Claims:1. A driver unit for an interior permanent magnet motor, comprising:
sensor electronics configured to sense a phase voltage corresponding to one or more phase terminals of the interior permanent magnet motor to generate a corresponding phase voltage signal; and
a controller electrically coupled to the sensor electronics and configured to:
extract one or more triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a fundamental frequency of the phase voltage signal corresponding to the one or more phase terminals; and
determine an angular position of a rotor of the interior permanent magnet motor based on the extracted one or more triplen harmonics.
2. The driver unit of claim 1, further comprising an inverter electrically coupled to the controller and the one or more phase terminals of the interior permanent magnet motor and configured to adjust at least one of a phase voltage and a phase current applied to the one or more phase terminals based on one or more control signals received from the controller.
3. The driver unit of claim 1, wherein the controller is further configured to determine the fundamental frequency of the phase voltage signal based on at least one of the phase voltage signal and a phase current corresponding to the one or more phase terminals.
4. The driver unit of claim 1, wherein the controller is configured to sum the phase voltage signals to generate a sum signal, wherein the sum signal comprises triplen harmonics.
5. The driver unit of claim 4, wherein the controller is further configured to extract, from the sum signal, the one or more triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic of the fundamental frequency.
6. The driver unit of claim 1, wherein the controller is further configured to extract, from one or more of the phase voltage signals, the one or more triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic of the fundamental frequency.
7. The driver unit of claim 1, wherein the controller is further configured to:
compare magnitudes of the triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic with a threshold magnitude value; and
identify the one or more triplen harmonics having magnitudes greater than the threshold magnitude value.
8. The driver unit of claim 7, wherein the controller is configured to compare, in a descending order of triplen frequencies, magnitudes of the triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic with a threshold magnitude value.
9. The driver unit of claim 7, wherein the controller is configured to extract a triplen harmonic for which a condition of corresponding magnitude being greater than the threshold magnitude value is first identified.
10. The driver unit of claim 1, wherein the controller is configured to extract a triplen harmonic of the order of the ninth harmonic and higher than the ninth harmonic comprising a highest magnitude.
11. The driver unit of claim 1, wherein, if a plurality of triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic is extracted, the controller is further configured to:
determine an average phase angle of phase angles corresponding to the plurality of triplen harmonics; and
determine the angular position of the rotor based on the average phase angle.
12. The driver unit of claim 1, wherein, if a single triplen harmonic of the order of the ninth harmonic and higher than the ninth harmonic is extracted, the controller is further configured to determine the angular position of the rotor based on a phase angle corresponding to extracted single triplen harmonic.
13. A motor assembly, comprising:
an interior permanent magnet motor comprising one or more phase terminals, a rotor, and a stator; and
a driver unit electrically coupled to the interior permanent magnet motor at the one or more phase terminals, wherein the driver unit comprises:
sensor electronics configured to sense a phase voltage corresponding to the one or more phase terminals to generate a corresponding phase voltage signal; and
a controller electrically coupled to the sensor electronics and configured to:
extract one or more triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a fundamental frequency of the phase voltage signal corresponding to the one or more phase terminals; and
determine an angular position of the rotor based on the extracted one or more triplen harmonics.
14. The motor assembly of claim 13, wherein the driver unit further comprises an inverter electrically coupled to the controller and the one or more phase terminals of the interior permanent magnet motor and configured to adjust at least one of a phase voltage and a phase current applied to the one or more phase terminals based on one or more control signals received from the controller.
15. A method for controlling an interior permanent magnet motor, comprising:
receiving phase voltage signals corresponding to one or more phase terminals of the interior permanent magnet motor;
extracting one or more triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a fundamental frequency of the phase voltage signal corresponding to the one or more phase terminals;
determining an angular position of a rotor of the interior permanent magnet motor based on the extracted one or more triplen harmonics; and
supplying at least one of a phase current or phase voltage to the one or more phase terminals based at least on the angular position of a rotor.
16. The method of claim 15, further comprising determining the fundamental frequency of the phase voltage signal based on at least one of the phase voltage signal and a phase current corresponding to the one or more phase terminals.
17. The method of claim 15, wherein extracting the one or more triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic comprises summing the phase voltage signals to generate a sum signal, wherein the sum signal comprises triplen harmonics.
18. The method of claim 17, wherein extracting one or more triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic of the fundamental frequency comprises:
comparing magnitudes of the triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic with a threshold magnitude value; and
identifying the one or more triplen harmonics having magnitudes greater than the threshold magnitude value.
19. The method of claim 18, wherein the comparison is performed in a descending order of triplen frequencies.
20. The method of claim 18, wherein extracting one or more triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic of the fundamental frequency comprises extracting a triplen harmonic for which a condition of corresponding magnitude being greater than the threshold magnitude value is first identified.
21. The method of claim 15, wherein, if a plurality of triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic is extracted, determining the angular position of the rotor comprises determining an average phase angle of phase angles corresponding to the plurality of triplen harmonics, and wherein the angular position of the rotor is determined based on the average phase angle.
22. The method of claim 15, wherein, if a single triplen harmonic of the order of the ninth harmonic and higher than the ninth harmonic is extracted, the angular position of the rotor is determined based on a phase angle corresponding to extracted single triplen harmonic.
, Description:BACKGROUND
[0001] Embodiments of the present disclosure relate to a motor assembly, and more
particularly to a motor assembly having an interior permanent magnet (IPM) motor and a driver
unit configured to determine an angular position of a rotor of the IPM motor.
[0002] Electric machines such as permanent magnet synchronous motors have been used in
variety of applications, including but not limited to electric pumps, electric or hybrid vehicles, as
well as home and industrial appliances that employ rotary components, traction motors, and the
like. Types of the permanent magnet synchronous motors may include surface permanent
magnet (SPM) motors and the IPM motors. A permanent magnet synchronous motor typically
includes a stator having stator winding including one or more phases, and a rotor having
permanent magnets. The rotor may be disposed within the stator. Typically, to operate the
permanent magnet synchronous motors, it is desirable that the phases of the stator winding are
operated in a predetermined sequence. Therefore, it is desirable to determine an angular position
of the rotor (hereinafter referred to as a “rotor position”) in order to determine voltage and/or
current that is to be applied to the stator winding.
[0003] Some of the currently available systems employ one or more position sensors and/or
encoders along with the permanent magnet synchronous motor to determine the rotor position.
Sometimes, an operation of the position sensors and/or encoders is unreliable under certain harsh
conditions including, but not limited to, increased temperatures (e.g., at the temperatures of about
a few hundreds of degree centigrade). Further, the position sensors and/or encoders occupy
additional space. Consequently, resulting motor assemblies employing such position sensors
and/or encoders are not as compact. Moreover, use of the position sensors and/or encoders
results in costly motor assemblies.
[0004] Further, some systems entail using a third harmonic of a back-electromotive force
(EMF) generated by a motor to estimate the rotor position. However, in case of motors, such as
the IPM motors which have saliency in the rotor, the back-EMF may vary with variations in
load. More particularly, the third harmonic of the back-EMF is affected by the load variations.
Especially, a phase angle of the third harmonic, which is indicative of the rotor position, is
altered due to the load variations. Consequently, use of information corresponding to the third
harmonic is unreliable for determining the rotor position of the IPM motors.
BRIEF DESCRIPTION
[0005] In accordance with aspects of the present specification, a driver unit for an interior
permanent magnet (IPM) motor is presented. The driver unit includes sensor electronics
configured to sense a phase voltage corresponding to one or more phase terminals of the IPM
motor to generate a corresponding phase voltage signal. The driver unit further includes a
controller electrically coupled to the sensor electronics and configured to extract one or more
triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a
fundamental frequency of the phase voltage signal corresponding to the one or more phase
terminals. The controller is further configured to determine an angular position of a rotor of the
IPM motor based on the extracted one or more triplen harmonics.
[0006] In accordance with yet another aspect of the present specification, a motor assembly is
presented. The motor assembly includes an IPM motor including one or more phase terminals, a
rotor, and a stator. The motor assembly further includes a driver unit electrically coupled to the
IPM motor at the one or more phase terminals. The driver unit includes sensor electronics
configured to sense a phase voltage corresponding to one or more phase terminals of the IPM
motor to generate a corresponding phase voltage signal. The driver unit further includes a
controller electrically coupled to the sensor electronics and configured to extract one or more
triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a
fundamental frequency of the phase voltage signal corresponding to the one or more phase
terminals. The controller is further configured to determine an angular position of a rotor of the
IPM motor based on the extracted one or more triplen harmonics.
[0007] In accordance with yet another aspect of the present specification, a method for
controlling an IPM motor is presented. The method includes receiving phase voltage signals
corresponding to one or more phase terminals of the IPM motor. The method further includes
extracting one or more triplen harmonics of an order of a ninth harmonic and higher than the
ninth harmonic of a fundamental frequency of the phase voltage signal corresponding to the one
or more phase terminals. Furthermore, the method includes determining an angular position of a
rotor of the IPM motor based on the extracted one or more triplen harmonics. Moreover, the
method includes supplying at least one of a phase current or phase voltage to the one or more
phase terminals based at least on the angular position of a rotor.
DRAWINGS
[0008] These and other features, aspects, and advantages of the present specification will
become better understood when the following detailed description is read with reference to the
accompanying drawings in which like characters represent like parts throughout the drawings,
wherein:
[0009] FIG. 1 is a diagrammatical illustration of a cross-sectional view of a typical interior
permanent magnet (IPM) motor;
[0010] FIG. 2 is a block diagram of a motor assembly, in accordance with aspects of the
present specification;
[0011] FIG. 3 is a flowchart of an example method of controlling an IPM motor, in accordance
with aspects of the present specification; and
[0012] FIG. 4 is a flowchart of an example method of extracting one or more triplen harmonics
of the order of the ninth harmonic and higher than the ninth harmonic, in accordance with
aspects of the present specification.
DETAILED DESCRIPTION
[0013] The specification may be best understood with reference to the detailed figures and
description set forth herein. Various embodiments are described hereinafter with reference to the
figures. However, those skilled in the art will readily appreciate that the detailed description
given herein with respect to these figures is for explanatory purposes as the method and the
system may extend beyond the described embodiments.
[0014] In the following specification, the singular forms “a”, “an” and “the” include plural
referents unless the context clearly dictates otherwise. As used herein, the term “or” is not meant
to be exclusive and refers to at least one of the referenced components being present and includes
instances in which a combination of the referenced components may be present, unless the
context clearly dictates otherwise.
[0015] As used herein, the terms “may” and “may be” indicate a possibility of an occurrence
within a set of circumstances; a possession of a specified property, characteristic or function;
and/or qualify another verb by expressing one or more of an ability, capability, or possibility
associated with the qualified verb. Accordingly, usage of “may” and “may be” indicates that a
modified term is apparently appropriate, capable, or suitable for an indicated capacity, function,
or usage, while taking into account that in some circumstances, the modified term may
sometimes not be appropriate, capable, or suitable.
[0016] In accordance with some aspects of the present specification, a motor assembly is
presented. The motor assembly includes an interior permanent magnet motor including one or
more phase terminals, a rotor, and a stator. The motor assembly further includes a driver unit
electrically coupled to the interior permanent magnet motor at the one or more phase terminals.
The driver unit includes sensor electronics configured to sense a phase voltage corresponding to
one or more phase terminals of the interior permanent magnet motor to generate a corresponding
phase voltage signal. The driver unit further includes a controller electrically coupled to the
sensor electronics and configured to extract one or more triplen harmonics of an order of a ninth
harmonic and higher than the ninth harmonic of a fundamental frequency of the phase voltage
signal corresponding to the one or more phase terminals. The term “triplen harmonic,” as used
herein refers to a harmonic of a fundamental frequency in multiples of three. For example, if the
fundamental frequency of the phase voltage is, then the triplen harmonics may include all
harmonics3 * * , where n is an integer. The controller is further configured to determine an
angular position of a rotor of the interior permanent magnet motor based on the extracted one or
more triplen harmonics.
[0017] FIG. 1 is a diagrammatical illustration of a cross-sectional view of a typical interior
permanent magnet (IPM) motor 100. The IPM motor 100 may include a stator 102 and a rotor
104 disposed in a housing 105. The stator 102 may include a plurality of stator poles 106 and
stator winding 108 disposed surrounding the stator poles 106. The stator winding 108 may be a
multi-phase (e.g., three-phase) winding.
[0018] Further, as depicted in FIG. 1, the rotor 104 is disposed within the stator 102. The
rotor 104 may include a rotor shaft 110, a rotor core 112, and a plurality of permanent magnets
114 (hereinafter referred to as “rotor poles” 114). The rotor core 112 may be mounted on the
rotor shaft 110. The rotor core 112 may be formed of a solid material block or a plurality of
laminates. Moreover, the rotor poles 114 are disposed within the rotor core 112. More
particularly, the rotor poles 114 are disposed in slots (not marked in FIG. 1) formed in the rotor
core 112.
[0019] In operation, when the IPM motor 100 is energized by supplying electricity to the stator
winding 108, current flowing through the stator winding 108 generates an electromagnetic field
around the rotor 104. The electromagnetic field interacts with a magnetic field of the rotor 104
resulting in a torque being applied on the rotor 104. Such torque, which is generated due to flux
linkage between the electromagnetic field (caused due to the stator winding 108) and the
magnetic field (caused due to the rotor poles 114), is hereinafter referred to as a “primary
torque.” Typically, in such IPM motor 100, there also exists a reluctance torque, hereinafter
referred to as a “secondary torque.” The secondary torque may be caused by a magnetic flux that
is induced in the rotor core 112 due to the presence of the magnetic field of the rotor poles 114.
For example, shape and location of the slots in the rotor core 112 are designed to channel the
magnetic flux such that the rotor 104 experiences the secondary torque to align the magnetic flux
lines with continuously changing electromagnetic flux lines generated by the stator winding 108.
Application of such torque (e.g., a combination of the primary torque and the secondary torque)
imparts a rotational motion to the rotor 104.
[0020] Typically, to operate the IPM motor 100, it is desirable that one or more of the phases
of the stator winding 108 are supplied with appropriate phase currents and voltages to achieve
desired torque and rotational speed (rpm) of the rotor 104. Information of an angular position
(hereinafter referred to as a rotor position) of the rotor 104 may aid in supplying suitable phase
currents and voltages, thereby effectively operating the IPM motor 100 such that the desired
torque and rotational speed of the rotor 104 are achieved. Therefore, it is desirable to determine
the angular position of the rotor 104 in order to adjust the phase current and phase voltage that is
to be supplied to one or more of the phases of the stator winding 108. To that end, some
embodiments of the present specification are directed to a driver unit capable of determining the
rotor position and a motor assembly employing such driver unit. In a particular embodiment, the
driver unit may determine the rotor position in the IPM motors without employing a position
sensor. Further, some embodiments of the present specification are directed to a method for
controlling the IPM motor.
[0021] FIG. 2 is a block diagram of a motor assembly 200, in accordance with aspects of the
present specification. In some embodiments, the motor assembly 200 may include an IPM motor
202, which is electrically coupled to a driver unit 204. In some embodiments, the IPM motor
202 may be similar to the IPM motor 100 of FIG. 1. The IPM motor 202 may include three
phase terminals 206, 208, 210, and a neutral terminal 212. More particularly, the phase terminals
206-210 may be electrically coupled to corresponding phases of a stator winding of the IPM
motor 202 for supplying phase currents thereto.
[0022] The driver unit 204 may receive a direct current (DC) power from a power source 214.
Further, an output of the driver unit 204 may be coupled to the phase terminals 206-210 of the
IPM motor 202 for supplying the phase currents to the stator winding of the IPM motor 202.
The driver unit 204 may include sensor electronics 216, a controller 218, and an inverter 220.
[0023] In some embodiments, the sensor electronics 216 may be electrically coupled to the
controller 218. The sensor electronics 216 may be configured to sense a phase voltage
corresponding to the phase terminals 206-210 of the IPM motor 202 to generate a corresponding
phase voltage signal. In some embodiments, the phase voltage(s) may be sensed with respect to
a voltage level at the neutral terminal 212. In some embodiments, the phase voltage(s) may be
sensed with respect to a voltage level at a virtual neutral (not shown in FIG. 2). In a non-limiting
example, the virtual neutral may be created by a set of three resistors connected across the three
phase terminals 206-210 of the IPM motor 202. In such an instance, when the phase voltage(s)
are sensed with respect to the voltage level at the virtual neutral, in some embodiments, only two
phases may be excited at any given time.
[0024] The sensor electronics 216 may include one or more sensors (not shown in FIG. 2)
capable of sensing voltage signals at the phase terminals 206-210. Additionally, in some
embodiments, the sensor electronics 216 may include a signal conditioning circuit (not shown in
FIG. 2) that may amplify the sensed voltage signals. In some embodiments, the phase voltage
signals may be representative of a back-electromotive force (EMF) of the IPM motor 202. In the
presently contemplated example, the phase voltage signals may include 3 (three) voltage signals
each of which is representative of the back-EMF of the IPM motor 202 at the respective one of
the three phase terminals 206-210. In a non-limiting example, the phase voltage signals may be
substantially sinusoidal.
[0025] In some embodiments, the driver unit 204 may also include one or more current sensors
221 disposed in current paths from the inverter 220 to the one or more of the phase terminals
206-210. In a non-limiting example, a current sensor 221 may be disposed between outputs of
the inverter 220 and the three phase terminals 206-210, as depicted in FIG. 2.
[0026] In some embodiments, the inverter 220 may be electrically coupled to the controller
218 and the phase terminals 206-210 of the IPM motor 202. The inverter 220 may be configured
to control supply of phase currents to the one or more phase terminals 206-210 based on a
control command received from the controller 218.
[0027] The controller 218 has an input port 217 and an output port 219. The input port 217
and the output port 219 may include a plurality of terminals, hereinafter, respectively referred to
as “input terminals” and “output terminals,” respectively. The controller 218 may be electrically
coupled to the sensor electronics 216 and the one or more current sensors 221 at the input port
217. Moreover, the output port 219 of the controller 218 may be coupled to the inverter 220
(described later). In one embodiment, the controller 218 may include a specially programmed
general purpose computer, a microprocessor, a digital signal processor, and/or a microcontroller.
The controller 218 may also include input/output ports, such as ports 217 and 219, and a storage
medium, such as, an electronic memory. Various examples of the microprocessor include, but
are not limited to, a reduced instruction set computing (RISC) architecture type microprocessor
or a complex instruction set computing (CISC) architecture type microprocessor. Further, the
microprocessor may be of a single-core type or multi-core type.
[0028] In some embodiments, the controller 218 may be configured to control the IPM motor
202 when the IPM motor 202 is operating. In some embodiments, the IPM motor 202 may be
started in an open loop mode. For example, typically in the open loop mode start, the controller
218 may be configured to control the driver unit 204 such that phase voltage/current(s) with a
predefined frequency with a predefined voltage to frequency ratio is applied to the IPM motor
202. Thereafter, the frequency of the phase current(s) may be gradually increased so that the
rotor rotates synchronously with the electromagnetic field caused by the stator winding 130 until
rotation of the rotor of the IPM motor 202 reaches a predefined speed where the back-EMF
magnitude reaches predefined level such that the triplen harmonics may be extracted from the
back-EMF. In some embodiments, to start the IPM motor 202, the controller 218 may be
configured to control the driver unit 204 such that the phase voltage(s) and/or current(s) is
applied to the IPM motor 202 based on an inductance profile of the IPM motor 202. In some
embodiments, the inductance profile of the IPM motor 202 may be indicative of the rotor
position. Once the IPM motor 202 is started, in one embodiment, the controller 218 may be
configured to control the IPM motor 202 by performing one or more steps depicted in FIG. 3.
FIG. 3 is a flowchart 300 of an example method of controlling an IPM motor (e.g., the IPM
motor 202), in accordance with aspects of the present specification. In one embodiment, the
controller 218 may be configured to perform steps 302-310 of FIG. 3 to control functioning of
the IPM motor 202. For ease of description and clarity, FIG. 3 is described in conjunction with
FIG. 2.
[0029] At step 302, the controller 218 may be configured to receive the phase voltage signals
from the sensor electronics 216. The phase voltage signals received by the controller 218 from
the sensor electronics 216 may or may not be on a real-time basis. Further, in one embodiment,
the controller 218 may receive the phase voltage signals in a continuous fashion. In another
embodiment, the controller 218 may be configured to receive the phase voltage signals
intermittently. For example, the controller 218 may be configured to receive the phase voltage
signals at regular intervals of time (i.e., periodically), or at random intervals of time (i.e.,
sporadically).
[0030] Subsequently, at step 304, the controller 218 may be configured to extract one or more
triplen harmonics of an order of a ninth harmonic and higher than the ninth harmonic of a
fundamental frequency of the phase voltage signal corresponding to the one or more phase
terminals 206-210. Further details of the method of extracting the one or more triplen harmonics
of the order of the ninth harmonic and higher than the ninth harmonic is described in detail in
conjunction with FIG. 4.
[0031] It may be noted that the phase angle of a triplen harmonic is indicative of an angular
position of the rotor (i.e., the rotor position). Accordingly, at step 306, the controller 218 may be
configured to determine rotor position of the IPM motor 202 based on the extracted one or more
triplen harmonics. More particularly, the controller 218 may be configured to determine the
rotor position based on a phase angle of the extracted one or more triplen harmonics, which is of
the order of the ninth harmonic and higher than the ninth harmonic. In some embodiments, the
rotor position may be determined based on the phase angle of the extracted triplen harmonics.
[0032] In some embodiments, in order to determine the rotor position, the controller 218 may
be configured to identify the phase angle of the extracted triplen harmonic(s) of the order of the
ninth harmonic and higher than the ninth harmonic. In a non-limiting example, the controller
218 may be configured to identify the phase angle based on a zero crossing position of the
extracted triplen harmonic(s) with respect to the zero crossing position of the fundamental
harmonic. The term “zero crossing position” for a given harmonic refers to an angular position
at which the given harmonic changes its magnitude from a positive value to a negative value, or
vice-versa.
[0033] In particular, in some of these embodiments, the rotor position may be same as the
phase angle of the extracted triplen harmonics. Consequently, in these embodiments, the
controller 218 may be configured to determine the rotor position as being equivalent to the phase
of the extracted triplen harmonics. In some embodiments, the rotor position may be equivalent
to the phase angle of the extracted triplen harmonics with a phase-shift, where the phase-shift
may be positive or negative. In some embodiments, an amount of the phase-shift may depend on
the current drawn by the IPM motor 202.
[0034] In particular, in some embodiments, if a single triplen harmonic of the order of the
ninth harmonic and higher than the ninth harmonic is extracted (at step 304), the controller is
further configured to determine the rotor position based on a phase angle corresponding to the
extracted single triplen harmonic, at step 306. In a non-limiting example, the rotor position may
be similar to the phase angle corresponding to the extracted single triplen harmonic. In some
embodiments, if a plurality of triplen harmonics of the order of the ninth harmonic and higher
than the ninth harmonic is extracted, the controller is further configured to determine an average
phase angle of phase angles corresponding to the plurality of triplen harmonics. Subsequently,
the controller 218 may be configured to determine the rotor position based on the average phase
angle. In some embodiments, the rotor position may be similar to the average phase angle. In
some other embodiments, the rotor position may be equivalent to the average phase angle with
the phase-shift, where the phase-shift may be positive or negative. In some embodiments, the
amount of the phase-shift may depend on the current drawn by the IPM motor 202.
[0035] In certain embodiments, the controller 218 may be configured to determine the phaseshift
based on a look-up table, for example. In a non-limiting example, the look-up table may be
generated based on a finite element analysis of the IPM motor 202. The look-up table may
include different values of the phase-shift corresponding to different values of the current drawn
by the IPM motor 202. As previously noted, the current drawn by the IPM motor 202 may be
determined by the controller 218 based on the signals received from one or more of the current
sensors 221. Accordingly, when the phase angle (or the average phase angle) is determined, the
controller may also be configured to identify the phase-shift based on the current drawn by the
IPM motor 202 based on the look-up table. Subsequently, the controller 218 may be configured
to determine the rotor position as the sum of the phase angle (or the average phase angle) and the
identified phase-shift, where the phase-shift may be positive or negative.
[0036] In some embodiments, in order to determine the rotor position, it may be advantageous
to use the triplen harmonics of the order of ninth harmonic and higher than the ninth harmonic in
comparison to the third harmonic. This is because the triplen harmonics of the order of the ninth
harmonic and higher than the ninth harmonic of the back-EMF (e.g., the phase voltage signal(s))
are affected lesser due to respective preceding harmonics of the inductance profile of the IPM
motor 202 in comparison to effect of a second harmonic of the inductance profile on the third
harmonic of the back-EMF. For example, the distorting effect of an eighth harmonic of the
inductance profile on the ninth harmonic of the back-EMF is lower in comparison to a distorting
effect of the second harmonic of the inductance profile on the third harmonic of the back-EMF as
a magnitude of the eighth harmonic is significantly lower than the magnitude of the second
harmonic. Consequently, the effect of load current variations is reduced on the triplen harmonics
of the order of ninth harmonic and higher than the ninth harmonic of the back-EMF.
[0037] Furthermore, in some embodiments, at step 308, the controller 218 may be configured
to generate one or more control signals based at least on the rotor position determined at step
306. In certain embodiments, the controller 218 may generate one or more control signals
additionally based on a desired torque and a desired operating speed (rpm) of the IPM motor
202.
[0038] In addition, at step 310, at least one of the phase current or the phase voltage may be
supplied to the one or more phase terminals 206-210 based at least on the rotor position to
facilitate operation of the IPM motor 202 at a desirable speed while maintaining a desirable
torque. More particularly, the inverter 220 may be configured to adjust the supply of the phase
current and/or the phase voltage based on the one or more control signals received from the
controller 218. For example, based on the control signals from the controller 218, the inverter
220 may be configured to control amplitude, frequency, and/or phase of the phase current and/or
the phase voltage being supplied to the phase terminals 206-210 such that the IPM motor 202
may be operated at the desired speed while maintaining the desired torque.
[0039] FIG. 4 is a flowchart 400 of an example method for extracting the one or more triplen
harmonics of the order of the ninth harmonic and higher than the ninth harmonic, in accordance
with aspects of the present specification. In particular, the flowchart 400 represents detailed
process for performing the step 304 of FIG. 3 to extract one or more triplen harmonics of the
order of the ninth harmonic and a triplen harmonic higher than the ninth harmonic of the
fundamental frequency of the phase voltage signal corresponding to the one or more phase
terminals 206-210.
[0040] As previously noted, the controller 218 may be in receipt of the phase voltage signals
from the sensor electronics 216 at step 302. In some embodiments, at step 402, the controller
218 may optionally be configured to sum the phase voltage signals to generate a sum signal. In
some embodiments, the sum signal includes the triplen harmonics of the fundamental frequency.
[0041] Further, in some embodiments, at step 404, the controller 218 may also be configured
to determine the fundamental frequency of the phase voltage signal based on at least one of the
phase voltage signal and a phase current corresponding to the one or more phase terminals 206-
210. Typically, the fundamental frequencies of all three phase voltage signals are substantially
similar. As previously noted, the phase current drawn by the IPM motor 202 at one or more of
the phase terminals 206-210 may be supplied to the controller 218 by the current sensors 221. In
some embodiments, the fundamental frequency may be similar to a frequency of the phase
current (received from the current sensors 221) corresponding to the one or more phase terminals
206-210. In some embodiments, the fundamental frequency may be similar to a frequency of the
phase voltage signals (generated by the sensor electronics 216) corresponding to the one or more
phase terminals 206-210.
[0042] It is to be noted that in FIG. 4, although the step 404 is shown subsequent to the step
402, the step 404 may also be executed prior to or in parallel with the step 402, without limiting
the scope of the present specification.
[0043] Furthermore, at step 406, the controller 218 may extract the triplen harmonics of the
order of the ninth harmonic and higher than the ninth harmonic. In some embodiments, the
controller 218 may extract the triplen harmonics of the order of the ninth harmonic and higher
than the ninth harmonic from the sum signal. In some embodiments, the controller 218 may
extract the triplen harmonics of the order of the ninth harmonic and higher than the ninth
harmonic from one or more of the phase voltage signals.
[0044] In one embodiment, in order to extract the triplen harmonics of the order of the ninth
harmonic and higher than the ninth harmonic, the controller 218 may be configured to determine
their respective harmonic frequencies based on the determined fundamental frequency (). For
example, the controller 218 may determine the ninth harmonic frequency () as9 * .
Similarly, the controller 218 may also determine the harmonic frequencies corresponding to the
triplen harmonics higher than the ninth harmonic.
[0045] Advantageously, for higher order of triplen frequencies, effects of load variations on
the corresponding triplen harmonics may reduce. However, with increase in the order of the
triplen frequencies, magnitude of the respective triplen harmonics decreases. Consequently,
although it may be desirable to use higher order triplen harmonics for the determination of the
rotor position, it may be desirable to identify a particular triplen harmonic, may be based on the
respective magnitude of that particular triplen harmonic. Therefore, in some embodiments, the
controller 218 may be configured to identify a particular triplen harmonic of the order of the
ninth harmonic and higher than the ninth harmonic based on the respective magnitudes of the
particular triplen harmonic. Further, in some embodiments, to identify the particular triplen
harmonic, the controller 218 may be configured to compare magnitudes of the triplen harmonics
of the order of the ninth harmonic and higher than the ninth harmonic with a threshold magnitude
value. In one embodiment, the controller 218 may be configured to compare the magnitudes of
the triplen harmonics of the order of the ninth harmonic and higher than the ninth harmonic with
the threshold magnitude value in a descending order of the triplen frequencies. Further, once the
comparison is performed, the controller 218 may be configured to identify the one or more
triplen harmonics having magnitudes greater than the threshold magnitude value.
[0046] In some embodiments, the controller 218 may be configured to identify a single triplen
harmonic based on the threshold magnitude value. In particular, if corresponding magnitude of a
particular single triplen harmonic is greater than the threshold magnitude value, the particular
single triplen harmonic is identified by the controller 218. When the comparison is performed in
the descending order of the triplen frequencies, in some embodiments, the controller 218 may be
configured to identify a single triplen harmonic for which a condition of corresponding
magnitude being greater than the threshold magnitude value is first identified. In some other
embodiments, the controller 218 may be configured to identify a plurality of triplen harmonics of
the order of the ninth harmonic and higher than the ninth harmonic having respective magnitudes
that are greater than the threshold magnitude value.
[0047] In some embodiments, the controller 218 may be configured to identify a single triplen
harmonic (of the order of the ninth harmonic and higher than the ninth harmonic) having highest
magnitude.
[0048] In some embodiments, once a single or a plurality of triplen harmonics is identified, the
controller 218 may be configured to extract the identified triplen harmonic from the sum signal.
In some embodiments, the controller 218 may extract the identified triplen harmonics by
multiplying a sinusoidal signal of corresponding harmonic frequency with the sum signal. For
example, if the identified triplen harmonic is the ninth harmonic (i.e., a single triplen harmonic),
the controller 218 may be configured to multiply a sinusoidal signal of frequency 9 * with the
sum signal in order to extract the ninth harmonic. Similarly, if the identified triplen harmonics
are ninth, fifteenth, and twenty first harmonics (i.e., a plurality of triplen harmonics), the
controller 218 may be configured to separately multiply the sum signal with sinusoidal signal of
frequencies9 * , 15 * , 21 * , respectively, to extract the ninth, fifteenth, and twenty first
harmonics.
[0049] In some other embodiments, once a single or a plurality of triplen harmonics is
identified, the controller 218 may be configured to extract the identified triplen harmonic from
any of the phase voltage signals, for example, by using a notch filter. In some embodiments, the
controller 218 may extract the identified triplen harmonics by multiplying a sinusoidal signal of
corresponding harmonic frequency with a given phase voltage signal of the phase voltage
signals. In some embodiments, a result signal of the multiplication may be additionally passed
through a low pass filter. For example, if the identified triplen harmonic is the ninth harmonic
(i.e., a single triplen harmonic), the controller 218 may be configured to multiply a sinusoidal
signal of frequency 9 * with the given phase voltage signal to extract the ninth harmonic.
Similarly, if the identified triplen harmonics are ninth, fifteenth, and twenty first harmonics (i.e.,
a plurality of triplen harmonics), the controller 218 may be configured to separately multiply the
given phase voltage signal with sinusoidal signals of frequencies9 * , 15 * , 21 * , ,
respectively, to extract the ninth, fifteenth, and twenty first harmonics.
[0050] In some other embodiments, the controller 218 may be pre-configured with a selection
of a specific triplen harmonic of the order of the ninth harmonic and higher than the ninth
harmonic. In one embodiment, information corresponding to the determined triplen harmonics
that needs to be extracted may be stored in a memory associated with the controller 218. For
example, once the sum signal is generated by the controller 218, the controller 218 may extract
the determined triplen harmonic from the sum signal. In a non-limiting example, if the
determined triplen harmonic is the ninth harmonic, the controller 218 may be configured to
multiply a sinusoidal signal of frequency 9 * with the sum signal (or the given phase voltage
signal) to extract the ninth harmonic.
[0051] Any of the foregoing steps and/or system elements may be suitably replaced,
reordered, or removed, and additional steps and/or system elements may be inserted, depending
on the needs of a particular application, and that the systems of the foregoing embodiments may
be implemented using a wide variety of suitable processes and system elements and are not
limited to any particular computer hardware, software, middleware, firmware, microcode, and
the like.
[0052] Furthermore, the foregoing examples, demonstrations, and method steps such as those
that may be performed by the controller 218 may be implemented by suitable code on a
processor-based system, such as a general-purpose or special-purpose computer. Different
implementations of the systems and methods may perform some or all of the steps described
herein in different orders, parallel, or substantially concurrently. Furthermore, the functions may
be implemented in a variety of programming languages, including but not limited to C++ or
Java. Such code may be stored or adapted for storage on one or more tangible, computer
readable media, such as on data repository chips, local or remote hard disks, optical disks (that is,
CDs or DVDs), memory or other media, which may be accessed by a processor-based system to
execute the stored code.
[0053] The systems and methods described herein aids in determining a rotor position in IPM
motors. More particularly, the systems and methods described herein facilitates determination of
the rotor position without employing any position sensors and/or encoders, thereby reducing
overall cost of the motor assemblies. Also, the motor assembly in accordance with the
embodiments of the present specification is compact as no position sensors and/or encoders are
employed. Furthermore, systems and methods described herein facilitate reliable and accurate
determination of the rotor position by using information corresponding to one or more the triplen
harmonics of the order of ninth harmonic and higher than the ninth harmonic.
[0054] It will be appreciated that variants of the above disclosed and other features and
functions, or alternatives thereof, may be combined to create many other different systems or
applications. Various unanticipated alternatives, modifications, variations, or improvements
therein may be subsequently made by those skilled in the art and are also intended to be
encompassed by the following embodiments.