Virtual Submodule Concept for Fast Semi-Numerical Modular Multilevel Converter Loss Estimation

During the design phase of a modular multilevel converter (MMC), an accurate loss evaluation of the submodule (SM) plays an important role. In this paper, a method based on the analytical description of the MMC key waveforms that allows to directly obtain the average semiconductor and capacitor losses that each SM will experience is introduced, under different operating conditions or control schemes. To verify the proposed concept, the results are compared with the losses obtained from a switched model with closed-loop control, where the analytical MMC key waveforms are approached in steady state. The proposed method provides a great flexibility and a significant reduction of the simulation / computational time otherwise needed to evaluate SM losses under various operating conditions

FPGAs in Industrial Control Applications

The aim of this paper is to review the state-of-the-art of Field Programmable Gate Array (FPGA) technologies and their contribution to industrial control applications. Authors start by addressing various research fields which can exploit the advantages of FPGAs. The features of these devices are then presented, followed by their corresponding design tools. To illustrate the benefits of using FPGAs in the case of complex control applications, a sensorless motor controller has been treated. This controller is based on the Extended Kalman Filter. Its development has been made according to a dedicated design methodology, which is also discussed. The use of FPGAs to implement artificial intelligence-based industrial controllers is then briefly reviewed. The final section presents two short case studies of Neural Network control systems designs targeting FPGAs

Cross connected multilevel voltage source inverter topologies for medium voltage applications

Multilevel voltage source inverters where first introduced in the early 1980s. Since then, they have been continuously developed, offering a wide new research area in power electronics. The popularity of multilevel solutions come from the advantages that they offer: improved output quality, voltage sharing in high voltage applications, increased power density or reduction of filtering costs. Two completely new and innovative cross-connected topological families for advanced multilevel voltage source inverters are introduced in this thesis. The motivation for this work stems out from the need to generate multiple output levels while keeping the reliability as high as possible. The offered solutions are able to address the problematic, but of course they do not come without a price: A higher control complexity and more semiconductor blocking voltage capability are necessary in the design of such advanced converters. The Cross Connected Intermediate Level (CCIL) Voltage Source Inverter is the first of the two new topologies presented here. It is built as a cascade of stages using capacitors which are connected to each other by means of cross connected cell structures. The CCIL can be used in several configurations, like redundant or non-redundant switching state configurations for instance. A graphical model based on the physical properties of the inverter is proposed and an original fuzzy logic controller is designed for the balancing of the capacitor voltages and modulation of the inverter. The control algorithm is implemented and verified in simulations. The results are used to benchmark the topology against standard solutions and the conclusions are used to define what applications could benefit from such a converter structure. The Common Cross Connected Stage (CCCS) Voltage Source Inverter is the second original contribution of this work in terms of topology. It is built using the cross connected stage and its capacitor in a common configuration for the three phases of the inverter. Such a design allows to use only one stage per three phases. Because of the intrinsic three phased properties of this topology, a model based on space phasor representation is introduced. With the help of this model, a novel space phasor modulation strategy is derived and proposed. It allows to generate the three phased output voltages while using the available redundancies for balancing of the capacitor voltages. The resulting algorithm is first implemented and tested in simulation, and in a second step a test setup is built and the modulator is coded in VHDL. The simulation and experimental results obtained validate the topology and control concepts. A benchmarking of the CCCS solution is also done to understand what are the benefits and drawbacks of this solution. Analysis and comparison of the new topologies allow to evaluate in an objective way the contributions brought by this work. It is found that the newly proposed solutions cover an area of multilevel inverters where not so many solutions were available prior to this work: Generation of multiple output levels with reduced number of passive and active components (thus increasing the reliability). The drawback is a higher blocking voltage requirement. Conclusions and case study are proposed to help assess the expected performances and choose the most suitable solutions for given applications

Control Strategies for Improving Reliability and Efficiency in Modular Power Converters

The significance of modular power converters has escalated drastically in various applications such as electrical energy distribution, industrial motor drives and More Electric Aircraft (MEA) owing to the benefits such as scalability, design flexibility, higher degree of fault tolerance and better maintenance. One of the main advantages of modular systems is the ability to replace the faulty converter cells during maintenance instead of the entire system. However, such maintenance cycles can result in a system of converter cells with different aging. A system with cells having different aging arises the threats of multiple maintenance, lower reliability and availability, and high maintenance costs. For controlling the thermal-stress based aging of modular power converters, power routing strategy was proposed. The thesis focuses on the different implementation strategies of power routing for modular converters. Power semiconductors are one of the most reliability critical components in power converters, and thermal-stress has been identified as the main cause of their failure. This thesis work concentrates on the power semiconductor reliability improvement algorithms. For improving system lifetime, virtual resistor based power routing algorithms for single stage and multi-stage modular architectures have been investigated through simulations and validated with experiment. A unified framework for routing the power in complex modular converter architectures is defined based on graph theory. Popular converter architectures for Smart Transformer (ST) and MEA applications are modeled as graphs to serve as the basis for developing power flow optimization. The effectiveness of graph theory for optimizing the power flow in modular systems is demonstrated with the help of proposed algorithms