Quote:
Originally Posted by jyanof
The power components (mosfets/igbts) will need to be switched identically in sync.
A rough hypothetical: Imagine that the two 1000A controllers are at full output, there is 2000A flowing in the motor loop, and the mosfets are on. If one controller's set of mosfets switch off before the other set, there will still be 2000A flowing, but now it's all flowing through one controller. poof! (The diodes only conduct when the mosfets are off and allows voltage at the drain pin to rise above B+)
Not that it can't be done, but I don't think it's necessarily as simple as wiring them up in parallel.
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I think there could be another way to run 2 controllers in parallel. The 2000A flowing through one controller is actually just peak amps, the average amps through each controller is still 1000A in the above example. So if one of the controllers is seeing 2000 amps at any one point in time then the other is seeing 0 amps, and then they swap so the first one is seeing 0 amps and the second is seeing 2000 amps. If 2 appropriately sized inductors are added between the output of each controller and the motor (one inductor per controller) then the current will be smoothed out and keep the diodes happy in both controllers.
The controller and motor form a buck converter.
Buck converter - Wikipedia, the free encyclopedia Fig 1 on the Wikipedia entry shows the basic layout of a buck converter. The field coils in the motor are used as an inductor, but there is nothing stopping you from using an external inductor. In my last EV I used an Agni PM brushed DC motor, and in the instructions it stated that if you used the motor with a Curtis controller (the ones that whine at low speed) you need to add an external inductor. The reason for this was the whine is caused by the low switching speed (about 1.5 khz) of the controller and since the permanent magnet motor had no field coils it could only use the armature coils to complete the buck converter circuit. At higher frequencies the inductance of the armature was sufficient. This suggests that the required inductance wouldn't need to be very great for running parallel controllers at 16khz, but I wouldn't know where to start with the calculations.
Buck converter - Wikipedia, the free encyclopedia Look at the layout of the multi-phase synchronous buck converter, one inductor per phase. In this example they evenly space the phases, that is they intentionally don't keep them in phase.
So I still think it is possible to use 2 standard controllers to run one motor, provided you add an inductor between each controller and the motor. The advantages would be using 2 lower powered, proven controllers to give you more power, and at a later stage you could sell one or both of the controllers when you move onto the next project, or a bigger controller. Remember, this crazy idea of mine
was started by Jim and Darin's tractor project and their need of more amps. That got me thinking, they already have one good controller, shame they couldn't just build another one the same and connect it up.
Greg
P.S. Since getting my latest EV on the road in May, I have done over 2,000 miles with my rev 2C controller.
