AC/AC converter --- Buck

What rating, Boss? 5VA? 500kVA?

Low Frequency of 60hz and this voltage is fed to the residential and commercial units, so I believe that 600 times lets say 60 amp maybe 36 kva I would say!

Why are you bucking when everyone else is using transformers, then? Doesn't that tell you something?

Crabtree!

Is it possible to have a transformer that gives me such ability to have (305-660 volts) gets converted to lower than 305 volts and below 305 volt just passed through the circuit toward the AC/DC of (80-305 volts)?

Something smart to differentiate the voltages.

I re-state that the current is not injected and I am aiming just to feet the voltage into my AC/DC converter. No current limitation!

In fact the current won't be injected. Then only given data is the voltage between 90-60 volt. The circuit decides what the current must be.

The examples in the referenced document are designed to operate at 10kHz and 20kHz not the 60Hz you mentioned in a subsequent post.

There's different types of impure. Maybe filtering, page 26 onwards of your reference, will help you...or not.

Do you have pictures of the waveforms you are getting?

Wal,

That's right! Mine is low frequency of 60 Hz. Then, choosing the right capacitors and inductors are so essential to filter out the improper freq. and have a pure SIN wave.

I will provide you with proper waveform shortly.

Olewi,

I found GlobalSpec, a mature and reasonable forum to discuss the technical projects while you guys politely and respectively answered to my questions. ( at least so far so good :) ) Whereas, on the other so call scientific Forums they start to insult me in a worst way possible that was tolerable at all!

they believe that I am insane and wide range voltage is not possible to get converted by a non- transformer included devices at all!

Sometimes, you are looking for something that is not available in the market and you put more effort to inject your creativity to your design and have it build by yourself.

In fact, even if I use a transformer in a wide range of 90-660 volts I need to get a voltage between 80- 305 volts on the secondary to feed my AC/DC converter on the board.

Let's say 660 to 120 by a step down transformer but it is not possible to use the same transformer to have 120 or so down to the 80 or so. In other words, a smart circuit to pass (90-305 volts) through the circuit and lower the voltages between (305-660).

1. Yes, the transformers are easily available in the market but they are heavy and for my purpose I need a adjustable one! That is right design a such converter is not easy at all, I bet!

2. But as I said I need an automatic voltage detector and converter circuit in a wide range!

3. Yes, they are undoubtedly reliable and have less power dissipation.

4. Correct!

5. So detailed!

Yes, in the academical world we are unfortunately bounded within theory and go no further!

That's a pretty good response from an OP . GA.

The complexity, design and even possibility seriously depends on the current or power levels you want to convert.

Existing wide input voltage range AC to DC converters are available which can then feed a DC to AC converter providing a stable clean output voltage (generally 12 or 24VDC in, 230V or 110VAC out). For low currents this can be done using simple controller microchip circuits, for larger currents using stand-alone power converter products (but only up to a certain size).

What output current or power levels are you realistically planning on?

What's the end application and expected budget or sell price?

Hello CaE, . . . Yes, this forum is a lot more forgiving than others. Some will turn the dumb questions from imbeciles into a comedy, . . . others will just ignore them.

Yes, certainly, you have to have good reasons for taking a very difficult route to solve your problem then to take the easy way out. You have not divulged any reasons as to why you are taking the difficult path.

Nothing like this is available on the market, . . . it is all custom built and designed. Sounds to me like you have nothing better to do so you set out on this unusual track.

NO problems with the transformer, . . . one can be designed with appropriate taps on the primary, as well as on the secondary, . . . providing you with more range than you will ever need.

No problem with multiple outputs, . . . you can have two, or three, or more at teh same time.

1, You must be kidding, . . . a 600 volt 36kVA inverter will occupy ten times the volume and weigh the same as a 36kVA transformer. It will also have fans on the top driving the heat out of the system.

2. No, problem, . . . use a tapped transformer with an automatic voltage regulator, . . . this can be provided - in a step version, . . . or continuously adjustable. Transformers are more "solid state" than "solid state" electronics.

3. Most reliable and highly efficient . . .

you are bounded Only if you chose to limit yourself or be limited by others !

Academics are typically the least bounded then others . . .

This appears to be California, so all bets are off.

This appears to be California, so all bets are off.

Hey now, let's not jump to disparaging California just yet, "Ca" is also used in reference to Canada.

So, "Ca"Engineer, what is your heartburn over the tried and true method of "bucking" the voltage with a transformer? Is it because you have an unknown wide variety of possible input voltages? Because if so, there are other well established ways of dealing with that. In addition, what is the overall scope (not details) of the system? Are you just wanting to change voltage in preparation to feeding a Switch Mode Power Supply of some sort? More info may allow us to help you more effectively, regardless of which "Ca" you hail from.

JRaef,

I am not insisting in buck or step-down method to convert the voltage! I simply need to have a circuit to inject a voltage between 90-660 into and feed my AC/DC converter with an input of (80-305 volts). That's all!

BTW,As for nourishing the curiosity appetite, I live in a Canadian society! :)

I think i understand what you want or probably not..

Here goes....

Your AC/DC converter, aka rectifier, probably a switched mode power supply, can accept a supply between 80 and 305VAC, right?

You have the most incredibly unstable supply on the planet that swings between 90 and 660VAC

You want a buffering device between your wildly swinging primary power source and your AC/DC convertor that will:

• peg the maximum voltage exposed to your AC/DC convertor to no more than 305VAC if it swings up to 660VAC

• Your lowest possible level source voltage (not including zero) is 90VAC, which is higher than the lower end of the AC/DC converters lowest operating thresh hold so is not an issue.

Right?

I would die for Bay Area! That is my dreamland Tornado!

Buck converter is for DC-DC voltage step-down conversion. Not suitable for your stated application. Please read more carefully.

http://en.wikipedia.org/wiki/Buck_converter

AC-AC conversion (frequency and/or voltage) is usually accomplished by rectifying the AC source to DC, THEN using a series of switches (2-6 devices BJT, IGBT ,MOSFET, etc.) to PWM the DC bus into a close approximation of a sinusoidal output.

Something "similar" to this:

http://en.wikipedia.org/wiki/Variable-frequency_drive

If you need voltage AND frequency control, research VFD's. If you only need a specific voltage reduction, use a transformer. See post #5 olehwi for why a transformer is preferred.

Mjb,

VFD article looks good and seems to be a worth-reading article! Good to know thanks! As I said I am not insisting on using a buck converter I just need to fit (90-660) to a voltage of (90-305)!

I wouldn't put too much faith in the simulated circuit in the thesis you mentioned. Modelling software is not perfect and just because they got it to work in the software doesn't mean it will work in the real world. No real world circuits were produced in that thesis to validate the proposed model in the real world.

Let me guess, you tried to replicate the circuit exactly as you saw it and it didn't work how it is supposed to!

:o

Without delving into the circuit in more detail it is possible they altered the theoretical parameters of the circuit to get it to work as they wanted it to (this is really common unfortunately). Pity we cannot do that in real life, it would make our jobs so much easier.

;)

In a real world application a transformer would be used. Even a custom made transformer would be cheaper and more reliable.

Why do you ask by the way, is this a real world application or are you interested in learning about electronic switching AC/AC conversion techniques?

Jack!

Agreed! The reality is a way from the simulation by ORCAD, P-SPICE, LT-SPICE or so but not too much a way from!

I believe the bias of transistors are important to switch on/off the circuit and also the right inductor and capacitance as well.

After all, I am still wondering what those pulses are coming from the gate of MOSFETs. Perhaps some sources to bias them and activate the switches.

of course I need something to push into the product line and eventually have it in the real world!

http://edudirectory.50webs.com/signal/RAMP%20GENERATOR.htm

This site might help as there are several circuit designs of which could be combined with proper filtering to attain the results you are looking for.

There is no instruction or example of how to bias the MOSFETs! Here are the waveforms and the circuit as follows.

The circuit shown in the paper you referenced could work. The input frequency appears to be 50Hz and the IGBTs are "switched" at 20kHz. When the resulting output is filtered to remove the 20kHz fundamental and higher harmonics, it appears to be a good approximation of the original 50Hz sinusoid with a reduced voltage amplitude (ref page 23).

If you choose proper components and values, the circuit simulation should work fine. Your posted images are small but I can see a couple problems with your spice schematic. Please note the IGBTs are switched ON/OFF. Biasing, which usually implies operation in a linear region, does not really apply to this design.

The amount of additional work required to make this a real, robust, safe, practical, and agency (UL, FCC, EN, CE, etc.) approved circuit suitable for general production can be quite large.

Based on the limited information in this thread, it appears you may need a few years of further study and practical circuit design experience. Sorry, not trying to be rude. This circuit controls lethal voltages and currents. The designer must be aware and cautious of these conditions and provide safeguards for anyone using the circuit.

Schematic of the circuit:

Schem

Vin:

Vout:

That is right! Experience is a must but for the prototype version you may put more effort and it will be ended up with something partially acceptable and you will advance it later on. As you mentioned I need to keep hammering on transistor biasing and work on 60 Hz Freq.

Safety and having a perfect circuit to have it ready for the production line is so challenging, I know!

Fellows!

Eventually I got an almost pure SIN wave at the output but the thing is when I inject 660 volt, at the output I get a low voltage which is good. However, in return by injecting 90 volt I get a very very small amount which is not good for our purpose. So, I need to have a potentiometer to change the components value each time I have a different voltage!

Here is the question for you. How can I this working automatically. I need something to detect the voltage and assign the right resistor for the circuit! Is this doable?

So, as you see, it is not a question of using or not using transformer, it is the matter of having a smart circuit that works in a wide range of voltage!

We have emulated a transformer with inductors and conductors but still have a wide voltage range to analyze.

What do you think?

Maybe using a voltage comparator? Um.... but the base to compare varies as the input is different! In other words, how is it possible that 660 is compared with 277 volt and 90 volt with something higher than?!

Um... so tricky so complicated! But sure there is a way around it!

Guys!

Let's forget about using any device other than step-down transformers to lower the voltage. So, here is the question for you. The voltage between 90-305 can get injected to the board without any conversion or can get mildly converted not deeply! Meaning that 90 cannot get converted to lower than 80!

However, the voltages between 305-660 must get converted to the lower than 305 volt. So, what is the solution?

Using comparator? Potentiometer?! Is this doable?

ok, lets ignore the transformer and assume you want to design a power inverter stage with the following specifications to add to the front of your theoretical modelled (and overly simplified for a real world design) circuit.

Input voltage: 660-305V AC

Output voltage: 90V AC

Current: 118A

Power: 36kVA

Does this sound about right?

You need a circuit (for example) that rectifies the AC to DC, chops the DC up using a pulse width modulated switch mode power supply (a transformer will be involved) to produce a stable output AC voltage.

If it were much, much lower power levels (mA to few A at extra-low voltages) then a much simpler circuit using one or more specialised integrated circuits could be used (handful of cheap components, relatively simple design). But this is a really complex, expensive and dangerous circuit you are trying to design as a real-world product requiring many (say 100+ components).

Your comments so far show me you are quite new to this and don't yet have the knowledge and experience to be attempting this. Most of us here wouldn't attempt to design and build this rather than buying a power supply solution, including me and I have worked on servicing much larger 600V inverters rated at hundreds of kW the size of tables.

Using comparator? Potentiometer?! Is this doable?

No, you need a lot more parts! You cannot just feed the voltage into a comparator IC and control the gates of some MOSFETS for example.

Um, have you even opened up an old computer 400W switch mode power supply from a computer (for example) and seen just how complex it is? There is a reason all those extra parts are necessary even though the power supply can be modelled in software with far fewer parts.

Why are you trying to do this again? I can understand trying to design a circuit in a modelling program to learn (which is great by the way), but you appear to be trying to build something that you plan on selling.

So what exactly are you trying to achieve?

Hey Jack!

Yes, this looks strange and impossible and I look so inexperienced when I tell you the story of the "smart voltage controller". However, this design to me is very necessary and to some extent possible!

While we have a automatic voltage detector, we don't need to change the parts, 90 goes through the circuit and directly reaches there on the board. On the other hand 660 needs to be lowered in order to pass through.

As for the current, No! It is not 118A! But it might be! It depends on the design of circuit. We do not inject the current. We have only voltages in our hand.

AC to AC or AC/DC and then DC/AC is not a big deal. I would like to know how to control the wide range of voltages in a way to have a unique circuit for this wide range.

with due all respect and your expertise, I need such design or I need at least some alternativies and intermediate design to achieve this goal!

I would suggest having a look online at switch mode power supply design to get some ideas as what you ask would have to be either brought or built from scratch out of individual parts.

Also have a close look at the major semiconductor manufacturer's websites as they have lots of controller chips and application notes that will help give you a clearer idea of how to attempt to do what you are trying to do. At the power levels you might be dealing with the solution is far from simple, even circuit board trace layout will become critical in getting the circuit to work properly.

It goes without saying that this is a very dangerous and difficult project.

We do not inject the current. We have only voltages in our hand.

You keep mentioning this but I still don't know what you mean by it. Are you talking about the control voltages on your switching power transistors or SCRs or similar?

Jack,

As for the following statement. Voltages are provided by a console starting from 90 volts to 660 volts. Those will be injected to test the device. We need to control them in order to have proper input for AC/DC converter on the board. Looking at the market's AC/DC, unfortunately there is no wide range input. ours only support up to 305 volts. What if we have 377 volts or 660 volt or 600 volt? That smokes the board!

"We do not inject the current. We have only voltages in our hand."

Yes, it is difficult and maybe dangerous as you said. But I was told to do so or find an alternative way to have this job done.

I will keep you updated on my findings!

Thank you for your time.

If you are using this wide AC input voltage range as a test injection voltage I still don't understand why you don't just use a transformer to step down the higher voltage to a more manageable level and just switch the input to the transformer if the supply voltage is too high for the existing circuit to handle.

In what application are you seeing the AC supply voltage vary by so large an amount? If it is a standard mains supply or even DC battery bank it will vary only a small amount from its base value.

Jack,

I have no problem any more with step-down transformer as I mentioned in my previous reply to this thread. However this is for one single voltage meaning that let's say you would like to design a machine to give you proper Quarters if the user puts in a bank-note of 5 should receive 20 Quarters and on the other hand by putting a bank-note of 10 you need to get double which is 40 Quarter.

It is not cost-effective to build two machines for bank-notes of 5 and 10 dollars separately! I out both banknotes in one machine and get different number of quarters. So different outputs for different inputs!

As for my device I need one design for 600 volt and 120 volt as well with different outputs!

My application is an electricity meter. As you know we have many network configuration such as 3 phase 4 wire with delta or star combinations. Therefore, we have a wide range of voltages.

There are some brands like Itron or Schnider Electric that produce electricity meters. They might use step-down transformer but he way that they manage different voltages is questionable and should be considered. That might give me some clues!

We may change that AC/DC component but we need an output of 12volt DC for sure!

If your application is as an electronic (smart?) electricity meter then that is quite different to what you mentioned at above. An electricity meter measures the power flowing through it, it doesn't alter it.

If it were me I would just have two (or more) different models, but then again I don't deal with this sort of thing.

What you actually want is to accurately scale a wide ac input voltage. There are simple ways, but a complete design doesn't immediately spring to mind.

Perhaps if you just simplified your request and reposted in a new thread (providing relevant adequate information this time) you will have better luck from others here.

Jack!

Don't get me wrong, we don't want to alter anything. The voltage should be stepped down to feed the AC/DC converter. BTW, I posed my question to other forum and got the following suggetsion as follows that might need to re-design the board but not from ground up!

http://www.ti.com/lit/an/slua721/slua721.pdf

The TI application says it is a non-isolated buck converter which may help me to have something to start with!

Ok, but that is just a constant voltage AC/DC power supply. If this is all you want to power your electronics then all you now want is something to accurately scale the AC voltage measurement input. A voltage divider network perhaps?

Jack,

No! It is said a wide range of input voltage between 80 and 500 Vac. I need to re-design it perhaps.