For the die-hard techies among you, there's an interesting article on brushless DC motor control in the Oct. 2000 issue of Embedded Systems Programming (page 149). This should be available in most University libraries and some public libraries. The author mentions that he will discuss a PID controller for these motors next month, but conveniently, it the same issue on page 86 is a general article on PID controllers.<br><br>The Prius has two brushless DC motors.<br><br>Robert Snyder

&gt; The Prius has two brushless DC motors.<br><br>Nope, they're three-phase AC synchronous permanent magnet motor/generators. Full details are in the "New Car Features" book.<br><br>All the same, there's a lot of similarity, in that the computer continuously senses the rotor position, and connects each winding to one or the other battery terminal through a bridge of IGBT transistors accordingly.<br><br>Thanks for the reference. Prius must be the most advanced system of embedded systems ever made available to consumers.<br><br> --Mike (writing from the embedded systems division of Synopsys)

Hi Mike,<br>Now I'm getting really confused. I originally thought the Prius had AC motors. Then I was told on one of these groups that they're really brushless DC motors. I found an article on brushless DC motor control and the circuit sure looks the same as that show in the New Car Features book. Now you say they're really three-phase AC synchronous permanent magnet motor/generators. (Actually the book says "Both the MG1 and the MG2 are compact, lightweight, and highly efficient alternating current permanent magnet synchronous type." But there's no accounting for English.)<br><br>The term "brushless DC motor" seemed strange to me since effectively AC goes into the motor, but the posters here and the article use this term.<br><br>My untrained eye can detect no physical difference in the motors (in both cases the drawings are "simplified") or in the primary components of the power circuitry (euphemistically called inverter circuitry). The control circuitry is all "black box", so I can't look for differences there.<br><br>So could you please set the record straight for me? What is the difference? Also, what is "synchronous" in the Prius MGs?<br><br>Robert (confused) Snyder

&gt; reconfigurable_logic said:<br>&gt; &gt; The Prius has two brushless DC motors.<br>&gt; Nope, they're three-phase AC synchronous <br>&gt; permanent magnet motor/generators. <br>Actually - with the feedback - they're more like honkin big servo-motors!<br>As far as advanced goes: You betcha! The more I mull over the THS system as a whole, the more in awe (Aw...) I am over the total concept.<br>My only engineering observation so far: (no - not cruise...) is the apparent fact that the CVT oil pump is driven only by the ICE. I'd feel MUCH better if there was (also) a CVT oil pump driven directly off the drivetrain (silent chain, reduction gears...)<br>Bill Powell

Hi Robert,<br><br>I'm certainly no traction motor engineer, but it looks like we're both right! They seem to use both terms for the same hardware. Toyota calls it AC three-phase, and the windings are tied together internally as in a three-phase motor.<br><br>But I did a Google search for 'brushless DC motor' and came up with this site: <a href=http://www.tacom.army.mil/tardec/electric_drive/motors/index.htm target=new>http://www.tacom.army.mil/tardec/electric_drive/motors/index.htm</a> which shows hybrid vehicle drive systems with 'brushless DC motors' and inverters that match the Prius motor and inverter architecture exactly. Permanent magnet rotor, three stator windings, three motor terminals connected to a six IGBT bridge across the battery. So you say tomato, I say AC three-phase...<br><br>My (sketchy) understanding of synchronous motors is that the rotor rotation is locked to the frequency of the stator currents. Like the motor in an old electric clock is locked to 60 Hz AC. Induction motors, which are the typical AC motor used in appliances and industrially, are non-synchronous. If I'm not mistaken, the difference between the rotor speed and that of the rotating magnetic field induces current in the rotor winding to make it magnetic. Our Prius motors have permanent magnets in their rotors instead.<br><br>Those US Army hybrid systems are pretty heavy-duty, by the way. Slide 8 shows a hybrid HMMWV, known to us civilians as a Hummer, that would satisfy any SUV driver's greatest fantasy. And slide 10 is an ecological answer to road rage ;-&gt;.<br><br>I have posted some of the diagrams and text about the motors and inverter over on egroups. I'll post those files over here tonight.<br><br> --Mike

Wow, now those are MOTORS! And huge power transistors also. Too bad they're only prototypes now.<br><br>I was surprized how jaggie the winding current waveforms were. I guess the Pulse Width Modulation frequency is only a few times faster than the 7092 RPM top speed of the motor.<br><br>Thanks for the cool link.<br><br>Robert Snyder

They are Brushless DC motors which has permanent magnets in them. The "AC" here refers to the way at which you drive the motor.<br><br>There are two standard ways of driving motors: drive the coils with trapezoidal waveform or sinusoidal waveform. <br><br>Trapezoidal waveform is very inefficient because there will be a lot of energy loss at the edges of the trapezoid, loss in the form of heat and noise. <br><br>The better way to drive Brushless DC motor is actually with Sinusoidal waveform where there are only smooth transitions and no real "edges" to create problem. When a Brushless DC motor is driven with Sinusoidal waveforms, it is said to be driven with "AC" signal (Alternate Current for AC). Some people would refer to it as an AC motor, but it is really a DC motor driven with AC signal.<br><br>Cheers.

&gt; When a Brushless DC motor is driven with Sinusoidal<br>&gt; waveforms, it is said to be driven with "AC" signal (Alternate Current for<br>&gt; AC). Some people would refer to it as an AC motor, but it is really a DC<br>&gt; motor driven with AC signal.<br><br>Neat, thanks for clarifying that.<br><br>It's clear that the inverter bridge just has on/off capabilities at any instant of time. Perhaps high speed pulses are varied in width or number and smoothed out by the stator winding inductance, to get an effectively sinusoidal waveform?<br><br> --Mike

&lt;It's clear that the inverter bridge just has on/off capabilities at any instant of time. Perhaps high speed pulses are varied in width or number and smoothed out by the stator winding inductance, to get an effectively sinusoidal waveform?&gt;<br><br>Yes. The inverters will get the PWM (pulse width modu.) signals, which are square waves with varying frequencies. The inductances in the motor will "smooth" them out. The technical term here is "inductance will integrate square wave voltages and result in a sinusoidal current."<br><br>Therefore, you can create different waveforms, ie. trapezoidal or sinusoidal, simply by changing the PWM frequencies!<br><br>There is a web-site at: www.analog.com/motorcontrol<br>that has details and tutorials into how to do motor controls, even on different types of motors. FYI, there are 3 main types: AC Induction motor (typically in your washer & dryers), BLDC (brushless DC motors), and SR (switched reluctance).<br><br>Cheers.