Menu 5
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Performance
82 Digitax ST Advanced User Guide
www.controltechniques.com Issue Number: 1
1: Short low speed test
• The motor is rotated by 2 electrical revolutions (i.e. up to 2 mechanical revolutions) in the forward direction. The drive applies rated current to the
motor during the test and measures the encoder phase angle (Pr 3.25) only. The phase angle measurement is taken when the motor has stopped
at the end of the test, therefore there must be no load on the motor when it is at rest for the correct angle to be measured. This test takes
approximately 2 seconds to complete and can only be used where the rotor settles to a stable position in a short time.
•Pr 3.25 is saved to EEPROM.
2. Normal low speed test
• The motor is rotated by 2 electrical revolutions (i.e. up to 2 mechanical revolutions) in the forward direction. The drive applies rated current to the
motor during the test and measures the encoder phase angle (Pr 3.25). The phase angle measurement is taken when the motor has stopped at
the end of the test, therefore there must be no load on the motor when it is at rest for the correct angle to be measured.
•Pr 3.25 is saved to EEPROM.
• A stationary test is performed to measure the motor resistance (Pr 5.17).
•Pr 5.17 is saved to EEPROM.
• A stationary test is performed to measure the motor inductance (Pr 5.24). When this test is complete the current loop gains (Pr 4.13 and Pr 4.14)
are over-written with the correct values based on the calculations given in Menu 4. It should be noted that the inductance measured is the
inductance in the flux axis. For many motors this will be 20 to 30% less that the inductance in the other axis. The inductance for the other axis
could be used to calculate the current controller proportional gain if required because there are no transient changes of current reference flux
axis. Therefore the gain can be increased by the user if required. The inductance for the other axis should be used to obtain optimal cross
coupling cancellation (see Pr 5.26 on page 85), and so the inductance parameter (Pr 5.24) could also be increased by the user if required.
•Pr 4.13, Pr 4.14 and Pr 5.24 are saved to EEPROM.
The whole test takes approximately 20 seconds and can be used with motors that take time to settle after the rotor has moved. During the motor
inductance measurement the drive applies current pulses to the motor that produces flux that opposes the flux produced by the magnets. The
maximum current applied is a quarter of rated current (Pr 5.07 or Pr 21.07). This current is unlikely to affect the motor magnets, however, if this level
of current could permanently de-magnetise the magnets the rated current should be set to a lower level for the tests to avoid this.
Either the short or normal low speed tests could be used with a servo motor that does not have an absolute encoder (i.e. incremental without UVW
commutation signals, SINCOS without comms etc.) to control a servo motor. A phasing test would need to be performed after each power-up, or loss
of encoder power supply if the motor rotates while the supply is not present before the motor could be controlled by the drive. If this method of control
is used the drive cannot do any error checking to ensure that the absolute position has not been lost due to unwanted encoder counts due to noise.
Either the short or the normal low speed tests can be used with a servo type encoder (Ab.Servo, Fd.Servo or Fr.Servo) that has only commutation
signals, i.e. the lines per revolution has been set to zero. When these tests are performed with this type of encoder the motor will continue to move in
the same direction after the first two electrical revolutions. It will then stop for either 0.8s (short test) or 4s (normal test) and then continue to move
again for part of an electrical revolution.
3: Inertia measurement
• The drive attempts to accelerate the motor in the forward direction up to
3
/
4
x rated load rpm and then back to standstill. Several attempts may be
made, starting with rated torque/16, and then increasing the torque progressively to x
1
/
8
, x
1
/
4
, x
1
/
2
and x1 rated torque if the motor cannot be
accelerated to the required speed. 5s acceleration time is allowed during the first four attempts and 60s on the final attempt. If the required speed
is not achieved on the final attempt the test is aborted and a tuNE1 trip is initiated. If the test is successful the acceleration and deceleration times
are used to calculate the motor and load inertia which is written to Pr 3.18.
•Pr 3.18 is saved to EEPROM.
The calculated inertia depends on the value of motor torque per amp entered in Pr 5.32. If this parameter is incorrect the inertia value will be incorrect.
However, as explained in the inertia test description , this will not affect the accuracy of automatic speed loop gain set up because Kt is also used in
these calculations and any inaccuracy cancels out.
The test algorithm attempts to remove the effect of any load on the motor other than the torque required to accelerate and decelerate the motor, i.e.
friction and windage losses, static torque load etc. Provided the average torque during acceleration and the average torque during deceleration are
the same the effect of the additional torque is removed and the inertia value is calculated correctly.
4. Stationary test to set up current controller gains only
• A stationary test is performed to measure the motor resistance (Pr 5.17).
•Pr 5.17 is saved to EEPROM.
• A stationary test is performed to measure the motor inductance (Pr 5.24). When this test is complete the current loop gains (Pr 4.13 and Pr 4.14)
are overwritten with the correct values based on the calculations given in Menu 4.
•Pr 4.13, Pr 4.14 and Pr 5.24 are saved to EEPROM.
This test can only be used with a motor when the correct phasing angle has been set in Pr 3.25, because rated current is applied in the flux axis
during the resistance measurement. If the phasing angle is not correct the motor may move and the results may be incorrect.
5. Minimal movement phasing test
Short current pulses are applied to the motor to produce a small movement and then to move the motor back to the original position. The size and
length of the pulses are gradually increased (up to a maximum of rated current defined by Pr 5.07) until the movement is approximately at the level
defined by Pr 5.38 electrical degrees.. The resulting movements are used to estimate the phase angle.
The test is carried out as follows:
• Current pulses are applied to determine the phasing angle
• An additional test is performed to ensure that the phasing angle is correct. If the test fails there is a delay and then test recommences. This is
repeated twice after which a tunE2 trip is initiated. The delay before recommencing the test is 200ms and then 400ms. These delays allow the
motor to stop moving if the test has initiated movement due to cogging torque.
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