Monday, May 23, 2016

Three-level three-phase grid connected inverter in current control mode

The next post is about a three-level three-phase inverter connected to a three-phase grid and in current control mode.

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Saturday, May 7, 2016

Single-phase three-level inverter

Posted the case of a single-phase three-level inverter in open loop.

Next will be three-phase three-level inverter in closed loop.

Tuesday, May 3, 2016

Releasing version 1.2.1

I have been out of action for the past two months. Traveling, immigration and then taxes. Now free from all of these I am back to my circuit simulator. I hope I can devote more time to this project as things are more or less working and I need to keep working on cases. Unfortunately it gets hard when I am neck deep in paperwork.

Anyway, here is the next version 1.2.1.

The only change is that I realized as the number of meters and plotted variables increases, it gets tough to count the variable column position in the output data file. So this version prints out the meter or plotted variable and the column number so that you could enter the column number directly into Gnuplot.

I am working on a three level three phase inverter case next. Hope that will be done in a week.

Monday, February 22, 2016

Releasing version 1.2.0

Finally got around to releasing the next version of the simulator. Only a minor change in the nodal analysis.

Will post the next case study of two inverters connected together - one working in voltage control mode and the other in current control mode.

Tuesday, February 16, 2016

Solver issues

After the last test case of an inverter with LC filter in voltage control mode, I have tried to simulate two inverters connected together - one in voltage control mode and the other in current control mode. To further complicate the system, the dc bus of the inverter in current control mode is formed by a three phase diode rectifier fed by a three phase ac source.

There have been strange glitches in the waveform that I could get rid off when I simulated the system at 100 nanoseconds. But then I felt that was way too demanding of such a system which should need 1 or 2 microseconds or maybe even more since both converters are switching at 5 kHz.

My first suspect was of the loop currents and felt that since the loops were being chosen randomly, they need to be rearranged to ensure that the d/dt of the ODEs were minimal. Several iterations and trials later, no change.

So the next suspect was the nodal analysis. Turns out this was the culprit. The main problem with nodal analysis is that impedances are vastly different. A diode when turned on has a resistance of 0.01 ohm while another diode that is off has a resistance of 100 megaohm. So the admittance matrix has elements that have a factor of 1e+10. This makes it prone to error.

One of the reasons for error turns out to be the nodal analysis that occurs after determining freewheeling operation. Apparently this one is particularly the case when an inductor is treated as a resistance when it has negligible current. By removing the check, the problem disappeared. That is an inductor is always treated as a current source in the nodal analysis immediately following freewheeling action.

The simulation is finally working with almost negligible glitches. Need to investigate the above effect a little more before I release the next version and post the next case. Hopefully by the end of the week.

Progress is going slow. But the good news is I have now moved on to multi-inverter systems. Hopefully, the next will be microgrids and renewable energy integration.

Sunday, January 24, 2016

Three phase inverter with LC filter

I posted the next test case of an inverter with LC filter on my website:

Also, I started a Facebook page for the project:

Wednesday, January 20, 2016

Releasing version 1.1.0

Been a long time. Have been fighting with a lot of bug fixes and most importantly figured out a way to make the simulator run faster. It is now approximately 6 times faster.

The download link is from my website:

I'll post the next text case which will be a three phase inverter with LC filter tomorrow.