Abstract: A control arrangement for a multilevel convertor employs an AC reference signal which is locked to the AC system frequency and is compared with a number of DC threshold levels. Intersections of the reference signal and threshold levels triggers the firing and turning-off of GTOs within the convertor to produce the desired multilevel voltage output. Normal changes in system voltage, for example, are compensated by variation of the phase relationship of the reference signal with respect to the system voltage, and/or of the voltage values of the threshold levels. Sudden and drastic changes, especially reductions, in system voltage level are sensed and used to alter the amplitude of the reference signal so as to reduce the difference between the convertor multilevel voltage and the system voltage, thereby reducing the stress on the GTOs during faults.

Abstract: The invention provides a radar system in which the average power output of the radar transmitter is increased to a value above its rated mean power during a dwell time during which the radar beam traverses a target of interest. The system includes a power supply arrangement which is operative normally to supply power to the transmitter and means for supplementing the power supply during periods in which the average power output of the transmitter is increased. In one embodiment the normally operative power supply consists of a plurality of individual power supplying inverters arranged normally to supply power to the transmitter sequentially and in turn, but in unison during periods in which the average power output is increased. In the output path of each inverter is included a re-circulatory current inductive circuit such that current tends to be maintained after the inverter ceases to supply power in its turn.