Three Phase Voltage Source Inverter with SPWM

In pulse width modulated inverters, the output voltage is controlled by controlling which of the following?
What will be the effect of increasing the number of pulses on inverter?
In sinusoidal pulse width modulation, __________ wave is compared with a ___________ type of wave?
In PWM, the comparator output is further given to a ____________?
In ___________ type of modulation method, the pulse width is not equal for all the pulses?