Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2000-03-17
2001-08-14
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S798000, C318S806000, C180S197000, C180S065510, C303S177000
Reexamination Certificate
active
06274998
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a controller for electric vehicles driven by motors with an inverter using vector control, particularly, a controller for electric vehicles performing torque control for re-adhering by detecting slipping or skidding generated between wheels and rails.
As a prior art, a method for controlling re-adhesion by detecting slipping or skidding of wheel of electric vehicles, and reducing generated torque of motors has been disclosed in JP-A-4-197004 (1992). A method for detecting re-adhesion of wheel was disclosed in JPA-4-69003 (1992). A technique for driving motors of electric vehicles of railway by vector control of inverters was disclosed in JP-A-5-83976 (1993).
In accordance with the conventional re-adhesion controlling method disclosed in the above JP-A-4-197004 (1992), the slipping of wheel is detected by a method which recognizes whether a changing rate with time (differential value) of the rotor frequency (proportional to the wheel velocity) of the induction motor exceeds a fixed detecting level or not, and a control to reduce the motor torque is performed only during a period when the slipping is detected. However, if the differential value becomes smaller than a designated value, the recognition of the slipping is canceled, and the motor torque is controlled to resume irrelevant to whether the wheel are practically re-adhered or not. Therefore, if the wheel is not re-adhered practically, slipping the wheel occurs instantaneously, and a problem occurs that the slipping phenomena are generated very often repeatedly.
A method for controlling the torque by detecting the re-adhesion is disclosed in the above JP-A-4-69003 (1992), and the method for detecting the re-adhesion is explained hereinafter referring to FIG.
10
. The re-adhesion is detected by recognizing that a twice differential value fr″ (an axis jerking value) of the rotor frequency fr (proportional to the wheel velocity) at the time t2 exceeds a designated value Le, after detecting the slipping at the time t1.
However, the following problem can be anticipated with the detection of slipping using the twice differential value fr″. First, if the wheel velocity behaves as shown in
FIG. 11
when re-adhering, the twice differential value fr″ of the wheel velocity does not exceed the designated value Le, and the re-adhesion can not be detected nevertheless the re-adhesion occurred at the time t2. Consequently, the torque is maintained in a reduced condition continuously, and a problem that the reduced acceleration of the electric vehicle is generated. Furthermore, in a case if the slipping, which has been likely to converge on an end, is re-generated at the time t1a as shown in
FIG. 12
, the twice differential value fr″ exceeds the designated value Le at the time t1a, and a problem that the re-adhesion is erroneously detected and the slipping is continued is generated.
These kind of problems can be caused when the skidding is generated. As explained above, the conventional technology has a problem that the re-adhesion can not be detected, or the re-adhesion is detected erroneously depending on conditions of slipping or skidding.
Currently, an inverter with vector control such as disclosed in JP-A-5-83976 (1993) come to be used as a controller of induction motors for driving electric vehicles. However, any technology to utilize performance of the vector control for controlling the re-adhesion has not been disclosed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a controller for electric vehicles, which can utilize the torque effectively to the physical limit of adhesion by utilizing a fast torque response of the vector control, and can make the velocities of acceleration and deceleration of the electric vehicles as high as possible even in a condition when the adhesion coefficient is low.
The present invention relates to a controller for electric vehicles comprising a vector control inverter, which controls motors for driving wheels of the electric vehicles, by dividing the primary current of the motor into an exciting current component and a vector current component, and controlling respective of the current components based on a respectively designated command; further comprises means for detecting a wheel velocity (including rotor frequency of the motors proportional to the wheel velocity), means for detecting slipping and skidding of the wheel based on a differential value (a changing rate with time) of the detected wheel velocity, means for detecting re-adhesion of the wheel based on the detected differential value and a twice differential value of the detected wheel velocity, and means for adjusting the designated command for the torque current component in response to the above two means for detection.
In accordance with the above method of the present invention, if the differential value of the wheel velocity exceeds a designated value when the electric vehicle is accelerated, it can be regarded as slipping occurs, and the control to reduce the torque current is performed. As the result, when the slipping velocity is decreased and re-adhesion occurs, the acceleration of the wheel is resumed. The re-adhesion point can be detected as a point when the differential value of the wheel velocity becomes negative and the twice differential value becomes positive. According to the above point, it can be determined that the slipping of the wheel is certainly converging on an end, the wheel is re-adhered, and the acceleration of the wheel is resumed. The torque current is maintained in a reduced condition until the re-adhesion is detected. Therefore, even if the torque current is resumed fast after the re-adhesion occurred, a possibility to cause re-slipping can be made low by confirming the re-adhesion. Consequently, the torque can be increased fast as much as the torque current is resumed fast, and the acceleration of the electric vehicle can be increased.
Even if the slipping occurs and before the re-adhesion is detected, the slipping is converging on an end when the differential value of the wheel velocity is decreased. Consequently, the decrease of the torque can be reduced by reducing the decrease of the torque current, and the acceleration can be increased as much as reducing the decrease of the torque. If skidding occurs when the electric vehicle is decelerated, the theory is quite same except the sign of detecting level is opposite.
As explained above, if the motor for driving the wheel is vector controlled, the torque current component in the primary current of the motor can be controlled independently. The torque current control influences only to leakage impedance of the motor, and it has a feature that time constant is small and control response is fast. Accordingly, if the re-adhesion control of the present invention is performed with the vector control, the re-adhesion performance having a fast response can be naturally obtained, and the torque can be utilized effectively to the physical adhesion limit.
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patent: 4785225 (1988-11-01), Horie et al.
patent: 5304912 (1994-04-01), Kajiwara et al.
patent: 5473225 (1995-12-01), Miyazaki
patent: 5480220 (1996-01-01), Kumar
patent: 5511866 (1996-04-01), Terada et al.
patent: 5532571 (1996-07-01), Masaki et al.
patent: 5847534 (1998-12-01), Tanamachi et al.
patent: 6152546 (2000-11-01), Daigle
patent: 4-69003 (1992-03-01), None
patent: 4-197004 (1992-07-01), None
patent: 5-83976 (1993-04-01), None
patent: 08182119 (1996-07-01), None
Ando Takeshi
Horie Akira
Itou Ken
Kaneko Takashi
Antonelli Terry Stout & Kraus LLP
Hiatchi Ltd.
Martin Edgardo San
Nappi Robert E.
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