Double ramp signal query

[hiy88]

The attached diagram is obtained from the article:
Control of high-frequency AC link electronic transformer
H. Krishnaswami and V. Ramanarayanan

I would like to ask;
Why the circled portion of the double ramp carrier wave is ignored when producing the S1 and S2 signals?

Please help me as I'm really confused with the double ramp PWM.

 

[kripacharya]

well that depends on the actual circuit used to generate S1 and S2. We don't have your book, so hard to say any more.
Note that S3 does transition at that point.