Hybrid and EV Regenerative Braking Systems

Hello, I am professor John Kelly and this is the  WeberAuto YouTube channel. Today we are going to   learn about regenerative braking systems in hybrid  electric vehicles and electric vehicles I have a   neat little demonstration I want to show you  I have a 2017 Prius eco transmission back here   this is the P610 transaxle and if you've seen any  of my other 40 or so videos on hybrid and electric   vehicles a couple of them deal with this trans  axle as far as how it works and the technology   inside of it but what we are looking at here is  the driver's side half of the transaxle and it's   laying sideways now in the case parallel to each  other I have two electric motors we have motor   generator one that's right here that hooks to  this sun gear and I can rotate it as you can see   and then over here we have motor-generator 2 and  I can rotate it now if you're not familiar with   motor-generator 1 or motor-generator 2 I have an  example of one right here this particular one is   from a Ford hybrid electric transaxle from a  2005 Escape but it's very similar to what you   would find in about any other hybrid a transaxle  this is the rotor of an electric motor it has very   strong permanent magnets inside of it and the  way it's oriented inside of this case here it   has a sun gear connected to the top of it just  like I have a sun gear connected to the top of   the motor that's down inside of this case now  this rotor spins inside of a state or and the   stator is also inside of this transaxle housing  back here it would be facing vertically like this   with this permanent magnet rotor inside of it  and free to rotate like I'm showing you back   here but the stator I want to show you has three  big electrical connections right here the U, V,   and W phases and if we look real close in here  you can see the copper wire windings and we have   a U, V, W, U, V, W, U, V, W and it just continues on and on  around the entire stator frame this metal part   here so the important thing to understand for  this demonstration is we have three big coils   of wire inside of the stator assembly in the  transaxle with a permanent magnet rotor there   are eight magnetic poles of north and south, north  and south on here as we rotate it and that spins   inside of the stator okay to understand what's  going on here with the stator and the permanent   magnet rotor spinning inside of it I've got a  little demonstration to demonstrate what's called   electromagnetic induction and basically what  that means is that anytime there's a magnetic   field crossing a wire or a coil of wire it will  induce or push current in that coil of wire so   as an example I have a small coil of wire right  here hooked to an old school amp meter and this   is an AC for alternating current amp meter so  if this needle goes this direction we would   have a positive amperage if the needle goes this  direction we have to have a negative amperage and   now I've got a permanent magnet here a horseshoe  magnet and I want you to notice that when I bring   the magnet close to the coil of wire the needle  goes in one direction so you go over to the right   but if I pull it away from the coil of wire it  goes in the other direction so as I approach the   coil of wire with the magnet the needle went in  one direction as I go away from the coil of wire   with the magnet, the needle goes in the other and  as long as there's movement we will have current   but notice as soon as I stop there's no current  so the same thing is happening with the three   coils of wire in the stator and the eight sets  of magnets rotating on that rotor of the motor   that spins inside of it so let's hook this little  amp meter to the output of MG1 stator over here   the three the three wires here on this stator the  U, V, and W phases have the equivalent connections   right over here of the except they're ordered  differently the V, U, and W connections for MG1's   stator and the V, U and W connections for MG2's  stator so let's connect this amp meter to the   stator here and see what happens all right I'm  going to rotate the rotor inside of the stator   and we should see the current alternating back and  forth alternating current AC current okay here we   go I'm just going to turn it real slow and we can see  it going back and forth so as we turn the rotor   we're inducing an alternating current on the wires  that leave the stator so I've got it hooked up to   two wires here that's the same as hooking it up to  say these two wires right here but there are three   three wires at the same time that are connected  so let's hook up three wires and watch the voltage   signal being generated on these three phases so  bring in my Pico 4425 oscilloscope here we'll   connect our blue lead to the V phase a red lead to  the U phase and the green lead to the W phase and   we will watch the output on the oscilloscope here  as I rotate the rotor inside of the stator now so   I can rotate the rotor faster than I can by hand  I'm going to connect an electric drill motor to   that Sun gear and rotate it I had to come up with  a little adapter here to hook a socket to the Sun   gear with a couple of holes clamps and some pieces  of a radiator hose okay now I will hook my drill motor   up this drill motor is going to bring this up  to approximately 1000 rpm but I'll bring it up   gradually and we will watch the three voltage  waveforms the three-phase voltages here we go went too high on the voltage, so there  were about 40 volts you slow it down my adaptors a little out of balance  here that's doing the job all right   I'm going to take a screen capture right there okay so what we're looking at here the blue  colored trace is the V phase the red is the   U and the green is the W and you'll notice that  they're almost in a sine wave shape but not quite   I always heard that it was a sine wave but  it's not, it's a bumpy sine wave and that may have   to do with the configuration of the magnets in the  rotor these rotors in this latest Toyota transaxle   have a different style of permanent magnet in  them and they're using what I've been told is a   negative Halbach cylinder to use less rare earth  magnets and yet come up with a strong magnetic   field the same way but they're using five magnets  in sort of a triangle shape configuration rather   than two magnets in a V configuration but we in  this screen capture we are at 30 volts peak and   if we come down and look at our measurements here  we're at 60 volts peak-to-peak our frequency was   roughly 60 Hertz, 60.79 Hertz at  this screen capture and our true RMS voltage was   twenty point five volts so each one of these  colors of traces on the oscilloscope screen   represents the voltage induced in the coil of wire  related to that phase so there are three of these   there are three coils of wire in the stator  and each one of those coils of wire has its   own voltage induced on it now as long as there's  not an electrical load connected to these wires   these rotors MG1 and MG2 can free spin now we are  talking about regenerative braking here so as your   draw your hybrid vehicle or your electric vehicle  and let off on the throttle the vehicle goes into   a coast mode in other words we're not using power  from the battery to accelerate you down the hill   as you Coast downhill or as you just slow down  as you let off on the on the accelerator pedal   under those conditions, these rotors can just spin  freely now an electric vehicle is only going to   have one motor but most hybrid vehicles have  two motors now if you step on the brake pedal   at all or pull your transmission shifter into  the B position for braking then these motors no   longer free spin we use the voltages induced on  those three-phase windings that we just looked   at on the oscilloscope and we connect those to an  electrical load now typically that load would be   the high voltage battery in your vehicle we would  take the three-phase voltages convert them back to   DC and run current back into the battery to charge  it up but when you put a load on these motors when   you're decelerating it makes them harder to turn  so this is real easy to turn right now but if I   take a load and I've just got a resistor right  here this is a 10-ohm 10-watt resistor and I'm   going to connect it to the same two phases that  we hooked our ammeter to now we've already seen   from our oscilloscope that we approach 50 volts  when we bring this up to a higher speed and if   we have 50 volts and 10 ohms that's 5 amps of  current 5 amps of current times 50 volts gives   us 250 watts that this 10-watt resistor would  have to be dissipating, but of course, it can't   so it's going to get really hot and probably  burn up let's watch what happens here I want   you to listen to the speed of the drill motor  watch the speed of the rotor itself here   and let's watch the resistor here also we'll see  if we can let the smoke out now remember this is   only with 50 volts these motors being clear up to  maximum 17,000 rpm and 600 volts okay here we go all right I'm holding the drill motor at a steady   speed I'm going to connect  the wire now to the resistor motor slows down every time I put a load  on that stator by connecting this wire   up here the motor slows down now let me  leave it connected speed it up with some and as you can see this the smoke coming out  we were exceeding the wattage rating of the   resistor the wires are not hot but that resistor  is certainly hot so what we just saw there is what   happens with regenerative braking instead of  a drill motor turning the rotor inside of your   transmission on your electric or hybrid vehicle  the tires through the half shafts through the   final drive differential are turning the motor  as you decelerate it's mechanically turning the   motor and then the three-phase voltage output that  we've looked at on these three wires is then run   through a rectifier bridge converted to DC and  put back into the battery but we can through   the inverter assembly under the hood change  the resistance of the load that is connected   to the stators here so we can have a high  resistance to where it's almost an open circuit   and spins freely or we can really turn up the  charge rate by decreasing the resistance and   make it really hard to turn now why is it hard  to turn well because when we put a load on the   output of these wires we are causing current  to run through the three-phase coils of that   stator and that current remember as we saw with  the ammeter is an alternating current it's it's   going positive negative positive negative every  time the voltage increases and gets positive it   creates a magnetic field around the stator  itself and then when the voltage decreases   and goes negative the field collapses and that  pulsating magnetic field as it collapses as the   voltage decreases creates an opposite polarity  magnetic field to the rotational polarity of   the magnets in the rotor which means the stator  windings will create the equivalent of a North   Pole the is facing the north pole of the rotor  as it tries to rotate and if you've ever played   with magnets and you try to push to North pulls  together it doesn't like it so the higher the   current in the stator coils of wire the stronger  the repulsive magnetic field is to allowing the   rotor to spin inside the stator itself and so  it mechanically through an electromagnetic field   through like magnetic poles repelling each other  it mechanically slows the vehicle down without   using the hydraulic brakes very much at all or at  all in most cases the hydraulic brakes under light   braking aren't used until the lower vehicle speeds  the regenerative braking does the majority of the   stopping but of course, that depends if you're  doing a panic stop you'll get kind of a mix of   regenerative braking and hydraulic braking now on  the transmissions that shifters that have the B   position for braking that turns up the charge  rate it gives us a smaller resistance and of   course that generates a lot of heat which is why  the inverters are liquid-cooled have their own   radiator section too and coolant to keep them cool  but on hybrid vehicles with two electric motors on   most of them that I've read about when you pull  the transmission into the be positioned it uses   both electric motors for regenerative braking  rather than just the big mg to that drives   the vehicle and then when you're when you don't  have the transmission in the B position and you   let off on the accelerator pedal and just slow  down then it just uses the one electric motor   the drive traction motor, the MG2, or Motor A, Motor  One, whatever it is depending on where whose brand   of hybrid it is now there's one other thing  that can affect regenerative braking and it's   something called negative torque so normally when  you accelerate the DC voltage from the battery is   converted to AC voltage to drive these motors but  when we decelerate as you just saw we induce our   own voltages onto these windings but it's  opposite polarity voltage to the voltage that is   used to drive the vehicle so let's say we're  inducing 50 volts in opposite polarity when   we decelerate if we use the inverter and we also  try to accelerate at the same time with 50 volts   50 volts versus 50 volts there's their equal and  there would be no current and there would be no   regenerative braking so we can use the inverter to  create a voltage that opposes the induced voltages   from the stator and control how much voltage we  apply versus how much we don't apply which is the   same as having a variable resistance here so that  is how regenerative braking systems work according   to my understanding so the last thing I want to  show you is if we take the three-phase voltages   induced on MG1's stator and we connect them  to the three-phase windings of MG2 what will   happen so let's try that let me grab some  jumper wires here I'm going to connect the V phase   from MG1 to the V phase of MG2 and then the  same thing with you and the same thing with the W so when I turn MG1's rotor its magnets induce  three-phase voltages onto these three wires and   that simulates what the inverter assembly does  up underneath the hood on most hybrids those   three-phase AC voltages then are applied to our  traction motor MG2 and it drives the drives the   motor so let's watch what's the direction of  rotation and the speed as I turn MG1 watch MG2   some of those MG2 spins with MG1 in the same  direction and once again I'm simulating with MG1   what the inverter assembly does DC to AC driving  the AC motor so we're using a set of spinning   magnets to induce voltages on the 3 phase windings  of MG1 stator that create a three-phase voltage   signal just like the inverter does that then runs  current through the three-phase windings of MG2   which creates pulsating magnetic fields that  pull and attract the sets of magnets in the MG2   rotor and pull it around so we use the magnet  to induce voltages we're using a voltage to pull   a magnet which is what the inverter assembly does  now if we reverse the U and the W leads over here   that's the same as putting your transmission  in Reverse so to go in Reverse now notice I'm   still spinning in the same direction mg 1 but  now notice MG2 is spinning backward and we   do that just by reversing those two those two  phases so if I put them back to their original   phase notice now we're spinning in the same  direction so that's some pretty cool stuff to   see so what's cool about this to me is that this  is a 2017 Toyota Prius transaxle the P610 that   normally runs on up to six hundred volts at bare  minimum it runs on a little bit less than battery   voltage which is around 201 to 207 volts  depending on which   battery you get but if we hook a voltmeter up  here and look at the voltages induced on these   wires as I rotate this by hand notice we're only  getting 3 volts, 2 to 3 volts is all which   is incredible the efficiencies of these motors  is amazing for this to even work on two or three   volts so right here we are able to demonstrate  how a hybrid electric transaxle or an electric   transaxle with just one motor works without  endangering ourselves which is a pretty   cool thing so now I need to finish putting  this trans axle back together and get it   in the Prius and we'll have another video when  it's all in and working again so this has been   a demonstration of three different things related  to regenerative braking one, we saw the three-phase   voltage output on the oscilloscope and how  the electromagnetic induction on three   coils of wire creates a three-phase voltage  number two we saw what happened when we put   a load and electrical load on the output of the  the windings here it physically slowed down the   rotor speed here has driven with my electric  motor simulating the tires and wheels of the   vehicle driving the vehicle and number three we  saw what happened when we connect the output of   one motor to the input of the other to drive it, so  neat stuff! Thank you for watching have a good day

Channel: WeberAuto

Views: 160,289

Keywords: EV brakes, Cadillac, RAM Trucks, Pacifica Hybrid, Professor, GM, Bosch, CAT, CCAR, Weber State Automotive, Chrysler, Lincoln, Toyota, Chevrolet, Daimler, BMW, Negative Troque, NACAT, NATEF, ASE, Weber State University, Guy in wheelchair, Dodge, Buick, Picoscope, Nissan, Aisin, GMC, Honda, WSU, Tesla, Mercedes Benz, hybrid brakes, STEM, Denso, Ford, Regenerative Braking, John D. Kelly, Fluke Meter, EV Brake Systems, Electric Vehicle Brakes

Id: dC_Qvs_scT0

Length: 24min 51sec (1491 seconds)

Published: Sat Nov 18 2017