Control Techniques unidrive sp Advanced User's Manual page 113

Parameter Keypad and
Menu 5
structure display
• 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 118), 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.
3: Inertia measurement
See inertia test for closed-loop vector mode. 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 for closed-loop vector mode, this will not affect the
accuracy of automatic speed loop gain set up.
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 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 parameter 03.25, 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 until the movement is approximately 5° electrical. 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.
• A test is performed to ensure that the feedback device direction is correct
• Parameter 03.25 (phasing angle) is updated and saved to EEPROM.
This test will operate correctly when the load is an inertia, and although a small amount of cogging and stiction is acceptable, this test cannot be used
for a loaded motor. The test can only be used where the total inertia is less than 0.1 x Trated kgm2, assuming no additional stictional load, where
Trated is the torque produced by rated current as defined by Pr 5.07 or Pr 21.07. In most cases the motor only moves by 5° electrical, however, it is
possible for the test to initiate additional movement due to cogging torque. The amount of movement depends on the design of the motor and is
similar to the movement produced by cogging torque when the drive is disabled. If the motor is moving at a speed that is higher than the zero speed
threshold (Pr 3.05) when the test is initiated a tunE3 trip is initiated.
This test can be used with any type of encoder, however, it is not recommended with Ab.Servo, Fd.Servo or Fr.Servo encoders because the absolute
position is not defined until two valid changes of the commutation signals have occurred after power-up or an encoder trip. Therefore if the test is
carried out before two valid changes have occurred, the movement produced during the test may be quite large and the result may be slightly
inaccurate. Once two valid changes have occurred the test operates in the same way as for other encoder types.
The current controllers are used to perform this test, however, the default gains may be too high. It is not possible to carry out the necessary test to
set up the current controllers before the phasing angle is known. If the gains are too high the minimal movement phasing test may cause an OI.AC
trip. If this happens the current controller gains should be reduced progressively until the test is successful. Once the phasing angle is known, the
stationary test to set up the current controller gains only (Pr 5.12=4) may be used to obtain the correct gain values for the current controllers.
6. Current controller gain calculation only
• No current is applied to the motor.
• The current loop gains are calculated based on the value of the motor inductance (Pr 5.24) and resistance (Pr 5.17) and written to Pr 4.13 and
Pr 4.14.
• Pr 4.13 and Pr 4.14 are saved to EEPROM.
This is intended to be used as a method of setting up the current loop gains from user defined values of motor inductance and resistance. The drive
should not be enabled to perform these calculations. If the parameter is set to 6 it is automatically cleared by the drive once the calculation is
complete. It should be noted that the value changes back to zero within a few hundred milliseconds of being set to 6 by the user.
112
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Issue Number: 7