My spice model looks good but in the hardware the bemf does not cross Vd/2. On some phases it is above Vd/2 and rising while on others its below Vd/2 and falling. I'm using a STSPIN230 as the triple half-bridge and am pulsing both the high-side and low-side simultaneously. My code samples the open winding when the PWM is ON. The 'zero-crossing' should be nominally around Vd/2. Any ideas why it's offset?
I've been following an AP Note from Microchip (AN1160) but my waveforms do not match the AP Note. Their figures show almost no PWM disturbance on the off winding. My simulation shows symmetric bemf in the off windings but also considerable pwm noise.
Should I instead be pulsing high side only and looking at bemf when PWM is off?
--- Thanks
