Can I control my transformation into a werewolf?

Solution 1:

Normally, you'll be able to use your Beast Form power whenever you want, once per day. This power lasts for 2 ½ minutes, but can be extended by feeding on dead things.

However, there is a quest that will affect your ability to control your power:

During Ill Met By Moonlight, you'll receive the Ring of Hircine. This cursed ring, once worn, can't be taken off and has a 10% chance every minute to cause you to transform against your will. Once the quest is complete, you'll get a non-cursed form (or lose the ring, depending on your choices).

Solution 2:

You will be able voluntarily to turn into a werewolf once per day (This ring that lets you do it multiple times). Once in werewolf form, you will have to feed on corpses to stay in werewolf form.

Solution 3:

From the Elder Scrolls Wikia

• Beast Form: (Skyrim) The Werewolf can transform into beast form for up to 2.5 minutes, which increases by 30 seconds if the werewolf feeds. Note- you may only feed upon the corpses of playable races. Falmer, for example, are inedible. Use caution when using the Beast Form in certain dungeons.
• Scent of Blood: (Skyrim 1st Totem) Detect life in a large area for 1 minute.
• Howl of the Pack:(Skyrim 2nd Totem) summon Two Wolves to fight at your side.
• Howl of Rage: (Skyrim 3rd Totem (default)) Causes nearby enemies up to level 25 to flee for 30 seconds.
• The three totems above have to be unlocked and then you can pray at them in the undercroft in Whiterun, you can use one at a time to as werewolf power.

Weaknesses

• No bonus from being well rested (Skyrim).