Monitor for inverter bridge commutation - uses signals from current pick=ups in bridge diagonals which are added and trip signal when sum is too large

摘要

The investor output is connected to an oscillating circuit. The invertor thyristors in opposite bridge branches are ignited in opposite phases by a control circuit, so that current flows through one diagonal in one half-period, and through the other diagonal in the other half-period. A current pick-up is inserted in each diagonal, whose output signals commutation disturbances to a switching device. The switching device sensitivity abruptly changes from zero to a maximum in synchronism with the invertor frequency. The switching device (20-25) sensitivity is a max. around the commutation instant, and zero during the remaining time. An adder (24) totals commutation signals, and a signal is tripped when the sum exceeds a threshold.