Browsing by Author "Roth-Stielow, Jörg"

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Analysis of the influence of static and dynamic eccentricity on back EMF of a permanent magnet synchronous motor
(2017) Fischer, Manuel; Roth-Stielow, Jörg
In this paper the measurement results that represent the back electromotive force (EMF) of a small drive permanent magnet synchronous machine (PMSM) are proposed. The focus is on the comparison between three mechanical configurations: the original one and a setup with static and dynamic eccentricity. Additionally, the influence of compensating currents is considered due to the circuitry of the windings belonging to one phase. This leads to quite similar gradients of back EMF in all three mechanical configurations.
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Comprehensive comparison of a SiC MOSFET and Si IGBT based inverter
(2019) Nitzsche, Maximilian; Cheshire, Christoph; Fischer, Manuel; Ruthardt, Johannes; Roth-Stielow, Jörg
The investment which is necessary to replace Si IGBTs with SiC MOSFETs in medium to high power DC-AC inverters needs to be balanced carefully against the advantages SiC offers. This paper compares a 20 kW Si IGBT inverter with a 20 kW SiC MOSFET inverter. The power semiconductor components are operated identically in a modular half bridge module to ensure comparability. Thereby the measurement of the switching losses is explicitly not the focus but the overall efficiency while taking volume, current ripple, switching frequency and inductance into account. The limits of reasonable operating range shall be evaluated and an overview on the benefits of SiC on system level will be given.
Open Access
Junction temperature control system to increase the lifetime of IGBT-power-modules in synchronous motor drives without affecting torque and speed
(2020) Wölfle, Julian; Nitzsche, Maximilian; Ruthardt, Johannes; Roth-Stielow, Jörg
Load changes of electrical machines driven by inverters cause temperature swings of the semiconductor devices in IGBT modules of the inverters. These temperature swings lead to mechanical strain in the different material layers of the IGBT-power-modules and limit the numbers of cycles to failure and therefore reduce the lifetime of the IGBTs. This paper presents a temperature control system which is paralleled to the standard torque control system. It aims to reduce the magnitude of temperature swings of the semiconductor devices of IGBT modules caused by load changes of an interior permanent magnet synchronous machine. The principle method is, to increase the temperature of the semiconductor devices of the IGBT-modules by creating higher power losses during low load conditions of the machine without affecting torque and speed. This reduces the magnitude of the load induced temperature swings of the semiconductor devices of IGBT-modules and increases its lifetime at the cost of increased power losses. Three variables have been identified that influence the power losses in inverter modules without necessarily affecting the output power of the permanent synchronous machine. These variables are switching frequency of the inverter, length of the clamping area when a discontinuous modulation is applied and the reactive component of the inverter current. The influence of each variable which regards to the losses in the IGBT-power-modules is explained and the related control methodology is described. The analytic results are verified by experimental results obtained from a test set up.
Open Access
Power electronic systems for electric aircraft
(2020) Nitzsche, Maximilian; Roth-Stielow, Jörg
Electric aviation poses several unique challenges which influence the development of power electronic systems for electric flight. This presentation focuses on the aspects of redundancy, semiconductor material (especially silicon carbide SiC), electromagnetic compatibility and reliability. These topics are discussed in relation to recent developments regarding electric aviation such as e.g. distributed electric propulsion (DEP) and modularity of power electronic systems.
Open Access
Precise voltage measurement for power electronics with high switching frequencies
(2018) Nitzsche, Maximilian; Zehelein, Matthias; Tröster, Nathan; Roth-Stielow, Jörg
In this paper different approaches in precise measurement of gate voltages as well as drain-source voltages of modern SiC and GaN transistors are compared. An approach to calculate the necessary bandwidth of a voltage probe to reproduce the voltage slope is presented. Furthermore, state-of-the-art voltage probes are compared in means of bandwidth, common mode reduction and response on EMI.