BACKGROUND
Embodiments of the invention relate generally to a method and system
for controlling a motor, and more particularly relate to a method and system for
controlling an alternating current (AC) motor outputting a motor torque changing
linearly with respect to a voltage phase angle of a voltage vector applied thereto.
An AC motor is controlled by a voltage vector outputted from a control
system and generates a motor torque for driving wheels of a hybrid vehicle or an
electric vehicle. The voltage vector is generated through converting a direct current
(DC) voltage from a DC power source. The motor torque changes with a voltage
amplitude and a voltage phase angle of the voltage vector. Currently, the motor
torque is controlled through regulating both the voltage amplitude and the voltage
phase angle. However, it's difficult to determine a good point of the voltage
amplitude and the voltage phase angle to ensure the motor torque as higher as possible
to ensure the DC bus voltage utilization rate.
An approach is provided to improve the motor torque and the DC bus
voltage utilization rate by fixing the voltage amplitude and varying the voltage phase
angle so that the motor torque is controlled only through changing the voltage phase
angle. For example, see Hideo Nakai et al., "Development and testing of the torque
control for the permanent-magnet synchronous motor," in IEEE Transactions on
Industrial Electronics, Vol. 52, No.3, June 2005. However, in this approach, the
motor torque changes nonlinearly with the voltage phase angle. A shortcoming of this
approach is that it cannot quickly and continuously calculate and control the motor
torque.
It is desirable to provide a method and system for controlling a motor to
address at least some of the above-mentioned problems.
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BRIEF DESCRIPTION
In accordance with one embodiment disclosed herein, a method is
provided for controlling a motor. The method includes obtaining via a signal unit
electrical signals of the motor. The electrical signals include a motor torque and an
angular velocity. The method further includes calculating via the calculating
component a voltage phase angle of a voltage vector. A command torque, the motor
torque, the angular velocity and a voltage amplitude of the voltage vector are inputs of
the calculating component. The voltage phase angle is a variable and the voltage
amplitude is a constant. The motor torque generated from the motor changes linearly
with respect to the voltage phase angle at a certain value of the angular velocity of the
motor and a certain monotonous range of the voltage phase angle. The method
further modulating via a modulator the voltage phase angle and the voltage amplitude
to a switching signal controlling an inverter. The method further includes converting
via the inverter a direct current voltage to the voltage vector according to the
switching signal and applying the voltage vector to the motor.
In accordance with another embodiment disclosed herein, a method is
provided for controlling a motor torque generated from a motor. The method includes
fixing a voltage amplitude of a voltage vector outputted from an inverter. The method
further includes changing a voltage phase angle of the voltage vector to control the
motor torque. The motor torque changes linearly with respect to the voltage phase
angle at a certain value of an angular velocity of the motor and a certain monotonous
range of the voltage phase angle.
In accordance with another embodiment disclosed herein, a control
system is provided for controlling a motor. The control system includes a signal unit
for outputting electrical signals of the motor. The electrical signals include a motor
torque and an angular velocity. The control system further includes a controller
coupled to the signal unit. The controller has a calculating component for calculating
a voltage phase angle of a voltage vector. Inputs of the calculating component
include a command torque, the motor torque, the angular velocity and a voltage
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amplitude of the voltage vector as a constant. An output of the calculating component
is the voltage phase angle. The motor torque changes linearly with respect to the
voltage phase angle at a certain value of the angular velocity of the motor and a
certain monotonous range of the voltage phase angle.
DRAWINGS
These and other features, aspects, and advantages of the present
disclosure 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:
FIG. 1 is a schematic basic block diagram of a motor system in
accordance with an exemplary embodiment;
FIG. 2 is a block diagram of an exemplary calculating component in a
controller for use in the motor system of FIG. 1; and
FIG. 3 is a block diagram of another exemplary calculating component
in a controller for use in the motor system of FIG. 1.
DETAILED DESCRIPTION
Unless defined otherwise, technical and scientific terms used herein have
the same meaning as is commonly understood by one of ordinary skill in the art to
which this disclosure belongs. The terms "first", "second", and the like, as used
herein do not denote any order, quantity, or importance, but rather are used to
distinguish one element from another. Also, the terms "a" and "an" do not denote a
limitation of quantity, but rather denote the presence of at least one of the referenced
items. The use of "including," "comprising" or "having" and variations thereof herein
are meant to encompass the items listed thereafter and equivalents thereof as well as
additional items. The terms "connected" and "coupled" are not restricted to physical
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or mechanical connections or couplings, and can include electrical connections or
couplings, whether direct or indirect.
FIG. 1 illustrates a schematic block diagram of a motor system 100 in
accordance with an exemplary embodiment. In FIG. 1, the motor system 100
generally includes a motor 10 and a control system 200 controlling the motor 10. The
control system 200 includes an inverter 20 coupled to the motor 10, a direct current
(DC) power source 30 coupled to the inverter 20, a modulator 40 coupled to the
inverter 20, a controller 50 coupled to the modulator 40, and a signal unit 60 coupled
to the controller 50.
The signal unit 60 is configured to obtain electrical signals of the motor
10. The electrical signals comprise a motor torque, Tern, and an angular velocity, 00, of
the motor 10 besides others such as motor currents and motor voltages. Some
electrical signals such as motor currents and motor voltages are acquired only through
detecting and some electrical signals such as the motor torque, Tern, and the angular
velocity, 00, may be acquired through detecting or calculating. In one embodiment,
the control system 200 comprises at least one sensor (not shown) coupled to the motor
10 and the signal unit 60 has an acquisition component 601 coupled to the sensor.
The sensors are configured to detect the electrical signals of the motor 10. The
acquisition component 601 is configured to receive the electrical signals, convert the
electrical signals to dates which can be processed by the controller 50 and provide the
dates to the controller 50. The motor torque, Tern. and the angular velocity, 00, are
acquired through detecting.
In another embodiment, the signal unit 60 further comprises a signal
processor 602 coupled to the acquisition component 601 and the controller 50 for
calculating the electrical signals based on parameters of the motor 10 such as the
number of pole pairs, inductances, flux linkage and so on. The sensors detect the
motor currents, the motor voltages and so on and then the acquisition component 601
provides them to the signal processor 602. The signal processor 602 calculates the
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motor torque, Tern, and the angular velocity, 0), based the motor currents, the motor
voltages and so on.
The motor torque, Tern, and the angular velocity, 0), are inputted into the
controller 50, The controller 50 is configured to provide a voltage phase angle,