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Tuning of the BEMF compensation parameters

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Tuning of the BEMF compensation parameters

This paragraph describes how the BEMF compensation parameters can be tuned in order to

obtain the best results. Setting the correct compensation parameters is fundamental to

Voltage mode algorithm performance.

The tuning sequence can be divided into the following steps:



Collecting the characteristics of the application and motor (Section 2.1)



Obtaining a preliminary set of parameters (Section 2.2)



Tuning the parameters in order to obtain the needed results (Section 2.3 on page 17).

2.1

Collecting the application characteristics

The compensation system is based on the electrical model of the stepper motor, so its setup

is strongly dependent on the motor characteristics.

The required information is:







measured with common measuring instruments.

If the user has an RLC meter, they can connect it to one of the motor phases and measure

the series R and L at 100 Hz (make sure the motor does not move). The resulting values are

applied to one of the phases.



Connect a DC voltage at one motor phase and apply the voltage and current probes of

the oscilloscope, as shown in Figure 6 A



Increase the voltage up to the value where the current equals the nominal value



For a better measurement, lock the rotor position



Unplug one terminal of the voltage source cable without switching it off and disable (or

set to the max.) the current limitation



Connect the voltage source rapidly and monitor, on the scope, the voltage and current

waveform



The measurement is good if the voltage trace is similar to a step and the current

increases exponentially (Figure 6 B)



Measure the time for the current waveform to rise up to 63% of the nominal value

(Figure 6 B)

