Abstract
The data-driven control approach is a control methodology in which a controller is designed without the need of a model. Parametric uncertainties and the associated unmodeled dynamics are therefore irrelevant; the only source of uncertainty comes from the measurement process. The CERN Power Converter Control Libraries (CCLIBS) have been updated to include data-driven H-infinity control methods recently proposed in literature. In particular, a two-step convex optimization algorithm is performed for obtaining the 2-degree-of-freedom controller parameters. The newly implemented tools in CCLIBS can be used both for frequency response measurement of the load and for controller synthesis. A case study is presented where these tools are used for an application in the CERN East Area Renovation Project for which a high-precision 900 A trapezoidal current pulse is required with 450 ms flat-top and 350 ms ramp-up and ramp-down times. The tracking error must remain within +/- 100 parts-per-million (ppm) during the flat-top (before the ramp-down phase starts). The magnet considered in the case study is of non-laminated iron type, hence the necessity of data-driven techniques since the dynamics of such a magnet is difficult to be modeled accurately (due to eddy currents losses). The power converter used is a SIRIUS 2P (with a current and voltage rating of 400 Arms and 450 V, respectively) whose digital control loop is regulated at a sampling rate of 5kS/s.
Highlights
The CERN power converter control libraries [1] have recently been updated to include tools both for frequency response function (FRF) measurement and for data-driven design of power converters digital control
The data-driven approach mitigates the problems associated with modelbased controller designs; this ensures that the measurement process is the only source of uncertainty
Data-driven control schemes can be realized in the time-domain and frequency-domain; in Converter Control Libraries (CCLIBS), or more accurately, in an extension of the Function Generator/Controller (FGC) [3] system that combines embedded control computers along with expert software tools, the frequency-domain approach is used (CCLIBS will be used as a shorthand both for CCLIBS themselves and this FGC extension)
Summary
The CERN power converter control libraries [1] have recently been updated to include tools both for frequency response function (FRF) measurement and for data-driven design of power converters digital control. CERN adopted the RST control structure for the control of the current in the particle accelerator magnets since LHC; the control is implemented by the FGC platform [3]. Particle accelerator magnets sometimes sufer from eddy currents losses which complicates their modeling process as electrical load of the power converter. The grid supply unit limits the power taken from the power grid to just 20 kV A with a modest 32 A / 400 V 3-phase line voltage
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