Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2002-05-13
2004-08-24
Duda, Rina (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S433000, C318S434000, C318S802000, C318S809000, C318S812000
Reexamination Certificate
active
06781333
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. 2001-163929 filed on May 31, 2001, including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a drive control apparatus and method for controlling driving of an alternating current motor (hereinafter simply referred to as “AC motor”).
2. Description of Related Art
For driving an AC motor by using a DC power supply, it is widely known to apply a voltage signal of pulse-width modulated (PWM) waveform to the AC motor by using an inverter. However, the PWM waveform voltage is utilized by the AC motor with a relatively low efficiency. Thus, the AC motor to which the PWM waveform voltage is applied cannot produce sufficiently high output or power in a high-speed rotation region.
In view of the above problem, another technology is known in which a voltage signal of rectangular waveform is applied to the AC motor so as to drive/rotate the AC motor. This technology makes it possible to increase power in a high-speed rotation region, and eliminates the need to supply a large amount of field-weakening current to the motor while it is rotating at a high speed, resulting in a reduction in copper loss. Furthermore, the technology makes it possible to reduce the number of times of switching in the inverter, and to thus reduce or suppress switching loss.
FIG. 5
is a block diagram showing the arrangement of a known drive control apparatus that drives an AC motor via a voltage signal of rectangular waveform. The drive control apparatus, which may be used in, for example, electric vehicles, controls the voltage signal applied to the AC motor such that the torque generated by the AC motor corresponds to a torque command value T* produced by an electronic control unit (ECU) (not shown).
A motor
2
, which is in the form of a permanent magnet synchronization type AC motor, is connected to an inverter
4
. The inverter
4
receives electric power from a battery (not shown), and supplies current to the stator windings of the U, V and W phases of the motor
2
. A rectangular wave generating unit
6
is connected to the inverter
4
. The rectangular wave generating unit
6
generates a switching (SW) signal for producing rectangular wave voltage with respect to each of the U, V and W phases. On the basis of the SW signals thus supplied, switching operations of the inverter
4
are controlled.
The rectangular wave generating unit
6
controls the phase of each SW signal, based on a voltage phase command &Dgr;&phgr; determined by a PI computing unit
8
and a rotor angle &thgr; that is output from a resolver
10
provided adjacent to the motor
2
.
For ease of discussion, a d-q coordinate system (magnetic pole coordinate system), rather than the quantities of the three phases U, V, W of a motor, is used to describe how a motor is controlled. The d-q coordinate system is fixed to a rotor of the motor in question, and voltage equations in a steady state of the motor are expressed in the d-q coordinate system as follows.
Vd=R·Id−&ohgr;·Lq·Iq
(1)
Vq=R·Iq+&ohgr;·Ld·Id+&ohgr;·&psgr;
(2)
In the above equations, Vd and Vq represent a d-axis component and a q-axis component of voltage applied across the stator, and Id and Iq represent a d-axis component and a q-axis component of current passing through the stator, while Ld and Lq represent d-axis inductance and q-axis inductance. Also, &ohgr; represents the angular velocity of the rotor; and &psgr; represents the flux linkage. The direction of the current vector (Iq, Id) changes in accordance with the direction of the voltage vector (Vq, Vd). The value Iq, which contributes to the torque T of the rotor, also changes in accordance with the direction of the voltage vector.
The voltage phase command &Dgr;&phgr; specifies the direction of the voltage vector, and is determined by the PI computing unit
8
so that the Iq provides a desired torque T. Hereinafter, a voltage phase command taken with reference to the d axis (that is, the angle of the voltage vector with respect to the d axis) is expressed as &Dgr;&phgr;, and a voltage phase command taken with reference to the q axis (that is, the angle of the voltage vector with respect to the q axis) is expressed as &Dgr;&phgr;′. The voltage phase commands &Dgr;&phgr;, &Dgr;&phgr;′ have the following relationship (3):
&Dgr;&phgr;=&Dgr;&phgr;′+90° (3)
When &Dgr;&phgr;′ is equal to 0°, the torque T is equal to 0. When &Dgr;&phgr;′ is equal to +90°, a maximum positive torque can be obtained. When &Dgr;&phgr;′ is equal to −90°, a maximum negative torque can be obtained.
In the d-q coordinate system, a desired torque T can be related to or associated with the voltage phase command &Dgr;&phgr; (or &Dgr;&phgr;′). However, motor control is actually based on the quantities of the three phases U, V, W of the motor. Specifically, the phases of current supplied from the inverter
4
to the windings of the U, V and W phases of the motor
2
change depending on the rotor angle &thgr; and the voltage phase command &Dgr;&phgr;. More specifically, the current of each phase is a function of the sum (&xgr;) of &Dgr;&phgr; and &thgr;′, where &thgr;′ represents an electrical angle that is associated with a mechanical rotational angle &thgr; of the rotor. Since the quantities of the three phases change in accordance with the rotor angle &thgr;, the rectangular wave generating unit
6
receives information regarding the rotor angle &thgr; from the resolver
10
, and controls the phases of the SW signals corresponding to the three phases of the motor as described above.
Further, the torque T which is currently being produced by the motor is estimated based on the electric power supplied to the motor
2
. An electric power computing unit
12
calculates the electric power supplied to the motor
2
based on the winding currents Iv, Iw of the V and W phases, which are obtained from respective current sensors
13
, the rotor angle &thgr;, which is obtained from the resolver
10
, and the voltage phase command &Dgr;&phgr;. The U, V and W phases shift 120° in phase from one another, therefore, the total sum of the currents Iu, Iv, Iw of the three phases is equal to zero in principle. Thus, the current sensors
13
are provided only for two phases (V and W phases in this embodiment), and the electric power computing unit
12
calculates the current value of the remaining phase (the U phase), based on the current values of the two phases measured by the sensors
13
. The currents of the three phases can be expressed as follows, where I represents the amplitude of current.
Iu=I·
sin(&xgr;+90°) (4)
Iv=I·
sin(&xgr;+90°−120°) (5)
Iw=I·
sin(&xgr;+90°+120°) (6)
The electric power computing unit
12
determines &xgr; from &Dgr;&phgr; and &thgr;. Here, the inverter
4
is supposed to generate rectangular waves that switch between a voltage level of −Vb/2 and a voltage level of Vb/2. The value Vb is transmitted from the inverter
4
to the electric power computing unit
12
. The electric power computing unit
12
calculates voltage fundamental waves Vu, Vv, Vw contained in the rectangular wave voltages of the respective three phases, according to the following equations (7), (8) and (9).
Vu
=(
Vb/
2)(4/&pgr;)·sin(&xgr;+90°) (7)
Vv
=(
Vb/
2)(4/&pgr;)·sin(&xgr;+90°−120°) (8)
Vw
=(
Vb/
2)(4/&pgr;)·sin(&xgr;+90°+120°) (9)
Then, the electric power computing unit
12
calculates an estimated power P based on the following equation (10).
P=Vu·Iu+Vv·Iv+Vw·Iw
(10)
A torque estimating unit
14
determines an estimated value of current torque T from the estimated power P determined by the electric power computing unit
12
, and the speed N of rot
Koide Satoshi
Yamada Eiji
Duda Rina
Toyota Jidosha & Kabushiki Kaisha
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