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
