Motor/Generator and Controller selection
Motor/Generator and Controller selection
(OP)
Hi all,
This is really not an area I am confident or perhaps even competent in so bear with me here.
I need to set up a test rig where I will have to monitor and control the power entering and leaving a drive train with three inputs/outputs (two degrees of freedom). The drive train will be controlled by setting two control inputs one of which will always be a power input via a motor the other one may be a second power input or a controlled power output.
As far as I can tell this will require 3 motors/generators each of which has to be able to operate in 3 different 'modes':
1. Power input / Control input mode: acting as a motor I need to be able to set the input power through either torque but more likely speed control.
2. Power output / Control Output mode: Acting as a generator I basically just need the motor/generator to act as a power sink for the system.
3. Power output / Control input mode: Like above except this time I need to be able to control the power being draw from the generator.
So my questions are as follows.
What sort of motors/generators would be suitable for this work? From what I've read a simple DC brushed motor should be able to fulfill both the motor and generator requirements and would be the easiest and cheapest option, is this correct?
And secondly what sort of controllers would be required? I think I have a handle on the 'modes' 1 and 2 with 'mode' 1 being controlled by a simple DC motor speed controller and 'mode' 2 being as simple as disconnecting the motor/generator from a power source and/or attaching a load. It's the third 'mode' that I really have no idea on i.e. how can I have two generators both attached to the drive train and control the amount of power being drawn by one of them?
Thanks in advance for any help, really sorry about the long post guys.
This is really not an area I am confident or perhaps even competent in so bear with me here.
I need to set up a test rig where I will have to monitor and control the power entering and leaving a drive train with three inputs/outputs (two degrees of freedom). The drive train will be controlled by setting two control inputs one of which will always be a power input via a motor the other one may be a second power input or a controlled power output.
As far as I can tell this will require 3 motors/generators each of which has to be able to operate in 3 different 'modes':
1. Power input / Control input mode: acting as a motor I need to be able to set the input power through either torque but more likely speed control.
2. Power output / Control Output mode: Acting as a generator I basically just need the motor/generator to act as a power sink for the system.
3. Power output / Control input mode: Like above except this time I need to be able to control the power being draw from the generator.
So my questions are as follows.
What sort of motors/generators would be suitable for this work? From what I've read a simple DC brushed motor should be able to fulfill both the motor and generator requirements and would be the easiest and cheapest option, is this correct?
And secondly what sort of controllers would be required? I think I have a handle on the 'modes' 1 and 2 with 'mode' 1 being controlled by a simple DC motor speed controller and 'mode' 2 being as simple as disconnecting the motor/generator from a power source and/or attaching a load. It's the third 'mode' that I really have no idea on i.e. how can I have two generators both attached to the drive train and control the amount of power being drawn by one of them?
Thanks in advance for any help, really sorry about the long post guys.





RE: Motor/Generator and Controller selection
My experience is from Volvo and Scania and there you either have motor test rigs with one AC or DC machine that (usually) brakes, but also can drive the engine or you have a transmission rig with three AC or DC motors where you can use any combination of driving/braking on any of the three electrical machines.
Controlling power flow into or out from an electrical machine is fully symmetrical and you can use speed or torque as the control variable. Often you use both alternatively with one being variable and the other acting as a limit (speed or torque limit). I am not able to see where the problem is.
Gunnar Englund
www.gke.org
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RE: Motor/Generator and Controller selection
Sounds like an ordinary dyno would be perfect, only thing is my application is on a much smaller scale than a motor vehicle, the entire test rig needs to be about 1m x 1m and as cheap as possible.
Could i use a small voltage regulator to control the output?
RE: Motor/Generator and Controller selection
There are several basic things that you need to know about if you want to build your own.
The first is what different motors/generators can do and what they cannot do. The Quadrant concept is one thing. It describes if a motor can run in two directions or not and if it can brake or not. For complete universality, you will need four quadrant drives on all three axles.
Then you need to understand fully the concept of the inner torque control loop and the outer speed control loop.
The final build will look entirely different depending on what your energy costs and precision needs are.It also depends on how often and for how long time you need to run the rig. And, probably most important, what torque and speed range you need.
The simplest controller would be a DC power supply with current limit (for torque setting). That would be a one quadrant drive. Add a reversing switch for the simplest two quadrant version. For braking, you either need regeneration or a braking resistor to burn joules. For small rigs, that can be a cheap and acceptable solution, but for tens of kilowatts and up it is not. There, you probably need a DC motor with a four quadrant thyristor controller. Or a VFD with regeneration. It all depends and the possible combinations are many. What are your needs in kW?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Motor/Generator and Controller selection
I think I just learned more in the last 10 minutes than i did all of yesterday.
My plan right now is to run the system at around 1-3kW. I think I'll try to find a commercially available 4 quadrant controller just because I'm really not confident with trying to build my own.
Thanks again I really appreciate it.
RE: Motor/Generator and Controller selection
That opens an interesting possibility to use standard VFDs without regeneration for all three motors. In that power range, you cannot buy anything simpler, cheaper or more robust than standard VFDs with standard induction motors.
The trick is to connect all DC links so that energy delivered by a braking motor is consumed by the other motors, that then are driving. Add a braking resistor and a chopper if you need to decelerate faster than coasting.
If you select VFDs with the right interface, you can easily do most of the measurements (speed, torque, power) using the VFDs themselves. Analogue interface is simple but a bus system will give you a lot more flexibility and possibilities to automate your tests.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...