How to set phase delay for a three phase igbt rectifier
The pulses used to fire the IGBT, must be in synchronism with the line voltage (phase vs. phase).
I can see you're using Simulink, and if I remember correctly (this several years ago), this software has a special block for generating the 6-pulse, and even the double-pulse. This block is connected by measuring block, directly to the supply voltage (for synchronization) and provided an input, where the conduction angle value in degrees is established.

Maybe you can achieve correctly generate pulses using discrete blocks of measurement, comparison, etc. but I recommend you investigate a little about modules for power systems in Simulink.

Here is the list of blocks available. Look under "Control and signal generation" for pulse generatos, PWM etc.

As for the voltage levels, with 690V you can get a maximum voltage of about 1612 V, with approximately 4% ripple. The size of the capacitor, must agree to the rectifier load (I suggest that you include in the simulation), that is, while the load demands more current, the greater the capacitor.
I recommend that you build the entire system in the simulator, including the load, and so you can determine which is the conduction angle (or the angle of shot) necessary to achieve the voltage.