SCR's were the beasts of burden for DC motor control using phase angle firing when fed off AC. You can even use them in DC systems, e.g. rail traction motor con

SCR's were the beasts of burden for DC motor control using phase angle firing when fed off AC. You can even use them in DC systems, e.g. rail traction motor control using forced commutation. SCR's once triggered don't turn off until the conducted current drops below the turn-on threshold so you wire a circuit across it using one or two more smaller scr's to apply a pulse of reverse flow current across it to force it off. Way slower switching times than IGBT mind you.