Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2002-01-24
2004-02-10
Nappi, Robert (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S132000, C318S254100, C318S430000, C318S432000, C318S434000, C318S434000, C318S720000, C318S724000
Reexamination Certificate
active
06690137
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for a synchronous motor, and more particularly to a highly accurate and high-performance synchronous motor drive system whose controlling mechanism is made simple by not using sensors to detect the motor's speed and position or a motor current sensor.
2. Descriptions of Prior Art
FIG. 33
shows a method for controlling a synchronous motor that does not detect the synchronous motor's magnetic pole position or motor current and does not use a position sensor either. This prior art uses a current sensor that detects a motor current instead of using a position sensor. This prior art is based on a synchronous motor vector control that uses a position sensor, but employs a magnetic pole position estimator and a speed estimator instead of a position sensor (hereinafter, this method is referred to as a “sensorless vector control method”). The configuration of this method, except for a magnetic pole position detecting section and a speed detecting section, is the same configuration as a vector control method that uses a position sensor.
In
FIG. 33
, there are shown a speed command generator
1
for generating a rotational speed command &ohgr;r*, a motor controller
2
Y, a PWM generator
3
for converting a voltage command to a PWM (pulse-width modulation) pulse, an inverter
4
, a synchronous motor
5
, a conversion gain
6
for converting a mechanical angle frequency to an electrical angle frequency, an Id* generator
8
for generating a d-axis current command Id*, a voltage command computing device
11
for computing dq-axis voltage commands Vdc* and vqc*, a dq inverse converter
12
for converting a dq-axis value to a three-phase alternating current value, an adder
13
for adding and subtracting signals, a speed controller
27
for adjusting Iq* so that an estimated speed value agrees with a speed command, a current controller
30
for correcting voltage commands Vdc* and Vqc* so that estimated current values Idc and Iqc agree with command values Id* and Iq* respectively, a magnetic pole position estimator
37
for estimating the magnetic pole axis of the motor, a speed estimator
38
for estimating a rotational speed of the motor, a dq coordinate transformer
39
for transforming a three-phase alternating current (AC) value to a rotary coordinate value, a direct current (DC) power source
41
for the inverter, a main-circuit section
42
of the inverter, a gate driver
43
for turning on and off semiconductor switching elements Sup to Swn of the inverter main-circuit based on a PWM pulse and a current sensor
44
for detecting a current of the motor.
Referring also to
FIG. 33
, a magnetic pole position estimator
37
corresponds to a magnetic pole position sensor and a speed estimator
38
corresponds to a speed sensor. In addition, as is the case with the vector controller having a position sensor, a speed controller
27
and a current controller
30
are provided to automatically make adjustments so that the speed and current agree with each command value. This is, for example, described in “Sensorless control of the permanent magnet synchronous motor's position by direct estimation calculation of axis error” on pages 963 to 966 of the proceedings III, No.97 issued by the Reports of JIASC Conference 2000, Japan.
A prior art of a control method which uses neither a position sensor nor a motor current sensor, shown in
FIG. 34
, has been disclosed in Japanese Application Patent Laid-Open Publication No. Hei 06-153526 and No. Hei 08-19263. Referring now to
FIG. 34
, a motor current estimator
40
estimates and computes a motor current from a DC current I
0
of an inverter and a PWM pulse shape. And the same reference numerals shown in
FIG. 33
are employed for denoting the same devices.
In
FIG. 34
, a motor current is not directly detected, but a DC current of an inverter is detected by a current sensor
44
. A motor current estimator
40
estimates a motor current from the detected value I
0
of the DC current and the output pulse shape of a PWM generator
3
and then outputs the estimated value I
1
c
to a controller
2
Y. Based on the I
1
c
, the controller
2
Y performs the vector-type sensorless control, for example, in the same manner as shown in FIG.
33
.
Next, operations of a motor current estimator
40
will be described with reference to FIGS.
35
(
a
) to (
e
). FIGS.
35
(
a
) to (
c
) illustrate shapes of a PWM pulse for each phase. Plus-side switches (Sup, Svp and Swp) are turned on when the value of each phase is “1” and minus-side switches (Sun, Svn and Swn) are turned on when the value of each phase is “0”. If there is a motor current, as shown in FIG.
35
(
d
), the detected DC current value I
0
of an inverter would appear as a waveform shown in FIG.
35
(
e
). The waveform in FIG.
35
(
e
) has four modes as described below:
(1) Mode 1: Sup=ON, Svp=ON,
Swp=ON→I0=0
(2) Mode 2: Sup=ON, Svp=ON,
Swp=OFF→I0=Iu+Iv=−Iw
(3) Mode 3: Sup=ON, Svp=OFF,
Swp=OFF→I0=Iu
(4) Mode 4: Sup=OFF, Svp=OFF, Swp=OFF→I0=0
Accordingly, “Iu” can be detected by using Mode (3) for detecting a DC current and “Iw” can be detected by using Mode (2). “Iv” can be calculated from Iu and Iw. Thus, it is possible to reproduce a motor current using the switching condition of the inverter main circuit and DC current values. As a result, if a motor current can be estimated, the above-mentioned sensorless vector control method would be able to be realized.
SUMMARY OF THE INVENTION
In the sensorless vector control method shown in
FIG. 33
, a motor must be equipped with a current sensor
44
. However, there is a problem that reliability may be decreased by using a sensor
44
and a cost problem also arises because an expensive current sensor may be required to realize highly accurate control. Further, the method shown in
FIG. 34
has a problem of high-frequency oscillations (ringing) of a current caused by switching operations. The possibilities of ringing occurring increase as the length of the wiring cable for the motor becomes longer, which makes it difficult to detect necessary current values. Furthermore, when a rotational frequency of the motor is low, the width of a PWM pulse becomes narrow, therefore, even though the wiring cable is shortened, the method is affected by noise and detection accuracy deteriorates.
An object of the present invention is to provide a high-performance drive system for a synchronous motor which ensures reliability without having a motor current sensor and is affected little by noise such as ringing.
A synchronous motor drive system in accordance with the present invention detects a DC current of an inverter which drives a synchronous motor, and based on the magnitude of the current, estimates torque current components that flow through the motor, and then based on the estimated value, determines the voltage which is applied to the motor, and finally estimates and computes the magnetic pole axis located inside the motor by using the estimated value of the torque current.
A synchronous motor drive system in accordance with the present invention comprises a synchronous motor, an inverter which applies alternating current to the synchronous motor, a DC power source which supplies power to the inverter, means for detecting a current supplied from the DC power source to said inverter, means for giving a rotation command to said synchronous motor, means for giving current commands Id* and Iq*, Id* on the dc-axis that is assumed to be the magnetic pole axis located inside said synchronous motor and Iq* on the qc-axis that is perpendicular to the dc-axis, and means for computing dc-qc-axis voltage commands based on said current commands Id* and Iq* and said rotation command, wherein control signals are sent to said inverter based on the voltage commands, torque current components inside said synchronous m
Endo Tsunehiro
Iwaji Yoshitaka
Sakamoto Kiyoshi
Takakura Yuhachi
Crowell & Moring LLP
Hitachi , Ltd.
Nappi Robert
Smith Tyrone
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