Chinese Grammar│Difference of「了 le、過 guò」

Related articles
→ Chinese Grammar│了 le
→ Chinese Grammar│過 guò (1)
→ Chinese Grammar│過 guò (2) (under editing...)
→ Chinese Grammar│Difference of "Verb +好 hǎo、完 wán、過 guò"

Introduce

Both 「了 le 、過[过] guò」indicates that an verb, action or event was completed or completion in the future.

What the difference between them? I'll do analysis point-by-point below.
Audio of below example sentences (Taiwan accent)

Chinese Grammar│Difference of「了 le、過 guò」

Difference 1 
When using "action, behavior or event + 了 le "：
It indicates that the action, behavior or event is completed or occurred in the past or future. In the same ,it can used when the event is ended, or unfinished.

When using "action, behavior or event + 過 guò"：
No matter whether the action, behavior or event is experienced in the past or in the future, it can only be described a experience (the event is completed)

e.g. After you go to Taiwan, remember to buy a souvenir for me

       你去了台灣後，記得幫我買紀念品。
                     [湾后，记    帮    买纪]
       nǐ qùle táiwān hòu, jìdé bāng wǒ mǎi jìniànpǐn

→  People use「了 le」here to indicates the future event is ongoing and not over yet.
      So, the order should be executed when the person still stay in Taiwan.

e.g. After you have been to Taiwan, you will miss it .

       你去過台灣後，會很想念它的。
                        [ 后，会 ]
       nǐ qùguò táiwān hòu, huì hěn xiǎngniàn tā de.

→  People use「過 guò」here to indicates the action will be taken place after the event become a experience.
     So, the person will miss Taiwan after he comes back from Taiwan.

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Difference 2
When using "action, behavior or event + 了 le"：
It can emphasize that the event has just completed or take place.
(No matter for present or future tense)

When using "action, behavior or event + 過 guò"：
It only emphasize that the event had completed after a while or a long time.
(No matter for present or future tense)

e.g. I went to Taiwan last year.
       去年我去了台灣。
       qùnián wǒ qùle táiwān.
→ 1.「了 le」emphasizes that the event was completed and also complete the sentence.
     2. If omitting the「了 le」,people may think you have something to say after this sentence.

e.g. I visited Taiwan last year.
       去年我去過台灣。
       qùnián wǒ qùguò táiwān.
→ 「過 guò」emphasizes that the I had experienced the events.

e.g. I just ate buns.
       剛[刚]才我吃了包子。
       gāngcái wǒ chīle bāozi.
→ 「了 le」emphasizes that the event was recently completed

e.g. I have eaten buns just now.
       剛才我吃過包子。
       gāngcái wǒ chīguò bāozi.
→ 「過 guò」emphasizes that the I had experienced the events.

e.g. Tomorrow after I went to Taipei, I went to buy souvenirs.
       明天我去了台北後，再去買紀念品。
       míngtiān wǒ qùle táiběi hòu, zài qù mǎi jìniànpǐn.
→ 「了 le」emphasizes to do other actions only after the event occurs or completes. 

e.g. After going to Taipei tomorrow, I will go to Taichung again.
       明天我去過台北後，再去台中。
       míngtiān wǒ qùguò táiběi hòu, zài qù tái zhōng.
→ 「過 guò」emphasizes to do other actions only after experiencing the event.

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Difference 3
When using "action, behavior or event + 了 le"：
It indicates the event may not over until now.
When using "action, behavior or event + 過 guò"：
It indicates the event is completed.
e.g. I went/goes/have been to Taipei.
       我去了台北。
       wǒ qùle táiběi.
→ I may still be in Taipei now, or may have already returned.

e.g. I had been to Taipei.
       我去過台北。
       wǒ qùguò táiběi.
→ Already come back from Taipei

Difference of negative usage

Both of them need to add「沒méi / 沒有méi yǒu」
But, negative usage are different between 「了 le、過 guò」.
→ 「了 le」is no longer spoken.
→ 「過 guò」should keep in sentence.

e.g. I didn't go to Taipei.
       我沒去台北。
       wǒ méi qù táiběi.
→ I didn't go this time, but I might have been before.

e.g. I have never been to Taipei.
       我沒去過台北。
       wǒ méi qùguò táiběi.

Usage when use 「過+了」
When using "action, behavior or event + 過 guò", people may use "過 guò +了  le" in same time based on one of below situations：

1. To improve completion of sentence.
2. To indicate that the action has just been completed

e.g. I had been to Taipei.
       我去過了台北。
       wǒ qùguòle táiběi.

＊ No negative usage for「過+了」