Transistor-based Converters Research Articles

Common-Mode EMI Unterminated Behavioral Model of Wide-Bandgap-Based Power Converters Operating at High Switching Frequency

With wide-bandgap semiconductors increasing their commercial availability, high switching frequency operation has become an accepted practice to increase power density in power converters. High switching frequency operation, nonetheless, increases the electromagnetic interference (EMI) emissions of converters, for which accurate models are needed in order to predict their EMI noise and aid in the design of necessary filters. To this end, this paper assays first the impact that high switching frequency has on converter EMI emissions, and second, uses an unterminated behavioral model (UBM) to predict the common-mode (CM) emissions in the conducted EMI range (150 kHz–30 MHz). To achieve this, a new extraction procedure is developed for a UBM to effectively capture the rich high-frequency content of the CM emissions, providing a solution to the inherent limitations of previous behavioral models developed for insulated-gate bipolar transistor-based converters. The experimental results obtained with two setups: a 3-kW, 300-V dc, silicon-carbide-based three-phase inverter switching at 70 kHz and a 1-kW, 400-V dc, gallium nitride -based three-phase inverter switching at 500 kHz are presented to validate the approach and the model capabilities.

Effect of Converter Topology on the Specific Energy Consumption of Alkaline Water Electrolyzers

Water electrolysis will be used to produce renewable hydrogen for energy storage and Power-to-X applications in the future renewable-energy-based energy systems. Therefore, the energy efficiency of hydrogen production will probably become a major issue. In this study, the effect of practical supply power converters on the specific energy consumption of megawatt (MW)-scale alkaline electrolyzers is studied and compared with an ideal dc power supply. The current quality and the stack specific energy consumption are studied in the case of traditional thyristor rectifiers and a transistor-based converter. The stack specific energy consumption is analyzed based on the simulated current waveforms and the electrical equivalent circuit of the electrolyzer stack. It is found that the transistor-based converter offers up to 14% lower electrolyzer stack specific energy consumption than the 6-pulse thyristor rectifier and up to 9.2% lower electrolyzer stack specific energy consumption than the 12-pulse thyristor rectifier as the current varies between 5000 and 1000 A. The simulated change in the stack specific energy consumption of the MW-scale alkaline water electrolyzer outweighs the losses occurring in the rectifiers. Further, selection of the ac voltage level may have a more adverse effect on the stack specific energy consumption with the thyristor rectifier topologies compared with the transistor-based topologies.

High-Efficiency mosfet-Based MMC Design for LVDC Distribution Systems

Low-voltage dc (LVdc) distribution networks have the potential to release larger capacity without having to upgrade the existing cables. One of the main challenges of LVdc networks is the extra customer-end dc–ac conversion stage. This paper proposes and evaluates a five-level Si mosfet -based modular multilevel converter (MMC) as a promising alternative to the conventional two-level insulated gate bipolar transistor-based converter. This is due to the comparatively higher efficiency, power quality and reliability, and reduced electromagnetic (EM) emissions. A comprehensive analysis of a Si mosfet five-level MMC converter design is performed to investigate the suitability of the topology for LVdc applications. Detailed theoretical analysis of the five-level MMC is presented, with simulated and experimental results to demonstrate circuit performance. To suppress the ac circulating current, especially the dominant second harmonics, this paper presents a double line-frequency proportional integral (PI) with orthogonal imaginary axis control method. Comparison of simulation and experimental results with those for double line-frequency proportional resonant control shows that the proposed PI controller has a better performance. In addition, it is simpler to implement and more immune to sampling/discretization errors.

Field-Experience Based Root-Cause Analysis of Power-Converter Failure in Wind Turbines

The frequent power-converter failure experienced in wind turbines has a strong economic impact through both the related turbine unavailability and the maintenance cost. Up to now, the prevailing mechanisms and causes underlying the converter failure in wind turbines are mostly unknown. Their identification is, however, a prerequisite for the development of effective solutions. This paper describes a multitrack empirical approach to failure analysis including systematic field-data evaluation, exploration of the real converter operating environment, and postoperational laboratory investigation of converter hardware. The analysis is carried out for two widely used multi-MW wind turbines with low-voltage, insulated-gate bipolar transistor-based converters (topology 1: doubly fed induction generator with partially rated converter, topology 2: induction generator with fully rated converter). The findings suggest that the principle failure mechanisms of power electronics found in other applications, namely solder degradation and bond-wire damage, play a minor role in the investigated types of wind turbines. Instead, the analysis reveals indications of insufficient protection of the converter hardware against the environment (salt, condensation, and insects) as well as indications of electrical overstress.

Multiport High-Power LCL DC Hub for Use in DC Transmission Grids

This paper proposes an LCL dc hub concept which plays the role of a dc substation in a dc grid. The hub is capable of connecting multiple dc transmission lines with different dc voltages. Each dc transmission line can be added to or isolated from the hub without affecting the operation of the other dc transmission lines. The hub is based on multiple ac/dc insulated-gate bipolar transistor-based converters and an internal passive LCL circuit without internal ac transformers. The LCL circuit is designed to interconnect multiple ac/dc bridges with different dc voltages and achieving minimal reactive power circulation at each converter bridge. Each ac/dc bridge controls its active power independently. The designed hub has the ability to ride through the dc faults by keeping the fault current within the order of its rated value. Detailed PSCAD/EMTDC simulations of a seven-port test system are presented to validate the proposed topology.

LCL DC/DC Converter for DC Grids

This paper proposes an LCL dc-dc converter concept which is capable of achieving very high stepping ratios with megawatt-level power transfers. The converter can find potential application in connecting high-power dc sources to high-voltage dc transmission including future dc transmission networks. This converter is based on two ac/dc insulated-gate bipolar transistor-based converters and an internal passive LCL circuit without internal ac transformers. The LCL circuit is designed to enable voltage stepping without any reactive power circulation and with potentially soft switching operation which minimizes the switching losses. The designed converter has the ability to achieve current regulation even under extreme external dc faults and, therefore, the converter can operate through dc faults. The switch utilization is better than similar topologies and losses are reasonably low. A dual-active-bridge transformer-based converter design is presented to compare with the proposed LCL converter. A detailed PSCAD model confirms conclusions using a 100-MW 20-kV/300 kV test system. An LCL 200-W 20-V/100-V dc/dc prototype converter is built to validate the proposed topology.