User talk:Vitaltrust

Hello visitor!

This is Vitaltrust's talk page. Use it for friendly communication purposes only!

Just let me know what you think!

= Active Topics =

I have no active topics at the moment.

If you would like to start a conversation with me, just edit this page and write what you like beyond this point. It is important to maintain the structure of this page, so please don't modify it and use my /Sandbox if you want to do experiments.

Some updates at Talk:TRIAC and User talk:Vitaltrust/TRIAC
I need to find a good reference to be able to put the info in the main space, but does that explanation of Talk:TRIAC help you? 71.41.210.146 (talk) 23:11, 15 April 2012 (UTC)
 * Sorry for the delay. Talk:TRIAC updated, and you're right. 71.41.210.146 (talk) 23:35, 25 April 2012 (UTC)
 * More updates, and I disagree with most of what you wrote this time. But we are actually converging; it's mostly about the formal definition of the boundary between the active and saturated regions of transistor operation, which the BJT article agrees are not clearly defined at biases of less than a volt.  71.41.210.146 (talk) 00:43, 7 May 2012 (UTC)

71.41.210.146 (talk) 04:59, 12 May 2012 (UTC)

Understanding inverters
Hi! I'm trying to better understand the basic operation of modern PV-related inverters. I have only a basic understanding of power electronics, so perhaps you might be able to help me out a bit?

I'm particularly interested in the difference between transformer and transformerless designs. I have read the descriptions of these technologies on the power supply side, but it is not clear whether or not the concepts are the same here. There's also a third term that I see, resonant converter, and I'm trying to understand if that's the same as transformerless or another concept.

I saw your work in a few articles in this area, so perhaps you can get me started in the right direction? Or perhaps point me to some expertise?

Thanks!

Maury Markowitz (talk) 16:17, 5 April 2012 (UTC)


 * Hi! Unfortunately, I don't work in the PV sector. I do have attended seminars and workshops also about PV-related topics, so I have a basic knowledge about PV inverters. I work on motor control systems, where inverter are used too, but are simpler because if you have to put energy into the power grid, like in the PV case, you have to generate a voltage with a low total harmonic distortion.


 * In general, an inverter is a circuit which can convert a continous voltage to a time-varing voltage, for example a sinusoidal one. This is accomplished by connecting the output of the circuit to either Vcc or -Vcc in different moments through solid-state switches and filtering out the high-frequency harmonic components. There are a number of different kinds of solid state switches: generally power MOSFETs are the fastest, but depending of the magnitude of the currents or voltages there are other choices: IGBTs, SCRs, GTOs, etc. The filtering process can be obtained by putting a suitable low-pass filter in the output stage, but with 'inductive' loads where current is more important than voltage, like in motor control systems, it is even not necessary.


 * As far as I know, the inverters in the PV sector are generally of a particular kind called multilevel. In a multilevel inverter the output is obtained starting from a certain number of DC power supplies, more than the two power supplies one finds in a standard inverter. This has a variety of advantages: first of all, the AC voltage has a lower high-frequency harmonic power in comparison with a same-rating two-level (standard) inverter and this means smaller and then cheaper output filters; second, the voltage rating of the solid-state switches is lower, but this is offset by the larger number of switches you have in the multilevel case.


 * Generally, the difference between transformerless and transformer design is that in the first case you don't have insulation between the input and the output, i.e. input and output have a common ground reference. On the contrary, in a transformer design the input is able to "float" with respect to the output: this is better from a safety perspective since you can touch live parts on the input stage without get electrocuted, but I think that a PV system is generally transformerless since those kinds of appliances are to be handled by installators and properly instructed technicians only, so safety requirements are looser than for home appliances.


 * Resonant converters are a class of DC/DC converters where the turn-off or turn-on of the solid-state switch happens when current or voltage across its terminals is near zero. This is achieved using resonance between the inductor (or the transformer primary side or parasitic inductance in a transformer design) and a capacitor or parasitic capacitance. This kind of converters are often used, because they are more efficient (less commutation loss) and, above all, are less disturbing from an EMI perspective. If you want to get an insight on this field, search for Zero-Current Switch (ZCS) or Zero-Voltage Switch (ZVS) on the internet.


 * I have never heard about resonant inverters, but it's possible that in the PV sector this principle is used to have switches commutated just when either their current is very low or so is their voltage.


 * I hope I gave you some tips to start looking for. As I told you, unfortunately I don't work in this sector. — Vitaltrust (talk) 22:07, 10 April 2012 (UTC)

I'm not sure the PV/non-PV difference is all that great. As it was explained to me, the difference is primarily that there is a DC-to-DC converter to convert the varying output from the panels into a fixed input for the inverter. There's also a technique known as MPPT that you have to apply, but that can be done in that DC-to-DC stage.

So do you think you can expand on the transformer less design a little? The diagrams of transformer-based designs seem simple enough - you send the DC signal into one side of the transformer and switch it on and off really rapidly, producing an output on the other side of the transformer that looks something vaguely AC-ish. Then you reverse the polarity and do the same for the negative side of the wave.

I suspect the same is basically true in the transformer-less case, but without changing the voltage (if they do) and using more inductors? The big claimed advantage of these designs is less copper, and to a smaller extent "less magnetics", so I know they don't simply replace the transformer with an equivalent LC circuit, but beyond that I'm a bit lost.

Maury Markowitz (talk) 12:47, 21 April 2012 (UTC)


 * MPPT stands for Maximum Power Point Tracking and is a technique which tries to get the maximum possible output power from PV cells, as the name indicates. To understand how it works, you have to start from the I-V curve of a typical PV cell, which is not something constant but varies with junction temperature and incoming sunlight. By the way, I have seen that the Wikipedia article about MPPT seems pretty good.




 * The output power is maximized where the product $$I \cdot V $$ is maximum, so the DC/DC stage, which is usually a boost converter, works imposing to the PV cell the current labeled as I max in the figure above. This means that the output of the boost stage is not voltage-stabilized, since it is not feasible to stabilize both output voltage and input current in a boost DC/DC converter, as far as I know. Indeed, I have read a datasheet of a boost MPPT controller manufactured by STMicroelectronics, the SPV1020 where there is no output voltage feedback, but just an output overvoltage protection which stops the converter at 40V, so I guess there is another DC/DC stage before the DC/AC stage, which stabilizes the input voltage of the output inverter.


 * Therefore, it is important to understand that:
 * a PV system employs a chain of DC/DC converters to stabilize the DC input voltage of the final inverter to something above $$V_{ac} \sqrt 2$$;
 * the output power of the whole system is monitored and stabilized at the sum of the maximum power points of the solar panels it is made of.


 * ...So do you think you can expand on the transformer less design a little?...
 * As I told you, I don't work in this sector, so it is better if you find someone directly involved in this topic if you want to be sure that what will be written is accurate and close to reality. I suggest you to try to involve those users who contribute to the articles about, for example, grid-tie inverters or MPPT or something else in that field: you will find them in the talk page or in the history of those articles. However, if you tell me what is the Wikipedia article to improve, I will take a look and see if I can do something.


 * ...The diagrams of transformer-based designs seem simple enough...
 * Can you post them here?


 * —Vitaltrust (talk) 18:20, 22 April 2012 (UTC)

Feel free to start a new issue here

= Obsolete Topics =

Inverter
Hi Cowie. I've added a brief explanation of the working principles of the two circuits you drew and placed into the article "Inverter". Take a look at it on page http://en.wikipedia.org/wiki/Image:Inverter_ckt_01cjc.png and let me know what you think. Vitaltrust (talk) 09:47, 20 August 2008 (UTC)
 * Regarding the functional explanation that you added to http://en.wikipedia.org/wiki/Image:Inverter_ckt_01cjc.png: I don't know whether or not it is appropriate to put that kind of information on the image page or if that was your intention. When I was contributing illustrations, I assumed that the image page was a "storage area" and a place to document the copyright status etc. I assumed that the only detailed descriptive text needed is whatever is included in the article or articles where the illustration is used. If you think it is helpful to include a functional explanation on the image page, I don't object. If you are proposing to put that material in the inverter article, I don't object to that either. However, the article really just an overview of what an inverter is and the general concept of how inverters work. It shouldn't get very much into the details of circuit design. If you think more is needed in the inverter article, add what you think is appropriate. C J Cowie (talk) 16:37, 20 August 2008 (UTC)
 * Ok, I will delete the description from the image page and maybe provide some kind of description directly into the article. Vitaltrust (talk) 17:26, 20 August 2008 (UTC)

Alleged Vandalism on Template:Infobox Kosovo by Vitaltrust
On February 17th, 2008 I received these two warnings by Rudget .

Please stop making test edits to Wikipedia. It is considered vandalism, which, under Wikipedia policy, can lead to blocking of editing privileges. If you would like to experiment again, please use the sandbox. Rudget . 16:43, 17 February 2008 (UTC)

This is the last warning you will receive for your disruptive edits. The next time you disrupt Wikipedia, you will be blocked from editing. Rudget . 16:49, 17 February 2008 (UTC)

''These warnigns were sent after I blanked the page Template:Infobox Kosovo, which I deemed no loger usefull. Following the warnings, I was blocked for 24 hours from any editing capability (despite, after the "last warning", I didn't make any edit).''

My Reply
First of all, the template is no longer used in the article "Kosovo", so I think it's a waste of space. Moreover, that template had become a place where people against Kosovarian independence showed their frustration and no longer reflected the reality. I can't understand why Rudget and the administrator ChrisO consider my contribution as a form of "vandalism". Another question which arises is why Rudget left unchanged the (politically biased) sentence "Independence annulment: February 17, 2008" after reverting my modifications.

One can be in favour or not in favour of the independence of Kosovo, but politics should be left away from Wikipedia.

I have requested to ChrisO to have my edit rights reinstated, but I have received no answer yet.


 * My edits were not based on a supposed political allegiance. Large swathes of information was removed by yourself, yet if it was not in use, why so? Regards, Rudget . 17:38, 17 February 2008 (UTC)
 * The information had been already included in the article "Kosovo", which is (and was) protected. Nothing had been lost, since the history is always available. I blanked the page not for vandalising it, but because I was irritated by the continuing "do and undo" activity which was in place and because, as I said, it's no longer used in the main article and so I think it should be deleted. I'm very disappointed for having been blocked: I find it unfair. Vitaltrust, 17 February 2008, 17:54 (CET).
 * Just sit it out. If you're here to be constructive, you'll be fine after the block automatically expires. Regards, Rudget . 17:54, 17 February 2008 (UTC)

Article: Lion
A "pride" is the collective term for a group of lions. It was used correctly in the article, so I've undone the change.  Acroterion (talk)  15:24, 24 May 2008 (UTC)


 * Ok, I didn't know this. I thought that it was a mistake. Thanks for correcting me. Vitaltrust (talk) 15:32, 24 May 2008 (UTC)


 * That's what I thought: the term is defined rather far into the article, so it's not very obvious.  Acroterion  (talk)  15:39, 24 May 2008 (UTC)

Article: Harry Wu
On 31 May 2008, I removed the part "An inconsistency in his story is that had he been arrested, it would not have been possible for him to graduate by 1959" from the article about the Chinese dissident Harry Wu. The previous version is reported below, where I highlighted the sentence I removed:

Wu studied at the Geology Institute in Beijing, where he was first arrested in 1956 for criticizing the Communist Party during the brief period of liberalization in China known as the Hundred Flowers Campaign. He has also claimed that he protested the Soviet invasion of Hungary in 1956. An inconsistency in his story is that had he been arrested, it would not have been possible for him to graduate by 1959. In 1960 he was sent to the laogai ("re-education through labor"), the Chinese labor camp system, as "counterrevolutionary rightist."

Reason
As a neutral reader, I erased the sentence for the following reasons:
 * 1) The erased sentence seems to have been placed there only for political purposes. There is no doubt that Harry Wu was prosecuted by the communist government for his ideas.
 * 2) The fact that Wu had been arrested in 1956 does not imply that he would not graduate in 1959, because:
 * 3) one can be arrested and then immediately released;
 * 4) one can be allowed to study and take a diploma even while in prison.

When the issue is solved, I will summarize the result of the discussion here in my talk page. Meanwhile, use Talk:Harry Wu to contribute with your point of view until a consensus has been reached, so that every person involved can read.