Half-Bridge Welding Inverter Commutation for di/dt Control

The patent segments the inverter operation into distinct quadrants (Q1, Q2, Q3, Q4) with dedicated control strategies for each. By implementing quadrant-specific control logic that manages switch states and commutation timing differently for each operating mode, the system achieves four-quadrant control capability while maintaining the simpler half-bridge topology. This segmentation allows the inverter to handle motoring and generating modes, as well as positive and negative power flow, without requiring the full complexity of a full-bridge configuration.

The patent introduces an intermediary commutation circuit with commutation inductors and capacitors that mediates the current transfer between main switches. This commutation network provides a controlled path for current transition, reducing the stress on commutation diodes and switches. The commutation inductors store energy during the switching transition and release it smoothly, while commutation capacitors provide voltage clamping and energy recovery, thereby reducing excessive heat generation in the commutation components while maintaining reliable current commutation.

The patent implements beforehand cushioning by incorporating snubber circuits with capacitors and resistors parallel to the switches, and by designing the commutation network with capacitors that provide voltage clamping before excessive voltage can damage the switches. These protective elements are pre-configured to absorb voltage spikes and limit the maximum voltage stress on switches during commutation and transient events, thereby preventing switch failures while maintaining the necessary voltage clamping for safe operation.

The patent employs feedback control by sensing the output current and using this information to dynamically adjust the switching states of the inverter and the firing angles of thyristors or IGBTs. The control system continuously monitors the current decay rate and modulates the switching duty cycles to achieve the desired current profile. This active feedback control enables precise current decay rate adjustment without relying on fixed passive impedance elements, thereby minimizing power dissipation while maintaining controlled current transitions.

The patent achieves multi-functionality by designing the half-bridge inverter switches and commutation network to serve multiple purposes: they perform both the primary power conversion function and the arc reversal function. The same IGBTs or thyristors that control the main power flow are also used to apply the high voltage necessary for arc reversal by adjusting their switching sequences. The commutation capacitors and inductors that facilitate current transfer also provide the voltage boost needed for arc extinction and reignition. This universal use of existing components eliminates the need for separate assist circuitry, maintaining arc stability during reversal without adding extra circuit complexity.