Electricity: motive power systems – Battery-fed motor systems
Reexamination Certificate
1999-06-29
2001-05-22
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Battery-fed motor systems
C318S722000, C318S254100
Reexamination Certificate
active
06236172
ABSTRACT:
This application claims the priority of Japanese patent application No. JP-8-134939, the disclosure of which is expressly incorporated by reference herein.
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for driving an electric vehicle having an inverter for converting DC electric power (such as from a battery) into AC electric power, and a synchronous motor as the driving force of the vehicle, particularly a permanent-magnet type synchronous motor.
Development of a permanent-magnet type motor (hereinafter sometimes referred to simply as a “synchronous motor”) as a motor for driving an electric vehicle is progressing. The efficiency of the permanent-magnet type synchronous motor can be increased in a low speed and low torque region compared to an induction motor. An electric vehicle driving system using such a permanent-magnet type synchronous motor is disclosed, for example, in Japanese Patent Application Laid-Open No. 6-315201.
In an electric vehicle, for example an electric automobile, in order to obtain a braking force to the vehicle, so-called regenerative braking may be performed using the motor as a generator. In such an electric vehicle, there are some cases in which the motor may be driven at a high speed, above a maximum controllable rotating speed, during coasting on a descending road.
In controlling synchronous motors generally used in the industrial field, when the motor speed increases to a value which exceeds the controllable range, the motor is judged to be in an abnormal condition. In the case of an electric vehicle, the control system is designed so that the motor is controlled by repeatedly driving it up to a maximum allowable speed for the power-train system, and then operating it in a normal re-operation within the controllable range as the speed of the motor is decreased.
When the motor is driven at a speed above the maximum controllable speed, a protective relay provided between the inverter and the motor is actuated, so that the inverter is disconnected to protect it, (and also the battery and control circuits) against a high voltage induced in the permanent-magnet type synchronous motor (generator) when it is driven at a speed above the maximum controllable speed.
However, provision of an additional protective relay between the inverter and the motor makes control complex, the system large in size and higher in cost.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the problems described above and to provide a method and apparatus for controlling an electric vehicle driven by a synchronous motor, with high reliability.
Another object of the invention is to provide such a method and apparatus which provides good protection against failure of the inverter, even when the motor is driven at the maximum allowable rotating speed, at a low cost.
These and other objects and advantages are achieved by the present invention, which provides a driving system for an electric vehicle having a synchronous motor for driving the electric vehicle, an inverter for converting DC electric power from a battery into AC power which is provided to the synchronous motor, a smoothing capacitor connected in parallel to the converter for smoothing the DC electric power, and a PSM control means for performing ON-OFF control of a plurality of power switching elements composing the inverter, based on a torque reference and a motor current. According to the invention, a peak value of induced electromotive force of the synchronous motor of the electric vehicle at a maximum allowable rotating speed is set equal to or less than an allowable voltage of the smoothing capacitor of the inverter, and equal to or lower than a maximum allowable voltage of the power switching elements composing the inverter.
According to another characteristic of the present invention, there is provided a driving system for an electric vehicle having a permanent-magnet type synchronous motor for driving the electric vehicle, an inverter for converting DC electric power from a battery into AC power which is provided to the synchronous motor, a smoothing capacitor connected in parallel to the converter for smoothing the DC electric power, and a PSM control means for performing ON-OFF control of a plurality of power switching elements composing the inverter, based on a torque reference and a motor current. A peak value V
0max
of the maximum induced electromotive force at the maximum allowable rotating speed N
2
of the synchronous motor is set so that it satisfies the relation V
0max
≦V
Cmax
, where V
Cmax
is an allowable voltage of the smoothing capacitor.
Thus, according to the present invention, a peak value of induced electromotive force of the synchronous motor of the electric vehicle at a maximum allowable rotating speed is set to or less than an allowable voltage of the smoothing capacitor of the inverter, and lower than a maximum allowable voltage of the power switching elements of the inverter. In other words, a peak value V
Omax
of the maximum induced electromotive force at the maximum allowable rotating speed N
2
of the synchronous motor is set so that it satisfies the relation V
0max
≦V
Cmax
, where V
Cmax
is an allowable voltage of the smoothing capacitor which is a main part of the inverter.
Therefore, it is possible to provide a method and apparatus for driving an electric vehicle which can prevent failure of the inverter and overcharging of the battery, even when the motor is small in size and low in cost, driven at the maximum allowable rotating speed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.
REFERENCES:
patent: 4217527 (1980-08-01), Bourke et al.
patent: 4423362 (1983-12-01), Konrad et al.
patent: 5412293 (1995-05-01), Minezawa et al.
patent: 5583406 (1996-12-01), Mutoh et al.
patent: 5610483 (1997-03-01), Obara et al.
patent: 5635804 (1997-06-01), Tanaka et al.
patent: 5780980 (1998-07-01), Naito
patent: 6-315201 (1994-11-01), None
US magazine, Jahns, Th. M.—“Flux-Weakening Regime Operation of an Interior Permanent-Magnet Synchronous Motor Drive” IN: IEEE Transaction on Industry Applications, vol. 1A-23, copy No. 4, Jul./Aug. 1987, pp. 681-689.
Katada Hiroshi
Matsudaira Nobunori
Naito Shotaro
Obara Sanshiro
Shibukawa Suetaro
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Hitachi , Ltd.
Ro Bentsu
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