 |
Claims  |
|
|
What is claimed is:
1. A method for controlling the torque of a permanent magnet synchronous
motor wherein said motor is powered by an inverter connected to a
direct-current power source, said method comprising the steps of:
communicating a torque command signal from a user to a microcontroller;
sensing the alternating-current phase currents of said motor and
communicating electrical signals representing data concerning said phase
currents to said microcontroller;
sensing the position of the rotor of said motor and communicating
electrical signals representing data concerning said position of said
rotor to said microcontroller;
utilizing said microcontroller to implement a modulation technique to
generate electrical switching signals for creating electrical sinusoidal
waveforms;
utilizing said microcontroller to implement a vector control technique to
generate electrical control signals for adjusting the frequency and
magnitude of said sinusoidal waveforms according to said phase current
data, said rotor position data, the voltage supplied by said power source,
and said torque command signal, wherein generating said control signals
includes the step of referring to look-up tables in an electronic memory
when operating said motor in a constant torque mode to thereby generate
said control signals; and
utilizing said microcontroller to communicate said switching signals for
creating sinusoidal waveforms to said inverter to thereby transmit
sinusoidal waveforms to said motor and thereby control the torque of said
motor.
2. The method according to claim 1, wherein the step of sensing the phase
currents of said motor includes the step of utilizing current transducers
to sense said phase currents.
3. The method according to claim 1, wherein the step of sensing the
position of the rotor of said motor includes the step of utilizing an
encoder to sense said position of said rotor of said motor.
4. The method according to claim 3, wherein the step of utilizing said
microcontroller to implement a vector control technique includes the step
of determining the angular speed of said rotor of said motor by receiving
pulse train electrical signals from said encoder.
5. The method according to claim 1, wherein the step of utilizing said
microcontroller to implement a modulation technique includes the step of
implementing a space vector modulation technique.
6. The method according to claim 1, wherein generating electrical control
signals includes the steps of:
generating a desired value for a first command current variable, wherein
said first command current variable controls the flux of said motor; and
generating a desired value for a second command current variable, wherein
said second command current variable controls the torque of said motor;
basing said first command current variable value and said second command
current variable value on said rotor position data, said voltage supplied
by said power source, and said torque command signal; and
utilizing said first command current variable value and said second command
current variable value to generate said electrical control signals for
adjusting the frequency and magnitude of said sinusoidal waveforms.
7. The method according to claim 6, wherein generating electrical control
signals includes the step of utilizing a current controller to compare
said first command current variable value and said second command current
variable value with said sensed phase currents of said motor.
8. The method according to claim 1, wherein the step of referring to
look-up tables in an electronic memory includes the step of referring to
only two look-up tables to thereby generate said control signals.
9. The method according to claim 1, wherein the step of referring to
look-up tables in an electronic memory includes the step of referring to
look-up tables according to said torque command signal to thereby generate
said control signals.
10. The method according to claim 1, wherein the step of referring to
look-up tables in an electronic memory includes the steps of:
generating a desired value for a first command current variable from a
first look-up table, wherein said first command current variable controls
the flux of said motor;
generating a desired value for a second command current variable from a
second look-up table, wherein said second command current variable
controls the torque of said motor;
utilizing said first look-up table and said second look-up table only when
operating said motor in a constant torque mode; and
utilizing said first command current variable value and said second command
current variable value to generate said electrical control signals for
adjusting the frequency and magnitude of said sinusoidal waveforms.
11. The method according to claim 1, wherein generating electrical control
signals, when operating said motor in an extended speed mode, includes the
steps of:
generating a desired value for a first command current variable by varying
said first command current variable value until said first command current
variable value is as high as permitted by the maximum output voltage of
said inverter, wherein said first command current variable controls the
flux of said motor;
generating a desired value for a second command current variable as
dictated by said first command current variable value and an inherent
current limit of said motor, wherein said second command current variable
controls the torque of said motor; and
utilizing said first command current variable value and said second command
current variable value to generate said electrical control signals for
adjusting the frequency and magnitude of said sinusoidal waveforms.
12. A method for controlling the torque of a permanent magnet synchronous
motor wherein said motor is powered by an inverter connected to a
direct-current power source, said method comprising the steps of:
communicating a torque command signal from a user to a microcontroller;
utilizing current transducers to sense the alternating-current phase
currents of said motor;
communicating electrical signals representing data concerning said phase
currents to said microcontroller;
utilizing an encoder to sense the position of the rotor of said motor;
communicating pulse train electrical signals representing data concerning
said position of said rotor to said microcontroller;
utilizing said microcontroller to determine the angular speed of said rotor
of said motor from said pulse train electrical signals received from said
encoder;
utilizing said microcontroller to implement a modulation technique to
generate electrical switching signals for creating electrical sinusoidal
waveforms;
utilizing said microcontroller to implement a vector control technique to
generate electrical control signals for adjusting the frequency and
magnitude of said sinusoidal waveforms according to said phase current
data, said rotor position data, the voltage supplied by said power source,
and said torque command signal; and
utilizing said microcontroller to communicate said switching signals for
creating sinusoidal waveforms to said inverter to thereby transmit
sinusoidal waveforms to said motor and thereby control the torque of said
motor;
wherein the step of utilizing said microcontroller to implement a vector
control technique includes the steps of:
(1) determining a motor torque, a terminal voltage, and a maximum inverter
output voltage based on said command torque signal, said voltage supplied
by said power source, and said angular speed of said rotor;
(2) comparing said terminal voltage with said maximum inverter output
voltage;
(3) if said terminal voltage is greater than said maximum inverter output
voltage, skipping steps (4) through (8) and thereafter executing step (9);
(4) obtaining a desired value for a first command current variable and a
value for a second command current variable from look-up tables stored in
an electronic memory according to said motor torque, wherein said first
command current variable controls the flux of said motor, and wherein said
second command current variable controls the torque of said motor;
(5) determining a phase voltage based on said terminal voltage, said first
command current variable value, and said second command current variable
value;
(6) comparing said phase voltage with said maximum inverter output voltage;
(7) if said phase voltage is greater than said maximum inverter output
voltage, skipping steps (8) and (9) and thereafter executing step (10);
(8) if said phase voltage is no greater than said maximum inverter output
voltage, skipping steps (9) through (15) and thereafter executing step
(16);
(9) setting a desired value for a first command current variable equal to
zero;
(10) determining a desired value for a second command current variable
based on said motor torque and said first command current variable value;
(11) determining a phase voltage based on said terminal voltage, said first
command current variable value, and said second command current variable
value;
(12) comparing said phase voltage with said maximum inverter output
voltage;
(13) if said phase voltage is less than said maximum inverter output
voltage, increasing said first command current variable value and
repeating steps (10) through (12);
(14) if said phase voltage is greater than said maximum inverter output
voltage, decreasing said first command current variable value and
repeating steps (10) through (12);
(15) if said phase voltage is substantially equal to said maximum inverter
output voltage, executing step (16);
(16) determining a phase current based on said first command current
variable value and said second command current variable value;
(17) if said phase current is greater than an inherent current limit of
said motor, reducing said second command current variable value and
repeating steps (16) and (17); and
(18) utilizing said first command current variable value and said second
command current variable value to generate electrical control signals for
adjusting the frequency and magnitude of said sinusoidal waveforms.
13. A device for controlling the torque of a permanent magnet synchronous
motor wherein said motor is powered by an inverter connected to a
direct-current power source, said device comprising:
means for communicating a torque command signal from a user;
means for sensing the alternating-current phase currents of said motor and
communicating electrical signals representing data concerning said phase
currents;
means for sensing the position of the rotor of said motor and communicating
electrical signals representing data concerning said position of said
rotor; and
an electronic microcontroller unit electrically connected to said torque
command signal communication means, said rotor position sensing means, and
said phase current sensing means, said microcontroller unit including;
means for implementing a modulation technique, to generate electrical
switching signals for creating electrical sinusoidal waveforms, and for
communicating said electrical switching signals to said inverter to
thereby transmit sinusoidal waveforms to said motor and thereby control
the torque of said motor; and
means for implementing a vector control technique to generate electrical
control signals for adjusting the frequency and magnitude of said
sinusoidal waveforms according to said phase current data, said rotor
position data, the voltage supplied by said power source, and said torque
command signal, wherein said vector control technique implementation means
includes an electronic memory having look-up tables dedicated to
generating said control signals when operating said motor in a constant
torque mode.
14. The device according to claim 13, wherein said phase current sensing
means comprises current transducers.
15. The device according to claim 13, wherein said rotor position sensing
means comprises an encoder.
16. The device according to claim 15, wherein said microcontroller unit
includes means for calculating the angular speed of said rotor of said
motor by receiving pulse train electrical signals from said encoder.
17. The device according to claim 13, wherein said modulation technique is
a space vector modulation technique.
18. The device according to claim 13, wherein said vector control technique
implementing means includes:
means for generating a desired value for a first command current variable,
wherein said first command current variable controls the flux of said
motor; and
means for generating a desired value for a second command current variable,
wherein said second command current variable controls the torque of said
motor;
wherein said first command current variable value and said second command
current variable value are based on said rotor position data, said voltage
supplied by said power source, and said torque command signal; and
wherein said first command current variable value and said second command
current variable value are utilized to generate said electrical control
signals for adjusting the frequency and magnitude of said sinusoidal
waveforms.
19. The device according to claim 18, wherein said vector control technique
implementing means includes a current controller for comparing said first
command current variable value and said second command current variable
value with said sensed phase currents of said motor.
20. The device according to claim 13, wherein said vector control technique
implementing means includes an electronic memory having only two look-up
tables dedicated to generating said control signals.
21. The device according to claim 13, wherein said electronic memory
comprises:
a first look-up table for generating a desired value for a first command
current variable, wherein said first command current variable controls the
flux of said motor; and
a second look-up table for generating a desired value for a second command
current variable, wherein said second command current variable controls
the torque of said motor;
wherein said first look-up table and said second look-up table are utilized
only when operating said motor in a constant torque mode; and
wherein said first command current variable value and said second command
current variable value are utilized to generate said electrical control
signals for adjusting the frequency and magnitude of said sinusoidal
waveforms.
22. The device according to claim 13, wherein said vector control technique
implementing means includes:
means for generating a desired value for a first command current variable
by varying said first command current variable value until said first
command current variable value is as high as permitted by the maximum
output voltage of said inverter, wherein said first command current
variable controls the flux of said motor; and
means for generating a desired value for a second command current variable
as dictated by said first command current variable value and an inherent
current limit of said motor, wherein said second command current variable
controls the torque of said motor;
wherein said first command current variable value generating means and said
second command current variable value generating means are utilized only
when operating said motor in an extended speed mode; and
wherein said first command current variable value and said second command
current variable value are utilized to generate the electrical control
signals for adjusting the frequency and magnitude of said sinusoidal
waveforms. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
TECHNICAL FIELD
The present invention relates to a method and an electronic microcontroller
unit for controlling the torque of a permanent magnet (PM), synchronous,
alternating-current (AC) motor over an extended speed range, wherein the
method and the microcontroller unit are both suitable for controlling the
motor of an electric vehicle.
BACKGROUND OF THE INVENTION
Recent developmental advances in high-energy batteries, combined with the
development of smaller and more powerful motors, have made it possible for
new technological and commercial markets to open for a wide range of
products, including, for example, portable electric appliances, electric
entertainment equipment, and electric vehicles. With particular regard to
electric vehicles, improved electric motor drives have also been made
possible by the development of solid-state devices such as the MOSFET
(metal-oxide-semiconductor field-effect transistor) and the IGBT
(insulated-gate bipolar junction transistor), for each of such devices has
the capacity for switching and delivering a significant amount of
electrical power to a motor. In light of such, along with recent increases
in energy costs, energy conservation concerns, environmental concerns, and
strict legislation requiring improved internal combustion engine (ICE)
efficiency, the motor vehicle industry is pressing for the development of
improved electronic motor controls for electric vehicles.
The basic premise on which electronic motor control is based is that the
speed, torque, and direction of a motor are all controlled by
electronically switching or modulating phase currents and voltages which
are ultimately transmitted to the motor. In a closed-loop, electronic
motor drive and control system for a synchronous, three-phase,
alternating-current (AC) motor, for example, the basic elements of such a
system may include: (1) the AC motor, (2) a direct-current (DC) battery
(or battery pack), (3) a DC-to-AC inverter, (4) a user command signal
device, (5) current sensors, (6) a rotor position sensor, and (7) a
microcontroller or microprocessor unit.
In such a system, the user command device is connected to the
microcontroller unit and thereby enables a user (that is, the vehicle
operator) to select a desired speed or torque at which the motor is to
operate. The current sensors are utilized for sensing the phase currents
of the motor so that the microcontroller unit can process the currents for
feedback control purposes. Similarly, the rotor position sensor is
utilized for sensing the position of the rotor of the motor so that the
microcontroller unit can instantaneously determine the position and/or
speed of the rotor for feedback control purposes as well.
Further in such a system, the DC battery defines a DC power bus which is
connected to the inverter, and the inverter is connected to the AC motor.
The inverter serves to convert the DC power from the battery into three
sinusoidal (AC) phase current signals (i.sub.a, i.sub.b, i.sub.c) which
are transmitted to the stator of the motor to thereby operate the motor
and control the torque. The inverter includes three drivers wherein each
driver is dedicated to driving one of the three AC phase currents. Each
driver has two power switches, one "top" switch for driving a particular
phase current high and another "bottom" switch for driving the same phase
current low. Thus, the three drivers of the inverter have a combined total
number of six power switches. Common designations for these six power
switches are A_TOP, A_BOT, B_TOP, B_BOT, C_TOP, and C_BOT. The individual
conductive states ("on" or "off") of the six power switches dictate both
the frequency and the magnitude of the three phase currents which are
transmitted to the motor. The inverter receives electrical switching
signals from the microcontroller unit which dictate the conductive states
of the six power switches at any given point in time.
In general, to properly control the motor, the microcontroller unit must
perform two primary tasks. One, the microcontroller unit must generate
switching signals for helping the inverter create sinusoidal waveforms for
the motor. To accomplish this, the microcontroller unit must implement a
"modulation technique." There are many different types of modulation
techniques, some of which include, for example, sinusoidal pulse-width
modulation (PWM), third-harmonic PWM, 60.degree. PWM, and space vector
modulation (SVM). Two, the microcontroller unit must generate electrical
control signals for adjusting the frequency and magnitude of the
sinusoidal waveforms. To accomplish this, the microcontroller must
implement a "control algorithm." Although there are many general types of
control algorithms, such as, for example, open-loop volts-per-hertz
control, volts-per-hertz with DC current sensing control, direct or
indirect vector control (field orientation), and sensorless vector
control, a significant number of torque control motor drives implement an
indirect "vector control technique." In such a technique, both the phase
currents and the rotor position/speed of the motor are sensed to establish
closed-loop, feedback control of the motor.
In a vector control technique, electrical signals representing data
concerning the sensed phase currents are communicated to the
microcontroller unit from the current sensors. In addition, electrical
signals representing data concerning the position of the rotor are also
communicated to the microcontroller unit from the rotor position sensor.
Based on such communicated data, the microcontroller unit then
mathematically "maps" the measured phase currents as a stator current
vector (I.sub.a) onto a two-axis (direct axis "d," quadrature axis "q")
coordinate system for the purpose of achieving feedback control. In such a
d-q coordinate system, the stator current vector is broken down into two
current components, I.sub.d and I.sub.q, which are orthogonal to each
other on the coordinate system. The I.sub.d current component is used to
represent and control the flux of the motor, and the I.sub.q current
component is used to represent and control the torque of the motor. If the
d-q coordinate system is then mathematically "rotated" synchronously with
the rotor flux of the motor, both I.sub.d and I.sub.q can then be treated
and controlled as DC values, and the AC motor can thus be controlled
almost as if it were a DC motor. Thus, in this way, independent and
decoupled control of both the flux and the torque of the motor is
achieved.
In addition to sensing the phase currents and rotor position to generate
values for I.sub.d and I.sub.q, the microcontroller unit must further
implement the vector control technique to also generate a desired value
for a first (direct-axis) command current variable (I.sub.d *) and a
desired value for a second (quadrature-axis) command current variable
(I.sub.q *). Generated values for the first command current variable and
the second command current variable are ideal values which are most
desired and preferred and are used for controlling and operating the
motor. These generated values are based on and derived from, for example,
the sensed rotor position/speed data, the voltage supplied by the DC
battery, and a user command signal, all of which are electrically
communicated to the microcontroller unit. In ultimately generating the
values based on such communicated information, the microcontroller unit
must typically be involved in very complex and time-consuming processing.
Once both the "measured" I.sub.d and I.sub.q values and the "preferred"
I.sub.d * and I.sub.q * values are successfully determined and generated,
the microcontroller unit then typically utilizes a "current controller" to
compare the measured and preferred values. The current controller is
basically an implementation of difference equations. Based on the
comparison, the current controller then generates electrical control
signals, sometimes referred to as "adjustment" or "correction signals,"
which are used to help conform future "measured" I.sub.d and I.sub.q
values with the "preferred" I.sub.d * and I.sub.q * values. To accomplish
such, the control signals generated by the current controller are
subsequently and actively utilized by the microcontroller unit during
implementation of the modulation technique.
As briefly alluded to earlier herein, during implementation of the
modulation technique, the microcontroller unit generates electrical
switching signals which serve to dictate the conductive states of the six
power switches of the inverter. In this way, the modulation technique
helps the inverter create and modulate sinusoidal waveforms (the phase
currents) for ultimate transmittal to the motor. The control signals
generated during implementation of the vector control technique are
utilized by the microcontroller unit during implementation of the
modulation technique to adjust the frequency and magnitude of the
sinusoidal waveforms generated by the inverter. By adjusting the frequency
and magnitude of the sinusoidal waveforms transmitted to the motor in this
manner, feedback control of both the flux and torque of the motor is
thereby achieved.
At the present time, many AC motor feedback control systems implement
modulation techniques and/or control algorithms which require very complex
computations, long processing times, numerous look-up tables, and
excessive processing and memory space on a microcontroller or
microprocessor. As a result, such motor control systems are typically very
costly. Thus, there is a present need in the art for a lower-cost motor
control method and/or device which will provide optimal torque control for
an AC motor, preferably over an extended speed range, with minimal
computational complexity and minimal processing time.
SUMMARY OF THE INVENTION
The present invention provides a method for controlling the torque of a
permanent magnet (PM), synchronous, alternating-current (AC) motor
suitable for an electric vehicle. The motor is powered by an inverter
connected to a direct-current (DC) power source, such as a battery.
According to the present invention, the method basically includes the
steps of communicating a torque command signal from a user to a
microcontroller, sensing the alternating-current phase currents of the
motor and communicating electrical signals representing data concerning
the phase currents to the microcontroller, sensing the position of the
rotor of the motor and communicating electrical signals representing data
concerning the position of the rotor to the microcontroller, and utilizing
the microcontroller to implement a modulation technique to generate
electrical switching signals for creating electrical sinusoidal waveforms.
In addition, the method also basically includes the step of utilizing the
microcontroller to implement a vector control technique to generate
electrical control signals for adjusting the frequency and magnitude of
the sinusoidal waveforms according to the sensed phase current data, the
sensed rotor position data, the voltage supplied by the power source, and
the torque command signal. In this particular step, generating the
electrical control signals includes the step of referring to look-up
tables in an electronic memory only when operating the motor in a constant
torque mode. Lastly, the method also basically includes the step of
utilizing the microcontroller to communicate the switching signals for
creating sinusoidal waveforms to the inverter. In this way, the inverter
is able to generate sinusoidal waveforms, as dictated by the switching
signals received from the microcontroller, from the power supplied by the
DC power source. As a result, the inverter is also able to transmit the
sinusoidal waveforms to the motor, thereby ultimately controlling the
torque of the motor.
According to a preferred embodiment of the method, sensing the phase
currents of the motor is preferably accomplished by utilizing current
transducers. In addition, sensing the position of the rotor of the motor
is preferably accomplished by utilizing an encoder. Furthermore, utilizing
the microcontroller to implement a modulation technique is preferably
accomplished by specifically implementing a space vector modulation (SVM)
technique.
Further according to a preferred embodiment of the method, generating the
electrical control signals for adjusting the frequency and magnitude of
the sinusoidal waveforms is preferably accomplished by generating a
desired value for a first command current variable, wherein the first
command current variable controls the flux of the motor, and also
generating a desired value for a second command current variable, wherein
the second command current variable controls the torque of the motor. Both
the first command current variable value and the second command current
variable value are based on the sensed rotor position data, the voltage
supplied by the power source, and the torque command signal. Once the
desired values are generated, the first command current variable value and
the second command current variable value are utilized to help generate
the electrical control signals for adjusting the frequency and magnitude
of the sinusoidal waveforms. Furthermore, generating the electrical
control signals is also preferably accomplished by utilizing a current
controller to compare the first command current variable value and the
second command current variable value with the sensed phase currents of
the motor.
When operating the motor in a constant torque mode, referring to look-up
tables in an electronic memory to thereby generate the control signals is
preferably accomplished by both referring to only two look-up tables and
also referring to the look-up tables according to the torque command
signal. In a highly preferred embodiment of the method, referring to
look-up tables in an electronic memory to thereby generate the control
signals is accomplished by generating a desired value for a first command
current variable from a first look-up table, wherein the first command
current variable controls the flux of the motor, and also generating a
desired value for a second command current variable from a second look-up
table, wherein the second command current variable controls the torque of
the motor. Both the first look-up table and the second look-up table are
utilized only when operating the motor in the constant torque mode.
Alternatively, when operating the motor in an extended speed mode,
generating the electrical control signals is preferably accomplished by
generating a desired value for a first command current variable by varying
the first command current variable value until the first command current
variable value is as high as permitted by the maximum output voltage of
the inverter, wherein the first command current variable controls the flux
of the motor, and also generating a desired value for a second command
current variable as dictated by the first command current variable value
and an inherent current limit of the motor, wherein the second command
current variable controls the torque of the motor.
The present invention also provides a device for controlling the torque of
a permanent magnet (PM), synchronous, alternating-current (AC) motor
suitable for an electric vehicle. The motor is powered by an inverter
connected to a direct-current (DC) power source, such as a battery.
According to the present invention, the device basically includes means
for communicating a torque command signal from a user, means for sensing
the alternating-current phase currents of the motor and communicating
electrical signals representing data concerning the phase currents, and
means for sensing the position of the rotor of the motor and communicating
electrical signals representing data concerning the position of the rotor.
In addition, the device also basically includes an electronic
microcontroller unit electrically connected to the torque command signal
communication means, the rotor position sensing means, and the phase
current sensing means. The microcontroller unit basically includes means
for implementing a modulation technique, to generate electrical switching
signals for creating electrical sinusoidal waveforms, and for
communicating the electrical switching signals to the inverter to thereby
transmit sinusoidal waveforms to the motor and thereby control the torque
of the motor. The microcontroller unit also basically includes means for
implementing a vector control technique to generate electrical control
signals for adjusting the frequency and magnitude of the sinusoidal
waveforms according to the phase current data, the rotor position data,
the voltage supplied by the power source, and the torque command signal.
The vector control technique implementation means includes an electronic
memory having look-up tables dedicated to generating the electrical
control signals only when operating the motor in a constant torque mode.
According to a preferred embodiment of the device, the phase current
sensing means comprises current transducers, and the rotor position
sensing means comprises an encoder. The microcontroller unit preferably
includes a speed calculator unit for calculating the angular speed of the
rotor of the motor by receiving pulse train electrical signals from the
encoder. The modulation technique implementing means preferably implements
a space vector modulation technique.
Advantages, design considerations, and applications of the present
invention will become apparent to those skilled in the art when the
detailed description of the best mode contemplated for practicing the
invention, as set forth hereinbelow, is read in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described, by way of example, with reference
to the following drawings.
FIG. 1 is a functional block diagram illustrating, according to the present
invention, a device for controlling the torque of a permanent magnet (PM),
synchronous, alternating-current (AC) motor, wherein the motor is powered
by an inverter connected to a direct-current (DC) battery.
FIG. 2 is a flow diagram illustrating, according to the present invention,
method steps for controlling the torque of the motor in FIG. 1.
FIG. 3 is a vector diagram illustrating, according to the present
invention, two constant torque curves and how to select a minimum phase
current vector and associated command currents for a given torque to
thereby produce the maximum torque per ampere in a PM, synchronous, AC
motor.
FIG. 4 is a vector diagram illustrating, according to the present
invention, how the phase current and the phase voltage of a PM,
synchronous, AC motor can be mapped as a vector onto a two-axis (d-q)
coordinate system to achieve decoupled control of the flux and torque of
the motor in an extended speed mode.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a functional block diagram illustrating, according to the present
invention, a device 10 for controlling the torque of a permanent magnet
(PM), synchronous, alternating-current (AC) motor 40. The motor 40 is
powered by an inverter 20 connected to a direct-current (DC) power source,
in this case a battery 12. More particularly, the battery 12 has a
positive terminal 14 and a negative terminal 16. The positive terminal 14
is electrically connected to the inverter 20 via a line 18, and the
negative terminal 16 is electrically connected to the inverter 20 via a
line 22. The line 18 and the line 22 have a DC voltage potential
difference (V.sub.dc) therebetween and together define a DC power bus 24
which is connected to the inverter 20. The inverter 20 is preferably
implemented utilizing MOSFETs (metal-oxide-semiconductor field-effect
transistors) due to the high speed switching capability which is
characteristic of MOSFETs. However, if the inverter 20 is to accommodate
high voltage and current levels, the inverter 20 may instead be of the
type which utilizes IGBTs (insulated-gate bipolar transistors), Darlington
BJTs (bipolar junction transistors), or thyristors.
The inverter 20 transmits three sinusoidal, alternating-current (AC) phase
currents (i.sub.a, i.sub.b, and i.sub.c) to the motor 40 via a line 26, a
line 28, and a line 30 for operation and control of the motor 40. For
feedback control purposes, the phase currents transmitted to the motor 40
are sensed for determining instantaneous current flows. In the preferred
embodiment illustrated in FIG. 1, the phase current i.sub.a on the line 30
is sensed with a first current transducer 34, and the phase current
i.sub.b on the line 28 is sensed with a second current transducer 32.
Although other types of current sensors can be utilized with the present
invention, such as current-sensing resistors, Hall-effect current sensors,
and current-sensing transformers, current transducers are preferred for
their non-contact current sensing and electrical isolation characteristics
as well as their overall easy implementation. Once the phase currents are
sensed, digital electrical signals representing data concerning the phase
currents are communicated from both the first current transducer 34 and
the second current transducer 32 to a microcontroller unit 50.
During operation of the motor 40, the instantaneous angular position of the
rotor of the motor 40 is sensed with an encoder 42 for feedback control
purposes. According to the present invention, the encoder 42 can be any
known type of encoder, such as, for example, a resolver, a rotary encoder,
a linear variable differential transformer (LVDT), a rotational variable
differential transformer (RVDT), a Hall-effect sensor, an optical encoder
(such as a disk with apertures for quadrature sensing), and
magneto-resistive sensors. Once the position of the rotor of the motor 40
is sensed, digital electrical signals representing data concerning the
position of the rotor are communicated from the encoder 42 to the
microcontroller unit 50.
Both data concerning the phase currents and data concerning the position of
the rotor of the motor 40 are specifically communicated to a
transformation circuit 46 in the microcontroller unit 50 for
implementation of a "vector control technique." In particular, data
concerning phase current i.sub.a is communicated via a line 36 to the
transformation circuit 46, and data concerning phase current i.sub.b is
communicated via a line 38 to the transformation circuit 46. Data
concerning the position of the rotor is communicated via a line 44 to the
transformation circuit 46. The transformation circuit 46 is a conventional
three-phase to two-phase transformation circuit, with a-b-c to d-q
transformation and a forward vector rotator, wherein the measured values
for the AC phase currents, i.sub.a and i.sub.b, are converted into values
for two DC current components, I.sub.d and I.sub.q. The current component
I.sub.d is associated with controlling the flux of the motor 40, and the
current compone | | |
