The paper shows that, if a cage induction motor is fed with a quasi-square-wave current, the motor terminal voltage is approximately sinusoidal under normal operating conditions. A simple analytical approach, based on the assumption that the motor resistances and inductances do not change with frequency, is shown to describe adequately the motor-terminal voltage. The quasi-square-wave-current supply is derived by modification of a known variable d.c.-link-voltage invertor. These modifications result in numerous advantages. The modified invertor is capable of regeneration back into the mains supply, has only 12 noninvertor-grade thyristors, and is undamaged by short-circuiting of the output terminals or by misfire of the output thyristors. Overall, the invertor lends itself to a simpler electrical and mechanical arrangement.