@
Gerasimental and @
R.S great comments.
Exactly. It got lost because in researching the piece I didn't stumble across the distinction between the two. I am not an engineer, and have been simply playing journalist as I try to understand this fascinating tech. What I have not gotten down yet is the difference between PMSRM and PMSynRM machines. Virtually all the references I came across discussed the Switched Reluctance Machine, and there's even been an assertion that the "S" in "SRM" can mean either "Switched" or Synchronous", as though it's always referring to the same design.
If either of you care to describe the differences between the two designs I (and I'm sure others) would love to hear. For me personally I have yet to understand how a motor can be synchronous when it seems the electromagnets in the stator are always a bit ahead of the rotor... pulling it along. ;>
Broken down it's as follows:
A regular synchronous PM motor has permanent magnets somewhere in or on the rotor, those usually form a magnetic field that induces a sine wave into the stator windings. If the stator windings carry a current themselves, the rotor moves along at the same speed as the magnetic field of the stator. Imagine a magnetic compass needle following another magnet around.
The SRM uses the reluctance, so basically the rotor iron magnetizes. But other than with a synchronous machine, only one pole is excited and the salient poles in the core move until they are under that pole. Then the next pole gets excited and it makes another step.
A PMSynRM also uses reluctance, iron being magnetic, but also magnets and, other than the SRM, it moves continuously. The magnets are in the rotor and increase the magnetic flux.
A PMSRM again does those step movements and has the magnets on the stator.
A BLDC also does steps like the PMSRM, but has magnets on the rotor.
A big difference is the torque ripple and the duty cycle. In the BLDC, SRM and PMSRM the currents are rectangular, in the IPM, or PMSynRM they are modulated sine waves. Additionally in the SRM the currents through the windings don't change direction. So the effective current (root mean square) in the IPM windings is 1/sqrt(2) = 0.7, in the BLDC it's 0.66 and in the SRM it's either 0.33, or 0.5.
So with the same maximum current per winding, a sine waveform is the one with the most torque.
And since especially at high speeds, the rectangular wave form can't be done anymore, since the inverter is at it's voltage limit, the torque ripples increase.