Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2000-12-27
2003-01-07
Donels, Jeffrey (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S806000
Reexamination Certificate
active
06504336
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor controller for an electric power steering system which performs a steering assist operation by applying a torque generated by an electric motor to a steering mechanism.
2. Description of Related Arts
Electric power steering systems are conventionally known which are adapted to transmit a torque generated by an electric motor such as a three-phase brushless motor to a steering mechanism to perform a steering assist operation. A motor controller for such an electric power steering system has a construction as shown in FIG.
4
.
The motor controller includes a three-phase alternating current coordinate transformation section
91
for converting a current command value i* (effective value) into vectors in a three-phase alternating current coordinate system, i.e., a U-phase current command value i
ua
* and a V-phase current command value i
va
*, on the basis of an angle &thgr;
re
of a rotor of a motor M. The current command value i* is determined on the basis of a steering torque or the like applied to a steering wheel. The rotor angle &thgr;
re
is detected by a rotor angle detecting circuit
92
on the basis of an output signal of a resolver R provided in association with the motor M.
The U-phase current command value i
ua
* and the V-phase current command value i
va
* are inputted to subtractors
93
u
and
93
v
, respectively. An output of a U-phase current detecting circuit
94
u
for detecting a U-phase current i
ua
actually flowing through a U-phase of the motor M and an output of a V-phase current detecting circuit
94
v
for detecting a V-phase current i
va
actually flowing through a V-phase of the motor M are applied to the subtractors
93
u
and
93
v
, respectively. Therefore, a deviation of the U-phase current i
ua
from the U-phase current command value i
ua
* and a deviation of the V-phase current i
va
from the V-phase current command value i
va
* are outputted from the subtractors
93
u
and
93
v
, respectively.
The deviations outputted from the subtractors
93
u
and
93
v
are respectively applied to a U-phase current PI (proportional integration) controlling section
95
u
and a V-phase current PI controlling section
95
v
. Further, the U-phase current PI controlling section
95
u
and the V-phase current PI controlling section
95
v
receive a correction gain determined by a PI gain correcting section
96
on the basis of a rotor angular velocity &ohgr;
re
which is the rate of a change in the rotor angle &thgr;
re
. The U-phase current PI controlling section
95
u
and the V-phase current PI controlling section
95
v
respectively determine a U-phase voltage command value V
ua
* and a V-phase voltage command value V
va
* on the basis of the deviations inputted from the subtractors
93
u
and
93
v
and the correction gain inputted from the PI gain correcting section
96
.
The rotor angular velocity &ohgr;
re
is determined by a rotor angular velocity calculating section
97
on the basis of the rotor angle &thgr;
re
detected by the rotor angle detecting circuit
92
.
The U-phase voltage command value V
ua
* and the V-phase voltage command value V
va
* are inputted to a three-phase PWM (pulse width modulation) section
98
. The U-phase voltage command value V
ua
* and the V-phase voltage command value V
va
* are also inputted to a W-phase voltage command value calculating section
99
. The W-phase voltage command value calculating section
99
determines a W-phase voltage command value V
wa
* by subtracting the U-phase voltage command value V
ua
* and the V-phase voltage command value V
va
* from zero, and applies the W-phase voltage command value V
wa
* thus calculated to the three-phase PWM section
98
. That is, the three-phase PWM section
98
receives the U-phase voltage command value V
ua
*, the V-phase voltage command value V
va
* and the W-phase voltage command value V
wa
* inputted thereto.
The three-phase PWM section
98
generates PWM signals S
u
, S
v
and S
w
which correspond to the U-phase voltage command value V
ua
*, the V-phase voltage command value V
va
* and the W-phase voltage command value V
wa
*, respectively, and outputs the PWM signals S
u
, S
v
, S
w
thus generated to a power circuit P. Thus, the power circuit P applies voltages V
ua
, V
va
and V
wa
according to the PWM signals S
u
, S
v
and S
w
to the U-phase, the V-phase and the W-phase, respectively, of the motor M, which in turn generates a torque required for the steering assist.
The U-phase current command value i
ua
* and the V-phase current command value i
va
* are sinusoidally varied in accordance with a change in the rotor angle &thgr;
re
. The U-phase current i
ua
and the V-phase current i
va
are sinusoidal electric currents which are sinusoidally varied in accordance with the change in the rotor angle &thgr;
re
. With a higher rotation speed of the motor M, the changes in the U-phase current i
ua
and the V-phase current i
va
cannot follow the changes in the U-phase current command value i
ua
* and the V-phase current command value i
va
*, so that phase offsets may occur between the U-phase current i
ua
and the U-phase current command value i
ua
* and between the V-phase current i
va
and the V-phase current command value i
va
*. If such phase offsets occur, the motor M fails to generate a torque of a proper magnitude, thereby deteriorating the responsiveness of the steering assist and the convergence of the steering wheel. Therefore, the steering feeling may be deteriorated.
Another problem associated with the conventional motor controller is a difficulty in detecting an abnormality such as an offset which causes an electric current to flow through the motor M even if the current command value i* is zero. That is, the U-phase current i
ua
and the V-phase current i
va
, which are sinusoidal electric currents, instantaneously become zero (or cross zero) depending on the rotor angle &thgr;
re
. For accurate detection of the offset, it is necessary to constantly monitor the rotor angle &thgr;
re
so as to acquire the U-phase current i
ua
and the V-phase current i
va
at a time point other than a zero-cross point, or to calculate an effective value of the electric current flowing through the motor M on the basis of the acquired U-phase current i
ua
and V-phase current i
va
.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a motor controller for an electric power steering system which ensures an improved steering feeling.
It is a second object of the invention to provide motor controller for an electric power steering system which features easy detection of an abnormality such as an offset.
A motor controller according to the present invention is a motor controller (C) for an electric power steering system which performs a steering assist operation by applying a torque generated by an electric motor (M) to a steering mechanism (
1
), the motor controller comprising: a current command value setting circuit (
61
,
62
) for setting a current command value (i
a
*) indicative of an electric current to be applied to the electric motor; a d-q command value setting circuit (
66
) for setting a d-axis current command value (i
da
*) and a q-axis current command value (i
qa
*) in a d-q coordinate system on the basis of the current command value set by the current command value setting circuit; and a voltage controlling circuit for controlling a voltage to be applied to the electric motor on the basis of the d-axis current command value and the q-axis current command value set by the d-q command value setting circuit. The parenthesized alphanumeric characters denote corresponding components and the like in the following embodiment, but the embodiment is not intended to be limitative of the present invention.
In accordance with the invention, the d-axis current command value and the q-axis current command value in the d-q coordinate system are determined on the basis of the current command value set by the current command value setting circuit,
Donels Jeffrey
Koyo Seiko Co. Ltd.
Rabin & Berdo P.C.
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