The Wall Street Journal has an excellent review of China manages its currency in a fixed exchange rate with tightly controlled financial flows.

The Chinese currency: where it’s traded, how it’s controlled, what it all means

• The Yuan Moves—in a Controlled Way and Central Bank Tools
• The Yuan Trades in Two Markets
• China’s “war chest” to “defend” the price of the Yuan
• Why the Yuan is not truly global

Skip the “trilemma” video, its not helpful.