Electricity: motive power systems – Induction motor systems – Primary circuit control
Patent
1999-01-04
1999-12-07
Ip, Paul
Electricity: motive power systems
Induction motor systems
Primary circuit control
318805, 318807, 318430, 318139, H02P 540
Patent
active
059989599
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This application is a 371 of PCT/DE97/00123 filed Jan. 22, 1997.
The present invention relates to a control apparatus for an asynchronous machine, in particular as a drive for electric vehicles.
BACKGROUND INFORMATION
A conventional control apparatus is described in U.S. Pat. No. 5,481,168. In this conventional apparatus, the rotation speed of a three-phase induction motor is delivered via an analog/digital converter to a rotation speed measurement device in order to regulate an asynchronous machine. A setpoint transducer predefines a torque, and these signals are fed into a three-phase system to generate setpoint values. The sensed rotation speed of the asynchronous machine is compared to the predefined rotation speed, and the difference is delivered to the power section of an inverter as the setpoint value.
Another conventional control apparatus of this kind is the so-called "field-oriented" control system as described, for example, in Siemens Research and Development Reports 1972, F. Blaschke, "The field orientation method for controlling asynchronous machines", p. 184 ff., or in the textbook "Control of Electrical Drives," W. Leonhard, Springer-Verlag, pp. 214-222. With the field-oriented control system, both the amplitude of the stator flux vector and its position with respect to the rotor flux vector must be monitored at all times. One of the principal tasks in this connection is decoupling the torque-based and flux-based currents from the magnitude of the stator current vector. It is also important to ensure that they are at right angles to one another, in a rotor-based coordinate system, at all times. This requires sensing the stator currents of the three-phase system, transforming them into a coordinate system which rotates synchronously with the rotor flux, and comparing them with the setpoint definitions for the flux-forming component and torque-forming component of the current. The new current/voltage values applied to the motor are based on calculation and inverse transformation from the rotating reference system to the steady-state stator coordinate system. The field-oriented control system yields a constant torque even above the nominal rotation speed, improved velocity consistency even under fluctuating load conditions, and high efficiency at full load, but the technical outlay is high and costly.
SUMMARY OF THE INVENTION
The control apparatus according to the present invention achieves many of the advantages of the field-oriented control system with technically simpler means and in more economical fashion, and achieves better efficiency particularly in part-load operation, which is principally relevant for electric vehicles. The demands on the incremental transducer are low. Four-quadrant operation is possible. In addition, smooth starting from rest, or from a rolling motion at any speed opposite to the desired direction of motion, is achieved in outstanding fashion.
The setpoint-value entry device advantageously contains function tables for the rotor frequency and the amplitude of the stator current as a function of the desired torque setpoint. In addition, function tables can also be provided for the load angle pilot control. The machine parameters are reflected in the values obtained from the function tables. Each setpoint input is associated with a different value pair or value triplet.
In order to take into account the particular rotation direction of the asynchronous machine, the summing device possesses a first switching device which switches over automatically as a function of the particular rotation direction and with which the signals from the incremental transducer, that are proportional to the mechanical rotation frequency, are given a negative value in the reverse switch position and a positive value in the forward switch position.
In order also to take into account the desired rotation direction and the direction of the desired torque when defining the setpoint, the summing device additionally possesses a second switching device which switches ov
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W. Leonhard, "Control of Electrical Drives", 2nd Edition, Springer-Verlag, pp. 214-222, 1996.
Ip Paul
Robert & Bosch GmbH
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