Which part of my idea is wrong about infinite energy produced by EMF for certain circumstance? As a someone who is on the first year of EEE student,
facts in a simple way:


*

*time varying magnetic fields around conductors produce electricity

*for outer space, object will keep going at the same speed and in the same direction as long as zero net force on it
So, what if I set a circuit like, huge magnet on/in space and huge rotor(conductor) keep circulating at same speed within the magnetic field due to zero force on it ?(may need a initial speed with the help of,a rocket might be)
Of course I might get wrong with many concepts, so could you tell me about it?
 A: I assume the "infinite energy" you're wondering about is electrical energy from current induced in the huge circulating rotor.  As soon as you get an induced current there will be an induced magnetic field that will interact with the huge magnet and oppose the motion of the coil.  Ask Heinrich Lenz all about it. 
A: The essence of what you described lies in Maxwell/Faraday's equation:
$$ \nabla\times\vec E = -\frac{\partial \vec B}{\partial t} $$
Which indeed implies that an electromotive force is induced in a time-varying magnetic field. This induced current follows Lenz's law, which states that the current generates a magnetic field that opposes the change that caused it. 
So think of it by analyzing this diagram:

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imgele/lenz.gif
A current can be classically thought of as electrons (or protons) moving through a circuit, so moving charges produce magnetic fields, right? Just think of the direction in which the magnetic field is produced and the conservation of energy should pop right out from your analysis!
