Current stiff converters with resonant snubbers

A current stiff power conversion system, comprising:

• (a) a rectifier bridge of rectifier switching devices forming a rectifier connected between AC input lines and DC bus lines and responsive to rectifier switching device control signals;
• (b) a rectifier snubber capacitor connected across each of the rectifier switching devices;
• (c) a first active commutation unit connected across the DC bus lines in parallel with the bridge of rectifier switching devices and responsive to first active commutation switching control signals;
• (d) an inverter bridge of inverter switching devices forming an inverter connected between the DC bus lines and AC output lines and responsive to inverter switching device control signals;
• (e) an inverter snubber capacitor connected across each of the inverter switching devices;
• (f) a second active commutation unit connected across the DC bus lines in parallel with the bridge of inverter switching devices and responsive to second active commutation switching control signal;
• and
• (g) controller means for providing the rectifier switching device control signals to the rectifier switching devices and the first active commutation switching control signals to the first active commutation unit to control the rectifier switching devices to turn on and off under approximately zero voltage switching conditions to generate a DC signal on the DC bus lines from an AC signal on the AC input lines and to establish a zero current switching condition for the first active commutation unit and for controlling the first active commutation unit to turn on and off under said zero current switching condition to establish a resonance between the first active commutation unit and the rectifier snubber capacitors to establish said zero voltage switching condition for said rectifier switching devices, and for providing the inverter switching device control signals to the inverter switching devices and the second active commutation switching control signals to the second active commutation unit to control the inverter switching devices to turn on and off under approximately zero voltage switching conditions to generate an AC signal on the AC output lines from the DC signal on the DC bus lines and to establish a zero current switching condition for the second active commutation unit and for controlling the second active commutation unit to turn on and off under said zero current switching condition to establish a resonance between the second active commutation unit and the inverter snubber capacitors to establish said zero voltage switching condition for said inverter switching devices.

A method for controlling a current stiff power conversion system having a bridge of power conversion switching devices connected across DC bus lines to achieve approximately zero-voltage turn on and turn off the power conversion switching devices, comprising the steps of:

• (a) connecting a snubber capacitor across each of the power conversion switching devices in the bridge of power conversion switching devices;
• (b) connecting an active commutation unit in parallel with the bridge of power conversion switching devices across the DC bus lines;
• (c) turning off an outgoing one of the power conversion switching devices;
• (d) controlling the power conversion switching devices to establish a zero current switching condition for the active commutation unit;
• (e) turning on the active commutation unit under said zero current switching condition to establish a resonance between the snubber capacitors and the active commutation unit to reduce a voltage across the incoming power conversion switching device to approximately zero;
• and
• (f) turning on the incoming power conversion switching device when the voltage across the incoming power conversion switching device is approximately zero.