1. L4T Bending Power Converters: ‘ Implications of monitoring the current to 5% and 0.5%’ L4 BCC - 10 Nov 2011 David Nisbet TEEPC

2. Bending Power Converter The power electronics and control architecture: 10/11/2011TE-EPC - David Nisbet2 TEEPC Output voltage±450V Output current±900 A Pulse repetition rate1.11 Hz Flat-top precision~100 ppm From the workpackage: The same parameters are valid for all the bending converters (L4T: BHZ, BVT) (LT: BHZ20, BHZ30, BHZ40)

3. Controlling the magnet current FGC3 in the PSB (Nov 2011) For L4 bending: control of arbitrary current function to 100ppm accuracy 10/11/2011TE-EPC - David Nisbet3 TEEPC

4. An example of ‘state of the art’ The current of the LHC main quads and dipoles (50Hz samples): Measurements are always subject to sources of noise and perturbations 10/11/2011TE-EPC - David Nisbet4 TEEPC 756.906 A 756.911 A 30mA Imeas of RB (A56, A67) RQF (A56, A67) RQD (A56, A67)

5. The converter interlock architecture 10/11/2011TE-EPC - David Nisbet5 TEEPC

6. The converter interlock architecture 10/11/2011TE-EPC - David Nisbet6 TEEPC Analog comparison for ‘lower’ performance but highly reliable Digitise for high performance, but requires software, etc Converter ON/OFF

7. The converter BIC interface Simple AND of up to 3 conditions to generate a BEAM PERMIT : 1.‘Reliable and robust’ analog threshold validation: ±5% of nominal 2.‘Hi resolution but software’ threshold validation: ±0.5% of nominal 3.Power converter state (‘ON’ and ‘NO FAULT’) Up to 4 separate PERMITS for each power converter: – For example, allows evaluation of destinations and energy levels 10/11/2011TE-EPC - David Nisbet7 TEEPC Only when needed

8. Monitoring the magnet current Example of a scenario for the L4T Horizontal Bending (L4T and L4Z destinations) 10/11/2011TE-EPC - David Nisbet8 TEEPC ~150ms

9. Monitoring the magnet current Typical scenario of information available in the Control Room FGC will publish warnings if deviation from a pre-determined performance level is detected (eg 100ppm, 10 -4 ) – Data can be viewed through CCC alarm monitors – Operator (or control room software) may take appropriate action – Experts will be automatically informed Maximum deviation from reference value can be made available to SIS – SIS may inhibit subsequent pulses based on a pre-determined threshold (eg between 10 -3 and 10 -4 ) BEAM PERMIT will be given to BIS if measured value is within ±0.5% – If for any reason a software bug is present, the analog channel will guarantee the BEAM PERMIT is given only if real measured current value is also within ±5% 10/11/2011TE-EPC - David Nisbet9 TEEPC

10. Conclusion In an operational environment, we are wary of very tight thresholds affecting equipment availability – Electromagnetic compatibility, network perturbation Signals for the BEAM PERMIT cannot be heavily filtered as fast dynamic response is required The power group considers that a ‘Keep It Simple’ approach is the most appropriate method to ensure a reliable and robust BEAM PERMIT interface – A redundant signal architecture will be maintained for coherence with the BIS architecture – The signal is made available for subsequent treatment by the BIS The proposed approach is a compromise to achieve the tight tolerances requested – Analog comparison to obtain a robust permit signal path, but the tolerances must be consequently relaxed (±5%) – Digital comparison to obtain a precise interlock, but this also requires software The extensive reporting and diagnostics available from the FGC3 generation of power systems allows a phased approach if deviation from the reference currents is detected – Intelligent and complementary use of experts, warnings, SIS and BIS 10/11/2011TE-EPC - David Nisbet10 TEEPC