MC9S12ZVML: Delta Connection Motor with external driver

[Arrow]

Hi,

I got two questions now of using S12ZVML for sensorless motor control.

1. for Delta connection, the Back-EMF constant calculation:

    I measure the phase voltage at 1000rpm.Since phase voltage is equal to the line voltage，the constant in freemaster is Vpk(phase)/W(angleSpeed)? No need to divide sqrt(3)?

2. We use the external driver and interal current sense amplifier 0 for dc-bus current measurement.We left the HG/HS/VBS/VLS/LG/LS/LS0/CP/VCP all pins used by GDU unconnected.And enable the GDU ,and current sense amplifier 0. Howerever,the DC bus measurement value is bigger than the real value.

Is it ok to left these GDU relative PINs unconnected to just use the internal CSA?Or I need care about something else about the hardware design to use external driver?

Regards

Arrow

[StanoA · Accepted solution]

Please provide more detail information about your application and the reason you need the external MOSFETs driver instead of internal one.

Here are comments to you question:

 1) It's true that BackEMF changes with Delta connection, however there is no need to recalculate this value. The reason is that we simply consider the motor as a black-box with a Y connection. It means we control the motor as Y connected and therefore we with take the Y-value of BackEMF.

2) 

In case the GDU is not used, there's no need to enable it. GDU pins can be unconnected (nor grounded, nor pulled up). Internal OpAmp needs to be enabled. There is no programmable amplifier gain hence the issue with wrong value may come from wrong scaling. Please refer to the following document /user guide - MCSXSR1CS12ZVMUG for more details. Regarding the external driver, you need to follow the datasheet of given driver and recommendations of driver manufacturer for the design. There is guideline from NXP site to describe external driver with S12ZVM.

https://www.nxp.com/webapp/Download?colCode=MCSXSR1CS12ZVM-UG&location=null

Attached is the *.zip file which can help you with your design. 

I wish you many success.

Best Regards,

Stano.

[Arrow]

Hi StanoA It is a 24V fan controller application. 1 Got it.Just take the Vline_line/1.732 as Y connection to calculate the back emf constant. 2 The GDU pre driver should be enabled to use the internal CSA function as the MC9S12ZVMRM's GDU chapter. We use a TL431 to generate 2.5V reference with a 0.22uF bypass capacitor.It seems that TL431 has a instability boundaries with the load capacitance.We will check if this is the root cause. Regards Arrow