Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2003-09-25
2004-10-05
Duda, Rina (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S705000, C318S718000, C318S721000, C318S632000, C318S609000, C318S254100
Reexamination Certificate
active
06801011
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a control apparatus for a synchronous motor which controls the synchronous motor by speed sensorless vector control, and more particularly to a method of estimating the position of a magnetic pole for the synchronous motor.
BACKGROUND ART
Vector control is taken as one of methods of carrying out the control of a synchronous motor. The vector control is intended for maintaining a phase difference between an exciting current (a d-axis current) held to be constant and a torque current (a q-axis current) corresponding to a necessary torque to be an electrical angle of 90 degrees, thereby obtaining an efficiency and a responsiveness which are equivalent to or more than those of D.C. motors.
In general, it is necessary to measure the speed of the synchronous motor by using a speed sensor in order to carry out the vector control of the synchronous motor. However, it is advantageous that the speed sensor is not adopted in respect of a cost and a reliability. For this reason, there is used speed sensorless vector control for estimating the synchronous motor speed without actually measuring the synchronous motor speed by the speed sensor and carrying out vector control by using an estimated value. In the speed sensorless vector control, the position of a magnetic pole is first estimated and a speed is estimated from the position of the magnetic pole in order to estimate the speed of the synchronous motor.
Conventionally, a synchronous motor control method for estimating the position of the magnetic pole of the synchronous motor in a zero frequency region in which the driving frequency of the synchronous motor is almost zero, that is, during a super-low speed operation, thereby outputting a suitable torque for a load has been reported by the following document.
Reference 1: M. Schroedl, “Sensorless control of induction motors at low speed and standstill,” in Proceedings ICEM' 92 (International Conference on Electrical Machines September 1992), pp. 863-867.
Reference 2: M. J. Corley and R. D. Lorenz, “Rotor Position and Velocity Estimation for a Salient-Pole Permanent Magnet Synchronous Machine at Standstill and High Speeds”, IEEE Transactions on Industry Applications, Volume 34, Number 4, July/August, pp.784-789, 1998.
Reference 3: Yamano, Noguchi, Kondoh “Position Sensorless Speed Control Method of Saliency-type PM Motor including Low Speed Region”, Technical Meeting on Semiconductor Power Converter, IEEE Japan, SPC-97-13, pp. 75-82, 1997.
These methods feature that a high-frequency voltage or high-frequency current having a different frequency from a driving frequency is superposed on a synchronous motor and the synchronous motor is controlled by using the position of a magnetic pole which is estimated based on the electrical saliency of the structure of a rotor.
FIG. 1
shows an example of a control apparatus for estimating the position of a magnetic pole to control a synchronous motor according to the conventional art described above.
The control apparatus for the synchronous motor according to the conventional art is constituted by a PWM voltage type inverter (PWM VSI: Voltage Source Inverter)
2
, a high-frequency generator
4
, a two-phase and three-phase transformer
3
, a current controller
5
, a low-pass filter (LPF)
6
, d-q transformers
7
and
8
, a bandpass filter (BPF)
9
, a high-frequency impedance estimator
10
, a magnetic pole position estimator
21
, a current detector
12
, an adder
38
and subtractors
39
to
41
, and carries out the vector control of a synchronous motor
1
.
The subtractors
39
and
40
subtract actual current values i&ggr; and i&dgr; from current commands i&ggr;* and i&dgr;*, respectively. The current controller
5
executes the current control by generating and outputting the voltage commands V&ggr;* and V&dgr;* in such a way that each of the deviations between the current values i&ggr;, i&dgr; and their corresponding current command values i&ggr;*, i&dgr;*, which are output from the subtractors
39
and
40
, becomes zero.
The high-frequency generator
4
generates a high-frequency voltage V
inj
having a frequency f
inj
which is different from a driving frequency. The adder
38
adds the high-frequency voltage V
inj
generated by the high-frequency generator
4
to a &ggr; component (a magnetic flux component) V&ggr;* of a voltage command value to be an output from the current controller
5
.
The two-phase and three-phase transformer
3
converts a result of the addition in the adder
38
and a &dgr; component (a torque component) V&dgr;* of the voltage command value into a three-phase voltage command value and gives a command to the PWM voltage type inverter
2
. The PWM voltage type inverter
2
controls the synchronous motor
1
based on the command given from the two-phase and three-phase transformer
3
.
Moreover, the current detector
12
detects a current value i
s
of the synchronous motor
1
. The d-q transformer
7
coordinate transforms the current value i
s
detected by the current detector
12
into a control axis by using an estimated magnetic pole position &thgr;{circumflex over ( )}.
The low-pass filter (LPF)
6
feeds back, to the subtractor
39
, a value obtained by removing the same frequency component f
inj
as the high-frequency voltage V
inj
superposed by the adder
38
from the current value coordinate transformed into the control axis by the d-q transformer
7
. By such a structure, the current control is executed in such a manner that each of the deviations between the exciting component (i&ggr;*), the torque component (i&dgr;*) and their corresponding current command values is set to be zero by the current controller
5
.
The subtractor
41
subtracts 45 degrees (&pgr;/4 radian) from the estimated magnetic pole position &thgr;{circumflex over ( )}. The d-q transformer
8
converts the phase of the detected current value i
s
into that of the subtractor
41
, thereby transforming the detected current value i
s
into an impedance observation axis positioned in a place shifted from-the estimated magnetic pole position &thgr;{circumflex over ( )} by 45 degrees.
The bandpass filter (BPF)
9
extracts the component of the same frequency component f
inj
as the high-frequency voltage command value V
inj
superposed by the adder
38
, and inputs high-frequency current components i
dm
and i
qm
thus extracted and the high-frequency voltage command value V
inj
to the high-frequency impedance estimator
10
. The high-frequency impedance estimator
10
estimates high-frequency impedances Z
dm
and Z
qm
on two points which are advanced and delayed from a &ggr; axis by an electrical angle of 45 degrees.
A magnetic pole position estimator
13
estimates such a magnetic pole position &thgr;{circumflex over ( )} that two high-frequency impedances Z
dm
and Z
qm
are equal to each other. Moreover, the magnetic pole position estimator
13
is constituted by a subtractor
31
, a multiplier
32
and an integrator
33
as shown in FIG.
2
. The subtractor
31
obtains a difference between the high-frequency impedances Z
qm
and Z
dm
. The multiplier
32
outputs a value obtained by multiplying an output sent from the subtractor
31
by a control gain (K
p
+K
i
/s). K
p
represents a proportional gain and K
i
represents an integral gain. The integrator
33
integrates the output value of the multiplier
32
and outputs the integrated value as the estimated magnetic pole position &thgr;{circumflex over ( )}. In other words, the magnetic pole position estimator
13
regulates a PI regulator comprising the subtractor
31
and the integrator
32
in such a manner that Z
dm
and Z
qm
are coincident with each other, and an output is integrated by the integrator
33
to obtain the magnetic pole position estimated value &thgr;{circumflex over ( )}.
Next, description will be given to the operation of the control apparatus for the synchronous motor according to the conventional art.
In the control apparatus for the synchronous motor according to the conventional art shown in
FIG
Duda Rina
Kabushiki Kaisha Yaskawa Denki
Sughrue & Mion, PLLC
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