A Better Current Limit

摘要

A novel control circuit reacts to an over current condition in a DC to AC powerconversion circuit, such as a phase modulated full bridge, to always bring the operatingpoint to a safe condition. The circuit uses information about the direction as well as theamplitude of the primary current to control active power switching elements to drive thecurrent toward zero. This is consistent with pulse-by-pulse current limiting, allowing theconverter to operate in current limit on each cycle, resuming normal operation on thefollowing cycle when the abnormal condition is removed. This works well even if thesensing information is delayed or heavily filtered, or if the switch signals are delayed inreaching the switch elements. The algorithm has been realized in a programmable logicarray, including blanking of noisy inputs not meeting the conditions for return to normaloperation during an over current event. The resulting converter control is more resistantto abnormal load conditions, maintaining converter operation in the presence of transientshort circuits or arcs, and protecting the converter hardware.