The invention relates to a method and a device for the determination of the motor constant of an electric motor by measuring motor parameters on the running motor.
To date in electronic motor controls there are used for the motor moment regulation and/or motor moment restriction motor moment constants kM. With the aid of this relationship:
M
Mot
=k
M
·I
Mot (1)
the produced inner motor moment (without friction losses, therefore inner moment) can be determined on the basis of the measured or regulated motor current IMot.
As a rule, thereby the motor moment constant is determined by measurement techniques over a statistically sufficient number of motors on a motor test bed and then stored as constant in the motor control.
For the determination of the motor moment constant there is employed as a rule a torque measurement device and a current measurement device and the motor moment constant is then calculated via the formula
It is here clear that a great measuring outlay is necessary for the determination of the motor moment constants and only (depending on application) a mean, maximum or minimum value of the motor moment constant can be employed for the motor control, insofar as no calibration is carried out for each motor.
The invention is based on the object of reducing the measuring effort for the determination of the motor moment constant. Furthermore the possibility is to be opened up of making a self-calibrating motor control possible.
The invention is achieved by means of the method indicated in claim 1 and the device indicated in claim 6.
A concrete realization of the method in accordance with the invention can consist, in accordance with claim 2, in that the generator voltage UEMK produced by the motor is measured, and in that the motor moment constant kM is calculated according to the following formulae.
For a DC motor
and for a 3-phase synchronous motor
The above formulae arise as follows:
There applies:
P
Mech
=M·ψ (5)
Where PMech is the mechanical motor power, M the motor moment and ω the angular frequency.
There applies further for an ideal loss-free DC motor
P
el
=U
EMK
·I
Mol (6)
and for an ideal loss-free 3-phase synchronous motor
P
el
=U
EMK, phph
·I
Mot·√{square root over (3)} (7)
Where Pel is the electrical motor power, UEMK the generator voltage produced by the motor and IMot the generator current produced by the motor.
There further applies for both motor types
PMech=Pel (8)
Equating formulae (5) and (6) one then obtains for the DC motor
U
EMK
·I
Mot
=M·2π·fMot (9)
And equating formulae (5) and (7) for the 3-phase synchronous motor
U
EMK, phph
·I
Mot, phph
·√{square root over (3)}
=M·2π·fMot (10)
in which fMot is the speed of rotation of the motor which also is described as revolution frequency or rotational frequency. The speed of rotation is a physical parameter with the dimension 1/time. As a rule, it is indicated for motors as revolutions/minute.
From formula (9) there is provided for the DC motor:
From formula (10) there is provided for the 3-phase synchronous motor
If one combines formulae (2) and (11), formula (3) thus arises.
If one combines formulae (2) and (12) and sets cos phi=1, formula (4) arises. Both could be proven.
Configurations of the method in accordance with the invention directed specifically to DC motors and 3-phase synchronous motors are subject of claims 2-5.
A first configuration of the solution in accordance with the invention for a DC motor can consist in that the motor is taken to a predetermined speed of rotation, externally driven, before the measuring of the generator voltage, which is then used for the calculation of the motor moment constant. With this variant the speed of rotation is fixed and need not be measured first; only the generator voltage produced by the motor must still be measured.
An alternative configuration of the invention, also for a DC motor, can consist in that by applying an operating voltage the motor is started before the measuring, that the operating voltage is then switched off, and that the measuring of the generator voltage is effected after fading away of the inductive operating current and at the same time the speed of rotation is measured via an external speed of rotation measuring device. With this variant an external speed of rotation measuring device is also required besides the measuring device for the generator voltage; however, the external drive is not needed.
A further configuration of the invention for a 3-phase synchronous motor can consist in that initially the motor is started without load by applying an operating voltage, in that then the operating voltage is switched off and after fading away of the inductive operating current the generator voltage is measured, wherein the speed of rotation is provided from the cycle duration of the generator voltage produced. With this variant there is likewise needed only a measurement device for the generator voltage since the rotational frequency, as mentioned, is provided from the cycle duration of the produced generator voltage.
With none of the above described variants is a torque measurement device still required, which previously was necessary in every case and in equipment technology terms is rather complex.
To be able to realize highly exact moment control, the open-circuit current must be determined. This open-circuit current contains motor internal losses (e.g. relating to magnetization and friction losses) which then take part as offset in the calculation of the motor moment.
By means of the method an intelligent control can be realized with which the connected motor can be measured so that it is then able to deliver very exactly the desired moment. Through this a calibration with an external moment test device can be forgone in most cases.
Exemplary embodiments of the invention will be described below with reference to the drawings. There is shown:
In
After the DC motor 3 has started, at first it is separated from the DC current supply system 1 with the double-throw switch 2 until the inductive operating current has faded away. The double-throw switch 2 is then switched over into the switching position indicated by broken lines. In this switching position a voltage measurement device 5 is connected with the terminals of the DC motor 3 which measures the generator voltage UEMK of the motor 3. The measurement result is delivered to a computer 6. The measurement result of speed of rotation measuring device 4 is further delivered to the computer 6 via the double-throw switch 2. The computer 6 determines the motor moment constant kM from the generator voltage UEMK and from the speed of rotation fMot by division according to the formula (3) given in the introduction.
With the variant shown in
The circuit shown in
With the measuring means for the generator voltage of the motor and its speed of rotation, and the device containing the computer for the determination of the motor moment constants kM, motor control electronics can be realized which can automatically measure the motors in accordance with the described method. In this way production variations of the motor can compensated and a very exact moment control be realized without a calibration being required. However, the device finds application not only in production but also in the laboratory in order to measure the motors without a complex test bed being necessary.
Furthermore there is also the possibility of integrating the device in accordance with the invention into a motor control which measures the connected motor, as described above, and uses the measurement results—that is, the motor moment constant here obtained—for the more exact control of the motor, in particular for a control/regulation of the torque.
Number | Date | Country | Kind |
---|---|---|---|
10 2007 020 068.6 | Apr 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP08/02941 | 4/14/2008 | WO | 00 | 12/23/2009 |