Browsing by Author "Goetz, Stefan"

Now showing 1 - 14 of 14
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    A Generic Scheduling Algorithm for Low-Frequency Switching in Modular Multilevel Converters with Parallel Functionality
    (IEEE Transactions on Power Electronics) Tashakor, Nima; Li, Zhongxi; Goetz, Stefan
    Since the introduction of modular multilevel converters (MMC), various additional features have been introduced for MMCs, among them parallel inter-module connectivity. However, such a parallel mode requires appropriate modulation and switching strategies to exploit its full potential. Low-frequency switching modulation is widely used with half-bridge modules and a large body of research focusses on the optimum control and scheduling of these methods. However, so far, a suitable adaptation for MMCs with parallel mode is missing, and existing methods perform suboptimum. This paper proposes a generic scheduling algorithm for simple and low-cost integration with low-frequency switching modulation. The proposed method reduces control complexity, minimizes power loss, and can be combined with most modulation techniques, including nearest-level modulation (NLM) and selective harmonic elimination (SHE). The text provides a general algorithm for integrating this method with other control levels and analyzes its effect on MMCs with parallel functionality. Moreover, it examines the performance of the system with NLM combined with the proposed scheduler and compares it to other alternatives. Results show up to 50% reduction in power loss with a similar modulation technique as well as significantly lower THD and power loss compared to optimized phase-shifted carrier modulation as another sensorless alternative method.
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    A high-frequency pulsating dc link for electric vehicle drives with reduced losses
    (IEEE Industrial Electronics Society (IECON)) Zhongxi, Li; Goetz, Stefan
    This paper proposes a motor drive suitable for electric vehicles (EVs) with notably reduced losses as compared to conventional drives. The proposed drive feeds the dc-link with a dynamically reconfigurable battery formed by cascaded half-bridges containing battery units. The reconfigurable battery concurrently forms a modular multilevel dc-link able to synthesize variable dc-link voltages, which can adjust the dc link voltage to run a motor to operate at the optimum load point or even to contribute to modulation and greatly reduce the switching loss of the main inverter—in this case a standard two-level three-phase inverter. Up to 2/3 switching actions are avoided in the main inverter, which can run at maximum duty cycle and fundamental-frequency commutation. The saved switching effort in the main inverter is shifted to the modular multilevel dc link, but with much less loss due to the fractionized switching voltage and the use of field-effect transistors (FETs). At high drive speeds, the converter halves the total loss compared to a standard inverter only; at lower speeds and thus smaller modulation indices, the advantage is even more pronounced because of the dynamically lowered dc-link voltage. Other benefits include alleviated insulation stress for motor windings and direct battery balancing. The proposed motor drive is verified on a down-scaled setup with eight modules constituting the dc link.
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    A Review of Multilevel Converters with Parallel Connectivity
    (IEEE Transactions on Power Electronics) Fang, Jingyang; Blaabjerg, Frede; Liu, Steven; Goetz, Stefan
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    Advances in Transcranial Magnetic Stimulation Technology
    (2015-06-05) Peterchev, Angel V; Deng, Zhi-De; Goetz, Stefan
    © 2015 by Wiley-Blackwell. All rights reserved. This chapter provides overview of the state of the art of transcranial magnetic stimulation (TMS) devices, including pulse sources with flexible control of the output waveform parameters and a wide variety of coil designs. It discusses technologies for accurate TMS targeting, including electric field models, frameless stereotaxy, and robotic coil holders. The chapter addresses technological aspects of ancillary coil effects such as heating, noise, vibration, and scalp stimulation. TMS requires high energy pulses that present a technical challenge for the design of practical, flexible, and efficient pulse sources. The chapter covers technical considerations for the integration of TMS and neuroimaging devices. It discusses various coil configurations and their electric field characteristics as well as technical advances in coil field modelling, positioning systems, efficiency and cooling, noise and scalp stimulation, and sham. The chapter summarizes technical considerations for the integration of TMS and neuroimaging devices.
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    Ageing Mitigation and Loss Control in Reconfigurable Batteries in Series-Level Setups
    (2022) Kacetl, Tomas; Kacetl, Jan; Tashakor, Nima; Goetz, Stefan
    This paper presents a novel control method that reduces the low-frequency ripple of dynamical-ly reconfigurable battery technology to reduce cell ageing and loss. It furthermore shifts the residual ripple to higher frequencies where the lower impedance reduces heating and the dielectric capacitance of electrodes and electrolyte shunt the current around the electrochemical reactions.
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    Low-Cost Parameter Estimation Approach for Modular Converters and Reconfigurable Battery Systems Using Dual Kalman Filter
    (IEEE Transactions on Power Electronics) Tashakor, Nima; Goetz, Stefan
    Modular converters or reconfigurable battery energy storage systems are a promising approach to eliminate the dependence on the weakest element in previously hard-wired battery packs and to combine heterogeneous batteries (so-called mixed-battery systems). But their need for expensive sensors and complex monitoring as well as control subsystems hinders their progress. Estimating parameters of each module can substantially reduce the number of required sensors and/or communication components. However, the existing estimation methods for cascaded modular circuits neglect important parameters such as the internal resistance of the battery, resulting in large systematic errors and bias. This paper proposes an online estimator based on a dual-Kalman filter (DKF) that exploits the slow dynamics of the battery compared to the load. The DKF algorithm estimates the open-circuit voltage (OCV) and internal resistance of each module by measuring only the output voltage and current of the system. Compared with the state of the art, the proposed method is simpler and cheaper with only two sensors compared to ≥ N + 2 (N is the number of modules). Furthermore, the proposed algorithm achieves a fast convergence through optimal learning rate. Simulations and experimental results confirm the ability of the proposed approach, achieving < 1.5% and < 5% estimation error for OCV and the internal resistance, respectively.
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    Modular Multilevel Converter with Sensorless Diode-Clamped Balancing through Level-Adjusted Phase-Shifted Modulation
    (IEEE Transactions on Power Electronics) Tashakor, Nima; Kilictas, Muhammet; Bagheri, Ehsan; Goetz, Stefan
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    Modular Power Electronics System for Charging an Electrically Operated Vehicle
    (US 10,391,870 B2) Goetz, Stefan; Reber, Volker
    A power electronics system for charging at least one elec trically operated vehicle , wherein the power electronics system has at least two modules each having at least one terminal pair with DC output , at least one rectifier , at least one AC input , at least one DC link and a number of switching elements the switching elements are arranged at and / or between the DC outputs of the at least two modules in such a way that , between the at least two modules , at least one series and one parallel circuit configuration can be selectively dynamically set by suitable switching states of the switching elements .
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    Neuronavigation
    (2022) Goetz, Stefan; Kammer, Thomas
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    Neuronavigation
    Goetz, Stefan
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    Novel low-side/high-side gate drive and supply with minimum footprint, high power density, and low cost for silicon and wide-bandgap transistors
    (IEEE Transactions on Power Electronics) Kacetl, Jan; Kacetl, Tomas; Jaensch, Malte; Goetz, Stefan
    High-power silicon field-effect transistors as well as IGBTs and particularly wide-bandgap semi¬conductor transistors typically need negative turn-off voltage for a secure off-state, resilience to spurious turn on, and rapid transition through the saturation mode. We present a gate driver configuration with compact and very efficient supply of the high and low sides of power transistor bridges with asymmetric bipolar control voltages without the need for costly and lossy isolated DCDC converter and only low-voltage active components. The underlying negative voltage gate driver supply circuit consists of only a few cost-efficient components, its electrical potential is referenced to the source of the controlled semiconductor power switch, and its operation is synchronized with the gate driver output. It outcompetes the established use of isolated DCDC converters in gate circuits with negative voltage needs with respect to cost, size, reliability, and efficiency. Importantly, the proposed negative voltage supply allows bootstrapping without the need for controllable high-voltage semiconductors for the sake of further cost reduction. We present detailed design rules of the circuit and experimentally validate circuit and control. In the automo-tive prototype implementation, size of the gate driver sup-ply was reduced by 61 %, cost by 57 %, and loss by more than 16 %.
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    Switch-Clamped Modular Multilevel Con-verters with Sensorless Voltage Balancing Control
    (IEEE Transactions on Industrial Electronics) Nima, Tashakor; M., Kilictas; Jingyang, Fang; Goetz, Stefan
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    Systems and Devices for Quiet Transcranial Magnetic Stimulaton and Method of Using Same
    (US 63/079,182) Koponen, Lari; Goetz, Stefan; Peterchev, Angel
    This invention discloses a magnetic stimulation coil (300) for magnetic stimulation in the brain and the peripheral nervous system with reduced sound emissions and a method for manufacturing such stimulation coil. The stimulation coil comprises at least one coil winding core (101, 201) and at least one double casing (310). The magnetic stimulation coil is designed to minimize sound emission through proper assembly of said components.
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    Transcranial Magnetic Stimulation Technology with Fully Adjustable Pulse Shape and Sequence
    Goetz, Stefan; Zhongxi, Li; Jinshui, Zhang; Angel, Peterchev