i'm looking for the maximum gain that can be taken from the multilevel inverter circuits based on different types of control techniques (SPWM,SVM,MPC,...etc)
In my current project I have done extensive simulations on various configurations. In a generic VSC configuration I compared PWM, SPWM, Unipolar SPWM and found the last one to produce output voltage in range of 0.7-1.5 times of PWM technique. Additionally the harmonics are pushed to higher order in range of 40th harmonic with upto 2kHz switching frequencies. in your present question the specifics of your requirements would decide the maximum gain that you can achieve. I gave up on MLI due number of switching devices required and added complexity of control.
No of Switches in MLI = 2(m-1)
No of sources in MLI = (m-1)/2
where m is number of levels in output voltage.
Ex m=5 for five level inverter needs 8 switches, 2 sources equally split.
if you are aiming your inverter for solar applications, this is a hard situation in achieving with added complexity of shading, availability of sun, sun tracking, MPP tracking etc. Same applies to wind systems.
next you need to check if your end use is single phase or three phase.
Trying Selective Harmonic Elimniation may remove lower harmonics, provide voltage gain of around 2 and at less cost, no added component as this is totally offline technique with programmable features. Modifying modulation index with closed loop control is also a possibility.