# Small signal analysis for 3-phase inverter

+1 vote
1,956 views
I built a simulation of a three-phase inverter with an arbitrary RLC load. I am controlling the inverter as a voltage source (which means I control the output filter capacitor voltage). I would like to use the small signal analysis blocks in PLECS to plot some bode plot. Can I do that? Since the demo in the software and videos online only talk about DC/DC converters. Thanks!
asked Feb 7, 2018
Hell Yunpeng,

Did you have any luck plotting a bode plot of the AC system with PLECS? I currently have a transfer function for my 3phase system but I wanted to validate my MATLAB bode plot with one from PLECS. However, the small-signal tool from PLECS hasn't been able to plot anything for me yet.

## 3 Answers

+1 vote
Hi yunpeng,

I'm not experienced in inverters, but would suggest to do small signal analysis at different DC operating points. Can you give more information about the control system?

Cheers

Falk
answered Feb 15, 2018 by (253 points)
+3 votes

You will have a hard-time solving this problem by means of small signal analysis.

Instead of working with Bode plots, my recommendation would be to break down the problem into two nested control loops, and take an analytical approach to designing the controllers.

1. Inner (three-phase) current loop
2. Outer voltage loop
For this to work, you need sufficient output capacitance so that output voltage variations are slow with regards to the current regulation, and can be rejected by the current controller, possibly with a little "feedforward" assistance.

There is plenty of technical literature on how to design three-phase current controllers. One of my favorite papers is "Current and Flux Regulation in Field-Weakening Operation", by Fernando Briz, Alberto Diez, Michael W. Degner, Robert D. Lorenz.

Once you have a solid inner current loop, the outer voltage regulation becomes quite trivial.

Take a look at the PLECS "Boosted Motor Drive" demo model, which contains an example of a three-phase current controller as well as a DC voltage regulator. Not precisely what you are trying to do, but very similar building-blocks in terms of the controls.

answered Feb 28, 2018 by (68 points)
0 votes

Hi  yunpeng  generally for inverter, they are normally buck converter and you are not using contolling theory like DCDC but more like LC filter damping. I think all the answer you need are in this cookbook:

https://www.amazon.com/Digital-Control-Electronics-Synthesis-Lectures/dp/1627057536

answered Jul 5, 2019 by (106 points)