Estimation of Output Voltage Ripple in Phase-Staggered Series-Connected Two-Quadrant Power Converters for Electromagnets in Particle Accelerators

In booster synchrotron, fast-ramped power converters (FRPCs) are used for ramping up the magnetic field of electromagnets connected in series, at a fast rate, typically 1,000s of ampere per second. In large accelerators, the number of electromagnets is large. Therefore, during ramping, the peak value of driving voltage becomes prohibitively large considering the insulation requirement of the magnets and cables. The power converter is therefore developed by connecting a suitable number of smaller voltage rated modules in series. The series-connected modules are operated in phase-staggered mode to reduce the output voltage ripple or to reduce the filtering requirement to meet the prescribed ripple voltage. Since the filter component values predominantly decide the dynamic response, the achievable small-signal bandwidth of the control loop and hence the achievable tracking accuracy of the ramping output current are essentially governed by the filter components. To optimise the filter design, quantification of overall ripple voltage is crucial, that too under the most practical conditions considering non-ideal conditions. In this paper, estimation of overall ripple voltage is performed for series-connected two-quadrant power converters (TQPCs) operating in phase-staggering mode for ideal and non-ideal conditions. Simulation and experimental verification results are shown to be in good agreement with the analytical results.