IEEE Consultants' Network of Long Island

Two Pole DC Rail Voltage Decoupler - John Dunn, Consultant, Ambertec, P.E., P.C.

The following sketch is of a two-pole rail voltage decoupling circuit.  

 
The circuit works by doing a current division between capacitor C1 and the remainder of the circuit whose impedance is examined as follows:   

Turn-On of AC Voltage - John Dunn, Consultant, Ambertec, P.E., P.C.

You might think intuitively that by switching AC power into any load at the zero crossing of the line voltage's sine wave, that you would minimize input current surges, but that conception is not always true.

If your load involves a power transformer with which you will have a magnetization inductance, you will be better off to close the on-switch at the peak of the AC voltage waveform at its 90° (or 270°) time.

This point is illustrated in the following sketch which is derived using the recursive differential equations method.   

Microinverters Combine PV Modules - Dick LaRosa

An article in NASA Tech Briefs v 35, n 5, May 2011, pp 16-18 caught my attention. The title is "Microinverters are Launching a Solar Renewable Revolution" and it was written by James Washburn, a project manager at Siemens Industry, Inc., Alpharetta, GA. The last time I did anything with PV, people were combining the DC outputs of PV modules and feeding the result into huge inverters that incorporated maximum power point trackers. These had to accommodate an array of PV modules that might not have uniform access to sunlight. PV modules were connected in series, and these series strings were combined in parallel. If one PV junction was shaded, it produced no hole-electron pairs to carry the current of the other junctions in series with it, so each junction required by-passing with a forward-connected diode, and each module in a series string had to be by-passed with forward connected diodes. Then the partially-shaded series strings were combined in parallel, even though they might have different voltages, and the maximum power point tracker had to make the best compromise to match this mess up to the grid. Maybe I don't have this story right, in which case feel free to correct me.

The article shows a cute little Siemens module that connects to a single PV panel and inverts the output, synchronizes the phase with the AC line, adjusts to extract maximum power from the panel, and checks to see whether the AC grid is intact, so that we are not energizing a grid that some service man thinks is dead. I don't know how all this gets done, but the article implies that all these microinverters can be combined in parallel across the AC line without adverse interaction. I understand simpler things, like the large direct currents, DC arcing and grounding problems that these microinverters eliminate. That's it for now on this subject. I just wanted to call attention to some significant progress in PV and power electronics.

Dot Matrix Average of Dots - John Dunn, Consultant, Ambertec, P.E., P.C.

The frequency of usage of letters in a six-hundred word essay was used to estimate the average power dissipation of an alpha-numeric, 7 x 5 dot matrix display using LEDs.

Each letter has some particular number of dots turned on. The letter "A" for example, activates seventeen dots. Then from the essay, each letter was found to have some frequency of usage which again, for the commonly used letter "E", was 13.54%, but for the rarely used letter "Q", was only 0.03%.

The average usage in ordinary text turned out to be of 15.6 dots per character.