State Space Modelling and Control of the Modular Multilevel Converter

In der vorliegenden Arbeit wird ein neuer Ansatz zur Modellierung von Systemen basierend auf dem Modularen Multilevel Umrichter (MMC) vorgestellt. Mit Hilfe dieses Ansatzes ist es möglich, neue, effiziente Regelungsalgorithmen für das System zu entwerfen. In Zukunft wird es für netzeinspeisende Umrichter immer wichtiger, nicht nur stabil, sondern auch netzverträglich operieren zu können. Ausgehend von analytischen Differentialgleichungen wird ein Zustandsraummodell des MMC abgeleitet und eine Methode zur Entkopplung des Systems abgeleitet. Mathematische Werkzeuge erlauben eine systematische Analyse der auftretenden Steuer- und Ausgangsgrößen. Eine einfache Matrixdiagonalisierung erlaubt eine allgemeine Transformationsregel für MMC-basierte System zu formulieren. Daraus resultieren einfache Möglichkeiten, Leistungsterme zu identifizieren, die die Zweigenergien des Systems im erlaubten Betriebsbereich halten können. Zusätzlich werden Freiheitsgrade der Kreisströme und der Nullspannung formuliert. Wie für MMC-basierte Topologien erwartet, können sie zur Reduzierung der Energiepulsationen der Zweige eingesetzt werden. Mit der vorgestellten Modellbeschreibung ist es möglich, neue Optimierungsverfahren unter Einbeziehung aller Freiheitsgrade durchzuführen, die eine Reduzierung der Energiepulsationen ermöglichen

Control Strategy for Modular Multilevel Matrix Converters at High Output Frequencies

This paper presents a new control strategy for Modular Multilevel Matrix converters where the output frequency is higher then the input frequency. In operating points when ω$_{out}$ $\geq \$ ω$_{in}$ the energy pulsation in the converter cells are dominated by the second harmonic of the input frequency. These energy pulsations can be identified and compensated by inducing additional currents. The results are verified by simulation for a laboratory scaled prototype of the Modular Multilevel Matrix Converter

Hardware-in-the-Loop Test Rig for Rapid Prototyping of Battery Management System Algorithms

Testing the performance of a battery management system (BMS) is extensive and crucial due to its importance for the overall battery safety and performance. In this paper, a hardware-in-the-loop (HiL) test bench is presented for rapid prototyping, testing and evaluation of BMS algorithms in realtime. The system is designed to work with real cell packs without any additional electronics or casing. This approach avoids the high cost and effort of building a full battery system and therefore simplifies algorithm testing on different cell types and cell pack topologies. An extended Kalman Filter based state-of-charge-algorithm is developed and compiled in C-Code in MATLAB/Simulink to run on a digital signal processor (DSP) in real-time. The capabilities and advantages of the setup are shown with experimental HiL tests of the developed BMS algorithm in comparison to software-in-the-loop (SiL) tests

Energy Pulsation Reduction in Modular Multilevel Converters Using Optimized Current Trajectories

In power electronics, the modular multilevel converter (MMC) is an easily scalable topology with an high output voltage quality. It is suitable for the transmission of large amounts of electrical power over long distances, which supports the realization of the ongoing energy transition. State-of-the-art methods require a comparatively large total cell capacitance in the system for energy pulsations during operation. In the present paper, in order to minimize this total capacitance, first a new method is developed to model the system, and second, by help of this model, optimal current trajectories are calculated. These currents are used for control to reduce the energy pulsation over the complete operating range, and thus, to better utilize the hardware. The new method independent on the Clarke transformations is implemented on a laboratory scale setup, and measurement results are presented which validate the new method. Furthermore, the new method is compared to the state-of-the-art method of the compensation of the 2nd harmonic and outperforms the latter significantly. This applies to the entire operating range for different power factors. A total reduction of up to 44% of the energy pulsations is achieved

A Modular Multilevel Matrix Converter for High Speed Drive Applications

The Modular Multilevel Matrix Converter (M3C) performs a direct three-phase AC to AC power conversion and is highly suitable for medium voltage high power drive applications. One area of application are high speed drives such as compressors. However, additional balancing power components which reduce the output power capability of the M3C when input and output frequencies are similar occur. This paper analytically examines the operation behavior and power capability in these operation points in order to assess whether the M3C can generate these additional components without oversizing the converter\u27s components. Subsequently, the theoretical evaluation is verified by a laboratory scaled prototype with a rated power of 15 kW

Hardware-in-the-Loop Setup for a Modular Multilevel Converter with Integrated Batteries

A hardware-in-the-loop setup to emulate a modular multilevel converter (MMC) with batteries integrated in its submodules is presented. It allows the testing of control methods without a real converter. A state-space MMC model is introduced, extended by RC battery models and implemented on an FPGA. The scalability of battery models for converters with large numbers of submodules is shown. The emulation closes the loop for a combined MMC-controller and battery management algorithm under test, running on an ARM processor. Given the modular approach, the level of detail for power electronics, batteries and control schemes can be adapted independently

Operating Performance of the Modular Multilevel Matrix Converter in Drive Applications

The Modular Multilevel Matrix Converter (M3C) is an emerging topology, especially suitable for high torque low speed drive applications in the medium voltage range. One special benefit is the overload capability of the output currents. Up to 200% of the nominal values can be reached near standstill to overcome breakaway torques without additional efforts. This contribution gives an experimental verification of the operating performance by using a low voltage laboratory prototype with 5 cells per arm. In addition, different energy balancing methods, depending on the operating point are presented. Finally, possible applications for the M3C are discussed

Cell design of a square-wave powered 1AC-3AC modular multilevel converter low voltage prototype

This paper presents a novel design calculation scheme for low voltage Modular Multilevel Converters. One of the most important design values is to estimate the lifetime of the electrolytic cell capacitor. Therefore, a novel calculation method for the arm capacitor root mean square current is presented. Additionally, a new algorithm to estimate the power losses without a detailed simulation of the switching events is introduced. The results from these calculations are used to construct a low voltage Modular Multilevel Converter with 8 cells per arm

Modular Multilevel Converters as Active Filters to Mitigate Low Frequency Current Harmonics in Converter Fed Grid Applications

This paper describes a method to improve converter fed grid structures with Modular Multilevel Converters (MMC). In grids with decentralized energy production and bidirectional power flow, an increasing number of power electronic loads and sources make power quality an important issue to ensure grid stability. The MMC topology is highly suitable to meet the requirements of a low Total Harmonic Distortion (THD) and voltage stability due to its high quality output voltages. In combination with power line communication based on harmonic injection, MMCs compensate low frequency grid current harmonics and imbalances to improve the power quality. A standalone laboratoryscale converter-fed microgrid including low voltage MMCs shows the capability of the developed control algorithms