Position sensorless motor control apparatus

Details Position sensorless motor control apparatus Position sensorless motor control apparatus

2000-01-26

2002-10-08

Ro, Bentsu (Department: 2837)

Electricity: motive power systems

Switched reluctance motor commutation control

C318S434000, C318S721000

Reexamination Certificate

active

06462491

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a position sensorless motor control apparatus which drives a motor for rotation by estimating rotor angle without using position sensors. More particularly, the invention relates to a position sensorless motor control apparatus that achieves high resolution and high accuracy angle estimation, achieves angle estimation even in the presence of phase voltage saturation, and achieves high accuracy angle estimation even-when a back electromotive force constant changes.
Brushless motors which do not use mechanical commutation mechanisms need to be electrically commutated based on rotor angle.
In conventional motor control apparatuses, position sensors such as Hall elements, resolvers, or optical encoders mounted on brushless motors have been used to obtain rotor angle information. The provision of such a position sensor has necessarily added to the cost and increased the size of the brushless motor.
Position sensorless motor control apparatuses that achieve reduced cost and reduced size by eliminating the position sensor are known in the art, including one disclosed in Japanese Unexamined Patent Publication No. 64-43095 (hereinafter referred to as the prior art 1) and one described in “Collection of Papers, The Institute of Electrical Engineers,” Vol. 117-D, No. 1, pp. 98-104, 1997 (hereinafter referred to as the prior art 2). These prior art position sensorless motor control apparatuses will be described below. In the following description, some of the value names used in the above cited literature are changed to maintain consistency with those used in the embodiments of the present invention.
These prior art position sensorless motor control apparatuses are designed to control Y-connected three-phase brushless motors.
A block diagram of the, position sensorless motor control apparatus of the prior art 1 is shown in
FIG. 27
, and a timing chart for the same is shown in FIG.
28
. In
FIG. 28
, some of the signal names are changed for the convenience of comparison with the present invention.
In
FIG. 27
, the position sensorless motor control apparatus of this prior art first detects phase currents (iu, iv, and iw) flowing through stator windings for the respective phases, phase voltages (vu, vv, and vw) applied to the respective phase stator windings, and a voltage (vn) at a neutral point. Next, the following equations (1), (2), and (3) are calculated to obtain back electromotive force values eu, ev, and ew of the voltages induced in the respective phase stator windings. In the equations, R designates the resistance and L the inductance. Further, d(iu)/dt, d(iv)/dt, and d(iw)/dt are the time derivatives of iu, iv, and iw, respectively.
eu=vu−vn−R·iu−L·d
(
iu
)/
dt
  (1)
ev=vv−vn−R·iv−L·d
(
iv
)/
dt
  (2)
ew=vw−vn−R·iw−L·d
(
iw
)/
dt
  (3)
The back electromotive force values eu, ev, and ew are input to a comparator circuit
35
(FIG.
27
). The comparator circuit
35
compares the back electromotive force values eu, ev, and ew with the respective back electromotive force values multiplied by a predetermined constant k (0≦k), i.e., k·eu, k·ev, and k·ew, to determine their magnitude relationships, and outputs signals (b) C
1
, (c) C
2
, (d) C
3
, (e) C
4
, (f) C
5
, and (g) C
6
representing the results of the comparisons (FIG.
28
). These signals are input to a logic circuit
36
(FIG.
27
). The logic circuit
36
outputs drive signals (h) DSU+, (i) DSU−, (j) DSV+, (k) DSV−, (l) DSW+, and (m) DSW− for driving an output unit
16
(
FIGS. 27
) for the stator windings (FIGS.
27
and
28
). The currents flowing through the stator windings are controlled by the drive signals, and the rotor rotates in a prescribed direction.
The prior art 1 compares the magnitudes of the respective back electromotive forces and determines the energization period of each phase, but does not have an angle estimation unit for estimating the rotor angle of the motor. In the timing chart for (b) C
1
in
FIG. 28
, a high period of C
1
is shown, but no detailed information within the high period of C
1
is presented that is, whether C
1
is currently at the beginning, in the middle, or at the end, of the high period is not known. Furthermore, since the angular velocity of the motor is not detected, it is not known how long the high period of C
1
will last. It is only possible to know which of the signals C
1
to C
6
is high at a particular point in time.
Accordingly, the motor cannot be driven with a sinusoidal or like waveform for smooth rotation. In embodiment 1, the voltage applied to each phase of the motor during its energization period is constant.
One object of the present invention is to drive a motor smoothly by estimating the angle of the motor and driving the motor with a sinusoidal waveform.
A block diagram of the position sensorless motor control apparatus of the prior art 2 is shown in
FIG. 29
, and an analytical model of the motor and its driving circuitry is shown in FIG.
30
.
In
FIG. 29
, the prior art 2 first obtains an error signal, &Dgr;&ohgr;=(d&thgr;/dt)−(d&thgr;mb/dt), representing the difference between a target angular velocity (d&thgr;/dt) and the estimated angular velocity (d&thgr;mb/dt) output from an estimated model, and supplies the error signal &Dgr;&ohgr; to a velocity control block (PI control circuit). The velocity control block outputs a target current for generating the torque required to achieve the target angular velocity. Actual current i is subtracted from the target current The resulting difference &Dgr;i is input to a current control block (PI control). The current control block outputs the voltage required to flow the target current as a voltage expressed on &ggr;−&dgr; axes. This required voltage is summed with the back electromotive force (em) output from the estimated model. The sum voltage expressed on the &ggr;−&dgr; axes is first converted into voltages on u, v, and w axes representing the voltages to be applied to the respective stator windings, and then, these voltages on the u, v, and w axes are actually applied to the respective stator windings of the motor.
As described above, the u, v, and w axes are stationary axes corresponding to the respective phases of the stator windings.
The &ggr; and &dgr; axes are coordinate axes with the origin at the center of the magnetic dipole of the rotor of the brushless motor model estimated by the position sensorless motor control apparatus, the direction of the &ggr; axis being the same as the direction of the estimated rotor's magnetic dipole (i.e., the axis joining the S pole to the N pole) and the &dgr; axis being advanced relative to the &ggr; axis by 90 degrees in the positive direction (in the counterclockwise direction), and the coordinate axes rotates with the estimated rotor.
Likewise, the d and q axes are coordinate axes with the origin at the center of the magnetic dipole of the actual rotor of the motor, the direction of the d axis being the same as the direction of the actual rotor's magnetic dipole (i.e., the axis joining the S pole to the N pole) and the q axis being advanced relative to the d axis by 90 degrees in the positive direction (in the counterclockwise direction), and the coordinate axes rotates with the actual rotor.
In the feedback loop shown in
FIG. 29
, the phase currents flowing in the stator windings of the respective phases are detected, and the phase current values are coordinate converted to generate a &ggr;-axis current value i&ggr; and a &dgr;-axis current value i&dgr;.
The relationships between the currents i&ggr;, i&dgr; and the voltages v&ggr;, v&dgr; can be expressed by the following equations (79) and (80) (where i&ggr; and i&dgr; are the &ggr;-axis current component and the &dgr;-axis current component, respectively). &thgr;m is the estimated rotor angle.
v&ggr;={R+L
&ggr;(
d&thgr;m/dt
)+
L
&ggr;(
d/dt
)}
i&ggr

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