View Single Post
Old 12-03-2014, 04:27 PM   #1355 (permalink)
EcoModding Apprentice
Join Date: Nov 2012
Location: East Midlands
Posts: 180
Thanks: 13
Thanked 81 Times in 52 Posts
Originally Posted by thingstodo View Post

Yes, you can drive a motor (and a vehicle, for that matter) with V/Hz but it is not very efficient. The motor heats up. The FOC shifts the phase Voltage and Current (so I'm told) so that you are minimizing the core losses. With V/Hz you are doing a linear estimate on a non-linear load, and the extra current you pump into the motor is dumped as heat. We use V/Hz on pumps and fans. The load varies proportional to the cube of the speed. So 1/2 speed is about 1/8 load. Running in V/Hz is simple and allows us to replace motors without 'tuning' the controller to the new motor. But it wastes a bit of power.

I have no experience with an encoder on a V/Hz driven load. As I understand it, the controller does not have the option of changing the output voltage separate from the frequency when in V/Hz?
V/Hz is just a dumb term that is incorrectly used by manufactures to define a controller with no intelligence of its own. The technical name is scalar control and just derives that for a decrease in frequency one has to reduce the voltage as well to keep the same magnetic flux, which is also true for Field Oriented Control.

Scallar control can be modified to use in a vehicle. Closed loop control, space vector modulation and adaptive output voltage are used to achieve great efficiency.

One doesn't necessarily need Field Oriented Control to achieve good performance, although it makes development easier between different motor types.

Now if by V/Hz you want to say 'open loop scalar control', yes that's pretty much un-driveable on a road vehicle unless the driver has some practice. Its not something nice though.
  Reply With Quote
The Following 2 Users Say Thank You to cts_casemod For This Useful Post:
e*clipse (12-05-2014), thingstodo (12-03-2014)