Here's my theory: China is trying to position itself to be a global leader in energy. There was an article recently that China is building a large power line in Pakistan, and a little Googling turns up another between Kenya and Tanzania. China has been building power lines like crazy, and they have some of the largest in the world. Those large lines were designed by foreign companies like ABB and Siemens, but China gets all the design stuff from those projects. They're building the expertise in Chinese industries. So I think these projects are the same idea. Build your own projects to work out the bugs, then build them in other countries either for profit or for access to resources. They need the energy, anyway, and this helps them cut down on domestic pollution, too. If I make it sound like a conspiracy, I don't mean to. It's just good business.
I was surprised to learn of large HVDC projects in China, and can't tell if the image is a real test facility or something from Nikola Tesla fan fiction.
China recently split their AC system, with only DC ties connecting Yunnan province to the rest of the China grid. Those DC ties are huge, and before the split a DC trip could have overloaded the AC lines. It's a bold move, and it seems to make sense. I haven't seen any followups that the system isn't working.