inverters

[@ndreaR]

Hello, everyone!
I am trying to understand the dynamics of operation behind an inverter, especially for the regulation of pumps, fans, etc. in plants. I wanted to propose this scheme (which I made without inspiring books and dispenses so it could also be a complete ahahah cable) of I as I guessed the operation of an inverter. I leave you to the commented scheme and obviously corrections, insights are extremely welcome! ! I posted in the mechanical design section because I don't want to treat the subject from a purely electronic/electronic point of view but mainly as an integration of a mechanical system

 

[DoctorBomber90]

I'm trying to answer you.
When you use/buy a three-phase asynchronous motor, you usually have a tot of features such as:

• nominal power to the electric motor shaft;
• power voltage (if connected to star and if connected to triangle);
• the protection index;
• the number of nominal turns;
• other features.

if you connect the engine to the power grid (domestic or industrial), he will always rotate to the number of laps present on the plate, because the power supply is always 50 hz.
the number of turns of a three-phase asynchronous motor is described by this formula.

[imath]n=\frac {60*f}p[/imath]​

you can change the number of turns or by acting on the number of polar pairs or on the frequency.
if the frequency of the network is always 50hz, the number of turns of the engine will never change.
then adopt an inverter that allows you to change the input frequency perceived by the engine itself, linearly and at your liking.
example:
without adjustment
f=50 hz, p=2 n--->1500 rpm;
with inventerf=40hz, p=2 n---->1200 rpm;n.b. you may change the number of couples but you can do it only in the design phase, or use the adjustment of dahlander (known as a double triangle link) that allows you to double the number of polar pairs perceived by the engine.
example:
without adjustment
f=50 hz, p=2 ---=1500 rpm
with adjustment
50 hz, p=4---->n=750 rpm

 

[TETRASTORE]

@ndrear: "I leave you to the commented scheme and obviously corrections, insights are extremely welcome!!"​

Yes, using the inverter to change the flow rate by lowering the engine turns and consequently those of the pump, achieve an energy saving that you would not use the valve.
a shoe example with your application you can see it in this thesis on page 23 (use of speed regulators) of the document.

 

[@ndreaR]

I'm trying to answer you.
When you use/buy a three-phase asynchronous motor, you usually have a tot of features such as:

• nominal power to the electric motor shaft;
• power voltage (if connected to star and if connected to triangle);
• the protection index;
• the number of nominal turns;
• other features.

if you connect the engine to the power grid (domestic or industrial), he will always rotate to the number of laps present on the plate, because the power supply is always 50 hz.
the number of turns of a three-phase asynchronous motor is described by this formula.

[imath]n=\frac {60*f}p[/imath]​

you can change the number of turns or by acting on the number of polar pairs or on the frequency.
if the frequency of the network is always 50hz, the number of turns of the engine will never change.
then adopt an inverter that allows you to change the input frequency perceived by the engine itself, linearly and at your liking.
example:
without adjustment
f=50 hz, p=2 n--->1500 rpm;
with inventerf=40hz, p=2 n---->1200 rpm;n.b. you may change the number of couples but you can do it only in the design phase, or use the adjustment of dahlander (known as a double triangle link) that allows you to double the number of polar pairs perceived by the engine.
example:
without adjustment
f=50 hz, p=2 ---=1500 rpm
with adjustment
50 hz, p=4---->n=750 rpm

Thank you, all very clear! I also went to deepen the dahlander regulation that I had never heard before! while for the three-angle star connection besides changing the power voltage allows me to change also the direction of rotation?

 

[TETRASTORE]

while for the three-angle star connection besides changing the power voltage allows me to change also the direction of rotation?

Yes, with appropriate connection.

 

[DoctorBomber90]

Thank you, all very clear! I also went to deepen the dahlander regulation that I had never heard before! while for the three-angle star connection besides changing the power voltage allows me to change also the direction of rotation?

Then. the star/triangle link can also change you Asorbit current from the engine.
Usually asynchronous engines are designed/set with the triangle connection and then, give you the possibility to change the connection.
use the triangle connection under normal working conditions, while using the star connection when you need to require greater use of the current.

example: you need to create a vehicle with a three-phase asynchronous motor but you realize that:

• the weight of the vehicle itself is excessive;
• you are in counterpendence;
• other reasons.

So, if you want to start making him move, you must have one couple in point higher and, consequently, a higher current.
At least I think I remember that. if someone could correct me would do me a big favor (so I take too).

 

[TETRASTORE]

use the triangle connection under normal working conditions, while using the star connection when you need to require greater use of the current.

so, if you want to start making him move, you must have one couple in point higher and, consequently, a higher current.

vice versa.
this type of connection is used (today less frequently) when there are major inertial masses in the starting phase for which it is necessary to predict a progressive in the start penalty abrupt start together with a high peak of current absorbed, for example: heavy crane beams, drive large conveyor belts with load start under hopper, etc.
the start is done with the star connection (230 v, low torque and 1/3 of the current absorption) then, after a time (milliseconds) predetermined by a timer, the switching takes place in the triangle (400 v, larger torque), when the device is already in motion for which the maximum torque is avoided however the peak of the highest absorbed current that would result in an oversized of the whole electrical system.qui further information.

 

[DoctorBomber90]

@terastore Thank you very much for the delucidation. In fact, while writing my post #6, I had some doubt that the absorbed current was higher in the star connection than in the triangle.