How can DC-to-DC power transformers improve efficiency in power electronics?

In summary, the conversation discusses a new method for connecting different voltage level HVDC lines without conversion to AC using "bucket and ladle" charge pumps. This method involves using a collection of capacitors in series with bypass switches and switching them at high frequencies to achieve bidirectional power flow. The switching frequency is limited by switching speeds and a little inductance is thrown in to charge resonantly. The simulation shows successful power transfer with minimal loss, but calculating power losses in power electronics is difficult.
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anorlunda
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I am sharing this to brag about my former boss and mentor Lionel Barthold. He is well into his 90s, but his mind is so sharp that he continues with brilliant inventions. I'm very proud of him.

What would power level DC-DC transformers be good for?
  • Connecting different voltage level HVDC lines without conversion to AC.
  • Direct connection of solar farms to HVDC without conversion to AC.
  • Offshore wind farms are best connected to land with underwater HVDC cables. They can generate low voltage DC and connect to HVDC without conversion to AC.
How does it work? You can read the details in this CIGRE paper, or this patent application. Or you can read my 10 cent simplified version below.

The basic element is a "column" which is a collection of a large number of capacitors in series, with a bypass switch around each capacitor. Connect the column to the high voltage side and the capacitors charge up. Now disconnect the high voltage side (all switching is done at current zeroes), bypass some of the capacitors and connect the column to the low voltage side. But that's unstable, because on the next cycle the capacitors don't begin with equal initial charges. The solution is to choose different subsets of the capacitors for each half cycle. That is called the "sorting" solution for charge equalization. None of the capacitors ever get fully discharged. With a large number of capacitors to choose from, you can do a lot of smoothing. The switching frequency is as high as possible, limited by switching speeds. Also throw in a little L to charge resonantly.

I think it is very clever. All of us could solve the simple DC circuit for each half cycle. But the circuit configuration is changed 800 times per second. If we say that each of 500 capacitors can have 4 charge levels, and switching frequency is 400 hertz, then there are ##800*2^{500}*4^{500}## possible combinations per second. But ##4^N## is an overestimate because initial charges are not fully independent, they depend on the time history. Even so, the result is a very large number of switching+initial_condition configurations per second, well above ##10^{100}##. Some of the capacitors are redundant, allowing for failures.

The scheme is shown below. One "column" on the left and with three parallel "columns" on the right. The three columns help smooth the current. (Don't get confused, this is not three phase power, it is three DC devices in parallel.)
slask.png
Here's a schematic showing details of the switching electronics.
slask.png


Here's a little simulation. We have a 640KV bus, 200 km of HVDC line, the transformer, another 200 km of line, and an 800 KV bus. The transformer has 400 submodules in each column. Switching frequency is 400 hertz.

slask.png


The simulation shows a transient, +1000 MW transfer, zero MW, then -1000 MW, in only 6 seconds. demonstrating bidirectional power flow with the same bus voltages. The transients show below are at the transformer. The currents have an enormous amount of ripple, but it is high frequency. At the bus ends of the lines, the ripples are largely filtered out by the inductance and capacitance of the 200 km of line, so that the DC looks fairly smooth.

slask.png


Just wanted to share. I think this stuff is cool.
 
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Likes donpacino and jim hardy
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  • #2
"Bucket and Ladle" charge pump taken where no man has tread before !

That's great !

thanks ..
 
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Likes mheslep
  • #3
Thats really cool. I like it. just a note both of your links appear to go to the same article.

How do you think the power loses would compare vs a typical DC-AC-DC configuration.
Yes you are getting rid of the transformers but you gain the power loss that occurs with each capacitor discharge. Just curious if the simulation holds that data?

Again really cool!
 
  • #4
donpacino said:
both of your links appear to go to the same article.

Thanks, i repaired the link to the patent application.

To me, calculating power losses in power electronics is very difficult, so I can't answer your question. But the losses comparison for transforming DC voltage the conventional way should not be DC-AC/AC-DC but rather DC-AC/transformer/AC-DC.
 

FAQ: How can DC-to-DC power transformers improve efficiency in power electronics?

What is a DC-to-DC Power Transformer?

A DC-to-DC power transformer is an electronic device that converts direct current (DC) voltage from one level to another. It is used to step up or step down the voltage, depending on the application.

What is the purpose of a DC-to-DC Power Transformer?

The purpose of a DC-to-DC power transformer is to provide a stable and efficient way to convert DC voltage to a different level, which is necessary in many electronic circuits and devices. It allows for the use of different voltage levels in the same circuit without the need for additional power sources.

How does a DC-to-DC Power Transformer work?

A DC-to-DC power transformer works by using electromagnetic induction to transfer energy from one circuit to another. It consists of a primary and secondary winding, which are wrapped around a core made of magnetic material. When a direct current is applied to the primary winding, it creates a magnetic field, which induces a current in the secondary winding, resulting in a change in voltage.

What are the different types of DC-to-DC Power Transformers?

There are several types of DC-to-DC power transformers, including step-up, step-down, and isolated. Step-up transformers increase the voltage, step-down transformers decrease the voltage, and isolated transformers provide electrical isolation between the input and output circuits.

What are the applications of DC-to-DC Power Transformers?

DC-to-DC power transformers have a wide range of applications in various electronic devices, such as mobile phones, laptops, power supplies, and electric vehicles. They are also used in renewable energy systems, such as solar and wind power, to convert DC power to the required voltage level for grid connection.

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