Control Algorithms Developed for the Enhanced Radial Field Amplifier (ERFA) for JET

The company JEMA has delivered to the Joint European Torus (JET facility at Culham) the Enhanced Radial Field Amplifier (ERFA). This device is a high frequency, high power amplifier aimed at correcting instabilities due to fast plasma disturbances. The system is composed of four identical units connected in series through a connection box delivering up to +/-12kV +/-5kA (60MVAr) in four quadrant operation. Each unit is composed of an input converter stage, a DC link energy storage stage, an output inverter and an output bypass (for continuing operation in case of a unit failure). ERFA works as an energy exchanger between the internal DC link capacitors bank and the JET radial field coils. The input converter compensates for power losses in the JET coils and the ERFA during operation. The ERFA control system is fundamental for the amplifier performance to meet the speed of response required with the flexibility to achieve this for an unpredictable reference and for a wide range of load coil configurations. This paper covers the control architecture, the real-time evaluation and high speed response to the system requirements, and the fast exchange rate of data among ERFA units.
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