A d.c. traction drive is described comprising a synchronous motor, which may be brushless, supplied by a forcecommutated voltage-source invertor with thyristor firing controlled by rotor position. This implies control of load angle. An analytical basis for system design is presented, and the required ranges of variation of load angle to obtain motoring and braking operation with forward and reverse rotations are derived. A study of torque production at standstill with very high magnetic saturation yields a design method for synchronous motors used as traction motors in this type of system. New techniques for controlling current and torque are reported, and the performance of the system is demonstrated by tests on two experimental drives, the larger of which involves peak currents of 330 A.