Intelligent Fault Diagnosis Framework for Modular Multilevel Converters in HVDC Transmission

Open circuit failure mode in insulated-gate bipolar transistors (IGBT) is one of the most common faults in modular multilevel converters (MMCs). Several techniques for MMC fault diagnosis based on threshold parameters have been proposed, but very few studies have considered artificial intelligence (AI) techniques. Using thresholds has the difficulty of selecting suitable threshold values for different operating conditions. In addition, very little attention has been paid to the importance of developing fast and accurate techniques for the real-life application of open-circuit failures of IGBT fault diagnosis. To achieve high classification accuracy and reduced computation time, a fault diagnosis framework with a combination of the AC-side three-phase current, and the upper and lower bridges’ currents of the MMCs to automatically classify health conditions of MMCs is proposed. In this framework, the principal component analysis (PCA) is used for feature extraction. Then, two classification algorithms—multiclass support vector machine (SVM) based on error-correcting output codes (ECOC) and multinomial logistic regression (MLR)—are used for classification. The effectiveness of the proposed framework is validated by a two-terminal simulation model of the MMC-high-voltage direct current (HVDC) transmission power system using PSCAD/EMTDC software. The simulation results demonstrate that the proposed framework is highly effective in diagnosing the health conditions of MMCs compared to recently published results.

Optimization-Based Capacitor Balancing Method with Selective DC Current Ripple Reduction for CHB Converters

From its introduction to the present day, Cascaded H-Bridge multilevel converters were employed on numerous applications. However, their floating capacitor, while advantageous for some applications (such as photovoltaic) requires the usage of balancing methods by design. Over the years, several such methods were proposed and polished. Some of these methods use optimization techniques or inject a zero-sequence voltage to take advantage of the converter redundancies. This paper describes an optimization-based capacitor balancing method with additional features. It can drive each module DC-Link to a different voltage for independent maximum power point tracking in photovoltaic applications. Moreover, the user can specify the independent active power set points to modules connected to batteries or any other energy storage systems. Finally, DC current ripple can be reduced on some modules, which can extend the lifespan of any connected ultra-capacitors. The method as a whole is tested on real hardware and compared with the state-of-the-art. In its simplest configuration, the presented method shows greater speed, robustness, and current wave quality than the state-of-the-art alternative in spite of producing about 1/3 fewer commutations. Its other characteristics provide additional functionalities and improve the adaptability of the converter to other applications.

Future Renewable Energy Communities Based Flexible Power Systems

This paper presents a new holistic approach that combines solutions for the future power systems. It describes clearly how solar energy is definitely the best outlet for a clean and sustainable planet, either due to their use in both vertical (V) or horizontal (H) forms such as: hydroelectric V&H, wind V&H, thermo-oceanic V&H, water movement sea V&H (tides and waves), solar thermoelectric, PV, and surface geothermal energy. New points of view and simple formulas are suggested to calculate the best characteristic intensity, storage means and frequency for specific places and how to manage the most well-known renewable sources of energy. Future renewables-based power system requires a huge amount of flexibility from different type and size of controllable energy resources. These flexible energy resources can be used in an aggregated manner to provide different ancillary services for the distribution and transmission network. In addition, flexible energy resources and renewable generation can be utilized in different kinds of energy communities and smart cities to benefit all stakeholders and society at the same time with future-proof market structures, new business models and management schemes enabling increased utilization of flexible energy resources. Many of the flexible energy resources and renewable-based generation units are also inverter-interfaced and therefore the authors present future power converter systems for energy sources as well as the latest age of multilevel converters.

PRINCIPLES OF IMPROVEMENT OF MULTILEVEL AUTONOMOUS VOLTAGE INVERTERS

The article considers the properties of the most commonly used two-and multilevel inverter topologies used in systems for converting electricity from several primary power sources into the required high-quality output voltage for low-voltage networks and high-voltage consumers. However, a common disadvantage of most known multilevel converters is the increasing complexity of power structures, an increase in the number of primary power sources, power elements, and the cost of devices as the number of their voltage levels increases. Two schemes of alternative three-level autonomous voltage inverters with a high-frequency autotransformer with a midpoint and an example of constructing their digital control system are proposed. The analysis of their work on PSpice models in the OrCAD design system is carried out. The possibility of obtaining six voltage sublevels with fewer power elements and increased output voltage quality is shown, compared to the corresponding cascade multilevel inverters. The advantages and applications of autotransformer bridge voltage inverters in terms of energy and functionality compared to well-known multilevel inverters are presented. Ref. 8, fig. 7.

A Unified Switch Loss Model and Design Consideration for Multilevel Boost PFC With GaN Devices

Recently, multilevel converters with gallium nitride (GaN) devices have shown marvelous advantages for power factor correction (PFC) conversion to meet the increasingly higher efficiency and power density requirements. In the traditional design process for the multilevel PFC converter, it is necessary to separately optimize the devices of the corresponding breakdown voltage under different level number, which causes difficulty to the overall optimization of the entire system. In this paper, a unified minimum loss model for GaN switches regardless of voltage levels is proposed to optimize the efficiency based on device’s new figure-of-merit (NFoM) (NFoM = COSS(ER) RDS(on)). With the help of this unified minimum loss model, it simplifies the efficiency optimizing methodology according to the NFoMs of GaN devices for multilevel PFC converter. According to the methodology, a 2 kW cascaded H-bridge (CHB) PFC prototype is constructed to verify the design methodology, achieving over 99% efficiency with power density over 1000 W/in3 .

Five Level Flying-Capacitor Multilevel Converter Using Dynamic Voltage Restorer (DVR)

This paper deals with dynamic voltage restorer (DVR) controlled by a five-level flying-capacitor multi level converter. To decrease the power-quality disturbances in distribution system, such as voltage imbalances, harmonic voltages, and voltage sags. The organisation of this paper has been divided into three parts; the first one eliminates the modulation high-frequency harmonics using filter increase the transient response. The second one deal with the load voltage; and the third is flying capacitors charged with balanced voltages. The MATLAB simulation results effectively for five level flying capacitor multilevel converters charged with balanced voltage regulation.