# trapezoidal vs sinusoidal commutation

How do you know if a commercial driver is working with trapezoidal or sinusoidal commutation? If you measure the 3-phase voltage applied to the PMSM by means of an oscilloscope, will you see a difference?

• In a block commutation , the phase shift between each phases is 120degrees. However the diagram of block commutation shows only 60 deg phase shift. Does anybody know if a 60deg phase shift could commutate the BLDC correctly? – user11205 Nov 30 '15 at 21:33
• Please start a new thread if you have a new question. – Ben Dec 1 '15 at 2:37

• The trapezoidal waveforms don't look right. It is block commutation, which means that for each phase, it is positive for 2 states, tri-state for 1 state, negative for 2 states, and tri-state again for 1. When it is tri-state, the back-EMF varies so that it looks trapezoidal. Your diagram seems to show the $V_A$ at max for only 1 commutation state in each cycle – ronalchn Jun 19 '13 at 12:19