Electric drive systems

A fault-tolerant four-phase electric drive system comprises a rotary electric machine 112 having a permanent magnet rotor 301 and an alternate-wound stator 302 having eight evenly-spaced coils 303-310 arranged in pairs. Each coil in each pair is separated by 180 degrees. Each of the four phases (ΦA, ΦB, ΦC, ΦD) are separated by 45 degrees and comprises a respective one of the coil pairs and a respective drive circuit 201, 202, 203, 204 connected therewith. A controller 205 is connected with the first, second, third and fourth phase drive circuits to control operation thereof. In response to loss of operation of one of the first phase and the third phase, the phase drive controller may cease operation of both the first phase and the third phase, and in response to loss of operation of one of the second phase and the fourth phase, the phase drive controller may cease operation of both the second phase and the fourth phase. The first phase drive circuit and third phase drive circuit may be connected with a first dc bus 206, the second phase drive circuit and fourth phase drive circuit may be connected with a second dc bus 207.