A stator assembly, wherein the stator assembly comprises a stator core and a multi-branch rectangular conductor winding, an even number of stator slots are provided on an inner circumference of the stator core, and each of the stator slots is divided into multiple layers for accommodating rectangular conductors, the multiple layers comprising a first layer, a second layer, a third layer, a fourth layer, a fifth layer, a sixth layer, a seventh layer and an eighth layer; the multi-branch rectangular conductor winding is provided in the stator slots, and the multi-branch rectangular conductor winding comprises B number of parallel branches (4-1, 4-2, 4-3, 4-4), and B is an integer multiple of 4; a number of slots per phase per pole, Q, of the stator assembly is an odd number, Q and B satisfy a relationship that both (Q+1)*2B and (Q-1)*2B are integers, and each of the parallel branches (4-1, 4-2, 4-3, 4-4) equally passes through each layer in the stator slots, so that there is no phase difference of magnetic fields between the parallel branches; wherein the stator slots are numbered clockwise or counterclockwise as 1 to S, a 1st slot to an (S/2)-th slot are defined as a first region, and an (S/2)+1-th slot to an S-th slot are defined as a second region; the parallel branches (4-1, 4-2, 4-3, 4-4) are numbered in sequence with an odd number or an even number respectively; characterized in that, when the parallel branches (4-1, 4-2, 4-3, 4-4) are arranged in the stator slots, in each pair of magnetic poles in the first region, the parallel branches (4-1, 4-3) with an odd number appear (Q+1)*2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q-1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; in each pair of magnetic poles in the second region, the parallel branches (4-1, 4-3) with an odd number appear (Q-1) ∗ 2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q+1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; in each pair of magnetic poles in the first region, the parallel branches (4-2, 4-4) with an even number appear (Q-1) ∗ 2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q+1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; and in each pair of magnetic poles in the second region, the parallel branches (4-2, 4-4) with an even number appear (Q+1)*2B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q-1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer. the multi-branch rectangular conductor winding is provided in the stator slots, and the multi-branch rectangular conductor winding comprises B number of parallel branches (4-1, 4-2, 4-3, 4-4), and B is an integer multiple of 4; a number of slots per phase per pole, Q, of the stator assembly is an odd number, Q and B satisfy a relationship that both (Q+1)*2B and (Q-1)*2B are integers, and each of the parallel branches (4-1, 4-2, 4-3, 4-4) equally passes through each layer in the stator slots, so that there is no phase difference of magnetic fields between the parallel branches; wherein the stator slots are numbered clockwise or counterclockwise as 1 to S, a 1st slot to an (S/2)-th slot are defined as a first region, and an (S/2)+1-th slot to an S-th slot are defined as a second region; the parallel branches (4-1, 4-2, 4-3, 4-4) are numbered in sequence with an odd number or an even number respectively; characterized in that, when the parallel branches (4-1, 4-2, 4-3, 4-4) are arranged in the stator slots, in each pair of magnetic poles in the first region, the parallel branches (4-1, 4-3) with an odd number appear (Q+1)*2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q-1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; in each pair of magnetic poles in the second region, the parallel branches (4-1, 4-3) with an odd number appear (Q-1) ∗ 2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q+1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; in each pair of magnetic poles in the first region, the parallel branches (4-2, 4-4) with an even number appear (Q-1) ∗ 2/B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q+1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer; and in each pair of magnetic poles in the second region, the parallel branches (4-2, 4-4) with an even number appear (Q+1)*2B number of times in each one of the first layer, the second layer, the fifth layer and the sixth layer, and appear (Q-1)*2B number of times in each one of the third layer, the fourth layer, the seventh layer and the eighth layer.