FFT Questions??

Dear all,
I have collected some voltage and current waveform ( .CSV file)from the oscilloscope from three-phase inverter switching. I would like to have a software to analyze for me. However, I'm not quite familar with FFT because my previous work is all about classic Fouroer series for synthezing the square waveform . Can anyone tell me what's the most simple equations for FFT? Any really usefull free software for this?
Ok, here is one critical problem for me, the fundamental frequency is the frequency value during I capture the waveform or the desired frequency I want to produce??
By the way,anyone familar with Oscilloscope Tektronix TDS 3054B ? What's the FFT inside this osci? Because I have analyze the waveform using Osci and Top software but the result is different. It's a headache for me doing analysis without knowing what actually the measure parameter is.
Thankyou for your time !

experiment suggested?

Dear all,
Current I have to test my three-phase VSI circuit for getting some results. I am using PIC16f877 to control IGBT. My main concern is about harmonics reduction, power losses(efficiency), switching events, switching frequency and losses.
I don't know how to start the experiment. Has anyone here can give ne a suggestion on the procedure and equipments that allows me to take my measurement and results. Or anyone can show me the link for all these? Thank you!;p;

DC link

Hi! I'm having a question here:
there is an intermediate link between the converter and the inverter, we usually call dc link or dc bus voltage. This link usually is just a capacitor.
I would like to know what is the main different between using two capacitor and use only one capacitor? What's the effect on the inverter switching output?(the waveform value in positive and negative portion)
;p;

Inverter output

I used microcontroller to control the switching time of IGBT for three-phase induction motor. The motor is 0.25KW, 400/230V, 0.77/1.34A and is suggeted delta connection.
I wonder now, my output from the inverter should connect to any isolator or any component before connected to induction motor? Or else can connect directly? Please give some advice thankyou!

Induction motor speed control

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Hello, I'm new here and wish to know what is the relationship of speed, frequency and voltage of an induction motor. I plan to program a microcontroller for controlling the speed of three-phase induction motor. Anyway, I face a problem here, if I vary the amplitude, what's going on with the frequency?? I need some formula of calculation in order to help me to decide what freqeuncy is suitable for certain amplitude.