Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2000-06-21
2004-04-06
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S079000, C702S115000, C324S177000, C324S207250, C361S023000, C361S031000, C361S087000, C363S037000, C363S098000
Reexamination Certificate
active
06718273
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for simplified field-oriented control of asynchronous machines.
BACKGROUND INFORMATION
Field-oriented control of polyphase (phase-sequence) machines is described, for example, in F. Blaschke, “Das Verfahren der Feldorientierung zur Regelung der Asynchronmaschine” (The field orientation method for controlling an asynchronous machine), Siemens Forschungs- und Entwicklungsberichten (Siemens research and development reports) 1972, pp. 184 ff., or in the textbook “Control of Electrical Drives,” W. Leonhard, Springer Verlag, pp. 214-222. In field-oriented control, 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 to decouple the torque-forming currents (cross current IQ) and flux-forming currents (direct-axis current ID) from one another. It is also important to ensure that at every point in time, these currents are at right angles to one another in a rotor-referred coordinate system. This means that the stator currents of the three-phase system must be sensed, transformed into a coordinate system that rotates synchronously with the rotor flux, and compared to the setpoint definitions for the flux-forming component and the torque-forming component of the current. The new current/voltage values are applied to the motor after the calculation, and after transformation back from the rotating reference system to the stationary stator coordinate system. Field-oriented control yields a constant rotation speed even above the nominal speed, improved velocity consistency even under fluctuating output conditions, and high efficiency at full load.
With conventional systems for field-oriented control of asynchronous machines, however, the technical outlay for accomplishing control is relatively high and costly.
One new area of application for field-oriented control systems is, for example, vehicle electrical systems of motor vehicles. Future motor vehicle electrical systems will in some cases have much higher electrical power levels than present-day systems (for example, 4 to 6 kilowatts). This development may be expected, in particular, if accessories that are now mechanically driven are electrified. Such high power levels cannot be achieved with present-day claw-pole generators, since torque transfer via the V-belts becomes critical at these high power levels. Torque peaks at which slippage of the V-belt can occur are particularly critical.
It is advantageous in this context to utilize converter-controlled asynchronous machines.
SUMMARY
It is an object of the present invention to simplify conventional systems for field-oriented control of asynchronous machines.
A first method according to the present invention makes possible a field-oriented control system for asynchronous machines that is much less complex as compared to conventional solutions.
One advantage of using the first method is that separate current sensing can be dispensed with, and thus that the cost of at least two current converters can be eliminated.
As defined in an example development of the first method, in addition to the steady-state internal voltage, the stator voltage drop is also calculated on the basis of reference variables of the torque-forming currents.
As defined in another example development of the first method, the reference cross voltage component UHQ
soll
of the steady-state internal voltage is calculated using the formula
UHQ
soll
=&ohgr;
1
*&PHgr;,
where &ohgr;
1
=&ohgr;
mech
+&ohgr;
2
,
&PHgr;=∫(ISD
soll
−IMR
soll
)*R
Rot
*dt, and
&ohgr;
2
=ISQ
soll
/ISD
soll
/T
Rot
where &ohgr;
mech
is the angular frequency of the mechanical rotation speed of the three-phase machine, &ohgr;
2
the rotor angular frequency, ISQ
soll
the reference cross current, ISD
soll
the reference direct-axis current, T
Rot
the rotor time constant, &PHgr; the magnetic flux, IMR
soll
the reference magnetization current, and R
Rot
the rotor resistance, and the reference direct-axis voltage component UHD
soll
of the steady-state internal voltage is calculated using the formula
UHD
soll
=(
ISDL
soll
−IMR
soll
)*
R
Rot
.
On the basis of these formulae, it is particularly easy to generate the manipulated variables for representing the cross currents and direct-axis currents. It is no longer necessary to sense, the actual currents. A closed-loop control system implemented with conventional methods has thus been transformed, in a manner of speaking, into an open-loop control system that has steady-state properties of similar quality to those of conventional methods. The more accurately the individual machine parameters are known, the better the accuracy of the control system achievable with the first method.
When the first method is used, semiconductor switching with current mirrors may be utilized that independently sense short-circuit currents and thus can protect themselves. This action provides effective protection against any overcurrents that might occur. The current mirrors are advantageously integrated into semiconductor switches.
In a second method according to the present invention, the rotor angular frequency &ohgr;
2
of the asynchronous machine is ascertained in a manner in which a temperature influence is automatically taken into consideration. With the second method, the rotor angular frequency of the asynchronous machine can be ascertained very easily.
With a third method according to the present invention, it is possible to accomplish particularly uncomplicated sensing of at least two phase currents of an asynchronous machine. When the third method is used, the values of two phase currents are provided in time-synchronous fashion in a manner substantially improved as compared to conventional methods, as a result of which it is possible to dispense with the provision of two or more A/D converters.
According to an example embodiment of the third method, the first phase current is conveyed to two different A/D channels of a controller, the controller having only one A/D converter. With this feature, it is particularly easy to carry out the third method.
Advantageously, the time interval between the sensing of the value of the first phase current at a first point in time, and the sensing of the value of the second phase current at a second point in time, may be of the same length as the time interval between the sensing of the second phase current at the second point in time and the sensing of the first phase current at the third point in time. Identical time intervals make possible particularly simple calculated analysis of the acquired phase currents.
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Ueda et al., ‘Feasibility of Zero Phase Current Detection by Sensing Current at Each of the Three Phases in Power Distribution Networks’, Apr. 1995, IEEE , Vol: 10, No:2, pp. 613-620.*
F. Blaschke, “Das Verfahren der Feldorientierung zur Regelung der Asynchronmaschine” [The Field Orientation Method for Controlling an Asynchronous Machine], Siemens Forschungs und Entwicklungsberichten [Siemens research and development reports] 1972, pp. 184 et seq.*.
W. Leonhard, “Control of Electrical Drives,” Springer Verlag, pp. 214-222.
Eisenhardt Martin
Tschentscher Harald
Desta Elias
Hoff Marc S.
Kenyon & Kenyon
Robert & Bosch GmbH
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