To have regen on a sep-ex/shunt motor, don't you have to be going faster (downshift for faster rpm's) than you were driving unless a fancy flyback modulation schem is employed?
----- Original Message ----- From: "Lee Hart" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Wednesday, October 02, 2002 4:01 PM Subject: Re: SepEx Motors and Controllers for EVs > Rod Hower wrote: > >> A sepex system designed for an application is cost competitive and > >> superior to a series system. How do you make this work for an EV > >> market? It's very difficult. You have to depend on the operator to > >> program in the appropriate parameters for their application. This > >> is assuming the motor is the same. If you have several different > >> sepex motors it gets even more complicated. So the bottom line is > >> series is a Wal Mart solution. > > I think we are confusing simplicity with motor type (series = simple, > sepex = complex, AC = very complex). It's not that clear-cut. A sepex > controller can be even simpler than a series motor controller. > > A series motor has a natural torque-speed curve that looks a lot like an > ICE. Also, they run if you just apply a fixed voltage to them; that's > why even a contactor controller is practical. That's why series motors > are so popular. > > A PM or shunt motor allows an equally simple controller; all it needs to > do is provide a DC voltage. You can vary the voltage with contactors or > a PWM controller to vary the speed. You'd leave the field of a shunt > motor at full voltage to simulate a PM motor. > > But the torque-speed curve of the PM or shunt motor is considerably > different than an ICE. It works, but will feel strange to the driver. > The throttle acts like a cruise control setting; it determines the speed > regardless of hills. You can add complexity to the controller to make it > behave in a more familiar fashion; but that's a choice, not a > requirement. Electric bikes (for example) don't bother. > > Also, the PM or shunt motor with fixed field works best at high rpm and > low torque; it is not as efficient at low speed and high torque (because > it requires low voltage and high current). You are more likely to need a > transmission with a PM or shunt motor. > > A sepex motor is just a shunt motor with independent control of the > field. You don't have to have two controllers (one for armature and one > for field), though that gives you the greatest versatility. For example, > I ran my old aircraft starter-generator (a sepex motor), with just a > 2-step contactor controller on the armature, and a rheostat in the > field. This is an extremely simple controller; even simpler than that > for a series motor -- yet it gave me stepless throttle control, and full > regen. > > Thus, there is no *need* to tailor the controller to the motor, but you > may *want* to do it as a matter of finesse. The motor makes the extra > control capability an option, but it is not mandatory to use it. > > Otmar wrote: > > I have developed a few sep-ex drive systems for low voltage > > industrial use. My programmer and I made one on Zilla platform > > running a sep-ex ADC 9" motor for his Honda Del Sol conversion. It > > works pretty well, but there are drawbacks. > > > > As discussed before, the motor design could use interpoles, which we > > don't have on ours. > > Lacking interpoles or compensating windings, you want to keep your field > stronger than your armature. This automatically happens with a PM or > shunt motor because they are always at full field. Arcing becomes a > problem only if you try to run high armature current *and* weaken the > field (low sepex field current) at the same time. > > > In order to do low speed regen in the controller, the high current > > section that drives the armature needs twice the silicon of a series > > drive. Then there is the increased complexity of the small H bridge > > field controller. > > Were you using the extra silicon in the armature controller to do a > boost converter? If you have sufficient field control, you can just > connect the armature to the battery thru a big diode (and that diode is > already there as part of the MOSFETs). This gives you regen at higher > speeds, but not down to zero speed. > > > Overall I decided that in the volumes we are doing, for the hobbyist > > market, a AC drive makes more sense. The incremental cost in silicon > > for AC drive is not that big anymore, and the benefits are numerous. > > I agree if you are making a "high feature" drive (one that totally > emulates an ICE, runs transmissionless, does regen to zero speed, etc). > -- > Lee A. Hart Ring the bells that still can ring > 814 8th Ave. N. Forget your perfect offering > Sartell, MN 56377 USA There is a crack in everything > leeahart_at_earthlink.net That's how the light gets in - Leonard Cohen >
