Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems
Reexamination Certificate
2001-03-07
2002-01-15
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
Hysteresis or reluctance motor systems
C318S254100, C318S132000, C318S434000
Reexamination Certificate
active
06339308
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vector control method for a synchronous reluctance motor. More particularly, the invention relates to a vector control method using an estimator, instead of a salient pole position angle detector mounted on a rotor, in order to secure cosine and sine information of a rotor's salient pole position angle necessary for a vector rotators for the vector control.
2. Description of the Related Art
To obtain superior drive control performance of a synchronous reluctance motor, the vector control method is conventionally employed as a well-known control method for controlling a stator current, which is essential for superior performance. The vector control method has a current control process which divides and controls the stator current contributing to the generation of a torque into a d-axis component and a q-axis component of rotational d-q coordinates composed of mutually orthogonal d and q axes which mutually cross at right angles.
Generally, d-q coordinates synchronized with the position of the main salient pole of the rotor with zero spatial phase difference are employed as rotational d-q coordinates for the vector control system. In other words, the use of synchronous d-q coordinates whose d-axis is oriented to direction of the main salient pole of the rotor and whose q-axis is orthogonal to the d-axis is very popular. Generally, the position angle of the main salient pole direction must be known in order to maintain the rotational d-q coordinates in a synchronized state free from the spatial phase difference with the main salient pole direction. Conventionally, in order to accurately ascertain the position angle, a salient position angle detector represented by an encoder mounted on the rotor.
FIG. 13
is a block diagram schematically showing a typical example of the vector control method using a salient pole position angle detector employed in a device which is in turn mounted on a standard synchronous reluctance motor which can disregard iron losses. In
FIG. 13
,
1
is a synchronous reluctance motor,
2
is a salient pole position angle detector,
3
is a power inverter,
4
is a current detector,
5
a
,
5
b
are a 3-2 phase converter and a 2-3 phase converter,
6
a
,
6
b
are vector rotators,
7
is a cosine and sine signal generator,
8
is a current controller,
9
is a command converter,
10
is a speed controller, and
11
is a speed detector. Components
4
to
9
in
FIG. 13
configure a vector controller. For clarity and simplicity, a single solid bold line in
FIG. 13
indicates a 2×1 vector signal deeply related to the present invention. Block diagrams in the following are illustrated in the same manner.
In a conventional device such as in
FIG. 13
, the salient pole position angle detector
2
detects the main salient pole direction as an angle with respect to the center of a U-phase winding, and the cosine and sine signal generator
7
outputs its cosine and sine signals to the vector rotators
6
a
,
6
b
. Together, these comprise a means for determining a spatial phase of the rotational d-q coordinates. In the synchronous reluctance motor, the rotor speed is the rotation speed of the rotor's salient pole. In other words, the rotor salient pole position angle and the rotor speed are in a relation of integration and differentiation, and it is known well by those killed in the art that speed information can be obtained from the salient pole position angle detector such as an encoder as well as the position angle information. The speed detector
11
is a one realizing such speed detecting means. The aforesaid five components
4
,
5
a
,
5
b
,
6
a
,
6
b
,
7
,
8
comprise a means for performing a current control process to divide the stator current into a d-axis component and a q-axis component on the rotational d-q coordinates, and to control the respective components to follow the current commands of the d-axis and the q-axis.
The 3-phase current detected by the current detector
4
is transformed by the 3-2 phase converter
5
a
into a 2-phase current on the stationary coordinates, which is, in turn, converted by the vector rotator
6
a
into 2-phase currents i
d
, i
q
, on the rotational d-q coordinates and sent to the current controller
8
. The current controller
8
generates voltage commands v*
d
, v*
q
on the rotational d-q coordinates and sends these to the vector rotator
6
b
so that the converted currents i
d
, i
q
follow respective current commands i*
d
, i*
q
. The vector rotator
6
b
converts the 2-phase signals v*
d
, v*
q
into 2-phase voltage command on the stationary coordinates and sends this to the 2-3 phase converter
5
b
. The 2-3 phase converter
5
b
converts the 2-phase signal into a 3-phase voltage command and outputs it as a command to the power inverter
3
. The power inverter
3
produces power corresponding to the command and applies it to the synchronous reluctance motor
1
to drive it. At that time, the current command is obtained by converting the torque command by the command converter
9
. In this example of the speed control system, a torque command is obtained as output of the speed controller
10
, to which the speed command and the detected speed are input. It is known well by those skilled in the art that when it is aimed to control the torque generation and not to configure the speed control system, the speed controller
10
and the speed detector
11
are not necessary. In such a case, the torque command can be directly applied from outside.
In order to realize the conventional vector control method for the synchronous reluctance motor, the salient pole position angle detector for detecting the salient pole position angle of the rotor is required, as described in the aforesaid typical example. However, fitting of the salient pole position angle detector such as an encoder to the rotor leads to the certain heretofore unavoidable problems, as described below.
A first problem is the deterioration in the reliability of the motor system. Although mechanically the synchronous reluctance motor is one of the strongest types of AC motor, as can be seen from the structure of the rotor, the salient pole position angle detector such as an encoder is mechanically much weaker than the motor body. Consequently, the placement of the salient pole position angle detector decreases extremely the overall mechanical reliability of the motor system. In addition to the deterioration in the mechanical reliability, the reliability decrease of the motor system due to the fitting of the salient pole position angle detector also occurs in an electrical aspect observed as contamination of the salient pole position angle detector signal with power supply noise, and also a thermal aspect observed as a temperature increase in the salient pole position angle detector due to heat from the rotor. Thus, the attachment of the salient pole position angle detector such as an encoder to the motor rotor has extremely decreased the reliability of the motor system.
A second problem is increase in motor size. The attachment of the salient pole position angle detector to the rotor increases the volume of the motor in its axial direction by at least several percent to as much as 50% or more according to the volume of the motor itself.
A third problem is the necessity to secure a source of power for operating the salient pole position angle detector, wiring of a signal line to receive a detection signal and a space for wiring. Naturally, to operate the salient pole position angle detector and to obtain information about the main salient pole position angle of the rotor from the detector, wiring therefor is necessary. The signal line is also generally required to have the same strength as the power line for driving the motor body in order to prevent degradation of the mechanical, electrical, and thermal reliability. As a result, a signal line having substantially the same size as the power line and also a space are generally necessary for a single motor
Leykin Rita
Nappi Robert E.
Okuma Corporation
Oliff & Berridg,e PLC
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