# US 2014/0191596 A1 · High efficiency permanent magnet machine

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- Number: US 2014/0191596 A1
- Document ID: US20140191596A1
- Status: Published application
- Kind: A1
- Application number: 14/146,059
- Filed: 2014-01-02
- Published: 2014-07-10
- Earliest claimed: 2013-01-04
- Inventors: Xinzhang Wu; Hanzhou Liu; Yang Hu; Louis Chow; Jon Harms; Martin Epstein; Wei Wu
- Web page: https://patentgrep.com/patent/US20140191596A1

## CPC

- H02K 1/16: Stator cores with slots for windings
- H02K 1/274: the rotor consisting of two or more circumferentially positioned magnets
- H02K 3/12: arranged in slots
- H02K 3/28: Layout of windings or of connections between windings (windings for pole-changing H02K17/06, H02K17/14, H02K19/12, H02K19/32)
- H02K 21/14: with magnets rotating within the armatures
- H02K 21/16: having annular armature cores with salient poles (with homopolar co-operation H02K21/20)
- H02P 6/153: {wherein the commutation is advanced from position signals phase in function of the speed}
- H02P 6/182: using back-emf in windings
- H02K 2213/03: Machines characterised by numerical values, ranges, mathematical expressions or similar information
- H02K: DYNAMO-ELECTRIC MACHINES (dynamo-electric relays H01H53/00; conversion of DC or AC input power into surge output power {H03K3/53})
- H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS

## Abstract

The present invention is a high efficiency permanent magnet machine capable of maintaining high power density. The machine is operable over a wide range of power output. The improved efficiency is due in part to copper wires with a current density lower than traditional designs and larger permanent magnets coupled with a large air gap. In a certain embodiment wide stator teeth are used to provide additional improved efficiency through significantly reducing magnetic saturation resulting in lower current. The machine also has a much smaller torque angle than that in traditional design at rated load and thus has a higher overload handling capability and improved efficiency. In addition, when the machine is used as a motor, an adaptive phase lag compensation scheme helps the sensorless field oriented control (FOC) scheme to perform more accurately.

## Claims

### Claim 1

An electric machine, comprising:
a rotor, the rotor further including:
having a cylindrical shape and a central axis;
an axial bore adapted to receive a shaft;
an outer circumference adapted to receive a plurality of permanent magnets comprising of permanent magnet material, wherein each permanent magnet has a magnetic flux density between 70 and 95 percent of a residual magnetic flux density of the permanent magnet material;
a stator, the stator further including:
having a cylindrical shape and a longitudinal axis;
an outer circumference;
a plurality of teeth disposed in an equidistant angular relationship, each tooth projecting inwardly toward the longitudinal axis, the teeth creating a discontinuous inner circumference configured to accept the rotor within the stator such that the longitudinal axis of stator is aligned with the central axis of the rotor and the rotor is rotatable within the inner circumference of the stator;
a stator slot of predetermined shape and size disposed between each tooth and adapted to receive a predetermined number of strands of conducting material to form an electrical winding around at least one tooth;
a current density ranging between 3 and 8 Amp/mm2;
a predetermined number of poles, whereby the number of poles is directly proportional to an electrical frequency of the electric machine and inversely proportional to a number of required coil windings;
a torque angle between 2 and 10 degrees; and
an air gap between the outer circumference of the rotor and the inner circumference of the stator when the rotor is disposed within the stator.

### Claim 2 (depends on 1)

The electric machine according to claim 1, further comprising a three phase electrical winding scheme where each phase has two groups and each group includes two coils connected in series.

### Claim 3 (depends on 1)

The electric machine according to claim 1, further comprising the rotor having a plurality of rotor sheets affixed to one another by a thermal insulating adhesive disposed between adjacent rotor sheets.

### Claim 4 (depends on 1)

The electric machine according to claim 1, further comprising the stator having a plurality of stator sheets affixed to one by a thermal insulating adhesive layer disposed between the adjacent stator sheets.

### Claim 5 (depends on 1)

The electric machine according to claim 1, further comprising a sensorless field oriented control, where a rotor angle is estimated by a sliding mode observer, the sliding mode observer module containing a first order low-pass filter for back electromotive force estimation.

### Claim 6 (depends on 1)

The electric machine according to claim 1, further comprising a control module configured to automatically calculate a phase lag compensation value based on rotational speed of the rotor and is applied to feedback increasing accuracy of the field oriented control.

### Claim 7 (depends on 1)

The electric machine according to claim 1, further comprising a housing enclosing the stator and rotor, wherein the housing includes a passive cooling mechanism.

### Claim 8 (depends on 1)

The electric machine according to claim 1, further comprising the stator teeth each having a generally uniform width, wherein the magnitude of the width is between 60 and 80 percent of the magnitude of a slot pitch.

### Claim 9 (depends on 1)

The electric machine according to claim 1, further comprising the rotor having between 8 and 16 poles when the intended rotational speed of the rotor is less than 3000 rpm.

### Claim 10 (depends on 1)

The electric machine according to claim 1, further comprising the rotor having between 2 and 12 poles when the intended rotational speed of the rotor is greater than 6000 rpm.

### Claim 11

An electric machine, comprising:
a rotor, the rotor further including:
a plurality of rotor sheets affixed to one another using a thermal insulating adhesive;
having a cylindrical shape and a central axis;
an axial bore adapted to receive a shaft;
an outer circumference adapted to receive a plurality of permanent magnets comprising of permanent magnet material, wherein each permanent magnet has a magnetic flux density between 70 and 95 percent of a residual magnetic flux density of the permanent magnet material;
a stator, the stator further including:
a plurality of stator sheets affixed to one another using a thermal insulating adhesive;
having a cylindrical shape and a longitudinal axis;
an outer circumference;
a plurality of teeth disposed in an equidistant angular relationship, each tooth projecting inwardly toward the longitudinal axis, the teeth creating a discontinuous inner circumference configured to accept the rotor within the stator such that the longitudinal axis of stator is aligned with the central axis of the rotor and the rotor is rotatable within the inner circumference of the stator;
a stator slot of predetermined shape and size disposed between each tooth and adapted to receive a predetermined number of strands of conducting material to form an electrical winding around at least one tooth;
the stator teeth each having a uniform width being between 60 and 80 percent of a slot pitch;
a current density ranging between 3 and 8 Amp/mm2;
a torque angle between 2 and 10 degrees; and
an air gap between the outer circumference of the rotor and the inner circumference of the stator when the rotor is disposed within the stator.

### Claim 12 (depends on 11)

The electric machine according to claim 11, further comprising a three phase electrical winding scheme where each phase has two groups and each group includes two coils connected in series.

### Claim 13 (depends on 11)

The electric machine according to claim 11, further comprising a sensorless field oriented control, where a rotor angle is estimated by a sliding mode observer, the sliding mode observer module containing a first order low-pass filter for back electromotive force estimation.

### Claim 14 (depends on 11)

The electric machine according to claim 11, further comprising a control module configured to automatically calculate a phase lag compensation value based on rotational speed of the rotor and is applied to feedback increasing accuracy of the field oriented control.

### Claim 15 (depends on 11)

The electric machine according to claim 11, further comprising a housing enclosing the stator and rotor, wherein the housing includes a passive cooling mechanism.

### Claim 16 (depends on 11)

The electric machine according to claim 11, further comprising a predetermined number of poles, whereby the number of poles is directly proportional to the electrical frequency of the electric machine and inversely proportional to a number of required coil windings.

### Claim 17 (depends on 16)

The electric machine according to claim 16, further comprising the rotor having between 8 and 16 poles when the intended rotational speed of the rotor is less than 3000 rpm.

### Claim 18 (depends on 16)

The electric machine according to claim 16, further comprising the rotor having 2 and 12 poles when the intended rotational speed of the rotor is greater than 6000 rpm.

### Claim 19

An electric machine, comprising:
a rotor, the rotor further including:
a plurality of rotor sheets affixed to one another using a thermal insulating adhesive;
having a cylindrical shape and a central axis;
an axial bore adapted to receive a shaft;
an outer circumference adapted to receive a plurality of permanent magnets comprising of permanent magnet material, wherein each permanent magnet has a magnetic flux density between 70 and 95 percent of a residual magnetic flux density of the permanent magnet material;
a stator, the stator further including:
a plurality of stator sheets affixed to one another using a thermal insulating adhesive;
having a cylindrical shape and a longitudinal axis;
an outer circumference;
a plurality of teeth disposed in an equidistant angular relationship, each tooth projecting inwardly toward the longitudinal axis, the teeth creating a discontinuous inner circumference configured to accept the rotor within the stator such that the longitudinal axis of stator is aligned with the central axis of the rotor and the rotor is rotatable within the inner circumference of the stator;
a stator slot of predetermined shape and size disposed between each tooth and adapted to receive a predetermined number of strands of conducting material to form an electrical winding around each tooth;
a three phase electrical winding scheme where each phase has two groups and each group includes two coils connected in series;
the strands of conducting material having a cross-sectional related to current density based on
J
=
4

I
π


d
2
and a low current density (J) ranging between 3 and 8 Amp/mm2;
a predetermined number of poles, whereby the number of poles is directly proportional to the electrical frequency of the electric machine and inversely proportional to a number of required coil windings;
the rotor having between 8 and 16 poles when the intended rotational speed of the rotor is less than 3000 rpm;
the rotor having 2 to 12 poles when the intended rotational speed of the rotor is greater than 6000 rpm;
a torque angle between 2 and 10 degrees;
an air gap between the outer circumference of the rotor and the inner circumference of the stator when the rotor is disposed within the stator, the air gap being inversely proportional to the torque angle based on
g
^
total
=
4
π

μ
0
B
R

sin


δ

N
^
a
P

1.5

2

I
A
,
rated
,
where ĝtotal is the air gap and δ is the torque angle;
each of the permanent magnets has a thickness proportional to the air gap such that geffBmR+μ0HmRlm=0, where geff is an effective distance of the air gap and lm is the thickness of each of the permanent magnets;
a housing enclosing the stator and rotor, wherein the housing includes a passive cooling mechanism;
a sensorless field oriented control, where a rotor angle is estimated by a sliding mode observer, the sliding mode observer module containing a first order low-pass filter for back electromotive force estimation; and
a control module configured to automatically calculate a phase lag compensation value based on rotational speed of the rotor and is applied to feedback increasing accuracy of the field oriented control.

### Claim 20 (depends on 19)

The electric machine according to claim 19, further comprising the stator teeth each having a generally uniform width, wherein the magnitude of the width is between 60 and 80 percent of the magnitude of a slot pitch.