Load-controlled inverter for induction furnace - has valves in bridge for bringing load capacitance and inductance oscillation without additional power circuit components

摘要

The load circuit of the inverter (4) is connected across the diagonal of the bridge and comprises a capacitor (C1) in parallel with a series combination of capacitor (C2), resistor (R) and inductance (L). The latter two components represent the furnace and its charge. The proposed starting process operates in three steps. First, one diagonal of the bridge (VA1,VA2) is turned on. Current flows from the d.c source (1), charges the capacitors, and the valves (VA1,VA2) extinguish at current zero. A short circuit is then applied to the system by firing two valves in series (VA1,VB2). At a certain current value the third stage is initiated by firing a diagonal valve (VA2). The short circuit current diverts to the incoming valve. At this stage the oscillation has in effect been started. A voltage is developed across the capacitor bank (C1) which ensures a current flow through the load in each half cycle.