The present conceptual design of the DEMO NBI foresees an acceleration voltage of 1 MV, subdivided in 5 steps of 200-kV each, as is the case of the ITER NBI. This voltage is provided by the Acceleration Grid Power Supply (AGPS), which shall also guarantee the capability of handling repetitive grid breakdowns and provide the required high dynamic response, low ripple and high accuracy. These requirements addressed the ITER AGPS design towards a challenging solution based on a two-stage approach, with a set of five step-up transformers integrated with HV diode rectifiers, each fed by a dedicated inverter. The research here presented aims at evaluating the possible utilization of Modular Multilevel Converters (MMCs) for the AGPS of future NBIs, trying to identify strengths and criticalities of this alternative approach. The MMC topology is promising due its intrinsic properties of modularity, efficiency, redundancy and scalability. A preliminary design of the DEMO AGPS has been carried out, where each 200-kV voltage step is generated by a MMC operating as a rectifier. The main circuit parameters of the MMC have been determined, considering normal and anomalous working conditions. A numerical model has been developed to verify the converter performances in stationary and dynamic conditions and to simulate breakdown and beam-off events. The area occupied by the proposed MMC-based AGPS has been tentatively estimated and compared to that of the ITER solution. The results of the analysis are shown in this paper, demonstrating that the precision and dynamic requirements are satisfied and the system could be able to handle also the anomalous working conditions. In addition, the charge transferred to the arc at grid breakdown is significantly lower compared to the ITER AGPS, implying less damages to the grids. Finally, pros and cons of the MMC and ITER solutions are discussed.
Application studies of the Modular Multilevel Converter topology to the Acceleration Grid Power Supply of the DEMO Neutral Beam Injector
Gaio Elena
2020
Abstract
The present conceptual design of the DEMO NBI foresees an acceleration voltage of 1 MV, subdivided in 5 steps of 200-kV each, as is the case of the ITER NBI. This voltage is provided by the Acceleration Grid Power Supply (AGPS), which shall also guarantee the capability of handling repetitive grid breakdowns and provide the required high dynamic response, low ripple and high accuracy. These requirements addressed the ITER AGPS design towards a challenging solution based on a two-stage approach, with a set of five step-up transformers integrated with HV diode rectifiers, each fed by a dedicated inverter. The research here presented aims at evaluating the possible utilization of Modular Multilevel Converters (MMCs) for the AGPS of future NBIs, trying to identify strengths and criticalities of this alternative approach. The MMC topology is promising due its intrinsic properties of modularity, efficiency, redundancy and scalability. A preliminary design of the DEMO AGPS has been carried out, where each 200-kV voltage step is generated by a MMC operating as a rectifier. The main circuit parameters of the MMC have been determined, considering normal and anomalous working conditions. A numerical model has been developed to verify the converter performances in stationary and dynamic conditions and to simulate breakdown and beam-off events. The area occupied by the proposed MMC-based AGPS has been tentatively estimated and compared to that of the ITER solution. The results of the analysis are shown in this paper, demonstrating that the precision and dynamic requirements are satisfied and the system could be able to handle also the anomalous working conditions. In addition, the charge transferred to the arc at grid breakdown is significantly lower compared to the ITER AGPS, implying less damages to the grids. Finally, pros and cons of the MMC and ITER solutions are discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
