of example, the compensation of the line impedance can decrease the total output impedance of the converter system due to a line inductance of 10 µH from 1.3 Ω to 0.37 Ω at 20 kHz. Furthermore, the compensation of the line impedance is found to be less prone to instability than the emulation of a defined inner impedance. With regard to the inner impedance emulation, the stability analysis discloses the dependency between the maximum allowable values of emulated inner inductance and inner resistance such that the system remains stable, which facilitates the evaluation of the implications of specific modifications of the converter hardware or changes of the structure of the control system on the stability boundaries. Without external inductance, a maximum inner inductance of 430 µH at the stability limit is achieved if the bandwidth of the impedance emulation is limited to 30 kHz. A detailed circuit simulation of the power stage and the digital control unit is used to verify the results of the analysis.
2017 IEEE 18th Workshop on Control and Modeling for Power Electronics (COMPEL), 2017
Integrated Voltage Regulators (IVRs) have become a viable solution for microprocessor's power... more Integrated Voltage Regulators (IVRs) have become a viable solution for microprocessor's power delivery. The active parts of the most recent IVRs are built in deep-submicron CMOS technologies and use stacked transistors to allow for the use of advanced low voltage devices with superior switching performance compared to the higher voltage long-channel devices. This paper evaluates three different topologies of CMOS half-bridge converters with respect to efficiency, implementation effort, suitability for on-chip integration, and multiphase applications: the conventional half-bridge converter, the half-bridge converter with conventional Active Neutral Point Clamping (ANPC), and a halfbridge converter with a modified circuit to achieve ANPC. In-depth analysis of the transient processes during switching for all three converters, based on Cadence simulations, reveal that both half-bridge converters with ANPC achieve proper balancing of the blocking voltages of the main transistors and ...
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Papers by Johann Kolar