A three speed motor

Bonjour tout le monde!

some news: the final simulations with FEMM are almost completed. I now have a pretty good idea on how the motor will perform and will very soon be able to order my laminated steel ... 

How time passes and thanks

It has been over two years since I started working on the Quadrupole electric motor. I had a few people exchanging knowledge with me and also, giving me good advice. So, I would like to take this opportunity to thank each of them.

The non-obvious behaviour

During my first simulations way back then, I noticed that BackEMF in the inner and outer coils of the stators were not equal. This meant that the airgaps of the two stator were also "unballance". So I tried to eliminate it and led me nowhere. I abandoned that path because it was time consuming.

So my adventure continued without paying attention do this behaviour of the Quadrupole. In this situation, I was more interested to have the Back-EMF waveform to mimic the voltage sinusoidal wave source.

To recall; the main objective with the Quadrupole motor is to achieve high torque, high speed, and not use as much as possible torque weakening technique to achieve speed.

I discovered that by disconnecting for instant the outer coils from the simulation it gave more speed but lower torque, so a pseudo-field weakening technique without the controller/inverter being involve, simple logic. I have never pay any attention in my early simulations since I did not quiet understood the torque and counter electromotive force constants. It is not obvious for non-practitioners in this field of research, but the Quadrupole motor can act as a three speed electric transmission!

How is this possible? Just because the Quadrupole motor is radially design! The radius and the circumference length of each airgap are always unequal. The magnetic flux densities of the air gaps will therefore uneven. Comparing this to an axial flux motor having two stators, the axial flux in the airgaps of both stator are always equal. So, what was not obvious became clear and hit me!

Three values for the torque and back-EMF motor constants in one motor

Another interesting thing about the Quadrupole motor is that its torque and BEMF constant will vary according to wire phase configurations.

If the outer and the inner stator coils are configured to be connected in series, the torque constant of the latest design, is 0.375 Nm/A and its BEMF constant is 0.375 V/rad∙s^-1.

If only the outer stator coils are used, the torque constant will now be 0.205 Nm/A and its BEMF constant is 0.205 V/rad∙s^-1.

If only the inner stator coils are in use, the torque constant will now be 0.145 Nm/A and its BEMF constant is 0.145 V/rad∙s^-1.

So the higher value of the torque constant, the higher will the torque be. On the other hand, the lower the BEMF values will be, faster the rotating speed be.

Configuring the new winding schemes

By modifying and reconfiguring the wire connections of the inner and outer winding, it is possible to have a three speed electric transmission-motor that could give a sporty-like drive as if the vehicle was equip with manual 3 speed mechanical transmission.

At the date of the publication of this post, the results of the latest Quadrupole motor are described below.

1) At first speed for high torque at 37.5 Nm and low speed of 3700rpm: the coils of the inner and outer coils are connected in series. This means that the windings of phases 1, 2 and 3 with respect to coils A, B and C of the outer stator are connected to their sister the windings of phases U, V, and W of the inner stator respectively.

2) At second speed for medium toque of 20.5 Nm and speed of 6700rpm, only outer stators windings A, B and C are active.

3) At third speed for low torque of 14.5 Nm and high speed of 9500 rpm, only inner stator windings U, V and W are active.

The above figures are achieve with a 144 Vdc and 100A peak (71 Arms).

Now, how will all this be controlled?

Probably, the easiest way to control the speed and torque by is be re-configuring on the fly the wiring connections by using a motor contactor. High power SSR could be use but a minimum of three will be required for each phase. Motor contactor is probably the best way to go for testing. However, how the inverter/controller will react to a fast change is unpredicted and will certainly be a nice challenge,

Or again, two controllers might also be a good option. One controller per stator and each controller will see a single motor. Having them connected in parallel, it will raise the efficiency of the whole scheme at the expense of raising the current, since they will be connected in parallel from the point of view of the battery pack. The controller / inverter will have to be "disconnected" by changing the value of the analog input of the speed demand. For example, we have the controller / inverter A connected to the phases of the outer stator and controller / inverter B connected to the inner stator phases and a button or handle could be used for electrical shift applications. First, the two inverters are used for the first mechanical/electrical speed and the throttle is use to sens the analogue signal to both of the inverters. By manipulating the button or handle, we move to the second speed by sending an analog 0 volt signal to the inverter B at and inverter A will continue to receive its signal from the throttle. For the third speed analog entered the inverter A will subsequently be set to 0 volts and the inverter B now receives its analogue signal from the throttle.

Advantages

The biggest advantage is that directly coupling the motor to the transaxle drive system of the vehicle will ease the coupling to an electric motor. Also avoiding to the manual transmission will also reduce mechanical losses and reduce weight.

Is this great or what?