Electric drive systems

1. A fault-tolerant four-phase electric drive system, comprising:

a rotary electric machine having a permanent magnet rotor and an alternate-wound stator having eight evenly-spaced coils arranged in pairs, each coil in each pair being separated by 180 degrees;

a first phase (ΦA) comprising a first one of the coil pairs and a first phase drive circuit connected therewith;

a second phase (ΦB) separated by +45 degrees from the first phase and comprising a second one of the coil pairs and a second phase drive circuit connected therewith;

a third phase (ΦC) separated by +90 degrees from the first phase and comprising a third one of the coil pairs and a third phase drive circuit connected therewith;

a fourth phase (ΦD) separated by +135 degrees from the first phase and comprising a fourth one of the coil pairs and a fourth phase drive circuit connected therewith; and

a controller connected with the first, second, third and fourth phase drive circuits to control operation thereof,

wherein the controller is configured to:

cease operation of both the first phase and the third phase in response to loss of operation of one of the first phase and the third phase; and

cease operation of both the second phase and the fourth phase in response to loss of operation of one of the second phase and the fourth phase,

wherein the first phase drive circuit and third phase drive circuit are connected with a first dc bus; and the second phase drive circuit and the fourth phase drive circuit are connected with a second dc bus.

2. The electric drive system of claim 1 , wherein:

the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit are connected with the first dc bus via respective electrical contactors operable by the controller;

the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit are connected with the second dc bus via respective electrical contactors operable by the controller.

3. The electric drive system of claim 2 , wherein, in a non-faulted mode of operation, the controller is configured to:

close contactors between the first phase drive circuit and the first dc bus, the second phase drive circuit and the second dc bus, the third phase drive circuit and the first dc bus, and the fourth phase drive circuit and the second dc bus;

open contactors between the first phase drive circuit and the second dc bus, the second phase drive circuit and the first dc bus, the third phase drive circuit and the second dc bus, and the fourth phase drive circuit and the first dc bus.

4. The electric drive system of claim 2 , wherein, in response to a fault on the first dc bus, the controller is configured to:

close contactors between the second dc bus and the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit;

open contactors between the first dc bus and the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit.

5. The electric drive system of claim 2 , wherein, in response to a fault on the second dc bus, the controller is configured to:

close contactors between the first dc bus and the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit;

open contactors between the second dc bus and the first phase drive circuit, second phase drive circuit, third phase drive circuit, and fourth phase drive circuit.

6. The electric drive system of claim 1 , wherein the stator has sixteen slots, each of which is defined by a wound tooth carrying a coil, and an unwound tooth not carrying a coil, and wherein the width of wound teeth is greater than the width of unwound teeth.

7. The electric drive system of claim 6 , wherein the width of wound teeth is twice the width of unwound teeth.

8. The electric drive system of claim 6 , wherein the slots are substantially trapezoidal in cross section.

9. A gas turbine engine comprising the electric drive system of claim 1 .