Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
1999-12-03
2001-02-13
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S720000, C318S721000, C318S432000, C318S434000, C318S434000
Reexamination Certificate
active
06188196
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosures of Japanese Patent Application Nos. HEI 10-360200 filed on Dec. 18, 1998 and HEI 11-107999 filed on Apr. 15, 1999, each including the specification, drawings and abstract, are incorporated herein by reference in their entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and a method for detecting an electrical angle of a rotor of a synchronous motor without requiring a particular sensor. The invention also relates to a motor control apparatus for controlling the operation of a synchronous motor by applying the electrical angle detecting apparatus.
2. Description of the Related Art
Various AC motors are used in industrial machines, railway vehicles and the like. Hybrid vehicles employing an AC motor as one of the drive sources have also been proposed. One type of such conventional AC motors is a synchronous motor in which multi-phase alternating currents are caused to flow through windings of the AC motor and a rotor is rotated by interactions between magnetic fields generated by alternating currents flowing through the windings and magnetic fields generated by permanent magnets. In order to achieve a desired rotating torque in a synchronous motor, it is necessary to control the multi-phase alternating currents supplied through the windings in accordance with the position of the rotor, that is, the electrical angle.
Typical methods for detecting the electrical angle use a sensor, such as a Hall device or the like. In such methods, however, the detection precision of the sensor and the reliability thereof against failures become problems in the pursuit of stable operation of the motor. With regard to generally termed salient pole type synchronous motors, a sensor-less detection method has been proposed which detects the electrical angle based on determination described below without requiring the use of a sensor as mentioned above. Since the method does not require a sensor, the method allows an improvement of the reliability against failures.
Among the methods for detecting the electrical angle of a salient pole type synchronous motor without using a sensor, a method that uses the following equations (1), (2) has been proposed for a case where the motor is operated at relatively high rotational speed (hereinafter, simply referred to as “high speed”).
Vd−R×Id−p
(
Ld×Id
)+&ohgr;×
Lq×Iq
=0 (1)
Vq−R×Iq−p
(
Lq×Iq
)−&ohgr;×
Ld×Id−E
=0 (2)
where V represents the value of voltage applied to the motor, I represents the value of current through a motor winding, and L represents the inductance of a motor winding. Affixes d and q placed on V, I, L indicate values taken in the directions of the generally termed d-axis and q-axis of the motor. The other variables in the equations represent as follows: R is the motor coil resistance; &ohgr; is the electrical rotating angular speed of the motor; E is the electromotive force generated by the turning operation of the motor. The electrical angular speed &ohgr; of the motor is calculated by multiplying the mechanical angular speed of the motor by the number of pairs of poles. Furthermore, p is a time differential operator. That is,
p
(
Ld×Id
)=
d
(
Ld×Id
)/
dt
The d-axis and the q-axis will be briefly described with reference to
FIG. 3. A
permanent magnet type three-phase synchronous motor can be expressed by an equivalent circuit shown in FIG.
3
. Referring to the equivalent circuit, an axis extending through the turning center of the motor and in the direction of the field generated by a permanent magnet is normally termed d-axis. An axis extending in the plane of rotation of the rotor and intersecting perpendicularly with the d-axis is termed q-axis. The angle formed between the d-axis and a U-phase in the equivalent circuit of
FIG. 3
corresponds to the electrical angle &thgr; of the motor.
The voltage equations (1), (2) always hold with respect to the d and q-axes. In the case of sensor-less control of a motor, a motor controller evaluates the equations based on an estimated electrical angle (corresponding to &thgr;c in FIG.
3
). The result of the evaluation has a calculation error in accordance with an error angle (&Dgr;&thgr; in
FIG. 3
) of the estimated electrical angle &thgr;c from a real electrical angle &thgr;. That is, if calculated values of current and voltage are used in the evaluation of the voltage equations (1), (2), the value of the left side of each equation becomes other than zero although the value is supposed to be zero.
An electrical angle at a certain timing is estimated by adding an amount of change in the electrical angle calculated from the motor operating speed to the electrical angle occurring at the previous timing. In this estimation, the error of the electrical angle is caused by two factors. One of the factors is an error in the calculation of an electrical angle that is used as a reference for estimating an electrical angle at that timing, that is, the electrical angle at the previous timing. The other factor is an error in regard to the motor operating speed. The equation (2), which holds with respect to the q-axis, includes a term of electromotive force E created by the turning operation of the motor. Therefore, an error produced in the equation (2) has a close relationship mainly with the error in regard to the motor operating speed. On the other hand, an error produced in the equation (1), which holds with respect to the d-axis, has a relationship mainly with the error in the calculation of the electrical angle. Taking into account the errors in the equations (1), (2) produced when values of current, voltage and the like at a certain timing are used in the calculation of the equations, the electrical angle at the previous timing may be corrected, so that the electrical angle at that timing can be calculated. If the thus-calculated electrical angle is used as a basis for calculating an electrical angle &thgr;c at the next timing, it becomes possible to calculate the electrical angle in a sensor-less manner and to control the motor operation.
An example of the method for calculating an electrical angle will be described below. If the time differential (d/dt) in the voltage equations (1), (2) is substituted with a time difference (amount of change/time), the equations can be transformed into equations (3)-(5).
&Dgr;
Id=Id
(
n
)−
Idm =Id
(
n
)−
Id
(
n
−1)−
t
(
Vd−RId+&ohgr;LqIq
)/
Ld
(3)
&Dgr;
Iq=Iq
(
n
)−
Iqm =Iq
(
n
)−
Iq
(
n
−1)−
t
(
Vq−RIq+&ohgr;LdId
)/
Lq
(4)
En=E
(
n
−1)−
kk
1
×&Dgr;Iq
(5)
In these equations, Id, Iq are currents along of the d and q-axes, that is, the magnetizing current and the torque current, respectively; Ld, Lq are inductances along the d and q-axes; and Vd, Vq are values of voltage applied to the windings. Affixes, such as (n) and the like, are attached to the variables on the basis of the fact that the operations expressed above are periodically repeated. Affix (n) indicates that a value of the variable at a given timing, and (n−1) indicates a value at the timing previous to the given timing. Idm and Iqm represent model values of the magnetizing current and the torque current, that is, theoretical values of current that are calculated on the basis of the voltage equations when it is assumed that the estimated electrical angle is correct. The period of the cycle of this operation is time t in the equations (3), (4).
The terms of time differential in the aforementioned voltage equations is transformed on the assumption that inductance takes a constant value. For example, the transformation is performed as in:
p
(
Ld×Id
)=
Ld×p
×(
Id
)
The other term p(Lq×Iq) is transformed in the same manner.
The other variables in the above equations represent as
Kawabata Yasutomo
Koide Satoshi
Yamada Eiji
Leykin Rita
Nappi Robert E.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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