Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
2002-02-25
2003-11-25
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S268000, C318S433000, C318S701000
Reexamination Certificate
active
06653808
ABSTRACT:
This application is based on and claims priority under 35 U.S.C. §119 with respect to Japanese Patent Application No. 2001-048251 filed on Feb. 23, 2001, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
This invention generally relates to an electric motor control device for controlling an electric current to be supplied to an electric motor based on H∞control theory.
BACKGROUND OF THE INVENTION
Switched reluctance motors (SR Motors) are conventionally employed as a driving source of electric vehicles. A conventional control device for controlling the switched reluctance motor is shown in FIG.
19
. In the control device, a required torque reqtrq determined based on an accelerator operating amount is converted to both a current command value I and an angular command value &thgr; based on a command value map. (The command value map is prepared to indicate a relation between an electric current supplied to the SR Motor and an angle location at a stator that the same directional electric current is supplied.) The controller further controls the amount of electric current corresponding to the current command value I and in schedule or timing corresponding to the angular command value &thgr;, and as a result the SR Motor generates a rotational torque corresponding to the required torque reqtrq. This control system is an open-loop system as shown in FIG.
19
.
The SR Motor mounted on the electric vehicle may be affected by resonance characteristics of springs used for suspension in the vehicle. The SR Motor mounted on the electric vehicle may further be affected by other resonance characteristics caused by torsional deformation of a drive shaft, tires and so on connected with the SR Motor. Especially when the required torque is quickly changed as shown in
FIG. 20
, a rotation speed may be pulsated. Then the pulsated rotation speed appears to be a vibration in longitudial directions of the electric vehicle body. The vibration of the vehicle body may cause discomfort to the vehicle's passengers.
To overcome the above drawback, a control method for correcting the current command value I and the angular command value &thgr; by employing a proportional derivative control (PD control) can be useful. According to this art, the vibration of the electric vehicle body can be reduced by determining a larger proportional value and a larger derivative value.
But, if the proportional value and the derivative value are determined to be large in the above PD control, noise in the motor rotation speed, which is detected by a motor rotation speed sensor, is also amplified. Thus the vibration due to the noise may be generated in the SR Motor. Moreover, stability of the control system may be spoiled. In consideration of the noise amplification and the stability of the control system, the proportional value and the derivative value are limited in size, thus the PD control cannot reduce the vibration of the electric vehicle body as sufficiently as expected. Moreover, when attempting to reduce the vibration using the above-mentioned PD control, the gain of the control system may also be reduced in all frequency domain, thus the tracking performance of the actual torque of the electric motor relative to the required torque in the control system may be spoiled. Furthermore, the acceleration performance of the electric vehicle is reduced. The above problems may also occur to an SR Motor employed as a driving source in another mechanism other than the electric vehicle.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an electric motor control device having a vibration reduction performance (the performance for reducing the vibration caused by a resonance of the electric vehicle body with the electric motor), an acceleration, a noise resistance, a robust stability, and so on that are compatible with each other at a high level.
According to a first aspect of the present invention, the electric motor control device determines a required torque in response to an operation amount for an electric motor. Then the controller, in the electric motor control device, calculates a correction amount based on an actual rotation speed of the electric motor detected by a rotation speed detecting device. Then the electric motor control device controls an electric current to be supplied to the electric motor depending on a command torque obtained by correcting the required torque with a correction amount calculated by a controller. For the electric motor control device, a reference model and an actual model have been previously prepared. The reference model indicates an ideal response of the electric motor having ideal tracking performance and vibration reduction performance relative to the required torque, and the actual model indicating an actual response of the electric motor. Then the required torque is regarded as an input amount to be input into the controller. While, a revolution speed difference is determined based on the difference between a first rotation speed, calculated by inputting the required torque to the reference model, and a second rotation speed, calculated by inputting the required torque to the actual model. The rotation speed difference is regarded as a controlled amount outputted from the controller. The controller is determined as an H∞norm of a transfer function between the input amount and the controlled amount to be smaller than a predetermined value. The electric motor control device controls the electric current to be supplied to the electric motor by using the determined controller.
In the above electric motor control device, the controller calculates the correction amount based on the actual rotation speed of the electric motor detected by the rotation speed detecting device. Then the controller corrects the required torque determined in response to the operation amount of the electric motor by the above correction amount. To obtain the controller, following processes are executed. First, the reference model and the actual model are prepared. The reference model has the ideal response of the electric motor to obtain good tracking performance and the vibration reduction performance relative to the required torque. The actual model indicates the actual response of the electric motor. Next, the required torque is regarded as the input amount to be inputted to the controller. The difference between the first rotation speed, calculated by inputting the required torque to the reference model, and the second rotation speed calculated by inputting the required torque to the actual model, is regarded as the controlled amount outputted from the controller. Then the H∞control problem is solved by determining the H∞norm of the transfer function between the input amount and the controlled amount is determined to be smaller than the predetermined value.
Thus the present invention has the following advantages. Since the above controller is mounted on the electric motor control device, the actual response of the electric motor is close to the reference model which has excellent tracking performance and vibration reduction performance. Accordingly, the electric motor can be operated with better tracking performance and vibration resistance.
According to a second aspect of the present invention, in the above electric motor control device, the controller is preferably determined based on a control system in which the required torque is inputted to both the reference model and the actual model through the first weight function.
By the above technical method, since the gain of the first weight function in a particular frequency domain is determined to be large, the response of the electric motor controlled by the controller in the same particular frequency domain is closer to the reference model.
According to a third aspect of the present invention, in the above electric motor control device, the gain of the first weight function in the low frequency domain is preferably determined to be larger than the gain in the high f
Ikeda Kenji
Inagaki Hiroyuki
Kato Hiroaki
Kuzuya Hideki
Sebe Noboru
Aisin Seiki Kabushiki Kaisha
Ro Bentsu
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