who can tell me,how make soft-starting .

[zhouhongwei]

who can tell me,how make soft-starting about 3-phase ac motor in 8051?
how trigger the thyrister ,it make 3-phase ac motor soft-start.
how program in 8051 or other Microcontrollers.
please tell me,think you !! think you!!

 

[mrcube_ns]

It's not simple.

Hardware:
- you have to make bridge with 6 diodes, so you get DC voltage about 500V
- second you have to add capacitor to filtrate that voltage (in 3 phase case you dont have to add cap.)
- have to build inverter, 6 IGBT(or MOSFET or bipolar transistor)

Software:
- in code memory make look up table of sinus signal (more elements of table more nice sinus you get)
- in software you have to make U/f=const.
- you have to make 3 pointers on sinus table in 120 degrees of sinus. Use timer to switch between two samples of sinus for same phase. With diferent amouts of time between two samples you'll get diferent frequences.


There are lot of soft/hard work.

Mr.Cube

 

[zhouhongwei]

thank your replay!could you give some article.

thank your replay!could you give some article.

 

[zhouhongwei]

who can help me! thank you!!

who can help me! thank you!!

 

[bobcat1]

Hi

I have done it once long time ago

You should program a power ramp e.g the power to the motor should grow slowly

DP(motor power)/Dt must be slow depend on how soft do you need the start

If you are using PWM to control motor speed you should start with a low value and incress it with time - creating a RAMP

best


bobi

 

[unimx]

For a three phase sofstarter you need the following:
Control section:
I have one sample program for an 8051 derivative so please pm me.


Power section:

1.- For each phase you need two SCR (or thyristor as you say) connected back to back so that they function as a controlled switch for the AC current/voltage.

2.- Depending on the main voltage, you need to protect the SCR using and Snubber Network, basically composed by an R-C arrangement along a varistor, please check the powerex or IR web pages for example.

3.- For firing the SCR and also for isolating the power section from the control one you have to choose Optoisolators or Pulse transformers along their associated resistors, diodes and capacitors.

I have a basic arrangement available, so anyone interested please pm.

4.- It is suggested to install one fast acting fuse (for semiconductor use) at each phase input.