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Discussion Starter · #1 ·
Currently working on a project to make an electrical "gear" in a three phase PMSM. To do this I am going to reconfigure the stator windings from series to parallel. Each phase has four windings, but I only want to be able to parallel connect two and two. I have made the decision to use back-to-back MOSFETs as this seemed to be the most efficient and cheapest option (triac is an option as well, but as I understood, the control is more difficult). First question will be, what is the optimal switching circuit?

Second, I need to control the MOSFETs. The motor runs on a 44 V battery with an inverter. Would it be possible to use this power supply for MOSFET control? If so, how? Would appreciate a circuit diagram of potential solutions:)

The motor is to be used in drones with three phase RMS currents reaching levels of 100A in the parallel connection.
 

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What does splitting the winding do for the motor speed and torque performance?

It seems that it would reduce the pole count from 4 to 2, and the resistance of the phase winding would decrease by a factor of 4. Is there a benefit to this?
 

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Discussion Starter · #6 ·
By reconfiguring to parallel the voltage constant would double. The available torque at higher speed would therefore be higher. The motor can then be optimized for low speed in series connection(which is were it will operate most of the time), increasing overall efficiency. Then the reconfiguration can be made when during operating point with high speed and torque. Of course this will increase double the current for the same speed (at low speeds), but will increase the max speed which is restrained by the battery voltage. I'll have to look into the losses this device will contribute to the system to see if its a viable solution, but I think it will decrease the overall losses:)
 

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You have an interesting idea.

Would you be able to reconfigure the coils manually into the parallel windings, then back drive it and measure the back-emf waveform at low, medium and high speed.

Getting higher torque may be limited by the heating in the coils with the higher currents.

Current may be limited by the inductance of the coils at higher speed.
 

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If you want to see the effect of series and parallel winding connections, just look at the specifications and performance data for the Dual and Single versions of the BorgWarner (formerly Remy) HVH series motors, which are available in both configurations.
 

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Discussion Starter · #9 ·
You have an interesting idea.

Would you be able to reconfigure the coils manually into the parallel windings, then back drive it and measure the back-emf waveform at low, medium and high speed.

Getting higher torque may be limited by the heating in the coils with the higher currents.

Current may be limited by the inductance of the coils at higher speed.
Thank you for your interest in the idea. I have already ran several tests and simulations with the motor, all confirming my believe that efficiency can be increased. For the rl tests I soldered the stator windings in series and parallel. Efficiency is around 9% higher for the series connection in low speed mode. However the speed range is low, and simulations show that the difference in efficiency decreases as the speed increases.

I am curious how small I can get the "switch box" and how much additional losses there will be regarding the integration of extra weight and electronics. A control circuit for the switching circuit would be really helpful!
 

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I am curious how small I can get the "switch box" and how much additional losses there will be regarding the integration of extra weight and electronics. A control circuit for the switching circuit would be really helpful!
I suspect that the controller plus switch box will be comparable in size and weight (and more expensive and complex) compared to just a controller which is sized to handle the current required to deliver the desired low speed performance and the voltage required to deliver the desired high speed performance. As a result, the simplest solution is to use one motor configuration (equivalent to the parallel configuration in this scenario), just like every production EV.
 

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Both the high and low current switch devices have to survive the highest voltage being stood off.

For the cost of the switching devices needed for this (I looked at this very thing a decade ago, which is how I knew about the locomotive patent, then published the idea in the public domain making it impossible to defend as a subsequent patent even though some patents have issued on the subject, anyway), which are pretty much sold out everywhere or you are limited to only buying two devices, it's cheaper to mechanically parallel a second motor as a torque doubler (Tesla et al adding a motor to the front of the car is another way)....or just build a larger machine.
 

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Currently working on a project to make an electrical "gear" in a three phase PMSM. To do this I am going to reconfigure the stator windings from series to parallel. Each phase has four windings, but I only want to be able to parallel connect two and two. I have made the decision to use back-to-back MOSFETs as this seemed to be the most efficient and cheapest option (triac is an option as well, but as I understood, the control is more difficult). First question will be, what is the optimal switching circuit?

Second, I need to control the MOSFETs. The motor runs on a 44 V battery with an inverter. Would it be possible to use this power supply for MOSFET control? If so, how? Would appreciate a circuit diagram of potential solutions:)

The motor is to be used in drones with three phase RMS currents reaching levels of 100A in the parallel connection.
This is commonly done in large industrial motors.

It's a lot easier than you think.

Just google "Wye-Delta two speed motor" and you'll get a lot of detailed information on how to do it
 
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