29th Symposium on Fusion Technology (SOFT 2016)

P2.023 Final design of acceleration grid power supply conversion system of MITICA neutral beam injector

6 Sep 2016, 14:20

1h 40m

Foyer 2A (2nd floor), 3A (3rd floor) (Prague Congress Centre)

Board: 23

Poster B. Plasma Heating and Current Drive P2 Poster session

Speaker

Loris Zanotto (Consorzio RFX)

Description

The Acceleration Grid Power Supply supplies the acceleration grids of the MITICA experiment, the full scale prototype of the ITER Neutral Beam Injector under construction in Padua (Italy) to tackle the technical challenges and prepare for the target performance objectives ahead of operation in ITER. The AGPS is a special switching power supply with demanding requirements: high rated power (55 MW), extremely high output voltage (-1MV dc), long duration pulses up to 1 hour and a unconventional operational scenario, where frequent short-circuits of the acceleration grids must be witheld by the system. The procurement of the AGPS is split in two: the low voltage Conversion System (AGPS-CS,) procured by the European domestic agency, and the high voltage DC Generators (AGPS-DCG), procured by the Japanese domestic agency. This paper deals with the AGPS-CS. Being an unconventional system, in-depth studies were carried out in the past years to assess the feasibility of the requirements, produce the functional specifications for the procurement and work out a suitable reference design . The executive design phase by Nidec-ASI, who was awarded the contract late 2015, is presently in progress; the basic choices of the reference scheme, composed of an input ac/dc converter connected via capacitive dc link to five Neutral Point Clamped (NPC) inverters, were endorsed by the Manufacturer. All the design details are now being finalized and suitable models developed to verify the system performance by means of numerical simulations. Special attention is devoted to the inverter modules, based on 6.5kV Integrated Gate Commutated Thyristors, which must comply with severe conditions in case of internal faults, due to the large amount of energy stored in the DC link capacitors. The paper will present the analyses to finalize the AGPS-CS design and will discuss the main design choices, in particular concerning the internal fault protections.