Optimal PWM switching strategies are presented for the current-source inverter (CSI) induction motor drive. These optimal PWM strategies are designed with the objective of improving the quality of the rotational motion of the drive at low operating speeds, thereby extending the viable range of operation and application of CSI drives. Optimal PWM switching strategies designed to minimise rotor speed ripple and rotor position error are presented, based on both 1/4-wave and 1/2-wave symmetric PWM stator current waveforms, and their superiority demonstrated using both experimental and computed CSI drive performance characteristics. It is shown that 1/2-wave symmetric PWM strategies designed to minimise rotor position error are superior to all previously developed PWM strategies, in terms of producing smooth rotor motion and reduced mechanical resonances, during low speed operation of the CSI drive. In contrast to previously developed CSI PWM strategies based on harmonic elimination/minimisation techniques, which are essentially open-loop strategies, it is shown that all the optimal PWM strategies are dependent upon motor operating conditions and are therefore closed-loop strategies.