You should know that in the case of high-power DC power supply, the switching frequency is difficult to increase. Why? Two important indicators for measuring switching devices are: the current is through, and the other is the withstand voltage. High-power switching devices are very expensive. Moreover, due to technical limitations, the power of a single switching device cannot be too large. Please search and read the most comprehensive! The fastest updated novel

Thyristors are the switching devices with the largest power, but the frequency is too low, and the power of GB's new generation of high-frequency switching devices is greatly limited.

Zhang Zheng knew this well. He participated in the design of a high-voltage DC transmission project from Sanxia hydropower to the river and sea. Each converter valve is composed of hundreds or thousands of GBs in parallel and then connected in series. The equalization and current equalization are very difficult to achieve. The driving signal of each GB is made of optical fiber. As long as there is a difference between a hair and the equalization and equalization flow fails, all switches in a valve will be burned out instantly, which will cause a terrible chain reaction.

Only a few companies in the world can do this kind of converter valve, and the pressure equalization process requirements are too high.

Even so, the switching frequency of the entire valve is about 1000hz.

The limit on switching frequency of high power is very large. A single switching device cannot meet the requirements. The frequency is slightly increased, and the difficulty of voltage equalization and current equalization increases exponentially.

The high-voltage DC generator developed this time requires 200k of DC output, the maximum current peak reaches a, and the short-term maximum power exceeds 160k, and a single switching device cannot achieve it. The state loss of the hard switching state is too large. Once the frequency increases, the switching life will drop geometrically. Tree is as follows: heyaпge. Close the mouth heart chapter

It is necessary to have soft switches, voltage and current equalization, and the weight must be light enough, so the frequency must be increased. This is a series of factors that increase the difficulty. Otherwise, how could a group of experienced professors be at a loss?

Zhang Zheng couldn't wait to ask Liu Chen for advice, and there were too many doubts in his heart.

"How could it be? If the switching frequency is 10k, I roughly calculate that the fluctuation will be above 5%.

"10k? That's far from enough. The switching frequency of this control mode is at least 100khz or more. The complete elimination of switching losses is for the purpose of high frequency. There is no need to use this structure for the order of 10k frequency."

"100khz?" Zhang Zheng's eyes widened. With such a high frequency, the weight of the overall equipment must have been greatly reduced, but...

"The GB cannot reach such a high frequency, so you can only use switching devices with color structure. The capacity of a single chip is very small, and this requires considering the complex voltage equalization and current equalization problem." Zhang Zheng looked bitter, and he felt that the ideal situation was to increase the frequency to 30k to achieve balance.

"This is simple, the color withstand voltage is fine, it is because the current is too small. We use this topology to switch the switch when the current is zero. Did you think of it? That is the natural current sharing condition. Just connect several switch tubes together in parallel to solve the problem of small capacity, and there is no need to add additional auxiliary circuit current sharing at all."

Zhang Zheng almost jumped up, waved his fists excitedly, and shouted: "Yes, the problem of switch capacity will be solved."

After thinking about it, I felt that it was not right, "It's hard to control at such a high frequency? And I also need to detect the resonant current crossing zero point, so the controller cannot react. Will the stability be too poor?"

"It is indeed a bit troublesome to implement hardware circuits, but it is not impossible." Liu Chen smiled. When he uses this structure to develop equipment, he usually puts the frequency at close to 200khz.

"How to achieve it? Can you tell me?"

"This is not something that can be explained clearly, Professor Zhang." Liu Chen smiled. He would not be so stupid that he would tell the skills he mastered with the person he met for the second time, even if the other party was a humble and polite professor.

Zhang Zheng also understood that if he asked this kind of advanced key technology, he would tell him immediately, unless it was a fool, and pondered for a moment: "Where can use this structure be able to achieve no overshooting and boost to 200k DC within 1s, and the weight is strictly required, and the stability is required to operate for more than five years, so the space e cannot be large."

When Liu Chen heard this, he was lit up. There were so many demanding requirements and the application situation was self-evident. He roughly guessed what kind of project this was. He thought carefully and said: "This ultra-high voltage DC device has very high insulation requirements, especially after a very high frequency, and using a fast rectifier diode, how many devices can it have withstand voltage levels?"

This can be considered. Zhang Zheng was amazed. The young man in front of him had absolutely rich experience in engineering development. He said: "We have considered relatively low-frequency operating conditions before. According to the frequency you mentioned, this kind of diode may have a low voltage withstand voltage, and about 20k withstand voltage is fine. In this way, the boost side of the boost transformer needs to be divided into more than a dozen windings, which is probably unstable, right?"

"Why do you need to divide the winding?" Liu Chen looked at him strangely, "It's enough for you to have this kind of pressure resistance level."

Zhang Zheng's face turned red and his voice became much smaller. He was criticized by someone recently for being a little inferior. "How to deal with the pressure resistance problem without windings?"

"This is simple. You can use a dual inverter structure or a simple rectifier circuit can be built into a voltage equalization bridge. There are many solutions. If the transformer is divided into three windings at most, it will be unstable. Two are the best. If you design the magnetic circuit, use the positive and negative structure to offset the e."

Talk freely and underestimate.

"Equilibrium voltage rectifier bridge? Do you understand this?" Zhang Zheng was completely impressed. In this way, the device's withstand voltage was solved and e was effectively controlled.

"It's not difficult to understand a little, but it's actually written in "Power Electronic Technology".

Is there any? Zhang Zheng thought desperately that he had organized and published a book. As a textbook for many schools, why didn’t he know the rectification bridge? This is a very advanced technology.

Liu Chen drew a rectifier bridge on the paper and handed it to Zhang Zheng, "Do you think this is not very simple? Just add two capacitors between each rectifier circuit, add one capacitor within each bridge, and it will be evenly voltage-free and filterable, but if you go down one by one, the value of the capacitor is very particular, and high-precision customized capacity must be used."

Zhang Zheng almost cried when he saw that he didn't expect that the simpler the structure, the more practical it was. He excitedly grabbed the paper tightly in his hand, fearing that the wind would run away.

He suppressed the urge to ask about the value of the capacitance, which is the secret of the researchers.

Nuomin has always been standing aside as a little maid, turning over milk tea and holding paper and pen. Although she couldn't understand a single word about the topic these two people were talking about, she felt very profound and powerful.

Looking at Liu Chen talking and drawing, while the university professor looked like a primary school student, and he was so admiring that he was so angry that he kept emitting stars in his eyes. (To be continued.)
Chapter completed!