3 phase inverter -- actually, VFD

[somenick]

Hello all, I have come once again seeking your advice!

I want to design a 3 phase vfd for my own personal use (rather BIG pump, if it makes any difference) and I have two questions for you (well, one serious one and one miscellaneous). But, before all that, let me give you a quick run-down on what I want to achieve:

1) Single phase 230V (AC) input
2) Three phase (AC) output
3) Able to control a 2.5HP (rated) 3-phase motor (230/400V so I will *probably* connect it with star topology but more on that later)

I have figured out the control circuitry for the output half, have run some simulations and everything looks good at least on paper.
That being said, my concern shifted towards the input.. So, question:

1) Will I NEED some sort of PFC regulating/controlling circuitry? What I mean by need, is "will such a circuit wreak havoc in my electrical system at home"?
I am guessing that it wouldn't hurt, and I think it's a good chance for me to include such a stage mostly for learning purposes. If that is the case could you point me in the right direction for a chip or even better some application note regarding such a circuit? I have come across a very good one from fairchild semiconductors (I believe 42047) which got me up to speed regarding the basics, I highly recommend it!

I wouldn't mind if I could achieve pfc correction as well as some kind of inrush current limiting together, if that's possible..

And a bonus one:
2) For the power (read "current") I want to control (remember, 2.5HP rated motor) is there any point in using IGBTs instead of MOSFETs for the inverter? I don't really think so, just looking for some confirmation that I am on the right track not giving a second thought about IGBTs..

 

[FvM]

Industry standard VFD use inrush current limiting, usually a series resistor with bypassing contactor before the filter capacitor, but no PFC circuit. In some cases input inductors for reduction of input peak current.

These days you can buy rather cheap chinese VFD, I doubt that you'll easily beat it's retail price with a self-elaborated inverter. It may be still worth the learning effect.

 

[D.A.(Tony)Stewart]

What design specs have you made?

A 3phase VFD for a 2.5Hp motor uses about 2kW at rated load and 10-16kW starting at full acceleration.

You want to make this with smooth speed control with PID loop or smooth power ramp?

Either way you need a big 3phase variable speed sine wave inverter.

 

[somenick]

What design specs have you made?

A 3phase VFD for a 2.5Hp motor uses about 2kW at rated load and 10-16kW starting at full acceleration.

You want to make this with smooth speed control with PID loop or smooth power ramp?

Either way you need a big 3phase variable speed sine wave inverter.

I don't think I understand...

I *know* how I will control it, I *have* the "3 phase variable speed sine wave inverter" as you call it, I just wanted to know what I could do to improve the input stage of my circuit..

What do PID loops and smooth power ramps have to do with my question?

- - - updated - - -

Industry standard VFD use inrush current limiting, usually a series resistor with bypassing contactor before the filter capacitor, but no PFC circuit. In some cases input inductors for reduction of input peak current.

These days you can buy rather cheap chinese VFD, I doubt that you'll easily beat it's retail price with a self-elaborated inverter. It may be still worth the learning effect.

Well since it's for my own personal use I don't mind the cost.. It's more about the 'learning effect' rather than the cost-effectiveness of it!

I've seen such resistors (and the appropriate bypass circuit) before, in some high power smps..

I guess that's the cheapest way to do it, or at least it doesn't seem very efficient to me!

 

[chuckey]

You must use a delta connected motor, else you are into some sort of transformer, either input to 440, or inverter output 230 to 440 three phase. As said build one for your own interest but to save the cost try to control a 100W three phase motor and buy a ready made 2KW one.
Frank

 

[FvM]

You must use a delta connected motor

Yes. The said 230/400 V motor in 230V (delta) connection should work.

It's still a big step from a working simulation to a real hardware inverter. There are many edaboard threads about burnt MOSFETs and IGBTs in academic and hobby inverter projects. With respective bus capacitor energy they use to explode quite spectacularly, besides general electrical safety measures, it's suggested to wear ear protectors and googles when working with it. Good luck.

 

[D.A.(Tony)Stewart]

I don't think I understand...

I *know* how I will control it, I *have* the "3 phase variable speed sine wave inverter" as you call it, I just wanted to know what I could do to improve the input stage of my circuit..

Each power switch stage can offer 100:1 out:in range with 99% efficiency try to extend that , drops surge handling ability and often 10:1 range is used in big VFD's. for RdsOn/Rgs ratios, even though for static DC control a MOSFET or IGBT can offer huge gains, the switching speed and ICSS is the gating factor.

The 2.5HP is nominal 2kW and 8x this value with rapid change in speed. Thats why you need to design for 16kW transients or have a variable speed control that ramps speed to limit surge using current/speed feedback and a PID controller. To control stability or at least a proportional feedback to limit rate of change in f under load.

Choosing the Driver ESR to be <% and heat transfer Rja is critical for VFD controllers, which is when IGBT's are advantageous with high V to avoid surge failures and excess power loss of 16kW surge potential.

In a car normally < 20% of max available Power is needed to sustain an urban speed, the rest depends on the drivers foot. or 5x steady state load.

which is why I asked... What are your worst case requirements for power on the VFD inverter?

 

[masud58]

Dear dont think about IGBT burning, I was also afraid like you. recently i have make one with discrete component. now i am going to make pcb for it.

look at
https://youtu.be/zbm_83YTkO4

good luck