Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

Max V/Hz value for motor

+1
−0

I want to run a specific motor in the open loop. How to calculate the maximum ratio of V/f to run it?

Am I looking at Ld or Lq value for this?

Let's say these are the characteristics - haven't chosen it yet, but this one should serve the purpose because all important parameters are specified.

Motor specs

History
Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

0 comment threads

2 answers

You are accessing this answer with a direct link, so it's being shown above all other answers regardless of its score. You can return to the normal view.

+0
−0

Volt/Hz

176V / 60 ?

Offtopic The motor appears to quite beefy from those specs, is it a traction motor? If it is a traction motor for a motor vehicle, driving it closed (FOC) loop will be night and day difference in how it behaves.

History
Why does this post require moderator attention?
You might want to add some details to your flag.

1 comment thread

General comments (1 comment)
+1
−0

Here is a copy of your specs to make them easier to discuss here:

None of those specs really tell you what the V/Hz of the generator inside that motor is. We could take a reasonable guess at if we knew that all the "Rated …" specs were at the same operating point, but that's not clear. What the spec calls "Rated" could be interpreted as "maximum", and the maximum conditions probably don't all apply at the same time. Note that (296 A)(176 V) = 52 kW, which is way more than the 20 kW power rating.

The easiest way to get some idea of the generator V/Hz is to run a motor unloaded at a known and fixed voltage and measure it's speed. For example, let's say we find the following:

    100 V
    1000 RPM = 16.7 Hz
    10 A
    2 Ω internal resistance

We know that the voltage drop across the internal resistance is (10 A)(2 Ω) = 20 V. The voltage across the pure motor/generator part is therefore (100 V) - (20 V) = 80 V. If there was no load at all, not even friction, on the motor, then the generator factor would be (80 V)/(16.7 Hz) = 4.8 V/Hz. In real life, the motor is still producing some torque to overcome friction and air resistance, so there has to be some small effective voltage left across the pure motor to allow producing the torque. Put another way, the generator can't be opposing all 80 V else there would be nothing left to turn the motor. Dropping the 4.8 V/Hz figure by 10% or so to 4.3 V/Hz is a reasonable guess.

A better way to get the V/Hz figure is to measure it outright by mechanically spinning the shaft and measuring the open-circuit resulting voltage. However, this doesn't work with all types of motors. In such cases, you can spin the shaft, then apply a varying voltage until the current is nulled out. That would be the open-circuit internal generator voltage for that shaft speed.


Is it usual to refer to "mechanical Hz" or "electrical Hz" when talking about V/Hz ratios?

If there is a V/Hz spec without any other qualification, I would take that as mechanical shaft Hz. For most purposes of using the V/Hz parameter, you care about the internal generator voltage as a function of how fast the shaft is turning. How that is implemented inside, including how many magnetic cycles the motor goes thru per shaft rotation, is usually irrelevant to the usage.

History
Why does this post require moderator attention?
You might want to add some details to your flag.

1 comment thread

General comments (1 comment)

Sign up to answer this question »