A MATLAB/Simulink Problem - What's wrong with this PWM generation method?

[powersys]

[Simulation Settings]
- Unless otherwise stated, the following simulation settings were used in all the simulations listed below.





[Block Parameters]
- Unless otherwise stated, the following block parameters were used in all the simulations listed below.





[Case-A]
- Note that the first input of the "Relational Operator" block is left open.





[Case-B]
- Note that the first input of the "Relational Operator" block is connected to the output of the "Repeating Sequence" block.
- Note that the output of the "Repeating Sequence" block is clamped at 0.1 and 0.9.





[Case-C]
- Note that the "Enable zero-crossing detection" of the "Relational Operator" block is UNCHECKED.
- Note that the output of the "Repeating Sequence" block is correct now.
- Note that the squareware shown in this case is slightly delayed compared to that of Case-B.





Questions

[a] Why is the output of the "Repeating Sequence" block distorted when it's connected to the "Relational Operator" block?

Why does the output of the "Repeating Sequence" block become OK when the "Enable zero-crossing detection" is UNCHECKED?

[c] Simulation file (*.mdl) is attached.


Cheers.