Permanent magnet synchronous motor
A permanent magnet synchronous motor includes a stator, a rotor rotatable relative to the stator, and a magnetic structure with a low coercive force magnet and a high coercive force magnet that are arranged magnetically in series with respect to each other to define a pole-pair of the permanent magnet synchronous motor. A magnetization level of the low coercive force magnet is changeable by a stator current pulse such that a stator magnetomotive force at a rated current is equal to or larger than a product of a magnetic field strength for fully magnetizing the low coercive force magnet and a thickness of the low coercive force magnet.
1. A permanent magnet synchronous motor comprising:
a stator;
a rotor rotatable relative to the stator; and
a magnetic structure with a low coercive force magnet and a high coercive force magnet that are arranged magnetically in series with respect to each other to define a pole-pair of the permanent magnet synchronous motor,
a magnetization level of the low coercive force magnet being changeable by a stator current pulse, and
a rated current of the permanent magnet synchronous motor being set such that a stator magnetomotive force at the rated current is equal to or larger than a product of a magnetic field strength for fully magnetizing the low coercive force magnet and a thickness of the low coercive force magnet.
2. The permanent magnet synchronous motor according to claim 1 , wherein
the stator, the rotor and the magnetic structure are further configured to satisfy the following formula (1):
M
M
F
≥
H
M
ax
t
Low
-
J
High
μ
0
μ
rh
t
High
+
(
J
Max
μ
0
μ
rl
+
H
Max
)
(
t
High
+
t
g
)
(
1
)
where MMF represents the stator magnetomotive force per pole at the rated current, H Max represents the magnetic field strength for fully magnetizing the low coercive force magnet, t Low represents a thickness of the low coercive force magnet, J High represents a magnetization of the high coercive force magnet, μ 0 μ rh represents a magnetic permeability of the high coercive force magnet, μ 0 μ rh represents a magnetic permeability of the low coercive force magnet, t High represents a thickness of the high coercive force magnet, J Max represents a magnetization of the low coercive force magnet fully magnetized, and t g represents an air gap length between the stator and the rotor.
3. The permanent magnet synchronous motor according to claim 1 , wherein
the stator, the rotor and the magnetic structure are further configured to satisfy the following formula (2):
M
M
F
≥
-
H
Min
t
Low
+
J
High
μ
0
μ
rh
t
High
-
(
J
Min
μ
0
μ
rl
+
H
Min
)
(
t
High
+
t
g
)
(
2
)
where MMF represents the stator magnetomotive force per pole at the rated current, H Min represents a magnetic field strength for demagnetizing the low coercive force magnet to a desired level, t Low represents a thickness of the low coercive force magnet, J High represents a magnetization of the high coercive force magnet, μ 0 μ rh represents a magnetic permeability of the high coercive force magnet, μ 0 μ r1 represents a magnetic permeability of the low coercive force magnet, t High represents a thickness of the high coercive force magnet, J Min represents a magnetization of the low coercive force magnet for demagnetizing the low coercive force magnet to the desired level, and t g represents an air gap length between the stator and the rotor.
4. The permanent magnet synchronous motor according to claim 1 , wherein
the stator, the rotor and the magnetic structure are further configured to satisfy the following formula (3):
J
Min
≤
J
Max
2
(
3
)
where J Min represents a magnetization of the low coercive force magnet for demagnetizing the low coercive force magnet to the desired level, and J Max represents a magnetization of the low coercive force magnet fully magnetized.
5. The permanent magnet synchronous motor according to claim 1 , wherein
the stator, the rotor and the magnetic structure are further configured to satisfy the following formula (4):
M
M
F
≤
J
Max
μ
0
μ
rl
t
Low
+
J
High
μ
0
μ
rh
t
High
(
4
)
where MMF represents the stator magnetomotive force per pole at the rated current, J Max represents a magnetization of the low coercive force magnet fully magnetized, μ 0 μ rh represents a magnetic permeability of the high coercive force magnet, μ 0 μ rl represents a magnetic permeability of the low coercive force magnet t Low represents a thickness of the low coercive force magnet, J High represents a magnetization of the high coercive force magnet, and t High represents a thickness of the high coercive force magnet.
6. The permanent magnet synchronous motor according to claim 1 , wherein
the low coercive force magnet and the high coercive force magnet have widths that are substantially equal to each other, respectively, and
the stator, the rotor and the magnetic structure are further configured to satisfy the following formula (5):
M
M
F
sin
(
Pmw
4
R
si
)
≥
H
c_min
t
Low
-
J
High
μ
0
μ
rh
t
High
-
(
J
Max
μ
0
μ
rl
-
H
c_min
)
(
t
g
+
t
High
)
(
5
)
where MMF represents the stator magnetomotive force per pole at the rated current, P represents a total pole number, mw represents a magnet width, R si represents a stator inner radius, H c_min represents coercive force of the low coercive force magnet fully magnetized, t Low represents a thickness of the low coercive force magnet, J High represents a magnetization of the high coercive force magnet, μ 0 μ rh represents a magnetic permeability of the high coercive force magnet, μ 0 μ rl represents a magnetic permeability of the low coercive force magnet, t High represents a thickness of the high coercive force magnet, J Max represents a magnetization of the low coercive force magnet fully magnetized, and t g represents an air gap length between the stator and the rotor.
7. The permanent magnet synchronous motor according to claim 1 , wherein
the low coercive force magnet includes a SmCo magnet,
the high coercive force magnet includes a NdFeB magnet, and
a thickness of the low coercive force magnet per pole-pair is equal to or more than 75% of a total thickness of the low coercive force magnet and the high coercive force magnet per pole-pair.
8. The permanent magnet synchronous motor according to claim 1 , wherein
the low coercive force magnet and the high coercive force magnet are stacked with respect to each other in a thickness direction to define the pole-pair of the permanent magnet synchronous motor, and
the high coercive force magnet is disposed closer to an air gap between the stator and the rotor than the low coercive force magnet is.