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Solid state pulsed power systems containing IGBT switches are mainly operating with input voltages between 400 V and 3 kV depending on the maximum allowable blocking voltage of the IGBTs. Nevertheless, high output voltages of several kilovolt can be achieved for example by the use of a pulse transformer, a Marx generator configuration or a combination of both. The pulse power (e.g. 20MW) is normally provided from a capacitor bank whereas the average power (here 25kW) is supplied by a converter connected to the mains, whose line to line voltage can vary from 177 V to 528 V world wide. Depending on the ratio of the mains to the capacitor bank voltage the converter has to work in a buck or boost mode. Additionally, due to the possible high repetition rate of pulse modulators (500-1000Hz) the capacitor bank has to be recharged before the next pulse is generated, which would demand a high dynamic voltage control. In the 3-phase buck boost rectifier a constant current through the buck boost inductor is needed to provide a unity power factor. But the pulse load in combination with the high dynamic voltage control would result in periodic peak currents at the converter input/mains and therefore a unity power factor at the input of the converter can not be guaranteed and the mains current would be distorted. Therefore, a new control for pulse load applications has to be implemented which achieves a unity power factor and an accurate regulation of the output voltage. First, in the paper the structure/operation principle of a standard buck boost converter is described and the problems resulting from the pulse load are discussed. Thereafter, a new control is derived which avoids the mentioned problems. Finally, the paper is concluded with measurement results for the input currents and the DC voltage during pulse operation.