Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Control technique for a 3-phase inverter

Status
Not open for further replies.

festivus

Newbie level 5
Joined
May 29, 2011
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,355
Hi

Is there a way of performing a voltage control on a 3-phase voltage source inverter without making use of the dqo transformation? Should the voltage reference signals for such a case be sinusoidal or constant rms values? Any sort of help would be great! Thanks.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,967
Helped
14,147
Reputation
28,553
Reaction score
12,834
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,259
You should clarify the inverter topology and application. Is it a kind of UPS with output inductors or a motor inverter? Do you have additional output filters?

Generally I would expect a sinusoidal reference for a sine UPS. And most likely a voltage control loop manipulating the reference magnitude using a multiplier. If you are able to control the instantaneous output voltage directly, depends on PWM frequency and output filter dimensioning.
 

festivus

Newbie level 5
Joined
May 29, 2011
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,355
It is the standard 3-arm inverter topology with a LC filter at the output side. For now, I was simulating such a technique.. So theoretically, any PWM frequency should be possible.
The multiplier that you are talking about, for one particular multiplier value, it seems to control for a certain range of input voltages only. How do you decide this multiplier value actually? I decided more on a hit-and-trial basis only.

Thanks a lot for the help. :)
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,967
Helped
14,147
Reputation
28,553
Reaction score
12,834
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,259
You didn't yet tell about the exact application. I assumed an UPS inverter where you try to keep the output voltage constant independant of load variations. I also assume, that the filter group delay effectively doesn't allow a direct closed loop control of instantaneous output voltage. A feedforward control based on measured load current may be possible however. So you can only implement a slow control loop reacting on rms or average rectified output voltage.

Obviously the voltage manipulation range will be limited.
 

festivus

Newbie level 5
Joined
May 29, 2011
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,355
Yeah, it is to keep output voltage constant independent of load variations. Actually, I had earlier simulated a half bridge 1-phase voltage source inverter using a direct closed loop control of instantaneous output voltage. It wasn't controlling too well for very different load values and/or reference voltage values.. So using a feed forward control should improve that, is it?
What if the control loop is reacting on instantaneous voltage instead of rms.. assuming balanced loads and that the output frequency remains constant?
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,967
Helped
14,147
Reputation
28,553
Reaction score
12,834
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,259
What if the control loop is reacting on instantaneous voltage instead of rms.. assuming balanced loads and that the output frequency remains constant?
I would expect loop stability problems with reasonable gain values. The behaviour can be checked in a simulation using actual filter parameters.
 

festivus

Newbie level 5
Joined
May 29, 2011
Messages
10
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,355
All right. I'll try both ways. Thank you!
Just one more thing, can you also help out a little regarding how to decide the parameters of the output LC low pass filter? Say, I want a 220V rms at 50 Hz output in a 1-phase inverter..
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
47,967
Helped
14,147
Reputation
28,553
Reaction score
12,834
Trophy points
1,393
Location
Bochum, Germany
Activity points
278,259
The filter parameters will also depend on switching frequency, nominal output power and acceptable THD.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top