arXiv subjects

Stefan M Goetz

Publications and source records attributed to Stefan M Goetz.

3 recordsLinked to original sources

arXiv2026

Four-Transistor Four-Diode (4T4D) Series/Parallel Chopper Module for Auto-Balancing STATCOM and Low Control and Development Complexity

Static synchronous compensators (STATCOMs) manage reactive power compensation in modern power grids and have become essential for the integration of renewable energy sources such as wind farms. Cascaded H bridges have become the preferred topology for high-power STATCOMs, but balancing module capacitor voltages remains a persistent challenge. Conventional solutions equip every module with a voltage sensor -- a component that is costly, temperature-sensitive, and prone to aging-related failures. Recent parallel-capable module topologies can balance voltage through switched-capacitor operation. The latest developments reduced the sensor requirement from one per module to one per arm. However, these implementations require twice as many individual transistors compared to series-only topologies. We present a STATCOM solution based on the four-transistor four-diode (4T4D) series\,/\,parallel chopper cell. This topology achieves bidirectional parallelization with only four transistors per module -- exactly as many as a conventional full bridge. Furthermore, we propose a dual-loop control strategy that fully eliminates module voltage sensors by inferring voltage levels from the modulation index. This scheme also improves output quality by regulating the modulation depth. We validated our proposal through simulation and experiments. We built a prototype to interface the grid. The prototype further passed robustness tests with step change, current direction reversal, and grid disturbance. This work demonstrates the first modular STATCOM implementation that combines minimum transistor count with complete elimination of module voltage sensors.

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arXiv2025

Four-Transistor Bipolar Series-Parallel Module Structure for Cascaded Bridge and Modular Multilevel Circuits

With their great scalability and flexibility, cascaded-bridge and modular multilevel converters have enabled a variety of energy applications, such as offshore wind power, high-voltage dc power transmission, power-quality management, and cutting-edge medical instrumentation. The incorporation of parallel connectivity between modules equips systems with advantages such as sensorless balancing, switched-capacitor energy exchange, and reduced impedance. However, existing topologies require many individual switches -- eight transistors per module. Efforts to use fewer switches, instead, have previously compromised their functionality. We propose a new module topology, named the direction-selective parallel (DiSeP) structure, which requires only four transistors per module -- the same as an H bridge -- but can achieve bidirectional equilibration, bipolar module output, and inter-module switched-capacitor features. This topology is highly attractive for existing converters with cascaded bridge elements, as the addition of only four diodes enables key features such as sensorless balancing and inter-module energy exchange. Thus, the module can outcompete H bridges in their applications, as it adds parallel modes without any additional transistors. Compared to double-H bridges (CH2B), it saves as many as half of the transistors. We elaborate on its working principles and key design considerations. We validate our theories on an experimental prototype with six modules. This prototype attains a total voltage harmonic distortion plus noise (THD+N) of 10.3% and a peak efficiency of 96.3%. Furthermore, the modules achieve autonomous sensorless balancing under open-loop control.

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arXiv2025

Conditional Nearest Level Modulation for Improved Switching Dynamics in Asymmetric Multilevel Converters

Modular multilevel converters have promising applications in clean energy, electric vehicles, and biomedical instrumentation, but need many modules to achieve fine output granularity, particularly of the voltage. Asymmetric multilevel circuits introduce differences in module voltages so that the quantity of output levels grows exponentially with the number of modules. Nearest-level modulation (NLM) is preferred over carrier-based methods in asymmetric circuits for its simplicity. However, the large number of output levels can overwhelm NLM and cause excessive transistor switching on some modules and output voltage spikes. We propose a conditional nearest-level modulation (cNLM) by incorporating mathematical penalty models to regulate switching dynamics. This approach improves output quality and reduces switching rates. Additionally, we present cNLM variations tailored for specific functions, such as enforcing a minimum switching interval. Experimental validation on an asymmetric multilevel prototype demonstrates that cNLM reduces the total output distortion from 66.3% to 15.1% while cutting the switching rate to just 8% of the original NLM.

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