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VFD Project

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v1.5

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hello everyone.
This is my first post in here and before starting, I embrace everyone with love:).

My project is VFD drive.
General-Single-phase-VSI-VFD.png
The VFD must work on phase voltage and must controll with Spwm. Control signal circuit is working well and the h bridge also good. But the problem is , im not sure to use power supply to my project.Motor of the output is 500VA single phase induction motor. It is working with 230V 50hz nominal voltage and frequency. Project must be small size of component so i desided to not use a transformer for this project. Although high current requirement , as you know the size of the transformer getting much more problem. Because of those issues , im not prefering transformer. Also the risk of the transformerless power supplies known in the past. Is there any possible circuit agains of transformerless scheme?
apn-ntc-limiter_01.png
 

MaxHeadRoom78

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Depending on the application, you may have a problem with controlling a 1ph induction motor with VFD.
The reason also you do not see many, if at all, is that the motor tends to drop out of run with load and/or low rpm.
And another reason you see DIY CNC'ers going with a 3 ph VFD & motor, using 1ph supply.
Any reason you are not using the more common Triac? Good for shaded pole, or PSC motors up to around 1/2hp
Max.
 

dr pepper

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Smaller <1hp industrial motors are usually wound in 'star' mode, you can usually reconnect such a motor in its terminal box to 'delta' mode this means you can get away with running ti from 240v.
So you can then have a drive that is powered from single phase which is capable of running a 3 phase motor.
Starting torque, speed control & many other aspects of an induction motor are far superior with 3 phase.
As an industrial electrician I've only seen a single pahse motor controlled by a drive once, and that didnt work too well.
 

v1.5

Member
Thanks for your comments.
First of all i was thinking of single phase vfd at first and then combine with other two phases. As you mentioned
here;
Depending on the application, you may have a problem with controlling a 1ph induction motor with VFD.
The reason also you do not see many, if at all, is that the motor tends to drop out of run with load and/or low rpm.
and here;
So you can then have a drive that is powered from single phase which is capable of running a 3 phase motor.
Starting torque, speed control & many other aspects of an induction motor are far superior with 3 phase.
As an industrial electrician I've only seen a single pahse motor controlled by a drive once, and that didnt work too well.
i didnt know those issues on motor control. So my new goal is to make a three phase vfd at first.
Smaller <1hp industrial motors are usually wound in 'star' mode, you can usually reconnect such a motor in its terminal box to 'delta' mode this means you can get away with running ti from 240v.
With delta connection the phase voltage must usually divided to sqrt(3). At this point i need a sophisticated power transformer , as a student , its hard to find out.Or i can do a dimmer circuit on three phase side to adjust the main voltage with SCRs and aslo rectify. Supply voltage issue is a real problem in my case and i havent figure it out yet.!Need some help of you guys ?
If you guys have any documents on vfd or inverter projects , i ll gladly happy to see them.
Thanks.Hans.
 
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rjenkinsgb

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If you search for three phase vfd / drive / inverter etc. with "dspic" you will find masses of info.
Microchip also do some motor control development kits.

Examples:






Edit
For info, you can get some quite cheap three phase power modules, with the six power devices appropriately connected internally - eg.


You still need the same drive circuits, but there is a lot less high voltage wiring involved and everything is already insulated for heatsinking.


Note that for the power input side, a "soft start" circuit is normal. A power resistor is connected between the input bridge rec and the power capacitors & the controller monitors the cap voltage. Once they are within the allowed voltage range and the voltage stops increasing, a relay links out the resistor so full power is available and the power output control can start.

Some power modules have the input bridge included as well.
 
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dr pepper

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Dimmer circuit ojnly regulate average power, to control an induction motor you need to change frequency.
 

shortbus=

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Although high current requirement , as you know the size of the transformer getting much more problem. Because of those issues , im not prefering transformer.

Why would you need a big transformer? If you have the correct voltage input your only transformer will be a small one to power the solid state components. This link gives some information on a chip and the circuit that is used in a single phase VFD, Fig. 6.3 in the link.
https://www.lz2gl.com › data › eg8010_datasheet_en
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Why would you need a big transformer?

Exactly.

A three-phase version is just like your first schematic in your first post in principle, but with a third half-bridge added for the third output!
(And a three phase input if it's to run on a three phase supply).

No commercial drive I have ever seen uses a transformer for the main power through the unit. They may have chokes for interference suppression etc., but not power transformers.

The only reason for a high-power transformer is for safety isolation while prototyping - but the internal voltages are still lethal if you touch across the caps or output, so extreme caution is still required, transformer or not...
 
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