经常(jīnɡchánɡ) = often 通常(tōnɡch ánɡ) = usually 常常(chánɡchánɡ)= always/ very often

jingchang and changchang emphasize the frequency:frequently tongchang stresses the "generality" : normally, usually, ordinarily No huge difference between jingchang and changchang. They are both adverbs. In oral Chinese we usually confuse these two words.But there's one exception: sometimes we say"这是经常的事"(it is a frequent thing),where "jingchang" is used as an adj (frequent). We seldom say"这是常常的事" (but no big problem, everyone will understand it) because changchang can't be used as an adj/attributive, it is an adv.Personally, I feel jingchang is a litte bit more formal. I agree with "Wozitoya". Don't worry if you can't distinguish between jingchang and changchang because orally we almost DON'T distinguish them when we express the meaning "frequently". Choose the one you like.x'D

If you want to distinquish these meanings. It will take you few hours to understand it, and possible another few days or weeks to digest it. If fact, these three phrases are similar in meanings. There were several answers to your question, but they are not the same. It is obviousley that their meanings are base on personal preferance. 经常,通常, 常常. precisely, they may not be the same, but they are the same in general.

这几个词都是副词，在句子中做状语。

它们都是近义词，根据语言环境和逻辑运用吧 jīnɡchánɡ是指次数较频繁,次数较多,可以当副词，也可以当形容词（如，这种事儿经常性有） tōnɡchánɡ比经常频繁一些； chánɡchánɡ和经常的意思差不多，但是比经常和通常更频繁。