Switched mode power supplies in the HERA proton ring

To feed the superconducting correction magnets of the HERA proton ring, switched mode power supplies have been developed at DESY (Deutsches Elektronen-Synchrotron). The nominal power is up to 35 kW. The current is in a range from 60 A to 360 A. The choppers work as buck converters, switching a primary voltage with a pulse width modulation (PWM). MOSFET transistors are used as switches. The primary voltage is delivered by six pulse diode rectifiers. One rectifier supplies up to 32 choppers. To achieve bipolar behavior of the unipolar units, mechanical polarity switchers are mounted. Dynamic zero crossing can thus be done with an error less than 800 ppm of the nominal current within 300 ms. Afterwards the error is less than 100 ppm. The load time constants (L/R) are between 0.01 and 9.4 s, with superconducting inductances between 1 mH and 4.5 H