The present invention relates to a method of detecting the initial
magnetic pole position of a permanent magnet type brushless motor and more particularly
to a method of detecting the magnetic pole position of a rotor when a sensorless
brushless motor is started.

BACKGROUND ART

In conventional brushless motors, use has been made of a method of
detecting a magnetic pole position with omission of a magnetic-pole-position detecting
sensor which is constituted of a resolver or a Hall-effect device.

When the rotation of a rotor is allowed at the time of starting in
reference to a method of the sort mentioned above for detecting a magnetic pole
position, it is possible to utilize a technique, as disclosed in Japanese Patent
Publication No. 3-239186A, for determining a rotor position (the magnetic pole
position) by switching between a synchronous operation mode wherein steady operation
is performed and a rotor-position detecting mode wherein the magnetic pole position
is detected, rotating the rotor by supplying such a gate pulse as to generate a
rotating magnetic field in each three-phase armature coil at the time of starting
a brushless motor and then causing a position detecting circuit to detect the voltage
induced in the armature coil.

When the rotation of the rotor is not allowed at the time of starting,
that is, when the magnetic pole position is estimated with the motor unoperated,
there is a technique, as proposed in IEEJ IAS Vol. 116-D, No. 7, pp. 736- 742
(1996) for determining the magnetic pole position with the motor unoperated by
supplying intermittent pulse-like voltage commands sequentially in a given direction
to the extent that the motor is unrotated, and estimating a position angle from
a difference of response, which varies in an anti-sinusoidal wavelike manner, of
each of the phase currents iα_{u} and iβ_{u}, iα_{v}
and iβ_{v}, iα_{w} and iβ_{w}, etc., which
are converted into the static coordinates.

However, there still exist the following problems in the aforesaid
prior art. The technique disclosed in Japanese Patent Publication No. 3-239186
is not applicable to a motor which makes it a condition that its rotor is at a
standstill before the operation of the motor because the motor has to be started
by rotating the rotor in order to determine the rotor position.

In the case of the technique made known by the IEEJ IAS Vol. 116-D,
No. 7, electrical parameters such as the inductance of the brushless motor, resistance
values or the like are needed to obtain the difference of the current response
by deriving each of the phase currents iα_{u}, iα_{v},
iα_{w} or the like from a three-phase voltage equation. Consequently,
the degree of difference of the current response is unclear in case these parameters
remain unknown and since the voltage command is not a stepwise alternating command,
overcurrent may flow, depending on the form of the voltage command, or the rotor
may be rotated; thus, there arise problems in view of its practical use.

'Sensorless operation of brushless DC motor drives', IEEE IECON 1993,
pp. 739 - 744 discloses the speed and position sensorless control of PM brushless
DC motors, whereby a technique is proposed for determining the magnetic pole position
with the motor unoperated by supplying intermittent pulse-like voltage commands
sequentially in a given direction to the extent that the motor is unrotated, and
estimating a position angle from a difference of response, which varies in an anti-sinusoidal
wavelike manner, of each of the phase currents, which are converted into the static
coordinates.

It is therefore an object of the present invention to provide a method
of estimating the initial magnetic pole position of a permanent magnet type brushless
motor adapted so that even though electrical parameters are not accurately acquired,
the initial magnetic pole position of a rotor in the brushless motor can be estimated
quickly without allowing overcurrent to flow and without rotating the rotor, namely,
without operating the motor.

DISCLOSURE OF THE INVENTION

In order to accomplish the object above, there is provided a method
of estimating a magnetic pole position of a permanent magnet type brushless motor
comprising the steps of:

setting a given γ axis and a given δ axis in an advanced from the
γ axis by an electrical angle of 90°;

forming a closed-loop electric current control system in the γ axis direction
while forming an open-loop electric current control system in the δ axis
direction;

calculating an interference current generating in the δ axis direction
when a current command in the γ axis direction is given as a stepwise alternating
current command;

advancing finely the γ axis by an angle of Δ&thetas; when a sign
of a product of an integral value of the interference current and a value of the
current command in the γ axis direction is positive;

delaying finely the γ axis by an angle of Δ&thetas; when the sign
is negative; and

making thereby the γ axis accord with either a d axis as a true magnetic
axis or with a -d axis advanced by 180° from the true magnetic axis.

In the method, a characteristic equation with respect to the response
of the interference current i_{δ} in the δ axis direction under
a condition of which the velocity of the permanent magnet type motor is zero is
expressed by the following equation (1):

Here,

i_{γ}: current in the γ axis direction;

i_{δ} : current in the δ axis direction;

v_{γ} : voltage in the γ axis direction;

v_{δ} : voltage in the δ axis direction;

L_{q} : q axis inductance;

L_{d} : d axis inductance;

R_{s} : stator resistance; and

&thetas;_{e} : electrical angular error between the γ axis and
the d axis.

In this case, with the formation of an open-loop current system in the q axis direction
and the formation of a proportionally-controlled closed-loop current control system,
the γ axis-current command value comes to i_{γRef}, v_{δ}
= 0, v_{γ} = K_{γ}
(i_{γRef} - i_{γ}),
whereby the state of which the speed the permanent magnet type motor is zero is
expressed by the following equation (2):
Moreover, the response of i_{δ} subjected to the Laplace transform
is expressed by the following equation (3):
i_{δ}(S) = K_{λ}a_{γδ}S / (S^{2}
+ [K_{γ}a_{γγ} + R_{s}(a_{γγ}
+ a_{δδ})]S + (K_{γ} +
R_{s})R_{s}(a_{γγ}a_{δδ}
- a^{2}_{γδ})) i_{γ Re}f(S)
Here, I_{δ}(S) represents a Laplace expression of i_{δ},
and I_{γRef}(S) represents the Laplace expression of i_{γ}.
Furthermore, a_{γγ}, a_{δδ} and a_{γδ}
are indicated by the following equation (4):
α_{γγ} = L_{q} + (L_{d}
- L_{q})sin^{2} &thetas;_{}e / (L_{d}L_{q})
α_{δδ}
= L_{d} + (L_{d} - L_{q})sin^{2}
&thetas;_{}e / (L_{d}L_{q})
α_{γδ}
= (L_{q} - L_{d})sin 2&thetas;_{}e / (L_{d}L_{q})

Furthermore, the integration ∫ i_{δ}dt of the interference
current i_{δ} in the δ axis direction in the case of giving
the current command in the γ axis direction as a stepwise alternating current
command is expressed by the following equation (5) on condition that a_{γγ}
= 1/Ld, a_{δδ} = 1/Lq and K_{γ} is sufficiently
large:

The product f_{γ} of the integral value of the interference
value and the γ axis-current command value is expressed by the following
equation (6):

In view of the fact that the aforesaid results, f_{γ}
and the axis electrical angular error &thetas;_{e} between the γ
axis and the d axis constitute a f_{γ}-&thetas;_{e} characteristic
which varies in a substantially sine wave form taking the f_{γ} on
the x axis and the &thetas;_{e} on the y axis. In this relationship, when
the γ axis is so adjusted to be advanced by only Δ&thetas;_{e}
if f_{γ} ≥ 0, and to be delayed by only Δ&thetas;_{e}
if f_{γ} < 0, the designated y axis finally and gradually converges
on the d axis (equivalent to &thetas;_{e} = 0) or -d axis (equivalent to
&thetas;_{e} = 180°) to ensure that the magnetic pole position can be estimated.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a conceptual block diagram of a method of estimating the initial
magnetic pole position of a permanent magnet type brushless motor according to
one embodiment of the present invention;

Fig. 2 is a flowchart showing the method of detecting the initial magnetic
pole position of the brushless motor shown in Fig. 1;

Fig. 3 is a waveform chart of the γ axis-current command shown in Fig.
1;

Fig. 4 is a diagram showing the relation between the γ and d axes shown
in Fig. 1;

Fig. 5 is a &thetas;_{e} - f_{γ} characteristic curve
shown in Fig. 2;

Fig. 6 is a diagram showing the corrected waveform of an estimated magnetic
axis &thetas;_{γ} shown in Fig. 2; and

Fig. 7 is a diagram showing another-phase corrected waveform of the estimated
magnetic axis &thetas;_{γ} shown in Fig. 6.

BEST MODE FOR CARRYING OUT THE INVENTION

One embodiment of the present invention will be described below with
reference to the drawings.

Fig. 1 is a conceptual block diagram of a method of estimating the
initial magnetic pole position of a permanent magnet type brushless motor according
to one embodiment of the invention. Fig. 2 is a flowchart showing the method of
detecting the initial magnetic pole position of the brushless motor shown Fig.
1. Fig. 3 is a waveform chart of the γ axis-current command shown in Fig.
1. Fig. 4 is a diagram showing the relation between the γ and d axes shown
in Fig. 1. Fig. 5 is a &thetas;_{e} - f_{γ} characteristic
curve shown in Fig. 2. Fig. 6 is a diagram showing the corrected waveform of an
estimated magnetic axis &thetas;_{γ}
shown in Fig. 2. Fig. 7 is a diagram
showing another-phase corrected waveform of the estimated magnetic axis &thetas;_{γ}
shown in Fig. 6.

In Fig. 1, a stepwise y axis-current command i_{γRef}
as shown in Fig. 3 is outputted from a γ axis-current generating circuit
1. A axis-current i_{γ} is obtained by inputting currents i_{u'}
i_{v} for driving a brushless motor 8 into an inverter section 5 via a
current sensor or the like and converting the currents in a three-to-two phase
conversion section 6. The i_{γRef} and i_{γ} are inputted
to a γ axis-current control section 2 to generate a voltage command v_{γ}*.

On the other hand, a δ axis-directed voltage command v_{δ}*
is also generated from a δ axis-current control section 3. However, v_{δ}*
becomes zero because a δ axis-directed control system has an open loop gain
of zero. Subsequently, in a &thetas;_{γ} generating circuit 7 (see
Fig. 4), a correction angle &thetas;_{e} is determined from the γ
axis-current command i_{γRef} and a δ axis-current i_{δ}
to update a γ axis angle &thetas;_{γ}. Accordingly, voltage
command magnitude V* and an output phase &thetas;_{v} are provided from
a vector control section 4 to the inverter section 5, however, since v_{δ}*
is zero, through V* = |v_{δ}*|, &thetas;_{v} = &thetas;_{γ}.

Next, the operation will be described.

Referring to a flowchart of Fig. 2, at least currents in two phases
out of the three-phase current of the permanent magnet type brushless motor 8,
in this case, currents i_{u}(K), i_{v}(K) which are respectively
a u-phase and a v-phase current (or any other combination of phase currents) at
the time of (K&peseta;T_{s}) seconds (T_{s}: current loop sampling
time) are first inputted (S101).

Subsequently, two-to-three phase conversion is carried out in accordance
with a position &thetas;_{γ} (K) (see Fig. 4) of the γ axis
away from an α phase to obtain i_{γ}(K), i_{δ}(K)
(S102). Then S103 is caused to. branch off according to the γ axis-current
command i_{γRef}(K) of the stepwise alternating current shown in
Fig. 3 (S103).

In an executing routine when i_{γRef}(K) is not zero
then, "Sign [i_{γRef}(K)]&peseta; ∫ i_{δ}dt" is
calculated on the basis of the decision made at S103 before being stored in f_{γ}(t)
(S104). At S105, S106 and S107 that follow, &thetas;_{γ} is changed
by Δ&thetas;_{e} according to the sign of f_{γ}(t)
as shown in Fig. 4, whereby adjustment is made so as to let the γ axis accord
with a d axis as a true magnetic axis.

First, a decision is made on whether f_{γ}(t) ≥ 0
or not and if f_{γ}(t) ≥ 0 is the then decided (S105: Yes), the
change quantity Δ&thetas;_{e} of &thetas;_{γ} becomes
positive (S106). If f_{γ}(t) > 0 is the result decided (S105:
No), the change quantity Δ&thetas;_{e}
becomes negative (S107).

The operation of making the γ axis accord with the d axis is
thus carried out and a current command i_{γRef}(K+1) for (K+1)T_{s}
seconds is prepared by means of timer interruption. Then stepwise i_{γRef}(K+1)
is given as shown in Fig. 3 (S108).

In the case of an executing routine when i_{γRef} (K)
= 0 branching off at the preceding step S103, a decision is made on whether i_{γRef}
(K-1) = 0 or not (S109) by changing the process flow according to the preceding
γ axis-current command i_{γRef} (K-1). If i_{γRef}
(K-1) = 0 is the then decided (S109: Yes), &thetas;_{γ} (K+1) = &thetas;_{γ}
(K) is left as it is (S110). If i_{γRef} (K-1) is decided to be not
0 then (S109: No), the γ axis position &thetas;_{γ} is updated
(S111) according to the Δ&thetas;_{e} determined in the executing
routines at and after the preceding S104. In other words, &thetas;_{γ}
is to be updated only once in the branch routines S109 - S111 according to the
Δ&thetas;_{e}. determined at S104 - S107.

Subsequently, the integral term of i_{δ} is reset for
the branch routines at forthcoming S104 - S107.

Figs. 6 and 7 show the results of tests actually made for adjusting
&thetas;_{γ}
through the aforesaid method of estimating the magnetic
pole positions under the conditions that the initial magnetic pole positions are
estimated when the γ axis and the d axis are initially shifted from each
other by an electrical angle of 90°, and the test results reflect the fact that
the d axis or -d axis was estimated at a speed of as high as about 0.1 second.

Thus, it has become possible to obtain the initial magnetic pole
position quickly by only estimating the position according to the positive and
negative signs of the product of the integral value of the interference current
i_{δ}
and the γ axis-current according to this embodiment of
the present invention. In the method, the use of integration for operations results
in reducing tendency to be affected by the noise of current sensors. Further, stable
estimated adjustment can be made since not the magnitude but only the positive
or negative sign of the current polarity is necessary for making a decision, and
since the inductance requires only a difference between L_{q} and L_{d}
but is not affected by the size of the difference. Still further, since the current
command i_{γRef} is given alternately, the average torque is to be
zero, the magnetic pole can be estimated while the motor is stopped with the rotor
unrotated.

As set forth above, in order to estimate a magnetic pole position
of a permanent magnet type brushless motor, the following steps are conducted.
A given γ axis and a given δ axis in an advanced from the axis by an
electrical angle of 90° are set. A closed-loop electric current control system
in the γ axis direction is formed while forming an open-loop electric current
control system in the δ axis direction. It is calculated an interference
current generating in the δ axis direction when a current command in the
γ axis direction is given as a stepwise alternating current command. The
γ axis is finely advanced by an angle of Δ&thetas; when a sign of a
product of an integral value of the interference current and a value of the current
command in the γ axis direction is positive. Alternatively, the γ axis
is finely delayed by an angle of Δ&thetas; when the sign is negative. Thereby,
the γ axis is made accord with either a d axis as a true magnetic axis or
with a -d axis advanced by 180° from the true magnetic axis. Therefore, even if
electrical parameters such as inductance, resistance or the like are not accurately
acquired, it is possible to estimate quickly the initial magnetic pole position
of a rotor with the motor unoperated, that is, with the rotor unrotated.

Anspruch[de]

Verfahren zum Schätzen der Magnetpolposition eines bürstenlosen Motors des
Permanentmagnettyps, das die folgenden Schritte umfasst:

Einstellen einer bestimmten γ-Achse und einer bestimmten δ-Achse,
die um einen elektrischen Winkel von 90° gegenüber der γ-Achse vorgerückt
ist,

Bilden eines geschlossenen elektrischen Stromregelkreises in der Richtung der
γ-Achse und Bilden eines offenen elektrischen Stromsteuerkreises in der Richtung
der δ-Achse,

Berechnen eines in der Richtung der δ-Achse erzeugten Interferenzstroms,
wenn ein Strombefehl in der Richtung der γ-Achse als schrittweise alternierender
Strombefehl ausgegeben wird,

Feines Vorrücken der γ-Achse um einen Winkel von Δ&thetas;, wenn
das Vorzeichen des Produkts aus einem Integralwert des Interferenzstroms und einem
Wert des Strombefehls in der Richtung der γ-Achse positiv ist,

Feines Verzögern der γ-Achse um einen Winkel von Δ&thetas;, wenn
das Vorzeichen negativ ist, und

wodurch die γ-Achse mit entweder einer d-Achse als wahrer magnetischer
Achse oder mit einer um 180° gegenüber der wahren magnetischen Achse vorgerückten
-d-Achse ausgerichtet wird.

Anspruch[en]

A method of estimating a magnetic pole position of a permanent magnet type
brushless motor comprising the steps of:

setting a given γ axis and a given δ axis in an advanced from the
γ axis by an electrical angle of 90°;

forming a closed-loop electric current control system in the γ axis direction
while forming an open-loop electric current control system in the δ axis
direction;

calculating an interference current generating in the δ axis direction
when a current command in the γ axis direction is given as a stepwise alternating
current command;

advancing finely the γ axis by an angle of Δ&thetas; when a sign
of a product of an integral value of the interference current and a value of the
current command in the γ axis direction is positive;

delaying finely the γ axis by an angle of Δ&thetas; when the sign
is negative; and

making thereby the γ axis accord with either a d axis as a true magnetic
axis or with a -d axis advanced by 180° from the true magnetic axis.

Anspruch[fr]

Procédé d'estimation d'une position de pôle magnétique d'un moteur sans balai
du type à aimant permanent, comprenant les étapes de :

établissement d'un axe γ donné et d'un axe δ donné qui est avancé
par rapport à l'axe γ d'un angle électrique de 90° ;

formation d'un système de commande de courant électrique en boucle fermée suivant
la direction d'axe γ tout en formant un système de commande de courant électrique
en boucle ouverte suivant la direction d'axe δ ;

calcul d'un courant d'interférence qui est généré suivant la direction d'axe
δ lorsqu'une commande de courant suivant la direction d'axe γ est réalisée
en tant que commande de courant alternatif par pas ;

avancement fin de l'axe γ d'un angle de Δ&thetas; lorsqu'un signe
d'un produit d'une valeur d'intégrale du courant d'interférence et d'une valeur
de la commande de courant suivant la direction d'axe y est positif ;

retardement fin de l'axe γ d'un angle de Δ&thetas; lorsque le signe
est négatif ; et

réalisation ainsi de l'accord de l'axe γ avec soit un axe d en tant qu'axe
magnétique vrai, soit un axe -d qui est avancé de 180° par rapport à l'axe magnétique
vrai.