Comments by "SeanBZA" (@SeanBZA) on "Ziroth" channel.

  1.  @ZirothTech  not really a new thing, just a standard synchronous motor with external excitation, using a planar transformer to power the rotor winding. Pretty much something common on high power generators, where they need to run long periods without stopping, making them useful in power generation for long run time, as the only thing you need to change is the oil bath oil in the bearings, and thus can run them for 10 years with no stopping, before stopping to clean and inspect them. Does not even need much in the way of electronics in the power transfer, you have a rotor coil with a bridge rectifier, and a exciter coil with some form of AC power, either simple H bridge at some fixed frequency, giving a constant current, or variable to allow you to vary current based on duty cycle of the bridge, allowing max field strength at low RPM with high current, and at high RPM you drop excitation to a lower level, or even turn it off, to allow the rotor to act like an induction motor, using the diode bridge to handle the freewheeling current, which will improve efficiency a lot, as now at speed no cogging losses in the magnetic system, while at low speed you get a very high breakaway torque. Much cheaper to make yes, and while you have a lot of copper in the rotor, and need to cool it as well to keep the heat down, it will work well, even with existing drives, with only minor changes to provide the excitation power, and the added temperature sensing needed. Your bridge rectifier will probably be improved by adding in active switches, as you otherwise will need beefy schottky diodes on a heat spreader to handle the high current, as high current is needed to get a strong field, and you will definitely want to reduce inductance. So schottky diodes rated around 100A per diode, or add in power mosfets, and a separate power winding to allow an active rectifier to be on the rotor as well. Slightly more complex, but allows an extra percent or two lower losses.
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  2.  @sawomirkuczek3214  Slip rings have a very bad problem with shed material, so pretty much all slip ring or commutator designs have to be open frame, so that the conductive dust can be blown out by the cooling fan. Make it sealed and you now have to add in a air path that has a particulate filter in it, which also has to handle high temperatures as well, which adds cost and mass. Inductive exciter is simple, a set of magnetic doughnuts that have a coil wound in the middle, separated by a small distance, so the one can rotate and the other be fixed, and you apply AC to the one, and get AC out the other, same frequency irrespective of the rotor turning or not. big issue is that for generators they apply high voltage AC, as the rotor is wound with lot of turns of thin wire, and a bridge rectifier to make the AC DC ,possibly with a capacitor on there to smooth it, allowing lower rotor loss, and thicker lamination's to be used. Here you need to vary the DC current over a wide range, so need to have fewer turns, and much higher current for the same field strength, so you need low inductance in the rotor coil, and thus the fewer turns, and the higher current means a big beefy bridge rectifier, with it's associated heat dissipation. My guess the thing that Mahle did was put 3 phase rotary transformer in, run it at a higher frequency, so they can use low cost powdered and sintered ferrite parts, and probably have a 3 phase H bridge running at around 40 kHz to excite the system, and secondary side put in an active bridge rectifier to handle the 50A or so of current flow. Overall cheaper than putting in 50A rated carbon brushes, which will be massive blocks of copper graphite, probably 50mm by 30mm, running on the rotor, and probably still dissipating more power in brush and contact loss than the electronic system as well. Making use of current components the biggest thing will be cooling, to keep the semiconductors cool ,as they are the most sensitive item, so the oil bath will help, simply using aluminium core PCB for the active switches, and then a board on top, fully conformal coated, that is attached using IDC connections, with a top layer being the connections to the ferrite transformer. All running in a thin oil, 0W10 is a common modern one, and you get even thinner oils as well, which pour and act like water. That then can be cooled easily, and the rest of the motor can run in it as well for rotor cooling, with a thermal transfer loop to provide cooling via a water and glycol external cooler, so you can get cabin heat out of the rejected heat as well.
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